Roof Assemblies and Rooftop Structures

CHAPTER 15 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

SECTION 1501 cludes the roof deck, vapor retar der, substra te or ther mal GENERAL bar rier, in su la tion, va por re tarder and roof cov er ing. 1501.1 Scope. The pro visions of this chap ter shall gov ern the ROOF COVERING. The cov ering appli ed to the roof deck desi gn, mat eri als , const ruct ion and quali ty of roof asse mbli es, for weather re sis tance, fire clas si fi ca tion or ap pear ance. and rooftop structure s. ROOF COVERING SYSTEM . See “Roof as sem bly.” ROOF DECK. The flat or sloped surf ace not includ ing its sup - SECTION 1502 port ing mem bers or ver ti cal sup ports. DEFINITIONS ROOF RE COVER. The proces s of insta ll ing an addi ti onal 1502.1 Gen eral. The fol lowing words and terms shall, for the roof cov ering over a pre pared exist ing roof cov ering without purposes of this chapter and as used else where in this code, re mov ing the ex ist ing roof cov er ing. have the meanings shown herein. ROOF REP AIR. Recon struc tion or rene wal of any part of an BUILT-UP ROOF COVERING. Two or more layers of felt exist ing roof for the purposes of its mainte nance . cemented to gether and sur faced with a cap sheet, min eral ag - gre gate, smooth coat ing or sim i lar sur fac ing ma te rial. ROOF RE PLACE MENT. The proces s of remo ving the exist - ¬ ing roof cov ering, re pair ing any damaged substra te and insta ll - INTERLAYMENT. A layer of felt or nonbituminous satu - ing a new roof cov ering. rated felt not less than 18 inches (457 mm) wide, shingled be - tween each course of a wood-shake roof cov ering. ROOF VEN TI LA TION. The nat u ral or me chan i cal pro cess of sup ply ing con di tioned or un con di tioned air to, or re mov ing ME CHAN I CAL EQUIP MENT SCREEN. A par tially en - such air from, at tics, ca the dral ceil ings or other en closed closed rooftop structure used to aes thet ical ly concea l heating, spaces over which a roof as sem bly is in stalled. ven ti lat ing and air con di tion ing (HVAC) elec tri cal or me chan i - cal equipment from view. ROOF TOP STRUC TURE. An enclos ed structure on or above the roof of any part of a building. METAL ROOF PANEL. An inter locking metal sheet ha ving a mini mum insta lled weather expo sure of 3 square feet (.279 m2) SCUPPER. An opening in a wall or para pet that allo ws water per sheet. to drain from a roof. METAL ROOF SHIN GLE. An inter locking metal sheet hav - SIN GLE-PLY MEM BRANE. A roof ing membrane that is ing an insta lled weather expo sure less than 3 square feet (.279 field appli ed using one layer of membrane mate ria l (either ho - m2) per sheet. mo ge neous or com pos ite) rather than mul ti ple lay ers. MOD IFIED BI TU MEN ROOF COVERING. One or more UNDERLAYMENT. One or more layers of felt, sheathing pa- lay ers of poly mer-mod i fied as phalt sheets. The sheet ma te ri als per, nonbituminous satu rated felt or other ap proved ma terial shall be fully adhered or mechan i cal ly at tached to the substra te over which a steep-slope roof cov ering is appli ed. or held in place with an appro ved bal last layer. PENT HOUSE. An enclos ed, unoc cu pied struc ture above the SECTION 1503 roof of a building, other than a tank, tower, spire, dome cupola WEATHER PROTECTION or bulkhead, oc cup ying not more than one-third of the roof area. 1503.1 Gen eral. Roof decks shall be cov ered with appro ved roof cov erings secured to the building or structure in ac cor- POS I TIVE ROOF DRAIN AGE. The drainage condi ti on in dance with the pro visions of this chapter . Roof cov erings shall which consid er ati on has been made for all loading defle cti ons be designe d, insta lled and maintai ned in accor dance with this of the roof deck, and addi ti onal slope has been pro vided to en- code and the appro ved manu f acture r’s instruc tions such that sure drainage of the roof within 48 hours of precip i ta ti on. the roof cov ering shall serve to protec t the building or structure . REROOFING. The proces s of reco v ering or re plac ing an ex - 1503.2 Flashing. Flashing shall be insta lled in such a manner isting roof cov er ing. See “Roof reco ver” and “Roof replace - so as to pre vent moisture enter ing the wall and roof through ment.” joints in cop ings, through mois ture-per me able ma te ri als and at in ter sec tions with par a pet walls and other pen e tra tions through ROOF AS SEM BLY. A system designe d to pro vide weather the roof plane. protec tion and resis tance to de sign loads. The system consis ts of a roof cov ering and roof deck or a single compo nent serving 1503.2.1 Lo ca tions. Flash ing shall be in stalled at wall and as both the roof cov ering and the roof deck. A roof as sembly in - roof in ter sec tions, at gutters, wher ever there is a change in

2003 SEATTLE BUILDING CODE 293 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

roof slope or direc ti on and around roof openings. Where signed in ac cordance with ANSI/SPRI ES-1, except the ba sic flash ing is of metal, the metal shall be cor ro sion re sis tant wind speed shall be deter mined from Figure 1609. with a thickness of not less than 0.019 inch (.483 mm) (No. 26 gal va nized sheet). 1504.6 Phys i cal prop er ties. Roof cov erings insta lled on low-slope roofs (roof slope < 2:12) in accor dance with Sec tion 1503.3 Coping. Para pet walls shall be properl y coped with 1507 shall dem onstra te physi cal inte grit y over the working life noncombustible, weather proof mate ri als of a width no less of the roof based upon 2,000 hours of expo sure to accel erate d than the thickness of the para pet wall. weather ing tests conducte d in ac cordance with ASTM G 152, ASTM G 155 or ASTM G 154. Those roof cov erings that are [P] 1503.4 Roof drainage. Design and insta lla ti on of roof subjec t to cycli cal flexural response due to wind loads shall not drainage system s shall com ply with the In ter na tional Uni form demon stra te any signif icant loss of tensil e strength for Plumb ing Code. unreinforced membranes or breaking strength for rein forced 1503.4.1 Gutters . Gutter s and leaders placed on the out side mem branes when tested as herein re quired. of buildings, other than Group R-3 as appli cable in Sec tion 1504.7 Im pact re sis tance. Roof cov erings insta lled on 101.2, pri vate garages and buildings of Type V construc - low-slope roofs (roof slope < 2:12) in accor dance with Sec tion tion, shall be of noncombustible mate ria l or a mini mum of 1507 shall re sist impact damage based on the result s of tests Sched ule 40 plasti c pipe. conducte d in ac cordance with ASTM D 3746, ASTM D 4272, 1503.5 Roof ven ti la tion. Intak e and exhaust vents shall be pro - CGSB 37-GP-52M or FM 4470. vided in accor dance with Sec tion 1203.2 and the manu f ac- turer’s in stal la tion in struc tions. SECTION 1505 FIRE CLASSIFICATION SECTION 1504 1505.1 Gen eral. Roof assem bli es shall be di vided into the PERFORMANCE REQUIREMENTS classes de fined be low. Class A, B and C roof as sem blies and 1504.1 Wind resis tance of roofs. Roof decks and roof cov er- roof cov erings re quired to be listed by this sec tion shall be ings shall be designe d for wind loads in accor dance with Chap- tested in accor dance with ASTM E 108 or UL 790. In addi ti on, ter 16 and Secti ons 1504.2, 1504.3 and 1504.4. fire-re tar dant-treated wood roof cov er ings shall be tested in ac - ¬ cordance with ASTM D 2898. The mini mum roof cov erings 1504.1.1 Wind resis tance of asphalt shingles . Asphalt insta lled on buildings shall comply with Table 1505.1 based on shingles shall be de signed for wind speeds in ac cordance the type of construc tion of the building. with Sec tion 1507.2.7. TABLE 1505.1a,b 1504.2 Wind resis tance of clay and con crete tile. Clay and MINIMUM ROOF COVERING CLASSIFICATION concret e tile roof cov erings shall be connect ed to the roof deck FOR TYPES OF CONSTRUCTION in ac cordance with Chapter 16. IA IB IIA IIB IIIA IIIB IV VA VB 1504.3 Wind resis tance of nonballasted roofs. Roof cov er- B B B Cc B Cc B B Cc ings insta lled on roofs in accor dance with Sec tion 1507 that are For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2. mechan i cal ly at tached or adhered to the roof deck shall be de- a. Un less oth er wise re quired in ac cor dance with the In ter na tional Ur ban signed to re sist the design wind load pressures for cladding in Wildland In ter face Code or due to the lo ca tion of the build ing within a fire Chap ter 16. dis trict in ac cor dance with Ap pen dix D. b. Nonclassified roof cov er ings shall be per mit ted on build ings of Group R-3, 1504.3.1 Other roof systems . Roof sys tems with built-up, as ap pli ca ble in Sec tion 101.2, and Group U oc cu pan cies, where there is a min i mum fire-sep a ra tion dis tance of 6 feet mea sured from the lead ing edge mod i fied bi tu men, fully ad hered or me chan i cally at tached of the roof. single- ply through fastene d metal panel roof system s, and c. Buildings that are not more than two stories in height and having not more other types of membrane roof cov erings shall also be tested than 6,000 square feet of pro jected roof area and where there is a min i mum in ac cordance with FM 4450, FM 4470, UL 580 or UL 10-foot fire-sep a ra tion dis tance from the lead ing edge of the roof to a lot line on all sides of the build ing, except for street fronts or pub lic ways, shall be 1897. per mit ted to have roofs of No. 1 ce dar or red wood shakes and No. 1 shin gles. 1504.3.2 Metal panel roof systems . Metal panel roof systems through fastene d or standing seam shall be tested in ac - 1505.2 Class A roof assem blies. Class A roof as semblies are cor dance with UL 580 or ASTM E 1592. those that are ef fec tive against se vere fire test ex po sure. Class A roof assem bli es and roof cov erings shall be listed and identi fied 1504.4 Bal lasted low-slope roof systems . Bal lasted low-slope as Class A by an appro ved testing agency. Class A roof assem - (roof slope < 2:12) single- ply roof sys tem cov erings insta lled blies shall be permit ted for use in buildings or struc tures of all in ac cordance with Sec tion 1507 shall be de signed in ac cor- types of construc tion. dance with ANSI/SPRI RP-4. Ex cep tion: Class A roof as sem blies in clude those with cov - 1504.5 Edge secur ement for low-slope roofs. Low-slope erings of brick, ma sonry, slate, clay or concret e roof tile, ex - mem brane roof sys tems metal edge se cure ment, ex cept gut - posed concret e roof deck, ferrous or copper shingles or ters, insta lled in accor dance with Sec tion 1507, shall be de - sheets.

294 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

1505.3 Class B roof assem blies. Class B roof assem blies are SECTION 1507 those that are ef fec tive against mod er ate fire-test ex po sure. REQUIREMENTS FOR ROOF COVERINGS Class B roof assem bli es and roof cov erings shall be listed and identi fied as Class B by an appro ved testing agency. 1507.1 Scope. Roof cov erings shall be appli ed in accor dance with the appli cable pro visions of this sec tion and the manu f ac- Ex cep tion: Class B roof as sem blies in clude those with cov - turer’s in stal la tion in struc tions. erings of metal sheets and shingles . 1507.2 Asphalt shingles . The insta lla ti on of asphalt shingles 1505.4 Class C roof assem blies. Class C roof assem blies are shall com ply with the pro visions of this sec tion and Table 1507.2. those that are effec tive against light fire-test ex po sure. Class C roof assem bli es and roof cov erings shall be listed and identi fied 1507.2.1 Deck requir ement s. Asphalt shingles shall be as Class C by an appro ved testing agency. fastene d to sol idly sheathed decks. 1507.2.2 Slope. Asphalt shingles shall only be used on roof 1505.5 Nonclassified roof ing. Nonclassified roof ing is appro ved slopes of two units verti cal in 12 units hori zon tal (17-per- ma te rial that is not listed as a Class A, B or C roof cov er ing. cent slope) or greater. For roof slopes from two units verti cal 1505.6 Fire-retar dant-tr eated wood shingles and shakes. in 12 units hori zon tal (17-percent slope) up to four units ver- Fire-retar dant-treated wood shakes and shingles shall be ti cal in 12 units hori zon tal (33-percent slope), double treated by impre gna ti on with chem ical s by the full-cell vac- underlayment ap pli ca tion is re quired in ac cor dance with uum-pres sure pro cess, in ac cor dance with AWPA C1. Each Sec tion 1507.2.8. bundle shall be marked to identi fy the manu f acture d unit and 1507.2.3 Underlayment. Unles s other wise noted, require d the manu f acture r, and shall also be la beled to identi fy the clas- underlayment shall conform to ASTM D 226, Type I, or si fica tion of the ma te rial in ac cor dance with the testing re - ASTM D 4869, Type I. quired in Secti on 1505.1, the treating com pany and the qualit y con trol agency. 1507.2.4 Self-ad her ing poly mer mod i fied bi tu men sheet. Self-ad her ing poly mer mod i fied bi tu men sheet shall com- 1505.7 Special pur pose roofs. Specia l purpose wood shingle ply with ASTM D 1970. or wood shake roof ing shall conform with the grading and ap - pli cati on require ments of Sec tion 1507.8 or 1507.9. In addi - 1507.2.5 Asphalt shingles . Asphalt shingles shall have tion, an underlayment of 0.625-inch (15.9 mm) Type X self-seal strips or be inter locking, and comply with ASTM wa ter-re sis tant gyp sum back ing board or gyp sum sheath ing D 225 or ASTM D 3462. shall be placed under mini mum nomi nal 0.5-inch-thick (12.7 1507.2.6 Fastene rs. Fastene rs for as phalt shingles shall be mm) wood struc tural panel solid sheathing or 1-inch (25 mm) gal va nized, stain less steel, alu mi num or cop per roof ing nom i nal spaced sheath ing. nails, mini mum 12 gage [0.105 inch (2.67 mm)] shank with a mini mum 0.375 inch-di ame ter (9.5 mm) head, of a length to pene tra te through the roof ing ma teri als and a mini mum of SECTION 1506 0.75 inch (19.1 mm) into the roof sheathing. Where the roof MATERIALS sheathing is less than 0.75 inch (19.1 mm) thick, the nails 1506.1 Scope. The re quire ments set forth in this sec tion shall shall pene tra te through the sheathing. Fastene rs shall com- ap ply to the ap pli ca tion of roof-cov er ing ma te ri als spec i fied ply with ASTM F 1667. herein. Roof cov erings shall be appli ed in accor dance with this chap ter and the man u fac turer’s in stal la tion in struc tions. In stal- 1507.2.7 At tach ment. Asphalt shingles shall have the mini - lati on of roof cov erings shall comply with the appli cable pro vi- mum number of fasten ers re quired by the manu f acture r and sions of Sec tion 1507. Sec tion 1504.1. Asphalt shingles shall be secured to the roof with not less than four fasten ers per strip shingle or two fas- 1506.2 Com pat i bil ity of ma te ri als. Roofs and roof cov erings teners per indi vidual shingle. Where the roof slope excee ds shall be of ma teri als that are com pat ible with each other and with 20 units verti cal in 12 units hori zon tal (166-percent slope), the building or structure to which the mate ri als are appli ed. specia l methods of fasten ing are require d. For roofs locat ed where the basic wind speed in accor dance with Figure 1609 is 1506.3 Ma te rial spec i fi ca tions and phys i cal charac ter is tics. 110 mph or greater, specia l methods of fasten ing are re- Roof-cov er ing ma te ri als shall con form to the ap pli ca ble stan - quired. Specia l fasten ing methods shall be tested in accor - dards listed in this chapter . In the absenc e of appli cable stan- dance with ASTM D 3161, modi f ied to use a wind speed of dards or where ma te ri als are of ques tion able suit abil ity, test ing 110 mph. by an appro ved agency shall be require d by the building of ficia l to de ter mine the char ac ter, qual ity and lim i ta tions of ap pli ca - 1507.2.8 Underlayment ap pli ca tion. For roof slopes from tion of the ma te ri als. two units verti cal in 12 units hori zon tal (17-percent slope), up to four units verti cal in 12 units hori zon tal (33-percent 1506.4 Prod uct iden ti fi ca tion. Roof-cov er ing ma te ri als shall slope), underlayment shall be two layers appli ed in the fol - be de liv ered in pack ages bear ing the man u fac turer’s iden ti fy- lowing manner . Apply a mini mum 19-inch-wide (483 mm) ing marks and appro ved testing agency labels require d in ac - strip of underlayment felt par al lel with and start ing at the cordance with Sec tion 1505. Bulk shipment s of ma teri als shall eaves, fas tened suf ficiently to hold in place. Start ing at the be ac compa nied with the same infor ma ti on issued in the form eave, apply 36-inch-wide (914 mm) sheets of underlayment of a certi f icat e or on a bill of lading by the manu f acture r. overlap ping suc ces sive sheets 19 inches (483 mm) and fas-

2003 SEATTLE BUILDING CODE 295 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

TABLE 1507.2 ASPHALT SHINGLE APPLICATION

COMPONENT INSTALLATION REQUIREMENT

1. Roof slope Asphalt shingles shall only be used on roof slopes of two units vertical in 12 units horizontal (2:12) or greater. For roof slopes from two units vertical in 12 units horizontal (2:12) up to four units vertical in 12 units horizontal (4:12), double underlayment application is required in accordance with Section 1507.2.8.

2. Deck requirement Asphalt shingles shall be fastened to solidly sheathed roofs.

3. Underlayment Underlayment shall conform with ASTM D 226, Type 1, or ASTM D 4869, Type 1.

For roof slopes from two units vertical in 12 units Underlayment shall be two layers applied in the following manner. Apply a horizontal (2:12), up to four units vertical in 12 units minimum 19-inch strip or underlayment felt parallel to and starting at the eaves, horizontal (4:12) fastened sufficiently to hold in place. Starting at the eave, apply 35-inch-wide sheets of underlayment overlapping successive sheets 19 inches and fastened sufficiently to hold in place.

For roof slopes from four units vertical in 12 units Underlayment shall be one layer applied in the following manner. Underlayment horizontal (4:12) or greater shall be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches, fastened only as necessary to hold in place.

In areas where the aver age daily temper a ture in Janu ary A membrane that consists of at least two layers of underlayment cemented is 25°F or less or where there is a possi bil ity of ice together or of a self-adhering polymer-modified bitumen sheet shall be used in form ing along the eaves caus ing a backup of wa ter lieu of normal underlayment and extend from the eave’s edge to a point at least 24 inches inside the exterior wall line of the building.

4. Application —

At tach ment Asphalt shingles shall have the minimum number of fasteners required by the manufacturer and Section 1504.1. Asphalt shingles shall be secured to the roof with not less than four fasteners per strip shingle or two fasteners per individual shingle. Where the roof slope exceeds 20 units vertical in 12 units horizontal (20:12), special methods of fastening are required.

Fasteners Galvanized, stainless steel, aluminum or copper roofing nails, minimum 12-gage 3 (0.105 inch) shank with a minimum /8-inch diameter head. Fasteners shall be long enough to penetrate into the sheathing ¾ inch or through the thickness of the sheathing.

Flashings In accordance with Section 1507.2.9.

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, °C = [(°F) - 32]/1.8, 1 mile per hour = 1.609 km/h.

tened suf ficie ntly to hold in place. For roof slopes of four used in lieu of normal underlayment and extend from the units verti cal in 12 units hori zon tal (33-percent slope) or eave’s edge to a point at least 24 inches (610 mm) inside greater, underlayment shall be one layer appli ed in the fol - the exte rior wall line of the build ing. lowing manner . Underlayment shall be appli ed shingle fashion, paral lel to and starting from the eave and lapped 2 Ex cep tion: De tached ac ces sory struc tures that con - inches (51 mm), fastene d only as neces sary to hold in place. tain no condi ti oned floor area.

1507.2.8.1 High wind attach ment . Underlayment ap- 1507.2.9 Flashings . Flashing for asphalt shingles shall plied in areas subjec t to high winds (greater than 110 comply with this secti on. Flashing shall be appli ed in accor - mph in accor dance with Figure 1609) shall be appli ed dance with this sec tion and the asphalt shingle manu f ac- with cor ro sion- re sis tant fas ten ers in ac cor dance with the turer’s printed instruc tions. man u fac turer’s in struc tions. Fas teners are to be ap plied along the overlap at a maxi mum spacing of 36 inches 1507.2.9.1 Base and cap flashing . Base and cap flash - (914 mm) on center . ing shall be insta lled in accor dance with the manu f ac- turer’s in struc tions. Base flash ing shall be of ei ther 1507.2.8.2 Ice dam membrane . In ar eas where the av er - cor ro sion-re sis tant metal of min i mum nom i nal 0.019- age daily tem pera ture in Janu ary is 25°F (-4°C) or less or inch (0.483 mm) thickness or mineral -surf aced roll roof - where there is a possi bil ity of ice forming along the eaves ing weighing a mini mum of 77 pounds per 100 square caus ing a backup of water , a membrane that consis ts of at feet (3.76 kg/m2). Cap flashing shall be corro sion-re sis - least two layers of underlayment cement ed togethe r or of tant metal of mini mum nomi nal 0.019-inch (0.483 mm) a self-ad hering poly mer mod i fied bi tu men sheet shall be thick ness.

296 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

1507.2.9.2 Valleys . Val ley lin ings shall be in stalled in ASTM D 2626 or ASTM D 249 Type I mineral -surf aced roll ac cor dance with the man u fac turer’s in struc tions be fore roof ing. ap ply ing shin gles. Val ley lin ings of the fol low ing types 1507.3.3.1 Low-slope roofs. For roof slopes from 21/ shall be per mit ted: 2 units verti cal in 12 units hori zon tal (21-percent slope), 1. For open valle ys (valle y lining exposed) lined with up to four units verti cal in 12 units hori zon tal (33-percent metal, the val ley lin ing shall be at least 16 inches slope), underlayment shall be a mini mum of two layers (406 mm) wide and of any of the corro sion-re sis - appli ed as follo ws: tant met als in Table 1507.2.9.2. 1. Starting at the eave, a 19-inch (483 mm) strip of 2. For open valle ys, valle y lining of two plies of min- underlayment shall be appli ed paral lel with the eral-surf aced roll roof ing shall be permit ted. The eave and fas tened suf ficiently in place. bottom layer shall be 18 inches (457 mm) and the 2. Starting at the eave, 36-inch-wide (914 mm) strips top layer a mini mum of 36 inches (914 mm) wide. of underlayment felt shall be appli ed overlap ping 3. For closed valle ys (valle ys cov ered with shingles ), succes sive sheets 19 inches (483 mm) and fastene d valle y lining of one ply of smooth roll roof ing suf fi ciently in place. comply ing with ASTM D 224 and at least 36 inches (914 mm) wide or types as descri bed in 1507.3.3.2 High-slope roofs. For roof slopes of four Items 1 and 2 above shall be per mitted. Specialty units verti cal in 12 units hori zon tal (33-percent slope) or underlayment shall comply with ASTM D 1970. greater, underlayment shall be a mini mum of one layer of underlayment felt appli ed shingle fashion, paral lel to, TABLE 1507.2.9.2 and start ing from the eaves and lapped 2 inches (51 mm), VALLEY LINING MATERIAL fastene d only as neces sary to hold in place. MINIMUM MATERIAL THICKNESS GAGE WEIGHT 1507.3.4 Clay tile. Clay roof tile shall com ply with ASTM Copper — — 16 oz C 1167. Aluminum 0.024 in. — — 1507.3.5 Concr ete tile. Con crete roof tiles shall be in ac - Stainless steel — 28 — cor dance with the phys ical test require ments as follo ws: Galvanized steel 0.0179 in. 26 (zinc-coated G90) — 1. The trans verse strength of tiles shall be de ter mined accord ing to Sec tion 6.3 of ASTM C 1167 and in ac- Zinc alloy 0.027 in. — — cordance with Table 1507.3.5. Lead — — 2.5 pounds 2. The absorp ti on of concret e roof tiles shall be ac cord- Painted terne — — 20 pounds ing to Sec tion 8 of ASTM C 140. Roof tiles shall ab- For SI: 1 inch = 25.4 mm, 1 pound = 0.454 kg, 1 ounce = 28.35 g. sorb not more than 15 percent of the dry weight of the tile dur ing a 24-hour immer sion test. 1507.2.9.3 Drip edge. Pro vide drip edge at eaves and ga- 3. Roof tiles shall be tested for freeze/thaw re sis tance bles of shingle roofs. Overlap to be a mini mum of 2 accord ing to Sec tion 8 of ASTM C67. Roof tiles shall inches (51 mm). Eave drip edges shall extend 0.25 inch show no breakage and not have more than 1 percent (6.4 mm) be low sheathing and extend back on the roof a loss in dry weight of any indi vidual concret e roof tile. mini mum of 2 inches (51 mm). Drip edge shall be me - chani cal ly fastene d a maxi mum of 12 inches (305 mm) TABLE 1507.3.5 o.c. A cricket or saddle shall be insta lled on the ridge side TRANSVERSE BREAKING STRENGTH of any chim ney greater than 30 inches (762 mm) wide. OF CONCRETE ROOF TILE (lbs.) Cricket or sad dle cov er ings shall be sheet metal or of the DRY same ma terial as the roof cov er ing. TILE PROFILE Average of five tiles Individual tile High profile 400 350 1507.3 Clay and concr ete tile. The in stal la tion of clay and con crete tile shall com ply with the provi sions of this sec tion. Medium profile 300 250 Flat profile 300 250 1507.3.1 Deck requir ement s. Con crete and clay tile shall be insta lled only over solid sheathing or spaced struc tural For SI: 1 pound = 4.45 N. sheath ing boards. 1507.3.6 Fas ten ers. Tile fas ten ers shall be cor ro sion re sis tant 5 1507.3.2 Deck slope. Clay and concret e roof tile shall be in- and not less than 11 gage, /16-inch (8.0 mm) head, and of suf fi- 1 stalled on roof slopes of 2 /2 units verti cal in 12 units hori - cient length to pene tra te the deck a mini mum of 0.75 inch (19.1 zontal (21-percent slope) or greater. For roof slopes from mm) or through the thickness of the deck, whiche ver is less. 1 2 /2 units verti cal in 12 units hori zon tal (21-percent slope) to At tach ing wire for clay or con crete tile shall not be smaller four units verti cal in 12 units hori zon tal (33-percent slope), than 0.083 inch (2.1 mm). Perim e ter fasten ing ar eas include dou ble underlayment ap pli ca tion is re quired in ac cor dance three tile courses but not less than 36 inches (914 mm) from ei - with Sec tion 1507.3.3. ther side of hips or ridges and edges of eaves and ga ble rakes. 1507.3.3 Underlayment. Unles s other wise noted, require d 1507.3.7 At tach ment. Clay and concret e roof tiles shall be underlayment shall conform to: ASTM D 226, Type II; fastene d in ac cordance with Table 1507.3.7.

2003 SEATTLE BUILDING CODE 297 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

TABLE 1507.3.7 CLAY AND CONCRETE TILE ATTACHMENTa, b, c GENERAL — CLAY OR CONCRETE ROOF TILE Maximum basic Mean roof wind speed height (mph) (feet) Roof slope up to < 3:12 Roof slope 3:12 and over 85 0-60 One fastener per tile. Flat tile Two fasteners per tile. Only one fastener on slopes of 7:12 and without vertical laps, two less for tiles with installed weight exceeding 7.5 lbs./sq. ft. 100 0-40 fasteners per tile. having a width no greater than 16 inches. The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved 100 > 40-60 clips. All rake tiles shall be nailed with two nails. The nose of all ridge, hip and rake tiles shall be set in a bead of roofer’s mastic. 110 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 120 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 130 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. All > 60 The fastening system shall resist the wind forces in Section 1609.7.2. INTERLOCKING CLAY OR CONCRETE ROOF TILE WITH PROJECTING ANCHOR LUGSd, e (Installations on spaced/solid sheathing with battens or spaced sheathing) Maximum basic Mean roof wind speed height (mph) (feet) Roof slope up to < 5:12 Roof slope 5:12 < 12:12 Roof slope 12:12 and over One fastener per tile every other One fastener required for every 85 0-60 Fasteners are not required. Tiles row. All perimeter tiles require tile. Tiles with installed weight with installed weight less than 9 one fastener. Tiles with installed less than 9 lbs./sq. ft. require a lbs./sq. ft. require a minimum of weight less than 9 lbs./sq. ft. minimum of one fastener per one fastener per tile. require a minimum of one fastener 100 0-40 tile. per tile. The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved 100 > 40-60 clips. All rake tiles shall be nailed with two nails The nose of all ridge, hip and rake tiles shall be set in a bead of roofers’s mastic. 110 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 120 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 130 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. All > 60 The fastening system shall resist the wind forces in Section 1609.7.2. INTERLOCKING CLAY OR CONCRETE ROOF TILE WITH PROJECTING ANCHOR LUGS (Installations on solid sheathing without battens) Maximum basic Mean roof wind speed height (mph) (feet) All roof slopes 85 0-60 One fastener per tile. 100 0-40 One fastener per tile. The head of all tiles shall be nailed. The nose of all eave tiles shall be fastened with approved 100 > 40-60 clips. All rake tiles shall be nailed with two nails The nose of all ridge, hip and rake tiles shall be set in a bead of roofers’s mastic. 110 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 120 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. 130 0-60 The fastening system shall resist the wind forces in Section 1609.7.2. All > 60 The fastening system shall resist the wind forces in Section 1609.7.2. For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 1.609 km/h, 1 pound per square foot = 0.0478 kn/m2. 5 a. Min i mum fas tener size. Cor ro sion-re sis tant nails not less than No. 11 gage with /16-inch head. Fasteners shall be long enough to pen e trate into the sheath ing 0.75 inch or through the thick ness of the sheath ing, which ever is less. Attaching wire for clay and con crete tile shall not be smaller than 0.083 inch. b. Snow ar eas. A min i mum of two fas ten ers per tile are re quired or bat tens and one fas tener. c. Roof slopes greater than 24:12. The nose of all tiles shall be se curely fas tened. 1 d. Hor i zon tal bat tens. Bat tens shall be not less than 1inch by 2 inch nom i nal. Pro vi sions shall be made for drain age by a mini mum of /8-inch riser at each nail or by 4-foot-long bat tens with at least a 0.5-inch sep a ra tion be tween bat tens. Hor i zon tal bat tens are re quired for slopes over 7:12. e. Per im e ter fas ten ing ar eas include three tile courses but not less than 36 inches from ei ther side of hips or ridges and edges of eaves and ga ble rakes.

298 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

1507.3.8 Ap pli ca tion. Tile shall be appli ed ac cording to the 2. 300 se ries stain less-steel fasten ers shall be used for man u fac turer’s in stal la tion in struc tions, based on the fol- cop per roofs. low ing: 3. Stain less-steel fasten ers are ac cept able for all types of 1. Cli ma tic con di tions. metal roofs. 2. Roof slope. TABLE 1507.4.3 3. Underlayment sys tem. METAL ROOF COVERINGS 4. Type of tile be ing in stalled. STANDARD APPLICATION ROOF COVERING TYPE RATE/THICKNESS 1507.3.9 Flashing. At the junc ture of the roof verti cal sur- ASTM B 209, 0.024 inch minimum thickness for roll-formed panels and 0.019 faces, flash ing and counterflashing shall be pro vided in ac- Aluminum cor dance with the man u fac turer’s in stal la tion in struc tions, inch minimum thickness for press-formed and where of metal, shall not be less than 0.019-inch (0.48 shingles. mm) (No. 26 galv anize d sheet gage) corro sion-re sis tant. Aluminum-zinc alloy ASTM A 792 AZ 50 The valle y flashing shall extend at least 11 inches (279 mm) coated steel from the cen ter line each way and have a splash di verter rib 16 oz./sq. ft. for metal-sheet roof-covering not less than 1 inch (25 mm) high at the flow line formed as Copper systems; 12 oz./sq. ft. for preformed metal part of the flashing. Secti ons of flashing shall have an end shingle systems. lap of not less than 4 inches (102 mm). For roof slopes of ASTM A 653 G-90 zinc-coated, three units verti cal in 12 units hori zon tal (25-percent slope) Galvanized steel and over, the valle y flashing shall have a 36-inch-wide (914 0.013-inch-thick minimum mm) underlayment of one layer of Type I underlayment run- Lead-coated copper ASTM B 101 ning the full length of the valle y, in addi ti on to other re- Hard lead 2 lbs./sq. ft. quired underlayment. In ar eas where the av er age daily tem per a ture in Jan u ary is 25°F (-4°C) or less or where there Soft lead 3 lbs./sq. ft. is a possi bil ity of ice forming along the eaves causing a Prepainted steel ASTM A 755 backup of water , the metal valle y flashing underlayment Terne coating of 40 lbs. per double base shall be solid cement ed to the roof ing underlayment for Terne (tin) and terne- box, field painted where applicable in slopes under seven units verti cal in 12 units hori zon tal coated stainless accordance with manufacturer’s (58-percent slope) or of self-adher ing polymer modi f ied bi - installation instructions. tu men sheet. For SI: 1 ounce per square foot = 0.0026 kg/m2, 1 pound per square foot = 4.882 kg/m2, 1507.4 Metal roof panels . The insta lla ti on of metal roof pan- 1 inch = 25.4 mm, 1 pound = 0.454 kg. els shall com ply with the pro visions of this sec tion. 1507.4.1 Deck requir ement s. Metal roof panel roof cov er- 1507.5 Metal roof shingles . The in stal la tion of metal roof ings shall be appli ed to a solid or closely fit ted deck, except shingles shall com ply with the pro visions of this sec tion. where the roof cov ering is specif ical ly designe d to be ap - 1507.5.1 Deck requir ement s. Metal roof shin gles shall be plied to spaced supports. appli ed to a solid or closely fit ted deck, except where the 1507.4.2 Deck slope. The mini mum slope for lapped, roof cov ering is specif ical ly designe d to be appli ed to nonsoldered seam metal roofs with out ap plied lap seal ant spaced sheathing. shall be three units verti cal in 12 units hori zon tal (25-percent 1507.5.2 Deck slope. Metal roof shingles shall not be in- slope). The mini mum slope for lapped, nonsoldered seam stalled on roof slopes be low three units verti cal in 12 units metal roofs with ap plied lap seal ant shall be one-half ver tical hor i zon tal (25-per cent slope). unit in 12 units hori zon tal (4-percent slope). The mini mum slope for standing seam of roof system s shall be one-quarter 1507.5.3 Underlayment. Underlayment shall conform to unit verti cal in 12 units hori zon tal (2-percent slope). ASTM D 226, Type I. In ar eas where the av er age daily tem - pera ture in Janu ary is 25°F (-4°C) or less or where there is a 1507.4.3 Ma te rial stan dards. Metal-sheet roof cov er ing possi bil ity of ice forming along the eaves causing a backup sys tems that in cor po rate sup port ing struc tural mem bers of water , an ice bar rier that con sists of at least two layers of shall be de signed in ac cordance with Chapter 22. Metal- underlayment ce mented togethe r or of a self-adher ing poly - sheet roof cov erings insta lled over structura l decking shall mer-modi f ied bi tumen sheet, shall be used in lieu of normal comply with Table 1507.4.3. underlayment and extend from the eave’s edge to a point at least 24 inches (610 mm) inside the exte rior wall line of the 1507.4.4 At tach ment. Metal roofing fastened di rectly to build ing. steel fram ing shall be attached by ap proved man u factur ers’ fas ten ers. In the ab sence of man u fac turer rec om men da - Ex cep tion: De tached ac ces sory struc tures that con tain tions, all of the fol lowing fasten ers shall be used: no condi ti oned floor area. 1. Gal vanized fasten ers shall be used for galv anized 1507.5.4 Ma te rial stan dards. Metal roof shingle roof cov - roofs. erings shall comply with Table 1507.4.3.

2003 SEATTLE BUILDING CODE 299 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

1507.5.5 At tach ment. Metal roof shingles shall be secured possi bil ity of ice forming along the eaves causing a backup to the roof in accor dance with the appro ved manu f acture r’s of water , an ice bar rier that con sists of at least two layers of in stal la tion in struc tions. underlayment ce mented togethe r or of a self-adher ing poly - mer-modi f ied bi tumen sheet, shall extend from the eave’s 1507.5.6 Flashing. Roof valle y flashing shall be of corro - edge to a point at least 24 inches (610 mm) inside the exte - sion-re sis tant metal of the same mate rial as the roof cov er - rior wall line of the build ing. ing or shall comply with the standards in Table 1507.4.3. The valle y flashing shall extend at least 8 inches (203 mm) Ex cep tion: De tached ac ces sory struc tures that con tain from the cen ter line each way and shall have a splash di verter no condi ti oned floor area. rib not less than 0.75 inch (19.1 mm) high at the flow line formed as part of the flashing. Secti ons of flashing shall 1507.7.4 Ma te rial stan dards. Slate shin gles shall com ply have an end lap of not less than 4 inches (102 mm). In ar eas with ASTM C 406. where the av er age daily tem per ature in Jan u ary is 25°F 1507.7.5 Ap pli ca tion. Min i mum headlap for slate shingles (-4°C) or less or where there is a possi bil ity of ice forming shall be in accor dance with Table 1507.7.5. Slate shingles along the eaves caus ing a backup of water , the metal valle y shall be secured to the roof with two fasten ers per slate. flashing shall have a 36-inch-wide (914 mm) underlayment direct ly under it consis ting of one layer of underlayment TABLE 1507.7.5 running the full length of the valle y, in addi ti on to SLATE SHINGLE HEADLAP underlayment re quired for metal roof shingles . The metal HEADLAP valle y flashing underlayment shall be solid ce mented to the SLOPE (inches) roof ing underlayment for roof slopes under seven units ver- 4:12 < slope < 8:12 4 ti cal in 12 units hori zon tal (58-percent slope) or of self-adher ing poly mer-mod i fied bi tu men sheet. 8:12 < slope < 20:12 3 slope ≥ 20:12 2 1507.6 Min eral-surfaced roll roof ing. The in stal la tion of mineral -surf aced roll roof ing shall comply with this secti on. For SI: 1 inch = 25.4 mm. 1507.6.1 Deck requir ement s. Mineral -surf aced roll roof - 1507.7.6 Flashing. Flashing and counterflashing shall be ing shall be fastene d to sol idly sheathed roofs. made with sheet metal. Val ley flash ing shall be a min imum of 15 inches (381 mm) wide. Valle y and flashing metal shall 1507.6.2 Deck slope. Mineral -surf aced roll roof ing shall be a mini mum un coat ed thickness of 0.0179-inch (0.455 not be appli ed on roof slopes be low one unit verti cal in 12 mm) zinc-coated G90. Chimne ys, stucco or brick walls units hor i zon tal (8-per cent slope). shall have a mini mum of two plies of felt for a cap flashing 1507.6.3 Underlayment. Underlayment shall conform to consis ting of a 4-inch-wide (102 mm) strip of felt set in plas- ASTM D 226, Type I. In ar eas where the av er age daily tem - tic ce ment and extend ing 1 inch (25 mm) above the first felt pera ture in Janu ary is 25°F (-4°C) or less or where there is a and a top coat ing of plasti c ce ment. The felt shall extend possi bil ity of ice forming along the eaves causing a backup over the base flashing 2 inches (51 mm). of water , an ice bar rier that con sists of at least two layers of 1507.8 Wood shingles . The insta lla ti on of wood shingles shall underlayment ce mented togethe r or of a self-adher ing poly - comply with the pro visions of this sec tion and Table 1507.8. mer-modi f ied bi tumen sheet, shall extend from the eave’s edge to a point at least 24 inches (610 mm) inside the exte - 1507.8.1 Deck requir ement s. Wood shingles shall be in - rior wall line of the build ing. stalled on solid or spaced sheathing. Where spaced sheath - ing is used, sheathing boards shall not be less than 1-inch by Ex cep tion: De tached ac ces sory struc tures that con tain 4-inch (25 mm by 102 mm) nomi nal di mensions and shall no condi ti oned floor area. be spaced on center s equal to the weather expo sure to coin - 1507.6.4 Ma te rial stan dards. Mineral -surf aced roll roof - cide with the placement of fasten ers. ing shall conform to ASTM D 224, ASTM D 249, ASTM D 1507.8.1.1 Solid sheathing requir ed. Solid sheathing is 371 or ASTM D 3909. re quired in ar eas where the av er age daily tem per ature in 1507.7 Slate shingles . The in stal la tion of slate shin gles shall Janu ary is 25°F (-4°C) or less or where there is a possi bil - comply with the pro visions of this sec tion. ity of ice forming along the eaves causing a backup of wa ter. 1507.7.1 Deck requir ement s. Slate shin gles shall be fastened to sol idly sheathed roofs. 1507.8.2 Deck slope. Wood shingles shall be insta lled on slopes of three units verti cal in 12 units hori zon tal (25-per- 1507.7.2 Deck slope. Slate shingles shall only be used on cent slope) or greater. slopes of four units verti cal in 12 units hori zon tal (4:12) or greater. 1507.8.3 Underlayment. Underlayment shall comply with ASTM D 226, Type I. In ar eas where the av er age daily tem - 1507.7.3 Underlayment. Underlayment shall comply with pera ture in Janu ary is 25°F (-4°C) or less or where there is a ASTM D 226, Type II. In ar eas where the av er age daily tem - possi bil ity of ice forming along the eaves causing a backup pera ture in Janu ary is 25°F (-4°C) or less or where there is a of water , an ice bar rier that con sists of at least two layers of

300 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

TABLE 1507.8 WOOD SHINGLE AND SHAKE INSTALLATION ROOF ITEM WOOD SHINGLES WOOD SHAKES Wood shingles shall be installed on slopes of Wood shakes shall be installed on slopes of four units 1. Roof slope three units vertical in 12 units horizontal (3:12) vertical in 12 units horizontal (4:12) or greater. or greater. 2. Deck requirement — — Temperate climate Shingles shall be applied to roofs with solid or Shakes shall be applied to roofs with solid or spaced spaced sheathing. Where spaced sheathing is sheath ing. Where spaced sheathing is used, sheathing used, sheathing boards shall not be 4 less than boards shall not be less than 1″ × 4″ nominal dimensions 1″ × 4″ nominal dimensions and shall be and shall be spaced on center equal to the weather spaced on center equal to the weather exposure exposure to coincide with the placement of fasteners. to coincide with the placement of fasteners. When 1″ × 4″ spaced sheathing is installed at 10 inches, boards must be installed between the sheathing boards.

In areas where the average daily Solid sheathing required. Solid sheathing is required. temperature in January is 25°F or less or where there is a possibility of ice forming along the eaves causing a backup of water. Interlayment shall comply with ASTM D 226, Type 3. Interlayment No requirements. 1. 4. Underlayment — — Temperate climate Underlayment shall comply with ASTM D Underlayment shall com ply with ASTM D 226, Type 1. 226, Type 1. In areas where the average daily An ice shield that consists of at least two layers An ice shield that consists of at least two layers of temperature in January is 25°F of underlayment cemented together or of a underlayment cemented together or of a self-adhering or less or where there is a self-adhering polymer-modified bitumen sheet polymer-modified bitumen sheet shall extend from the possibility of ice forming along shall extend from the eave’s edge to a point at eave’s edge to a point at least 24 inches inside the the eaves causing a backup of least 24 inches inside the exterior wall line of exterior wall line of the building. water. the building. 5. Application — — Attachment Fasteners for wood shingles shall be corrosion Fasteners for wood shakes shall be corrosion resistant resistant with a minimum penetration of 0.75 with a minimum penetration of 0.75 inch into the inch into the sheathing. For sheathing less than sheathing. For sheathing less than 0.5 inch thick, the 0.5 inch thick, the fasteners shall extend fasteners shall extend through the sheathing. through the sheathing. No. of fasteners Two per shingle. Two per shake. Exposure Weather exposures shall not exceed those set Weather exposures shall not exceed those set forth in forth in Table 1507.8.6 Table 1507.9.7 Method Shingles shall be laid with a side lap of not less Shakes shall be laid with a side lap of not less than 1.5 than 1.5 inches between joints in courses, and no inches between joints in adjacent courses. Spacing two joints in any three adjacent courses shall be between shakes shall not be less than 0.375 inch or in direct alignment. Spacing between shingles more than 0.625 inch for shakes and tapersawn shakes shall be 0.25 to 0.375 inch. of naturally durable wood and shall be 0.25 to 0.375 inch for preservative taper sawn shakes. Flashing In accordance with Section 1507.8.7. In accordance with Section 1507.9.8. For SI: 1 inch = 25.4 mm, °C = [(°F) - 32]/1.8.

2003 SEATTLE BUILDING CODE 301 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

underlayment ce mented togethe r or of a self-adher ing poly - (279 mm) from the center line each way and have a splash di - mer-modi f ied bi tumen sheet shall extend from the eave’s verter rib not less than 1 inch (25 mm) high at the flow line edge to a point at least 24 inches (610 mm) inside the exte - formed as part of the flashing. Secti ons of flashing shall rior wall line of the build ing. have an end lap of not less than 4 inches (102 mm). For roof slopes of three units verti cal in 12 units hori zon tal (25-per- Ex cep tion: De tached ac ces sory struc tures that con tain cent slope) and over, the valle y flashing shall have a no condi ti oned floor area. 36-inch-wide (914 mm) underlayment of one layer of Type I underlayment running the full length of the valle y, in addi - 1507.8.4 Ma te rial stan dards. Wood shingles shall be of tion to other require d underlayment. In areas where the av - natu ral ly dura ble wood and com ply with the require ments erage daily tem pera ture in Janu ary is 25°F (-4°C) or less or of Table 1507.8.4. where there is a possi bil ity of ice forming along the eaves caus ing a backup of water , the metal valle y flash ing TABLE 1507.8.4 underlayment shall be solid ce mented to the roof ing WOOD SHINGLE MATERIAL REQUIREMENTS underlayment for slopes under seven units verti cal in 12 APPLICABLE units hor i zon tal (58-per cent slope). MATERIAL MINIMUM GRADES GRADING RULES Wood shingles of naturally 1507.9 Wood shakes. The insta lla ti on of wood shakes shall 1, 2 or 3 CSSB durable wood comply with the pro visions of this sec tion and Table 1507.8. CSSB = Ce dar Shake and Shin gle Bureau 1507.9.1 Deck requir ement s. Wood shakes shall only be 1507.8.5 At tach ment. Fasten ers for wood shingles shall be used on solid or spaced sheathing. Where spaced sheathing cor ro sion re sis tant with a min i mum pen e tra tion of 0.75 inch is used, sheathing boards shall not be less than 1-inch by (19.1 mm) into the sheathing. For sheathing less than 0.5 4-inch (25 mm by 102 mm) nomi nal di mensions and shall inch (12.7 mm) in thickness, the fasten ers shall extend be spaced on center s equal to the weather expo sure to coin - through the sheathing. Each shingle shall be at tached with a cide with the placement of fasten ers. Where 1-inch by min i mum of two fas ten ers. 4-inch (25 mm by 102 mm) spaced sheathing is insta lled at 10 inches (254 mm) o.c., addi ti onal 1-inch by 4-inch (25 1507.8.6 Ap pli ca tion. Wood shingles shall be laid with a mm by 102 mm) boards shall be insta lled betwee n the side lap not less than 1.5 inches (38 mm) betwee n joints in sheath ing boards. adja cent courses, and not be in di rect alignment in al ter nate courses. Spacing betwee n shingles shall be 0.25 to 0.375 1507.9.1.1 Solid sheathing requir ed. Solid sheathing is inches (6.4 to 9.5 mm). Weather expo sure for wood shingles re quired in ar eas where the av er age daily tem per ature in shall not excee d that set in Table 1507.8.6. Janu ary is 25°F (-4°C) or less or where there is a possi bil - ity of ice forming along the eaves causing a backup of wa ter. TABLE 1507.8.6 WOOD SHINGLE WEATHER EXPOSURE AND ROOF SLOPE 1507.9.2 Deck slope. Wood shakes shall only be used on EXPOSURE (inches) slopes of four units verti cal in 12 units hori zon tal (33-per- LENGTH 3:12 pitch 4:12 pitch cent slope) or greater. ROOFING MATERIAL (inches) GRADE to < 4:12 or steeper No. 1 3.75 5 1507.9.3 Underlayment. Underlayment shall comply 16 No. 2 3.5 4 with ASTM D 226, Type I. In areas where the av erage daily No. 3 3 3.5 tem pera ture in Janu ary is 25°F (-4°C) or less or where No. 1 4.25 5.5 Shingles of naturally there is a possi bil ity of ice forming along the eaves causing 18 No. 2 4 4.5 durable wood a backup of water , an ice bar rier that con sists of at least two No. 3 3.5 4 layers of underlayment cement ed togethe r or a self-adher - No. 1 5.75 7.5 ing polymer -modi f ied bi tumen sheet shall extend from the 24 No. 2 5.5 6.5 edge of the eave to a point at least 24 inches (610 mm) in - No. 3 5 5.5 side the ex te rior wall line of the build ing. For SI: 1 inch = 25.4 mm. Ex cep tion: De tached ac ces sory struc tures that con tain no condi ti oned floor area. 1507.8.7 Flashing . At the junc ture of the roof and verti cal sur faces, flash ing and counterflashing shall be pro vided in 1507.9.4 Interlayment. Interlayment shall com ply with ac cor dance with the man u fac turer’s in stal la tion in struc - ASTM D 226, Type I. tions, and where of metal, shall not be less than 0.019-inch (0.48 mm) (No. 26 galv anize d sheet gage) corro sion-re sis - 1507.9.5 Ma te rial stan dards. Wood shakes shall comply tant metal. The val ley flash ing shall extend at least 11 inches with the require ments of Table 1507.9.5.

302 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

TABLE 1507.9.5 metal. The valle y flashing shall extend at least 11 inches (279 WOOD SHAKE MATERIAL REQUIREMENTS mm) from the cen ter line each way and have a splash di verter APPLICABLE rib not less than 1 inch (25 mm) high at the flow line formed MINIMUM GRADING MATERIAL GRADES RULES as part of the flashing. Secti ons of flashing shall have an end lap of not less than 4 inches (102 mm). For roof slopes of 3 Wood shakes of naturally durable wood 1 CSSB units verti cal in 12 units hori zon tal (25-percent slope) and Taper sawn shakes of naturally durable 1 or 2 CSSB over, the valle y flashing shall have a 36-inch-wide (914 mm) wood underlayment of one layer of Type I underlayment running Preservative-treated shakes and the full length of the valle y, in addi ti on to other require d 1 CSSB shingles of naturally durable wood underlayment. In ar eas where the av er age daily tem per ature Fire-retardant-treated shakes and in Janu ary is 25°F (-4°C) or less or where there is a possi bil ity 1 CSSB shingles of naturally durable wood of ice forming along the eaves causing a backup of water , the metal valle y flashing underlayment shall be solid ce mented Preservative-treated taper sawn shakes of Southern yellow pine treated in 1 or 2 TFS to the roof ing underlayment for slopes under seven units ver- accordance with AWPA Standard C2 ti cal in 12 units hori zon tal (58-percent slope). CSSB = Ce dar Shake and Shin gle Bureau. 1507.10 Built-up roofs. The insta lla ti on of built-up roofs shall TFS = Forest Prod ucts Lab ora tory of the Texas For est Ser vices. comply with the pro visions of this sec tion. 1507.9.6 At tach ment. Fastene rs for wood shakes shall be 1507.10.1 Slope. Built-up roofs shall have a de sign slope of a cor ro sion re sis tant with a min i mum pen e tra tion of 0.75 inch mini mum of one-fourth unit verti cal in 12 units hori zon tal (19.1 mm) into the sheathing. For sheathing less than 0.5 (2-percent slope) for drainage, except for coal-tar built-up inch (12.7 mm) in thickness, the fasten ers shall extend roofs that shall have a de sign slope of a mini mum one-eighth through the sheathing. Each shake shall be at tached with a unit verti cal in 12 units hori zon tal (1-percent slope). min i mum of two fas ten ers. 1507.10.2 Ma te rial stan dards. Built-up roof cov ering ma - 1507.9.7 Ap pli ca tion. Wood shakes shall be laid with a side teri als shall com ply with the standards in Table 1507.10.2. lap not less than 1.5 inches (38 mm) betwee n joints in adja - cent courses. Spacing be tween shakes in the same course TABLE 1507.10.2 shall be 0.375 to 0.625 inches (9.5 to 15.9 mm) for shakes BUILT-UP ROOFING MATERIAL STANDARDS and taper sawn shakes of natu ral ly dura ble wood and shall MATERIAL STANDARD STANDARD be 0.25 to 0.375 inch (6.4 to 9.5 mm) for preser v ati ve taper Acrylic coatings used in roofing ASTM D 6083 sawn shakes. Weather expo sure for wood shakes shall not excee d those set in Table 1507.9.7. Aggregate surfacing ASTM D 1863 Asphalt adhesive used in roofing ASTM D 3747 TABLE 1507.9.7 ASTM D 3019; D 2822; WOOD SHAKE WEATHER EXPOSURE Asphalt cements used in roofing AND ROOF SLOPE D 4586

EXPOSURE Asphalt-coated glass fiber base sheet ASTM D 4601 (inches) ASTM D1227; D 2823; D LENGTH 4:12 PITCH Asphalt coatings used in roofing ROOFING MATERIAL (inches) GRADE OR STEEPER 4479 Shakes of naturally 18 No. 1 7.5 Asphalt glass felt ASTM D 2178 durable wood 24 No. 1 10a Asphalt primer used in roofing ASTM D 41 18 No. 1 7.5 Asphalt-saturated and asphalt-coated ASTM D 2626 Preservative-treated taper 24 No. 1 10 organic felt base sheet sawn shakes of Southern 18 No. 2 5.5 Asphalt-saturated organic felt yellow pine ASTM D 226 24 No. 2 7.5 (perforated) 18 No. 1 7.5 Asphalt used in roofing ASTM D 312 24 No. 1 10 Taper sawn shakes of Coal-tar cements used in roofing ASTM D 4022; D 5643 naturally durable wood 18 No. 2 5.5 Coal-tar saturated organic felt ASTM D 227 24 No. 2 7.5 Coal-tar pitch used in roofing ASTM D 450; Type I or II For SI: 1 inch = 25.4 mm. Coal-tar primer used in roofing, a. For 24-inch by 0.375-inch handsplit shakes, the max i mum expo sure is 7.5 ASTM D 43 inches. damproofing and waterproofing Glass mat, coal tar ASTM D 4990 1507.9.8 Flashing . At the junc ture of the roof and verti cal sur faces, flash ing and counterflashing shall be pro vided in Glass mat, venting type ASTM D 4897 ac cor dance with the man u fac turer’s in stal la tion in struc tions, Mineral-surfaced inorganic cap sheet ASTM D 3909 and where of metal, shall not be less than 0.019-inch (0.48 mm) (No. 26 galv anize d sheet gage) corro sion-re sis tant Thermoplastic fabrics used in roofing ASTM D 5665, D 5726

2003 SEATTLE BUILDING CODE 303 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

1507.11 Mod i fied bi tu men roof ing. The insta lla ti on of modi - 1507.15.2 Ma te rial stan dards. Liquid-a ppli ed roof coat- fied bi tumen roof ing shall comply with the pro visions of this ings shall comply with ASTM C 836, ASTM C 957, ASTM sec tion. D 6083, ASTM D 1227 or ASTM D 3468. 1507.11.1 Slope. Mod i fied bi tu men mem brane roofs shall have a de sign slope of a mini mum of one-fourth unit verti cal SECTION 1508 in 12 units hori zon tal (2-percent slope) for drainage. ROOF INSULATION 1507.11.2 Ma te rial stan dards. Mod ified bi tu men roof 1508.1 Gen eral. The use of above-deck ther mal insu la ti on cov er ings shall com ply with CGSB 37-GP-56M, ASTM D shall be permit ted pro vided such insu la ti on is cov ered with an 6162, ASTM D 6163, ASTM D 6164, ASTM D 6222, appro ved roof cov ering and passes the tests of FM 4450 or UL ASTM D 6223 and ASTM D 6298. 1256 when tested as an as sembly . 1507.12 Thermoset single- ply roof ing. The in stal la tion of Ex cep tion: Foam plasti c roof insu la ti on shall conform to thermoset single- ply roof ing shall comply with the pro visions the ma te rial and in stal la tion re quire ments of Chap ter 26. of this sec tion. 1508.1.1 Cel lu losic fi ber board. Cel lu losic fi ber board roof 1507.12.1 Slope. Thermoset single- ply membrane roofs in su la tion shall con form to the ma te rial and in stal la tion re - shall have a de sign slope of a mini mum of one-fourth unit quire ments of Chapter 23. verti cal in 12 units hori zon tal (2-percent slope) for drain - age. 1507.12.2 Ma te rial stan dards. Thermoset single- ply roof SECTION 1509 cov er ings shall com ply with RMA RP-1, RP-2 or RP-3, or ROOFTOP STRUCTURES ASTM D 4637, ASTM D 5019 or CGSB 37-GP-52M. 1509.1 Gen eral. The pro visions of this sec tion shall gov ern the 1507.13 Ther mo plas tic sin gle-ply roof ing. The in stal la tion const ruct ion of rooftop structure s. of thermo plas tic single- ply roof ing shall comply with the pro - visions of this sec tion. 1509.2 Penthouse s. A pent house or other projec tion above the roof in structure s of other than Type I construc tion shall not ex - 1507.13.1 Slope. Ther mo plas tic sin gle-ply mem brane ceed 28 feet (8534 mm) above the roof where used as an en clo- roofs shall have a de sign slope of a mini mum of one-fourth sure for tanks or for ele vators that run to the roof and in all other unit verti cal in 12 units hori zon tal (2-percent slope). cases shall not ex tend more than 18 feet (5486 mm) above the roof. The aggre gate area of pent houses and other roof top struc- 1507.13.2 Ma te rial stan dards. Ther mo plas tic sin gle-ply tures shall not ex ceed one-third the area of the support ing roof. roof cov erings shall comply with ASTM D 4434 or CGSB A pent house, bulkhead or any other sim ilar pro jec tion above 37-GP-54M. the roof shall not be used for pur poses other than shelter of me- 1507.14 Sprayed polyur ethane foam roof ing. The in stal la - chani cal equipment or shel ter of verti cal shaft openings in the tion of sprayed polyure thane foam roof ing shall comply with roof. Pro visions such as louv ers, lou ver blades or flashing shall the pro visions of this sec tion. be made to pro tect the me chani cal equipment and the build ing inte rior from the ele ment s. Penthouses or bulkheads used for 1507.14.1 Slope. Sprayed polyure thane foam roofs shall pur poses other than permit ted by this secti on shall conform to have a de sign slope of a mini mum of one-fourth unit verti cal the require ments of this code for an addi ti onal story. The re - in 12 units hori zon tal (2-percent slope) for drainage. stricti ons of this sec tion shall not pro hibit the placing of wood flag poles or sim ilar struc tures on the roof of any build ing. 1507.14.2 Ma te rial stan dards. Spray-appli ed polyure - thane foam insu la ti on shall com ply with ASTM C 1029. 1509.2.1 Type of construc tion. Pent houses shall be con- structed with walls, floors and roof as require d for the build - 1507.14.3 Ap pli ca tion. Foamed-in-place roof insu la ti on ing. shall be in stalled in ac cor dance with the man u facturer’ s in - struc tions. A liq uid-ap plied pro tec tive coat ing that com- Ex cep tions: plies with Secti on 1507.15 shall be appli ed no less than 2 hours nor more than 72 hours follo wing the appli cati on of 1. On buildings of Type I and II construc tion, the ex - the foam. terior walls and roofs of pent houses with a fire sep- ara ti on distanc e of more than 5 feet (1524 mm) and 1507.14.4 Foam plastic s. Foam plas tic mate ri als and in - less than 20 feet (6096 mm) shall be of at least stal la tion shall com ply with Chap ter 26. 1-hour fire-resis tance-rated noncombustible con - struc tion. Walls and roofs with a fire sep a ra tion 1507.15 Liq uid-ap plied coat ings. The in stal la tion of liq - distanc e of 20 feet (6096 mm) or greater shall be of uid-appli ed coatings shall comply with the pro visions of this noncombustible con struc tion. In te rior fram ing and sec tion. walls shall be of noncombustible construc tion. 1507.15.1 Slope. Liquid-a ppli ed roofs shall have a de sign 2. On buildings of Type III, IV and V construc tion, slope of a mini mum of one-fourth unit verti cal in 12 units the exte rior walls of pent houses with a fire sepa ra - hor i zon tal (2-per cent slope). tion distanc e of more than 5 feet (1524 mm) and

304 2003 SEATTLE BUILDING CODE ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

less than 20 feet (6096 mm) shall be at least 1-hour ment shall be construc ted of and supporte d on Type I or II fire-re sis tance-rated con struc tion. Walls with a fire con struc tion. sepa ra ti on distanc e of 20 feet (6096 mm) or greater from a common propert y line shall be of Type IV 1509.5.1 Noncombustible construc tion requir ed. Any or noncombustible construc tion. Roofs shall be tower, spire, dome or cupola that excee ds 60 feet (18 288) in con structed of ma te ri als and fire-re sis tance rated height above the highest point at which it comes in contac t 2 as re quired in Table 601. Inte rior framing and with the roof, or that excee ds 200 square feet (18.6 m ) in walls shall be Type IV or noncombustible con - area at any hori zon tal sec tion, or which is intende d to be struc tion. used for any purpose other than a belfry or archi tec tural em - belli shment , shall be enti rely construc ted of and supporte d 3. Un pro tected noncombustible en clo sures hous ing by noncombustible mate ri als . Such struc tures shall be sepa - only me chani cal equipment and locat ed with a rated from the building belo w by construc tion having a mini mum fire sepa ra ti on distanc e of 20 feet (6096 fire-resis tance rat ing of not less than 1.5 hours with open- mm) shall be per mit ted. ings protec ted with a mini mum 1.5-hour fire-protec tion rat - 4. On one-story buildings, comb usti ble unroofed me - ing. Structure s, except aeria l supports 12 feet (3658 mm) chan ical equip ment screens, fences or sim ilar en - high or less, flagpoles , water tanks and cool ing towers, clo sures are per mitted where lo cated with a fire placed above the roof of any building more than 50 feet (15 sepa ra ti on distanc e of at least 20 feet (6096 mm) 240 mm) in height, shall be of noncombustible mate ria l and from adja cent propert y lines and where not ex - shall be supporte d by construc tion of noncombustible mate - ceeding 4 feet (1219 mm) in height above the roof rial. sur face. 5. Dormers shall be of the same type of construc tion 1509.5.2 Towers and spires. Towers and spires where en - as the roof on which they are placed, or of the exte - closed shall have exte rior walls as require d for the building rior walls of the build ing. to which they are attac hed. The roof cov ering of spires shall be of a class of roof cov ering as require d for the main roof of 1509.3 Tanks. Tanks having a capac it y of more than 500 gal- the rest of the struc ture. lons (2 m3) placed in or on a building shall be supporte d on ma- sonry, rein forced concret e, steel or Type IV construc tion pro vided that, where such supports are locat ed in the building SECTION 1510 above the low est story, the sup port shall be fire-re sis tance rated REROOFING as re quired for Type IA construc tion. 1510.1 Gen eral. Mate ria ls and methods of appli cati on used for 1509.3.1 Valve. Such tanks shall have in the bottom or on re cov er ing or re plac ing an ex ist ing roof cov er ing shall com ply the side near the bottom, a pipe or outlet, fitted with a suit - with the require ments of Chapter 15. able quick opening valve for dischar ging the content s in an emer gency through an ade quate drain. Ex cep tion: Reroofing shall not be require d to meet the min - imum design slope require ment of one-quar ter unit verti cal 1509.3.2 Lo ca tion. Such tanks shall not be placed over or in 12 units hori zon tal (2-percent slope) in Secti on 1507 for near a line of stairs or an el e vator shaft, un less there is a solid roofs that pro vide pos iti ve roof drainage. roof or floor under neat h the tank. 1510.2 Structural and con struc tion loads. Struc tural roof 1509.3.3 Tank cover. Unen clos ed roof tanks shall have cov - com po nents shall be ca pa ble of sup port ing the roof-cov er ing ers sloping to ward the outer edges. system and the mate ria l and equipment loads that will be en - coun tered dur ing in stal la tion of the sys tem. 1509.4 Cooling towers . Cooling towers in exces s of 250 2 1510.3 Re covering ver sus re place ment. New roof cov erings square feet (23.2 m ) in base area or in exces s of 15 feet (4572 shall not be in stalled with out first re moving all ex ist ing lay ers mm) high where locat ed on buildings more than 50 feet (15 240 of roof cov erings where any of the follo wing condi ti ons occur: mm) high shall be of noncombustible construc tion. Cooling towers shall not excee d one-third of the support ing roof area. 1. Where the exist ing roof or roof cov ering is water soaked or has de teri o rat ed to the point that the exist ing roof or Ex cep tion: Drip boards and the enclos ing construc tion of roof cov ering is not ade quate as a base for addi ti onal wood not less than 1 inch (25 mm) nomi nal thickness, pro - roof ing. vided the wood is cov ered on the exte rior of the tower with 2. Where the exist ing roof cov ering is wood shake, slate, noncombustible ma te rial. clay, ce ment or as bes tos-ce ment tile. 1509.5 Towers, spires, domes and cu polas. Any tower, spire, 3. Where the exist ing roof has two or more appli cati ons of dome or cupola shall be of a type of construc tion not less in any type of roof cov ering. fire-resis tance rat ing than require d for the building to which it Ex cep tions: is attac hed except that any such tower, spire, dome or cupola that excee ds 85 feet (25 908 mm) in height above grade, or ex - 1. Complet e and sepa rat e roof ing sys tems, such as ceeds 200 square feet (18.6 m2) in hori zon tal area or is used for standing-se am metal roof system s, that are designe d any purpose other than a belfry or an ar chitec tural em belli sh- to transmit the roof loads direct ly to the building’ s

2003 SEATTLE BUILDING CODE 305 ROOF ASSEMBLIES AND ROOFTOP STRUCTURES

struc tural sys tem and that do not rely on exist ing roofs and roof cov erings for support, shall not re quire the re moval of ex ist ing roof cov er ings. 2. Metal panel, metal shin gle, and con crete and clay tile roof cov erings shall be permit ted to be insta lled over exist ing wood shake roofs when appli ed in accor - dance with Sec tion 1510.4. 1510.4 Roof re cov er ing. Where the appli cati on of a new roof cov ering over wood shingle or shake roofs create s a comb usti - ble con cealed space, the en tire ex isting sur face shall be cov ered with gypsum board, mineral fiber , glass fiber or other appro ved ma te ri als se curely fas tened in place. 1510.5 Re in stal la tion of ma te ri als. Ex isting slate, clay or ce - ment tile shall be per mit ted for re in stal la tion, ex cept that dam - aged, cracked or bro ken slate or tile shall not be rein stalled. Ex isting vent flash ing, metal edgings, drain out lets, col lars and metal counterflashings shall not be rein sta lled where rusted, dam aged or de te ri o rated. Ag gre gate sur fac ing ma te ri als shall not be re in stalled. 1510.6 Flash ings. Flash ings shall be re con structed in accor - dance with ap proved man u fac turer’s in stal la tion in struc tions. Metal flashing to which bitu mi nous mate ri als are to be adhered shall be primed prior to in stal la tion.

306 2003 SEATTLE BUILDING CODE