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Fully Soldered Metal Roofing: More Complicated Than You Think

Nicholas Floyd, PE, and Amrish K. Patel, PE, LEED GA Simpson Gumpertz & Heger Inc. 2500 City West Blvd., Houston, TX 77042 Phone: 781-424-9547 • Fax: 781-907-9009 • E-mail: [email protected] and [email protected]

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 2 3 Abstract

Copper roofing has been used for centuries, particularly on ornate institutional or his­ torical buildings where access and roof maintenance are impractical. When fully soldered, roofing can provide a watertight, durable roof with a decades-long service life; how­ ever, these roofs are highly dependent on proper design and careful craftsmanship during installation. The presenters will discuss common issues with fully soldered metal roofing, including improper accommodation for thermal expansion, improper or joint detailing, and drain details for contemporary copper roofs that incorporate membrane underlayment.

Speaker

Nicholas Floyd, PE — Simpson Gumpertz & Heger Inc.

NiCK FlOYD is a senior project manager who specializes in the investigation and remediation design of building enclosures. His past and current copper roofing design and investigation projects include historical and large public structures, including the New York, massachusetts, Kansas, and iowa state capitol buildings. Floyd also has experience design­ ing and investigating various membrane roofing systems, slate roofing, masonry, plaza and below-grade waterproofing, fenestration systems, and architectural terra cotta.

Nonpresenting Coauthor

Amrish K. Patel, PE, LEED GA — Simpson Gumpertz & Heger Inc.

AMRISH PATEL is a senior staff ii at SGH. He specializes in roofing and waterproofing projects and has experience investigating and remediating multiple copper roof and wall cladding systems on large historical and landmark buildings for universities. His work expe­ rience also includes various other roofing and façade systems for a wide range of projects, including residential and commercial buildings, parking structures, plazas, schools, hospi­ tals, and many other structures in both public and private sectors.

1 2 4 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 Fully Soldered Metal Roofing: More Complicated Than You Think

INTRoDUCTIoN watertight to provide durable and reliable mit more heat to the work. The used Copper roofing has been used for centu­ performance. Fully soldered metal flashing for stainless also typically has a higher ries, and metal roofing is still regularly used is often similarly relied upon for watertight , making it more difficult to today, particularly on ornate institutional or performance. The material selection, expan­ keep hot enough to flow through seams. historical buildings where access and regu­ sion detailing, and jointing discussion con­ While copper and have lar roof maintenance are challenging. When tained in this paper also generally applies different material properties, they present fully soldered, metal roofing can provide to such flashing, though flashing is not the similar challenges in soldered roofing appli­ a watertight, durable roof with decades- focus of our discussion. cations. For simplicity, the following sec­ long service life; however, these roofs are tions use the terms “” or “metal highly dependent on both proper design Sheet Metal Materials roofing” interchangeably to indicate both and careful craftsmanship during instal­ Most architectural sheet metals can copper and stainless steel systems, unless lation. Industry guides—such as Revere’s be soldered (with the correct materials noted otherwise. Copper and Common Sense (C&CS), the and techniques); however, copper (either Copper Development Association’s Copper as uncoated “red” copper, --coated G ENER AL JOINING PROC EDURE S in Architecture Handbook, the Sheet Metal copper, or -coated copper) and stainless AND JOINING IS SUE S and Air Conditioning Contractors’ National steel are the most commonly used metals in Sheet metal is durable and watertight; Association’s (SmACNA’s) Architectural soldered roofing applications for the follow­ the problem is, it typically cannot be trans­ Sheet Metal Manual, and the National ing reasons: Both are common construction ported and installed in sheets larger than 3 Roofing Contractors Association’s (NRCA’s) materials readily available in sheet stock, to 5 ft. wide and 10 ft. long. As such, metal roofing manuals—provide designers and they are relatively easy to bend and join roofing performance relies significantly on installers with direction for basic system in the field, and they are well-suited for the joinery between sheets. For watertight details and general joining procedures (e.g., exposed roofing conditions due to their sheet metal applications, these joints are locking, riveting, and ), but careful relatively long expected service life and low typically soldered. Sealant or can consideration is required to carry these con­ risk of corrosion from atmospheric condi­ also form watertight joints; however, the cepts through to project-specific conditions. tions or contact with other typical construc­ blind application of sealant into locked In this paper, we discuss common pit­ tion materials (e.g., , flashing, and seams does not provide reliable watertight­ falls associated with fully soldered metal drain hardware). ness, and the sealant’s expected service roof applications, with particular focus on Copper is particularly well-suited for life is typically less than that of solder. joining procedures, detailing for thermal soldered roofing as it is relatively soft and For these reasons, sealant is typically only expansion, and drainage of “bi-level” metal easier to form and work in the field than appropriate for steep-sloped or noncritical roof systems that incorporate a membrane some other sheet metals. Copper also has applications (for example, note C&CS rec­ underlayment. high conductivity, which helps draw solder ommends sealant-filled joints only for roof into joints; and it does not oxidize as quickly slopes greater than 3:12). Welding or braz­ FULLY SoLDERED mETaL as some other metals, thus requiring less ing is often not practical for the thin sheets RooFINg aPPLICaTIoNS rigorous cleaning and application dur­ used in sheet metal roofing applications. “metal roofing” covers many applica­ ing soldering. tions and configurations, such as field-fab­ Stainless steel requires more patience Soldering ricated standing or batten seam, corrugated and skill to solder than copper, but it can Unlike welding, which requires higher panels, composite metal panels, prefabri­ also be used for soldered metal applications temperatures to melt the base material, cated “snaplock” systems, etc. most metal —particularly where required for aesthetic soldering is done at a lower temperature roofing applications are used on steep-slope reasons or where copper may result in green and involves melting a soft metal that roofs and are constructed with loose locked patina staining on porous materials below. bonds to the . Soldering uses a seams or lapped joints; these systems are Stainless steel sheets are stiffer and more heat source (e.g., a or solder­ not watertight and rely on the roof slope and difficult to form and work than copper of ing torch) to apply sufficient heat to the a weather-resistant underlayment material similar thickness. Soldering stainless steel base metal so that the solder flows freely to function. These types of water-shedding also typically requires higher heat due to and can be drawn (or “sweated”) into locked systems are not the focus of this paper. the material’s lower thermal conductivity. or lapped seams. This paper instead focuses on fully soldered Overheating the metal can result in warp­ To facilitate the soldering process, sol­ low-slope metal roofing and built-in gutter ing and buckling, so the soldering process dering alloys must have a relatively low applications. These applications collect or for stainless steel typically requires a cooler melting point and, typically, a lower ductili­ hold water (or ice/snow) and must remain iron in good contact with the metal to trans­ ty than the base metal; unfortunately, these

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 2 5 Figure 1 – Pretinning the copper sheet edge prior to seaming.

Figure 2 – Soldering a lapped and riveted seam with a soldering torch.

traits make the solder weaker than the base metal and prone to failure when exposed to tensile or stresses. To prevent joint failure from thermally induced stresses or mechanical loads (e.g., live loads, sliding snow, etc.), soldered sheet metal seams must be mechanically locked or—for thick­ er sheets—strengthened with . These mechanical attachment methods are dis­ cussed further in the next section. Copper roofing applications typically utilize tin-lead alloy . Tin is the pri­ mary soldering component, but the lead reduces melting temperature and adds duc­ tility to the alloy. Pure tin or tin- sol­ ders are used in lead-free applications and for stainless steel seams; these lead-free solders have a higher melting point and, thus, require more care and patience to sweat into seams, particularly on vertical or sloped applications. The following provides a very brief sum­ the soldering process. the desired surfaces. Pretinning is mary of typical soldering procedure. The • Flux. Flux is an acidic paste used to essentially the process of melting industry guides listed in the introduction dissolve oxides from the surface of and applying a thin layer of solder provide further description of these steps for the base material and improve the on the soldering iron and lock or interested readers. ability (flow) of the solder. seam surfaces that are to be sol- • Cleaning. The base metal must Excess flux should be removed from dered (Figure 1). Flat seam panels be cleaned immediately before pre- the completed seam surface; other- and other components that can be tinning or before soldering joined wise, it will stain or patina the base shop fabricated are often pre-tinned seams to remove all debris or con­ metal. by dipping sheet edges into a molten taminants that may prevent the sol­ • Pretinning. The soldering iron solder bath. der from flowing freely through the and base sheet metal (where fea­ • Dressing. Dressing is the process of seam. The soldering irons must also sible) should be pretinned prior to hammering down locks and seams be cleaned to remove any contami­ soldering to facilitate solder flow so that they are flat and tight, and so nants that may negatively impact and promote bond of the solder to that all surfaces within the joint are

1 2 6 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 within close proximity to promote and provides a neat appearance that may experience with sheet metal fabrica­ capillary action for the solder. be aesthetically desired in exposed applica­ tion and soldering, and to submit • Heat Source. Historically, architec­ tions (Figure 3). references, including current con­ tural sheet metal was soldered using While the concept of soldering is tact information, for past completed a pair of copper soldering “irons” straightforward, the actual exercise takes sheet metal work. that were heated with a gas or char­ practice and requires a skilled craftsman. • Require all workers who intend to coal pot. Most contractors now use insufficient solder can result in weak seams perform solder work to complete a a soldering torch, which utilizes a or gaps, or leave rivet heads exposed and “soldering test.” The test includes gas-burning nozzle to continuously prone to water infiltration. if the iron is soldering one lineal foot each of heat a heavy copper bit at the front moved too quickly along the seam, the sol­ a vertical lock joint and a vertical end of the torch. Either method der will cool quickly, and flow into the lock riveted joint (Figure 3); the soldered can produce acceptable results, but or lap will be limited. Moving the iron too samples are then cut and inspected because the torch bit is continu­ slowly can overheat the base metal, which by the designer (Figure 4). ously heated, it is typically much can cause warping and/or oxidation. lighter and easier to work with than Given the skill required to achieve This approach seeks to provide quality conventional soldering irons, which well-soldered seams and the difficulty in assurance and demonstrate the minimum require mass to retain heat while addressing inadequate soldering after the quality of workmanship that the contrac­ in use between turns on the heat fact, designers and owners would be pru­ tor and workers must meet for a given source. Architectural sheet metal dent to specify a reasonable quality assur­ project. It does not, however, provide any should not be soldered using an ance program, particularly on public work quality control of the completed product. open flame or with electric torches. or projects that require multiple bidders. A Completed seams can be visually inspected • Soldering. The heat source is used program successfully used by the authors for general quality, but (barring obvious to melt and maintain a small liquid includes the following: deficiencies) destructive testing is typically puddle of solder near the tip of the • Require the contractor (specifically required to confirm the efficacy of the sol­ soldering iron on the low side of the the mechanics performing the work) dering operation. seam (Figure 2). The iron or torch to have a minimum of five years’ bit is then dragged along the seam, heating the sheet metal evenly and adding solder as necessary to fill the lock or lap. If properly done, the heat will cause the solder to “sweat” (or be drawn) into the seam through capil­ lary action.

At vertical sheet metal joints or where extra quality assurance is desired, the seams should also be laced. Lacing involves applying additional solder across the seam in a stitched pattern. This second laced application of solder requires relatively uni­ form heating across the seam, which can help draw the initial solder application more fully through the lock or lap. It also helps to ensure full coverage of rivet heads/holes

Figure 3 – Solder test sample demonstrating lacing across the seam.

Figure 4 – Soldered test lock join cut for inspection. This sample would not pass because the solder is not sweated through the entire seam.

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 2 7 als (e.g., membrane underlayment) are not damaged. To the extent possible, rivets should be installed prior to setting the sheet metal in place, or rigid protection must be provided beneath the lapped joint. Well-executed seams require careful cut­ ting and of the base sheet metals to form uniform locks or laps. This seems like common sense, but can be a difficult process over atypical substrate geometries and/or if installers do not provide sufficient attention to detail. Improper seam construc­ tion or dressing will prevent capillary solder flow through the seam, or leave gaps that are too wide to be filled with solder Figure( 6). When possible, flat-seam roofing panels and other uniformly shaped sheets should be preformed and pretinned in the shop. The sheet metal’s attachment to the substrate must also be considered when selecting a joining method. Sheet metal cleats can be incorporated into locked joints, allowing for regular attachment to Figure 5 – A lapped and riveted joint using solid rivets. the substrate along seams. Riveted seams cannot incorporate such attachment; and, Mechanical Attachment – Lock Joints above) and most stainless steel applica­ as such, riveted roofing or gutter sections and Rivets tions, lock joints are not sufficient to devel­ rely on attachment along unriveted sheet Rigidly soldered sheet metal seams must op the full sheet strength, or may not be edges or hold-downs through the face of be as strong as the base sheet; otherwise, practical to fold; and riveted seams are sheets larger than 18 in. wide. they are prone to cracking or deformation required. Riveted seams are constructed when subjected to stresses from regular with a simple overlap, with rivets installed Solid Versus Pop Rivets thermal movement of the sheets or mechan­ through both sheets, typically in a staggered Two general types of rivets are avail­ ical loads. A simple lap with solder alone is pattern (Figure 5). Rivet installation requires able for sheet metal roofing applications: insufficient to develop the seam strength predrilling the base metal, and care must solid rivets and blind rivets (also known necessary for sheet metal roofing applica­ be taken to ensure the underlying materi­ as “pop” rivets). Solid rivets are mush- tions. As such, sheet metal roofing seams should be locked or lapped and riveted, to provide a mechanical bond between sheets; the solder provides some additional bond, but is primarily used to provide watertight seams. Lock joints are created by interlock­ ing ½- to ¾-in. bent hooks formed along the edges of adjacent sheets. For soldering applications, this lock is typically folded down flat against the base sheet metal surface, forming a “flat lock.” lock joints require straight and crisp cuts and folds so that the lock can be tightly “dressed” to allow for capillary solder flow through the entire joint. Where feasible, the majority of the sheet metal cutting and forming opera­ tion should utilize a shear and bending brake, respectively. Hand shaping, trim­ ming, and seaming should be performed only at locations where no other option is feasible. Figure 6 – Poorly constructed lap joint, resulting in a gap that was not filled with For thicker copper sheets (24 oz. and solder.

1 2 8 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 Figure 7 – Gutter liner constructed adjacent to its eventual in-situ location.

Figure 8 – Pop rivets viewed from the underside of the seam.

backs and present some challenges that are often misunderstood or ignored: • Pop rivets are hollow and typically weaker than solid rivets, and there­ fore are not suitable to develop the necessary seam strength in thicker sheet metals. Industry guides such as C&CS state, “in the absence of test data that shows that [pop] rivets have sufficient strength for use with 24-ounce and 32-ounce copper,” they should only be used for “non­ structural applications.” Designers can also choose to compare the rela­ tive shear strength of a selected pop rivet versus a typical solid rivet and adjust spacing or quantity to provide similar strength. Higher strength pop rivets can also be used. The key point is that pop rivets require some additional design and are not a direct substitute for conventional solid rivets. room-shaped fasteners that, once inserted Solid rivets require access to the under­ • Pop rivets form a “mushroom” head through the sheet metal seam, are fitted side of the seam and can be difficult to ham­ on the underside of the base materi­ with a burr (similar to a washer) and ham­ mer into place without damaging underlay­ al (Figure 8). These protruding heads mered or compressed until deformed into ment, plywood substrates, or the sheet metal. can damage or puncture membrane a shape, thus securing the sheets Access to the underside of the seams can be underlayment or restrict normal together. Blind rivets are also mushroom- difficult with large sheets. Where practical, expansion movement of the sheet. shaped, but have a hollow shaft that is filled sheets can be joined prior to installing into • Some pop rivets have mandrels that with a metal mandrel. To install, a special their in-situ location (Figure 7). are intended to break off and remain is used to pull the mandrel, causing Unless specified otherwise, sheet metal in the hollow rivet body. In these the shaft to deform and expand, and form roofing contractors tend to use pop rivets cases, the mandrel material must a barbell-like shape that secures the sheets due to their relative ease of installation. match (or be galvanically compatible together. Unfortunately, pop rivets have several draw­ with) the rivet body and sheet metal

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 2 9 seams are rigid, and The difficulty is in executing these the system must be guidelines in the field, particularly at atyp­ carefully detailed and ical geometries, and locating expansion installed to accom­ joints (which typically are not watertight) modate movement at in locations that do not compromise the expansion joints and roofing system’s performance or drainage roofing/gutter perim­ paths. The following guidelines are intended eters. to aid designers and installers in avoiding Industry guides common blunders that the authors have provide strategies for regularly observed in the field: typical roofing and • Fully soldered roofing and gutters gutter conditions. For will expand from their center or any example, C&CS rec­ fixed point (e.g., a drain body). As ommends, “Large such, most roofing and gutter instal­ areas of locked and lations require expansion provisions soldered flat-seam along all edges of the roof/gutter— [copper] roofing not just an expansion joint located should be divided into along a roof or gutter’s length. sections that are sep­ • Expansion joints or battens must be arated by expansion continuous through all rigidly sol­ battens…not more dered components (Figure 10). than thirty feet in • Soldered roofing perimeter termi­ any direction” (3.C.2). nations and gutter edges should C&CS also provides be cleated—not directly fastened—to a detailed table for allow movement along the termina­ spacing expansion tion. Figure 9 – Inadequate lacing. Note pop rivet heads are joints within fully sol­ • At rising walls, the sheet metal must visible through the solder. dered copper gutter be gapped from the substrate to lines for various gut­ accommodate sheet metal movement. materials; otherwise, galvanic corro­ ter sizes and copper thicknesses (9.B.9). • Soldered components should not be sion may result in staining or seam These guides also provide typical details for soldered to any nonrigid metal com­ failures. loose lock joints and battens that are com­ ponents (e.g., standing-seam roofing • Full solder coverage of pop rivets is monly used to accommodate expansion. or valleys). particularly important, as water can flow through the hollow rivet body (Figure 9). Capped pop rivets are available, but are not standard.

THERMAL ExPANSION Architectural sheet metal installations are often subjected to wide temperature changes in service, resulting in signifi­ cant thermal movement and stresses. The thermal movement in sheet metals is pro­ portional to the length of the subject mate­ rial and the temperature of the sheet, not to the changes in ambient temperature. Exposed to full sun, sheet metal can con­ ceivably reach temperatures 100°F higher than the ambient temperature. Copper and stainless steel have similar coefficients of thermal expansion and can be expected to expand approximately 1/8 in. per 10 ft. of length with a 100ºF temperature change. in many metal roofing applications, this thermal movement is accommodated within the loose-locked “flexible” seams; however, Figure 10 – Batten-type expansion joint. Provision for expansion was not carried in fully soldered roofing applications, the up the rising wall, resulting in the cracked solder joint in the flashing.

1 3 0 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 prolonged submersion. Water will eventually work its way through membrane punctures, seams, and holes (e.g., the numerous nail holes from cleats and sheet metal attachments). An adhered underlayment can be especially useful in low-slope applications, as water is more likely to find any defect in the sheet metal and collect on this secondary roofing layer. However, having two separate roofing layers causes the assembly to become complicated at the drain tie-in. None of the industry guides listed in the introduction provide a drain detail that includes self- adhering membrane underlayment with a typical clamping -type roof drain. Thus, the design respon­ sibility for this critical detail falls to the roof designer or installer, who is generally left with two conceptual approaches for designing this drain tie-in: 1) designs that allow drainage Figure 11 – Remedial expansion joint installed in a built-in gutter. Note water ponded on at the membrane level, and 2) those high side of expansion joint. that do not. • Expansion joints should be config­ cations (which can produce temperatures ured so as to not impede drainage upwards of 400ºF), and a separation layer Membrane-Level Drainage (Figure 11). If necessary, additional (e.g., building or paper) should be A relatively simple way to allow for drains should be added to decrease provided to prevent binding the sheet metal membrane-level drainage is to use a typical the roof or gutter length between to the underlayment at seams. clamping ring type roof drain and extend adjacent drains. Self-adhering membrane products have both the membrane and sheet metal into the benefit of full adhesion and some self- the drain body; then provide a spacer UNDERLaYmENT aND DRaINagE sealing characteristics around nail penetra­ or weep between the membrane and the Historically, metal roofing and gut­ tions. However, even a perfectly installed sheet metal to prevent the clamp ring from ter systems lacked any underlayment and membrane will not remain watertight under compressing and sealing the metal to the relied on simple sleeve drains soldered to a metal roof when subjected to regular or underlayment at the drain body (Figure 12). the sheet metal. This system lacks redun­ dancy, as the sheet metal provides only a single layer of defense with no backup pro­ tection against leakage, should a defect or puncture occur. Contemporary metal roofing systems now typically incorporate a self-adhering membrane underlayment below the metal. Membrane products are available in high­ temperature-resistant SBS asphalt or butyl formulations, which can accommodate the expected high in-service temperatures pres­ ent under metal roofing without flowing or degradation. All high-temperature mem­ branes and formulations are not equal, so selection of an appropriate membrane may require careful consideration at loca­ tions with higher anticipated service tem­ peratures. Even functional membranes may Figure 12 – A weep or shim between the sheet metal and membrane underlayment become soft or flow during soldering appli­ allows membrane-level drainage.

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 3 1 components into the drain bowl, and then clamp down both layers with the drain’s prefabricated clamp ring. This effectively seals the sheet metal and membrane layers to the substrate at the drain inlet. Unless other specific direction is provided, this is the method typically used by installers, in some cases with water block sealant installed between the membrane and sheet metal to further ensure a watertight tie-in at the sheet metal layer. Even if no sealant is provided, a tight clamping ring will severely limit any drainage from between the com­ pressed sheet metal and membrane layers. This option provides the greatest pro­ tection in the event of the roof drain line becoming clogged, since it prevents water from backing up under the sheet metal (Figure 14). Designers and building owners should take every precaution to prevent drainage issues; even though the drain detail may be watertight, standing water is never a good situation on a roof or in a Figure 13 – This configuration allows water to back up under the sheet metal if gutter. Even with good maintenance, drains the drain is clogged and backs up. can become clogged or pipes/outlets can freeze. This strategy maximizes the effectiveness of clips to hold drain strainer) at the The risk with this option is that the the membrane underlayment. By allowing sheet metal layer. For this to work, lack of membrane-level drainage essentially the membrane to drain, water is less likely the drain body must be set in a renders the membrane useless as a sec­ to accumulate on the membrane and leak sump so that the membrane-level ondary layer of protection. Any incidental through vulnerable nail holes, seams, or clamp ring does not impede drainage leakage through the sheet metal does not other defects. at the sheet metal surface. have a path to drain or dry out (both sheet Conversely, the method provides mini­ mal protection should the drain clog and Designers and in­ back up, as water can travel freely under stallers should consider the sheet metal (Figure 13). Also, while a this method if they have relatively simple concept, this method can confidence in the drain­ be difficult to detail. The shim or weep used age system and want must be a noncorrosive material compatible to maximize the effec­ with both the sheet metal and membrane. tiveness of the mem­ It also needs to be either secured or con­ brane underlayment figured around the drain body so it does and overall redundancy not move out of place during routine move­ of the roof assembly. ment or future drain maintenance. Finally, This option should not the shim or weep must fit with (or around) be used at locations the drain body’s geometry, which can vary where drains are prone significantly among manufacturers, models, to back up due to frozen and sizes. pipes or outlets, or roof Successful options the authors have areas that regularly col­ pursued to provide membrane-level drain­ lect leaves or debris that age include: can clog drains. • Using a reticulated foam weep baffle sheet, cut to fit around the drain no Drainage at inlet and installed between the Membrane Level membrane and sheet metal. The most basic tie- • Installing the clamping ring at the in for a clamping ring Figure 14 – Tightly securing the sheet metal and membrane level and providing a type drain is to simply membrane with a single clamp ring provides protection separate clamping ring (or soldered extend both roof system against drain backups.

1 3 2 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 metal and typical self-adhering membranes are strong vapor retarders), and water will collect on the membrane. Even a small volume of water can quickly fill the tight space between the sheet metal and the membrane, applying a pressure head on vulnerable fastener penetrations and seams in the membrane (Figure 15). Additionally, entrapped water between the sheet metal and membrane underlayment can acceler­ ate degradation of the sheet metal. Designers and installers should only consider this option if they have the utmost confidence in the sheet metal roof system (i.e., expansion is properly detailed, no loose locks are below the potential level of water and snow buildup, and there are no poten­ tial sources of water infiltration upslope that could direct water below the soldered roof system) or if there are known deficien­ cies with the drainage system that cannot Figure 15 – Without drainage, incidental leakage that collects on the membrane be remedied (e.g., regularly frozen pipes, underlayment will eventually leak to the interior. regular debris/clogging of drains). sion of the metal sheet and drainage compli­ locked or lapped and riveted, and Secondary Drainage cations if using a membrane underlayment. fully soldered to accommodate ther- Current building codes typically require These challenges require a well-thought-out mal and mechanical loads. a secondary (overflow) drainage system for design and careful execution by installers in • Riveted seams constructed with locations where the roof can hold water order to function as intended. solid rivets. Sequence the work to if the primary drains allow buildup. New Project documents and a well-executed, construct seams prior to installing sheet metal roofs that have both a main and fully soldered roof installation should in their in-situ location to the extent an overflow drain can utilize both options include the following: possible. above to provide maximum benefit. in this • Detailed direction for constructing • Carefully designed expansion provi­ configuration, the primary drain can be sheet metal seams for each type sions. Both designer and installer installed without membrane drainage (e.g., of application on the project. The must consider expansion for all typi­ watertight to prevent backflow), while the designer or contractor should incor­ cal and atypical geometries for the overflow drain can be designed to allow porate a quality assurance program project, as missing or short-circuited membrane-level drainage, as the overflow to ensure selected installers, includ­ expansion joints can result in dam­ drain is less likely to back up due to limited ing confirmation that mechanics age to perfectly constructed seams. use and water flow. actually performing the work have • Careful consideration for selection of the skills necessary to fabricate well- the membrane underlayment, design SUmmaRY soldered joints. of drainage provisions, and detailing Soldered sheet metal roofing can provide • Preformed and pretinned sheet of drains. The membrane underlay- a durable, long-lasting, and watertight roof­ metal from the shop. Limit cutting ment must be resistant to the service ing system in low-slope and gutter applica­ and forming sheet metal in the field temperatures to which it is exposed tions. However, these systems are depen­ for improved consistency and dura­ to remain functional. Improper drain­ dent on proper design and execution, par­ bility. Hand-shaping, trimming, and age design or installation can negate ticularly of joining or seaming procedures. seaming should be performed only the intended benefits of using a mem­ Soldered sheet metal roofing also presents when no other option is feasible. brane underlayment and increase the unique challenges related to thermal expan­ • Seams should be mechanically risk of leakage.

S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6 F l o y d A n d p A T E l • 1 3 3 NoTES

1 3 4 • F l o y d A n d p A T E l S y m p o S i u m o n B u i l d i n g E n v E l o p E T E c h n o l o g y • o c T o B E r 2 0 1 6