Step 4. Roof-Bearing Assemblies
ilclcngCI First, to have previously selected, from a wide variety of options, the combination of roof-bearing assembly (RBA) and tie-down system that is "right" for you and for your design. Second, to get the segments of your RBA safely up onto the wall (unless you have chosen to create the RBA in place, on top of the wall) and to make strong connections where they meet. Third, to "tie" this assembly to the foundation in such a way that the maximum expected wind velocity (a.k.a. the design wind load) cannot turn the RBA/roof into an ILFO (identified low-flying object).
Walk-Through Jt extend continuously around the structure. Every wall carrying any roof load will need an • During the process of finalizing your RBA, but modern roof designs for square and design and creating plans, you will have rectangular buildings very seldom bear on selected the type of RBA to be used. Among more than two of the four walls (assuming a the factors that can influence this decision square or rectangular building). Even so, one are: might still choose to have the RBA be a —whether the RBA will act as a lintel over continuous collar, in order to tie the whole openings; [This would allow you to use less building together. A rigid, continuous RBA wood in creating the nonbearing door and could also serve as the lintel over all door and window frames, but may bring you to use window openings in the building, thus more wood in the RBA itself. It will enabling all the frames to be similar guarantee a straight, and probably level, roof (lightweight, non-loadbearing). It would also line, but may limit the number and size of distribute some of the roof load (otherwise openings, since the load is concentrated on carried entirely by the columns of bales the bale columns between openings.] between the openings in two of the walls) onto —the distance between the points on the the other two walls. RBA at which the trusses/rafters/vigas/ There are, however, advantages to having wooden I-beams concentrate the roof load, the RBA discontinuous (i.e., only on the two the magnitude of the load at each point and loadbearing walls). It saves labor and the whether it is the same for each point; cost of materials (both to the planet and the —the degree of compactness of the bales wallet). If the roof design is a gable, and if that the RBA will rest on; bales are going to be used to fill in the eaves —and, your various concerns about the (the triangular areas formed by the sloping materials required for the different options roof surfaces), builders often put in a light- (e.g., regional availability for purchase or weight horizontal stiffener at the level of the scavenging, cost [planetary and pecuniary], separate RBA's, before stacking bales to fill the tools and skills required to work with the triangles. If securely fastened at both ends them). to the RBA's, it can provide some of the You will have also decided whether it will collar-benefit of a continuous RBA. For more on stiffeners, see page 130. Page 65 Roof-Bearing Assemblies Roof-Bearing Assemblies Page 66
• Before you can fabricate your RBA, you and that the walls are properly aligned and must decide how to dimension it. It is typical secured under the RBA. If your system for to make the width slightly less than the keeping the top of the wall centered under the average width of the bales. This ensures that RBA involves putting holes in whatever is the RBA, which generally acts as the nailer acting as the waterproof cap, be sure to for the stucco netting, does not extend out carefully seal any openings through which beyond the edge of the bale wall at any point. water could get down into the bales. Choosing the length dimensions is more * Unless your RBA already adequately complicated. There are two obvious protects the top of the walls from invasion by approaches, each with potential advantages: rodents, deny them access by utilizing various 1) Use the foundation dimensions, taking materials (e.g., cement-based mortar, metal into consideration whatever setback you want lath, sheet metal, plywood scraps, old boards) to have from the edge of the bales. The alone or in combination. advantages to this approach are that you can * With your wall tops positioned, as finish building all the segments of the RBA appropriate, under the RBA and with the before the wall-raising is finished, that any chosen mechanism in place to keep them in pre-ordered trusses are guaranteed to fit, as this position, "tie " the RBA securely to the planned, on it; and that you will be mightily foundation. For our "model", we have chosen motivated to end up with dimensions at the an external tie-down system (e.g., polyester top of the wall that are real close to those at cord strapping with buckles or crimped the bottom. seals). "U"-shapedpieces of "tubing" (e.g., 2) Use the actual dimensions of the top of irrigation distribution line, salvaged hose), your finished walls as your starting point. positioned at a chosen interval in the The advantage to this approach is that you foundation, provide sleeves for the strapping. can customize both the width and length You will, hopefully, have taken steps to ensure dimensions to accommodate the actual shape that no concrete could get into the tubing and dimensions of your wall top (if this is when you were doing your pour. your first building, you will be lucky not to Straight pieces of plastic pipe, passing end up with walls that flare out a little). horizontally through a "collar" type Possible disadvantages are that you must foundation, have also been used for sleeves. leave some segments of the RBA unbuilt until However, even with bevels created at the the walls are finished, and that you may not openings where the strapping cord emerges, be able (depending on their design) to the right-angle bend may put unwanted, extra pre-order trusses. stress on the strapping at these points. * For the type of RBA on our "model" Regardless of the type of sleeve used, building, fabricate the roof bearing assembly however, care must also be taken to ensure on the ground in transportable sections. that sharp corners have been eliminated Then move these sections to the top of the where the strapping passes over the RBA. wall and connect them, taking care to get Small pieces of sheet metal, bent to make a strong connections between sections right angle, work well. Or, you can buy pre- (especially at corners). Make sure that the bent metal gizmos (e.g., Simpson A35s) at a diagonals are also as nearly equal as possible construction supply yard. Page 67 Roof-Bearing Assemblies
Options for RBA's Least Rigid
Bamboo Plank or TJI Beam 2 Sheets of Plywood or OSB
* Could be used with loadbearing window frames and More Rigid angle iron to stiffen it over a non-loadbearing door frame.
Double TJI and 2"X6" Mongolian 2"X6" Ladder (see next page)
Two 2"X6"s 2"X6". 2"X4" w/ 2"X6" w/ w/2"X4" cleats continuous plywood plywood "web" Most Rigid
"1 Concrete Bond Beam TJI with plywood 2"X6" w/ plywood (added weight will shorten (closed box) (closed box) permissible spans; see page 31)
Note: 2" X 4" [5 X 10 cm] and 2" X 6" [5 X 15 cm] Roof-Bearing Assemblies Page 68 Some Examples of RBAs Truss Joist I-Beam (TJI) Box
The pieces used for The top is typically "blocking" can be covered with plywood, pieces of TJI or or the equivalent, after dimension lumber. the space is stuffed with loose straw (some Sheetrock, under builders have treated waterproof drape, as the straw with a fire fire break (optional) retardant)
TJIs can be ordered in lengths up to 60 feet [18m] to provide seamless rigidity.
waterproof drape
corner guard' strapping tie-down option
Double-Layer Ladder-Type Mongolian Prototype (suggested by Dan Smith &' Associates)
2"X6" [5X 15.2 wooden or metal peg occassional ' cm] or wider fill or cover gap driven into bale through cross-brace with old boards hole in cleat board to exclude secure strapping rodents firmly to RBA strapping tie-down option 1/2" [1.3 cm] or wider 2" X 8" or 10" polyester [5 X 20-25 cm] strapping stuff space with tie-down option 2" X 4" or 6" straw (be mindful [5 X 10-15.2 cm] of rodent access) coil-strapping adjustable strong, overlapped corner connection, tie-down option side pieces set in to metal buckle ideal for handling hip rafters on as diagonal ensure adequate traditional, lightly-framed hip roofs corner bracing seat on bales Page 69 Roof-Bearing Assemblies Seismic Considerations
Wooden Box Beam
occasional blocking (cavity external cable bent rebar filled with straw) on outside, tie-down pins to hold attach roofing / 2"X6" system wall in place [5X15 cm] felt, expanded stuffed all-thread 2"X4" metal lath \0 cm] straw tie-down and/or stucco 2"X notch top system netting, here [5 X 15 cm] bales bolts TOP extra cross-brace, drilled, positioned, and end-nailed wherever threaded rods penetrate pressure-treated plywood (suggested by Bob Theis) 2"X4" [5X10 cm] provides attachment for notch Concrete Bond Beam stucco netting BOTTOM ^^ bottom sleeve placed here if using internal , .-•;> ^r bale tie-down rod or cable reinforced expansion strip concrete imbedded slab floor V . J-bolt rebar tie-wire waterproofing
temporary or permanent form board dry rubble footing
Filling the Gap Between Rigid RBA and Frames
full bale, or tied \ \h "basket" J •' .'' 'J x top of expanded fhlrr hrlH f^jvi'1"^ ^"^ metal lath suspended from loose straw attached to RBA the rigid RBA / \g as lintel (acting as a \r opening lintel) by strip (or platform of ' strips) of plywood, or 1 ^=* ^i^^\; attached to platform expanded metal '-".,• equivalent lath 1 ':
^_ Roof-Bearing Assemblies Page 70 Tie-Down Systems: General Considerations
In non-loadbearing designs, the framework against the bales. Through-ties, connecting that supports the roof load also ties the roof the inner part to the outer part of a loop of to the foundation, or to the ground, itself. wire, cable or strapping, would further Lacking this framework, loadbearing designs increase the effectiveness of these loops, almost always include some mechanism to perhaps making any other tie-throughs keep the roof from lifting off. In the historic unnecessary. One possible chronology for Nebraska structures, metal or wooden stakes this idea would be as follows: were driven at an angle down into the walls 1) Attach vertically oriented strips of and the fastened to the rudimentary RBA. stucco netting to the RBA as soon as it is in There is no evidence to indicate that this was place. not adequate for that situation (hipped roofs with minimal overhangs), but caution (and 2) Insert lengths of strapping through the concerns of engineers and building sleeves in the foundation, passing one end officials) have led most modern builders to of each length up over the RBA. create ties from the RBA to the foundation. 3) Fasten the two ends of each length In a design involving no use of stucco together with a metal buckle, hand- netting, inside or out, the tie-down system tightening periodically to take the slack out (arguably) continues to perform an important of the strapping as the walls settle under the function, even after the surface coating is in roof load. place. This will be especially true if seismic 4) When the settling is complete, and forces or differential settling of the just before hand-tightening the strapping for foundation ever cracked this coating. If, the last time, pull down on the stucco however, cement-based plaster has been netting and fasten it securely to a wooden applied over stucco netting (especially if nailer attached to the side or top of the applied in vertical strips fastened securely to foundation. both the RBA and the foundation), any 5) Now, hand tighten the strapping one previously installed tie-down system is then last time. relegated to a strictly backup role. This 6) Complete the process by creating assumes, of course, that the structural some through-ties, to connect the strapping integrity of this plaster-membrane tie-down on the inside to that on the outside. remains intact for the life-span of the building. For description of a system that uses stucco netting as the only tie-down (Look, Ma, no backup!), see page 73. Several builders have experimented with placing the tie-down system outside the stucco netting, to hold the curtain of netting Drawing by Arlen Raikes Page 71 Roof-Bearing Assemblies Tie-Down Options
roof truss
wire or strapping passed cable over bottom chord of truss
Cripple connector (Cripples and tensioners available through: DARE Products, Inc. P.O. Box 157 Battle Creek, MI 49016 1-800-922-3273) dry rubble Single Ladder RBA footing Heavy Wire or Cable Under Grade Beam Double Ladder RBA Polyester strapping Eyebolt
2"X4" [5X10 cm] block on each side of rod to support washer ,corner guard and nut (e.g., plastic, metal, cardboard)
polyester 1/2" [1.3 cm] ^^ strapping rebar with all-thread rod coupling nut bent pvc pipe to welded to ends allow passage of joist hanger strapping (Note: slapping foamboard floor joist bevel the inside buckle edge, to prevent fraying, if pipe pea gravel infill aligned more horizontally)
£ engineered slab Moderately Rigid Open Box RBA "All-thread" rod/rebar ' Rigid TJI RBA J-bolt Polyester strapping PVC pipe in grade beam Roof-Bearing Assemblies Page 72 Tie-Down Strength and Spacing - Assessing What is Needed
It's easy to guesstimate that a shed roof with type of tie-aown, to determine how many no overhangs, on a small building, might such tie-downs should be placed along that need no other tie-down than its own weight. wall. Consider arranging the tie-downs in However, given a high profile roof, with groups of two or three per location along large overhangs, on a large building, in an the wall, thus reducing the number of area with a design wind load of 120 mph sleeves or pieces of attachment hardware. (3.2 km/second), even the bravest (or most Remember that one long piece of strapping, foolhardy) of us all might be reluctant to passed three times through a sleeve and stake the stability of our roof on a guess. over the RBA and then fastened, has far less To start with, we would want to know the strength than three separate loops fastened maximum uplift that our tie-down system individually. would conceivably have to resist. For a Manufacturers often provide information small, simple building, you may choose to on the breaking strength (a.k.a. tensile do the calculation yourself, using formulas strength) of things like cable and strapping, such as those provided in Cole and Wing but seldom say whether it, or the connection (1976). Or, regardless of the size of the (e.g., clamp, seal or buckle), will fail first. structure, you can have an engineer or Talk to the technical representative at the architect do this for you. Once you know company, and try to get her/him to provide the number of pounds of upward force to be the safe working load for the product as resisted by all the tie-downs along a given combined with the connector you wish to wall, divide this number by a conservative use. value for the safe working load for a given Increasing the Wall's Resistance to Shear Forces (Tie-down systems as backup to the wall surfacing materials) roof bearing assembly
standard vertical tie-down (offers little resistance to shear) collar beam
wooden corner metal coil-strapping or inserted, vertical diagonal cables diagonal cable brace heavier metal strap post to resist shear- double U-bolted and/or wire bolted at point of related compression together where they anchored top and intersection (optional) cross bottom Page 73 Roof-Bearing Assemblies Tie-Downs as Pre-Stressing Mechanisms Modern builders, being the impatient souls temporary external bracing), they create a that we are, have long dreamed of finding a light, wood-frugal RBA, onto which they lay simple way of using the tie-down system to a long, narrow, inflatable tube. On this tube pre-stress (i.e., mechanically compress) the they lay a ladder-like assembly that has the walls, prior to putting the roof on. This equivalent of hooks sticking out on both would permit immediate application of exterior sides. Having secured the bottom end of plaster to protect the walls. Ideally, the compress- strips of wire netting to the foundation or ing mechanism would apply a load in excess of toe-up, they then push the top end of each any eventual, combined dead and live loads, strip over the hooks. This is done both inside further stiffening the walls. Even with mud plaster and out. Now the fun begins, as they slowly (and perhaps without pinning) the walls could inflate the tube. Since the "ladder" can't go then withstand heavy wind loads without up (being held down by the netting), the RBA unacceptable deformation or cracking. has to go down, compressing the bales as it Starting with what was already being used does so. This arrangement has the for tie-downs, initial attempts were made to tremendous advantage of applying the use the in-the-wall, threaded rod system to downward force both uniformly and pull down the RBA, thereby pre-stressing the simultaneously along the whole length of the bales. Unfortunately, it was found that the RBA. Using numbers derived from the roof threads would strip before sufficient design, the live load for the location and compression had been achieved. Then, thanks structural testing, a target for compression is to the sharp eye of Greenfire Institute's Ted determined. When this amount of Butchart, along came the Gripple. This small compression has been achieved, the netting is metal disc contains cams that allow a wire or securely fastened to the sides of the RBA cable to pass through the disc in one direction before the ladder and tube are removed. only. Combined with a tensioning tool, this Testing of pin-less walls, pre-stressed with offered the potential of using a loop of wire or this system, has shown them to be as resistant cable to pull down on the RBA with enough to wind loading (at right angles to the wall), force to pre-stress the walls. Unfortunately, at as similarly pre-stressed walls pinned in the least when used with a rigid RBA, no normal fashion (see The Last Straw, Issue No. individual loop can be tensioned enough to 14, page 14). This suggests that, unless the pull the whole RBA down significantly. pins in a pre-stressed wall contribute to the Hope was fading fast when, in the great wall's shear strength (i.e., its resistance to tradition of the Royal Canadian Mounted being changed from a rectangle to a Police, the barking of sled dogs was heard in parallelogram), the pins are serving no the distance. Onto the scene, from Ottawa, structural purpose. Imagine not having to came engineer Bob Platts and architect Linda pin! For more information on this intriguing Chapman, with an ingenious system that system, contact Bob and Linda at Fibrehouse involves inflation. Limited, 27 Third Ave., Ottawa, Ontario, Here's how it works. After building the Canada, K1S 2J5; tel/fax (613) 231-4690; walls without pins (but utilizing a system for e-mail:
Challenge! to create a sheltering cap (some combination of ceiling, and/or roof, and insulation) that 1) is securely attached to the roof-bearing assembly, 2) protects the tops of your walls and your interior spaces from the elements, 3) adequately retards the movement of heat, and 4) does this efficiently (re: cost, materials, labor).
Walk-Through Jt where appropriate. * Securely attach all trusses (and any * You will, of course, have chosen a rafters) to the outside edge of the RBA using particular roof shape during the design the appropriate connectors (a.k.a. hurricane process. Our experience leads us to strongly ties or the equivalent). A strong tie-down favor shapes that will allow for overhangs system for the RBA will mean nothing if these (the wetter the climate, the bigger the attachments are weak. overhang) and for guttering, to prevent splash back onto the base of the walls. Should * Attach 2"X 4" [5 X10 cm] purlin strips, dedication to a regional architectural style, at 2' [0.6 m] intervals, to the roof framework. personal preference, or deed restrictions * Fasten 26-gauge metal roofing to the "demand" the use of parapet walls (low purlins with special, self-tapping screws extensions of the walls above the roof line), equipped with neoprene washers, using we suggest using a low-pitch, shed roof with standard caulking strips where adjacent parapets on only three sides (as illustrated on panels overlap. the next page). This enables water to move * Create screened, louvered, attic vents in unimpeded off the roof, preferably into a the goblets at each end of the roof peak, gutter. Even then, very savvy detailing is installing proper flashing where the bottom needed to prevent any water from getting into edge of the triangular gable t meets the the base of the parapet, and from there, down sloping metal roof. into the bales. For one architect's version of If designs with gabled roofs, consider a (hopefully) leak proof parapet detail, see installing a prefabricated ridge vent to Issue 8, page 28, o/The Last Straw. Although provide venting along the entire ridge line. bales have sometimes been used to form the Don't underestimate the value of adequate parapets, it is more common to frame them, venting. In hot climates (see Cook 1989), it using more wood but less waterproof will keep your house cooler. In cold climates membrane and plaster. (see Nissan and Dutt 1985; Lenchek et al. * Fabricate the central part of the roof 1987), it will prevent problematical moisture skeleton, using identical homemade or buildup. commercial trusses. Complete the end hips, * Attach some material to the underside of using hip trusses or traditional framing. the overhang created by the ends of the Double up the two end trusses if your hip trusses/rafters, leaving adequate, screened system concentrates extra load on them. vents to allow air movement up into the attic * Brace the roof skeleton as it grows, space. leaving this bracing permanently in place Adding the Roof Page 74 Adding the Roof Page 75
* With the roof skin now in place, move energy-efficient building. The bigger the inside and install any radiant heat barriers building, the bigger the ceiling area relative following manufacturer's directions. These to the total interior surface area of bale barriers can be particularly effective in walls. For a building with 1200 square feet reducing cooling requirements in very hot [111.5 square meters] of usable interior climates. For an excellent overview of this space and eight foot [2.44 m] high walls, the option, see Nisson (1990). ceiling area is virtually the same as the wall * Install all necessary ducting, stove pipe area. For a larger building, the ceiling area brackets, electrical boxes (e.g., for overhead will exceed that of the walls. It may not be lights, smoke detectors, fans), wiring and cost-efficient to create as high an R-value plumbing in the attic space. [RSI-value] in the ceiling as you'll have in * Install the ceiling materials) and insulate the walls, but do try to achieve the levels (or vice versa). Be sure to provide a way to recommended for superinsulated designs for easily gain access to the attic space. If the your climatic conditions. For recommend- access is from a space that is heated or ations, consult local architects/ designers that cooled, make sure that the removable panel is specialize in energy-efficient design, your well-insulated. state Energy Office or selected books (e.g., ^ Don't assume that just because your bale Nisson and Dutt 1985, Lenchek et al. 1987, walls have a high R- or RSI-value, you can Cook 1989, Lstiburek 1997). skimp on ceiling/roof insulation and have an
Some Standard Roof Shapes
Vault Dome Cone* Shed Shed w/Parapets
Gabled Offset Gabled Gambrel Hipped
* Prefabricated conical, metal roof kits are available from Butler Mfg. (816-968-6126). Adding the Roof Page 76
Dutch Hip Framing Options This option is often used on rectangular buildings as a more interesting substitute for a gabled roof. Depending on the framing system (three possibilities shown here), some roof weight can be distributed to the shorter end walls. This roof shape also overhangs all four walls. For detailed information on roof framing, see Gross (1984).
space for Historically, square or nearly-square bale-walled screened, buildings were covered with a lightly-framed hip louvered vent roof. The advantage is the nearly equal distribution of roof weight on all four walls.
A short ridge can be scabbed on to modify the pyramidal profile and provide for adequate common truss venting of the attic (doubled here) space (a very important consideration). Two-Story, Loadbearing Options Using Super-Trusses™ Page 77 Adding the Roof
* For more, see MWPS (1989a), Smulski (1994), Some Truss Types* and page 80 at bottom.
Howe truss fmk truss mansard truss monopitch truss
I\J\N/I/I/1 scissors truss flat truss attic truss "supertruss"
Roof Surface Options • Shakes (either wood or composite materials). A secure and durable roof surface is vital for the • Tile (pricey and heavy). Due to their long-term structural health of your straw-bale weight, tiles are not normally used in home. Periodic maintenance and eventual loadbearing designs. Traditionally, "tile" meant replacement are also very important. Many fired clay, but tiles made from tires, concrete, historic Nebraska structures died from "roof and composite materials are now available. The failure". For roof surfacing options, see Herbert latter can contain considerable amounts of (1989), Kolle (1995), and Malin (1995c). recycled materials. Among the many roofing surfaces that have • Living roofs (ARCHIBIO 1995b, 1995c). been used on bale buildings are: • Thatch (e.g., palm leaves, grass). • Metal (pricey, but easy to install and • Tarps (especially suited to vaults). durable). This typically means standard Although requiring periodic replacement, tarps galvanized or color-coated panels. In dry can provide a cost-effective, though none too climates, the shallow-corrugated, cold-rolled pretty, option. steel decking, normally used in high-rise Some of the less obvious factors that might construction as form work for poured concrete influence your choice of roof surfaces may floors, provides an interesting alternative. It include the following: comes ungalvanized (i.e., without a zinc coating) • The potability of water harvested off and quickly attains an attractive, rusted surface. different surfaces. Most types of tile and We would not, however, recommend its use in commercial steel roofing panels are favored wetter climates, especially those characterized by over products containing asphalt. acid rain. For more information on this option, • The weight of the material per unit area. call The Myers Group at 1-800-729-3325. Given some maximum load per square foot of • Single-ply membranes (pricey, tricky to loadbearing wall-top, lighter materials will install, but effective even on roofs with very permit longer spans. little slope, if correctly installed) (see Loomis • Degree of flammability. Not generally 1991). considered an important factor, but of vital • Asphalt-impregnated roll roofing importance in certain areas where the likelihood (inexpensive, easy to install, visually boring). of brush or forest fires is great. • Asphalt-impregnated, fake-shingle strips • The stylistic appropriateness for the (more work than roll roofing, but less boring). neighborhood and/or region. Adding the Roof Page 78
A Simple Straw-Bale Roof Idea mesh-reinforced A long-held desire of many straw-bale elastomeric ferro-cement coating aficionados has been to reduce the amount fill gaps with of wood used, while retaining adequate metal flashing cob mixture insulation. Vaults and domes can work. with drip ~ planks or Another idea, using ferro-cement and an edge elastomeric coating, is shown at right. gutter decking fascia and "stop" for bales The Shed Roof Option Due perhaps to its lack of visual pizazz, the superinsulation. They can be ordered in simple, low-pitch, shed roof is generally various heights and in custom lengths far shunned by both architects and owner- greater than you'll ever need. designer-builders. With a few porches, however, this ugly duckling takes on a Wooden I-Beam (TJI) modest charm. And for the owner-builder, at least in regions where snow loads are Allows deep insulation minimal, it offers some attractive with ventilation; saves advantages: large-diameter trees • If we exclude the flat roof (dumb, dumb, dumb) and the very low, gabled roof • The necessity of having one end of the (why bother?, and few do), it covers a given TJI's, or rafters, higher than the other, structure with the minimum square footage provides the opportunity to insert clerestory of roof surface. Less materials, less labor, windows directly under the roof, where they less cost. can be easily shaded by a modest overhang. • With a single gutter and down spout, all the water harvested off the roof can be Shed Roof Rafter Details channeled safely away from the base of the walls onto vegetation, or into a cistern for storage. • As with a gabled roof constructed with Use brace or wedge triangular trusses, the whole roof structure is at each rafter/TJI made up of a single, repeated element. Once you've got the first one attached correctly, all the rest are "no-brainers". • If 14 inches [35.6 cm], or more, high "truss joist Fs" (a.k.a. Til's, wooden Space the two outside rafters/TJI's I-beams) are used, long spans are possible, ! on each side of end-wall bales; I- - i with adequate space available for trim bales flush with roof END VIEW Page 79 Adding the Roof Options for Ceiling Materials • Sheet rock (a.k.a. drywall, gyp board). This equivalent. An unusual option here is old standard is cheap, relatively non-toxic, WheatSheet, a hard, paneling material made and fire-resistant. It is also heavy and by binding wheat straw with a resin. For cumbersome to install overhead without info, contact Naturall (sic} Fiber Board, Box specialized equipment. For tips on how-to, 175, Minneapolis, KS 67467; 913-392-9922. see Ferguson (1996). To get a continuous, —Rough cut planks. Something like black smooth surface, ready for painting, one must plastic sheeting, placed on the upper surface fill the joints and sand the filler material of the planks, will both provide an air/vapor smooth. No one we've ever met seems to barrier and keep fragments of your insulation enjoy the last-mentioned step, and many from dribbling down through the inevitable flat-out hate it. Some builders avoid this step cracks into your caviar. by filling the joints, staining the ceiling with a —Peeled saplings (a.k.a. lattias), cane, cheap, dark stain and then stapling rolls of bamboo, etc. Rather than placing them at reed or split-bamboo fencing to the ceiling. right angles to the beams , one can angle The long, black-coated staples used for them and reverse the direction between each telephone wire installation work well, and are consecutive beam to form an attractive nearly invisible, but do require a special staple "herringbone" pattern. gun. • PGB3. This unusual product, consisting • Wood in various forms. Depending on your almost entirely of compressed straw, comes in design, your wood may be attached to the sheets that are four feet by eight feet by one bottom of something (e.g., a none-too-pretty, and a half inches. The surface has a lot of pre-engineered truss) or on top of something texture and gives the board the properties of that you want to see (e.g., a handsome round an acoustical panel (for info contact BioFab at or squarish beam). People have used: (916)243-4032 or e-mail them at —Commercial tongue and groove planking
V peeled log (a.k.a. vigd) rough-cut planking RBA straw flakes Adding the Roof Page 80 Ceiling Insulation Options For unbiased articles comparing common • Loose straw, flakes or bales, including bales types of insulation, see Wilson (1995a; 1996). used both as the structural roof and the A wide variety of options have been used, insulation in domes and vaults (see Lerner including: 1997). Especially when using loose straw, it • Fiberglass, in several forms. is advisable to first treat the straw with a fire retardant. For specific information on • Cellulose, from recycled newspaper, in retardants, see page 19. One approach to several forms. treating loose straw has been to first immerse • Cotton fibers, from recycled fabric trim- it in the solution and then spread it out on mings, in several forms. tarps or a concrete slab for drying. If your • Foam board retardant is water soluble, you must re-treat • Structural, insulative panels (for a combined the straw if it is rained before you get it under ceiling and roof). Typically these panels have roof. foam sandwiched between two sheets of • Surplus sleeping bags containing "fiberfill". oriented strand-board (a.k.a., OSB). An Sometimes bought very cheaply (from the interesting alternative, made with straw U.S. Forest Service), and stacked several between the sheets, is being manufacture by high, they are performing well in one small Agriboard. Call them at (515) 472-0363 or structure in New Mexico. Human ingenuity e-mail them at
Raised-Heel Truss Ceiling
spaces within box-beam RBA insulation continuing out and between trusses stuffed over the exterior walls at with flakes of straw full thickness
bales resting on wooden slats carried by bottom chord of trusses (Lighter insulation, like blown cellulose, can rest directly on the sheetrock.) Step 6. Letting the Walls Compress
C/flclllcngCI to patiently allow the bale walls to complete their compressional response to the "dead load" exerted by the RBA/roof/ceiling/insulation system, and to use this opportunity to work comfortably inside your building on a variety of tasks.
Walk-Through with a waterproof membrane, you can catch your breath. Use this respite for things like: * Unless your design includes a tie-down —recreating and reconnecting with loved system that enables mechanical compression ones; (see page 73), you must now let the walls —tweaking any ornery bales into final gradually compress. Select two, or more, position; points along each wall at which to —adjusting the verticality of door and periodically measure the distance from the window frames, as needed, and connecting top of the toe-up (or floor surface) to the top them securely to the bale walls with dowels or of the RBA (or, later, the bottom of the metal pins; ceiling surface). Number the locations and —installing the doors and windows; record the measured distances such that you —and, creating the floor, if this has not can compare each set of measurements to the already been done. If the bales have been previous set. For two different approaches stacked on a wooden deck carried by basement to measurement, each reflecting for a walls, stem walls or piers/columns, the floor is different degree of anal retentivity, see page already in place. Similarly, a slab-on-grade 86. creates the floor and the foundation with a The initial response to loading is rapid, single "pour" of concrete. but then begins to taper off. Experience Although the floor may end up being suggests that complete compression may created at different points in different require any\vhere from three to about six buildings, we have chosen to deal with the weeks. Depending on initial bale compaction question of insulation under floors in just two and roof weight, total compression will vary places - right here and on page 88, where we from some fraction of an inch (a cm or less) illustrate several options. During the design to several inches (about five or six cm). process, you should have made a decision During the settling period, you should whether or not to insulate and if so, with what occasionally adjust your tie-downs to remove and to what degree. Among the things that any slack. When all of the measurements in you might consider are listed below: a set show no change from the previous set, 1. The regional climate and the micro- you can safely proceed with surfacing the climate at your site. walls, as described in Step 7. 2. The type, or types, of floor you have * With the tops of the bale walls now chosen. protected by the new roof and the bottom 3. Whether the floor will be heated and/or course sitting safely up off the ground on a cooled by pipes through which water or, less toed-up, waterproofed foundation and draped Page 81 Letting the Walls Compress Letting the Walls Compress Page 82 commonly, air will be circulated. for options regarding the creation and 4. Whether you are using a frost-protected, attachment of partition walls. shallow foundation, since floor insulation can —Extending the plumbing into, or up into increase the amount of insulation required at the interior space. If you do choose to install the perimeter (see HUD 1995). some, or all, of the partitions at this point, 5. The calculated or guesstimated payback you can also complete any plumbing that time for the investment, and the planetary belongs in them (see Massey 1994). costs of not doing it. There are two obvious ways to get any Our "model" building has a high-mass water lines (cold or hot) into your straw-bale floor created within the above-grade collar. house. The first is to bring any pipes in We are using no insulation around the under your foundation/footings and leave perimeter of our foundation or under our them "stubbed out" at the appropriate floor, since our "model" climate requires very locations when you create the floor. If a little heating or cooling. problem ever develops with one of these The finished floor surface should be at least buried pipes, you will either destroy part of 1.5" [3.9 cm] below the top of the collar to your floor (if you can pinpoint the leak) or, protect the bales from any interior flooding. more likely, abandon all piping under the We have specified a high-mass floor so that floor The logical thing to do then, is to winter sunlight (i.e., solar radiation), entering consider using the second option, which you through south-facing glazing, can hit, and be might have been better off using to begin absorbed by, the floor. This daytime storage with. of heat will prevent room air temperatures That involves bringing the pipe that from becoming uncomfortably high during the provides cold water to the structure up out of day. At night, this same heat will "bleed" the ground outside the wall, at one or more back out, helping to keep the space from locations opposite a single fixture (e.g., a becoming undesirably cool. kitchen sink), or opposite an interior —Creating non-loadbearing interior "plumbing wall", preferably framed with partitions, leaving an adequate gap above 2"X6" [5X15 cm] lumber. Skillful, careful use them to allow for the settling that may still of the tip of a small chain saw will create a take place. An alternative approach is to hole, sloped slightly upward toward the postpone creation of the interior partitions, inside, for a "sleeve " of plastic pipe. Insert with any incorporated plumbing and wiring, the sleeve and plug any space around it with until the interior surfacing is in place on the your cob mixture. The pipe(s) can then be exterior bale walls. Then, with all the plumbed through the bale wall and into the surfacing materials in place (and all the frame wall. To safely use this option, you compressing finished), you no longer needs to must be able to insulate the pipes to prevent guess how much of a gap to leave to allow for freezing, even during record low temp- settling. eratures. In colder climates this may not be This approach also minimizes the amount economically possible. of patching required if one eventually If you cannot avoid running water pipes relocates a partition wall. See pages 85-87 along straw-bale walls, at least isolate them Page 83 Letting the Walls Compress carefully and completely from the straw. never require sharpening, but (arguably) cut —Equipping the straw-bale walls with a little less quickly. They are available from wooden elements to enable the hanging of welding supply stores. If none of your local cabinets, bookcases, etc. If these elements hardware stores, or specialty tool suppliers, will be hidden by the plaster, map their carry the Lancelot contact King Arthur Tools position precisely on a diagram and save it at (800) 942-1300. for later use. We 'II cover some of the various options for hanging things on straw-bale walls in Step 8. —Installing, in any partitions created at this point and in the exterior walls, any phone jacks, antenna cable, electrical boxes and wiring (see Traister 1994, Cauldwell 1996). —Rounding/trimming off bales at exterior corners and at door and window openings, as desired, to provide for a "soft-profile" finished appearance. This is also the time to trim off any undesired protrusions on your wall surfaces (a line trimmer/"weed whacker" When using any of the above mentioned works beautifully for this). Any niches, tools to cut straw, you should always wear notches, alcoves, etc., should all be created at safety goggles and a dust mask (does this time using a small chain saw or, better someone have to die from "yellow-lung yet, a small electric grinder, equipped with a disease" before this becomes automatic?). cable-twist, flat wire wheel or a cutting wheel Chainsaws, grinders and even line trimmers with chainsaw teeth on the circumference are dangerous tools, capable of doing major (called the Lancelot/ Both are illustrated damage to the operator or those nearby. Use below. The wire wheels are cheaper and them only with great care.
Niches and Counter-Niches
(idea from Bill & Kalla Buchholz) (idea from Jon Ruez) Letting the Walls Compress Page 84
Bale Tweaking Tools
pipe 6" X 6" X 10 [1.5 X 1.5X25.4 cm] metal plate' Big Sledge Wooden Maul Tamper/"Persuader" handle mounted in hole or on side
• Wires in metal or flexible plastic conduit on wall Wiring Options surface; or in groove (dug with claw hammer, or cut with tip of chainsaw or circular saw); or run under Pound in 2" X 4" floor and "popped up" to boxes. [5X 10cm] stake,_ • Wires in surfaced-mounted "decorator" conduit then attach box (attached after the wall has been surfaced). with dry wall • Plastic-sheathed cable (e.g., Romex 12/2) pushed screws into 2 1/4" [5.7 cm]-deep groove cut into walls. Hold in place with "Roberta pins" (see page 92). • Cable run horizontally on a bale course during wall raising. Position wires about 3" [7.6 cm] from 1"X4" [2.5 X 10 cm] board the inner edge of the bales to prevent risk of hitting in seam between bales; box them when pinning). side-mounted; stucco netting If doing your own electrical, see Traister (1994) can be attached to both ends. and Cauldwell (1996); Re: EMFs from -wiring, see Pinsky (1995).
High-Mass Floor Options 1" X 1" [2.5 X2.5 cm] [0.6 m] Bricks or blocks (e.g., fired adobes) on sand —moveable patterned (see Ring 1990), stone on earth (Laporte 1993) frame Tiles on slab Earth (see Laporte 1993, Steen et al. 1994, Steen and Steen 1997b, and several articles in 1" X4" [2.5 X 10cm] Issue 17 of The Last Straw) Compacted soil-cement / rammed earth (see Coloring Concrete Berglund 1985, McHenry 1989, Easton 1996) • Mix dye with the concrete before pouring. Concrete • Sprinkle on and "float" in during final finishing. —regular slab-on-grade • Staining: commercial or homemade (artist —regular slab poured over bale insulation (see pigments, or use ferrous sulphate which is cheap illustration on page 88) and available from agricultural, chemical, or —scored or embossed slab (pressed-in pattern) fertilizer suppliers to get a yellowish, reddish —large, thick, poured-in-place "tiles" (frame brown). stays in place) • Apply special concrete paints. Page 85 Letting the Walls Compress Options for Interior Partitions • Standard frame (2"X 4" [5X10 cm] or Consider hanging a fabric partition from those 2"X6" [5X15.2 cm]), covered with sheetrock little gizmos that slide along a metal track or some other type of paneling. You may attached to the ceiling. This system saves want to use WheatSheet, a thin panel made space, while providing visual privacy when entirely from straw and a formaldehyde-free, needed. polymer-based binder. For access • Furniture walls. As above, floor standing information, see "Options for Ceiling elements like bookcases and storage units can Materials" on page 79. be used to provide visual privacy without • Infilled standard or widely spaced frame creating a permanent monument to to which stucco netting has been attached on over-building. both sides, creating cavities that are stuffed • Earth materials. with straw. Paster is then applied to the —Adobe (McHenry 1989, Houlen and resulting surface with hand or trowel, Guillard 1994) and Cob (Bee 1997, Smith producing an undulating surface reminiscent 1997) can be used to create handsome, of the finished bale walls. relatively narrow (8" [20.3 cm] is a suggested Another infill option would involve minimum), sound- dampening walls that also tamping "light clay/straw" mix into the space contribute to the thermal mass within the bale between formboards temporarily attached to envelope. No matter where situated, they will the frame (see Laporte 1993). contribute to the effectiveness of passive and • Shipping pallets that have been stuffed active cooling strategies, but are of less with flakes of straw (for sound insulation) benefit in passive solar heating strategies before being stacked and connected to form a unless they receive direct sunlight for a partition wall. A thick coat of earth plaster, significant part of the winter day. For specific well keyed into the spaces between the suggestions on combining earth materials with boards, will probably stay on just fine without straw bales in your design, see Issue 17 of stucco netting. Pallets which would otherwise The Last Straw. take up scarce space in a landfill, can usually —Rammed earth (Easton 1996) is seldom be acquired without money changing hands. considered for a partition wall unless the wall The planet will love you for converting a will also be carrying roof weight, as in the waste material into a free resource. hybrid design with the inverted trusses on • Wattle and daub. The "wattle" is a woven page 22, bottom left. framework of saplings, bamboo, reeds, etc., • Straw bales. Whole bales, either flat or on intertwined with smaller twigs or branches. edge, have seldom been used for interior The daub is usually earth plaster, smeared partitions, since the resulting walls (ditto for onto both sides of the panel. rammed earth) take up lots of precious space. • Hanging dividers. If the only function of a Three-tie bales converted into four-tie bales specific divider is to provide visual privacy, that are then cut in half, would reduce the why spend a lot of time and money building a straw thickness to about 11" [28 cm]. A wall heavy, "permanent" partition that you'll made from these "straw slabs", perhaps probably end up wanting to move eventually. sandwiched between 2"X6" [5X15.2 cm] Letting the Walls Compress Page 86
Marts' Method studs spaced about 4' apart, would still Steve's Method provide a good sound barrier and pleasantly thick walls. metal bracket We do know of one building (see below), where a standard bale wall, with doorways in it, was used as a loadbearing substitute for a ridge-beam. v\\
Separate "2"X2" [5X5 cm]
- • V v X N
• Compressed strawboard. The Segment of board typically used for partitions is ,\> \c ruler 2-1/4" [5.7 cm] thick and consists of graduated in millimeters compressed straw panels with paper x\ glued onto both faces. This type of \ board has been widely used in England,
Calibration and elsewhere, to replace sheetrock- mark covered frame walls. For information on PGB (Pacific Gold Board), contact BioFab, in northern California, at (916) 243-4032 or
XvX up in earth- or cement-based mortar \ N (see Reynolds 1990). \t angle, \
Generic tape measure Measuring Compression Progress Page 87 Letting the Walls Compress Attaching Partition Walls to Bale Walls Under certain circumstances (e.g., in areas with minimal seismic risk) and with certain Cob only Side View wall types (e.g., frame walls), attachment at the top and bottom of the wall may be judged sufficient. Typically, however, partition walls 2"X2" or 4" are attached to exterior bale walls. The [5X5 or 10 technique chosen in a particular case will cm] stake depend largely on the material(s) used in bamboo pin building the partition wall. sapling pin (e.g., willow) Some options, arranged by partition type, are shown below. Many can also be used (although some adaptation may be needed) to connect the walls of a straw-bale addition to a preexisting structure.
Frame Side View Straw Bale Top View longer, diamond-shaped, plywood washer with the two sharper points aligned vertically threaded rod
sharp pin (e.g., bamboo, rebar)
lag bolt sharp pins "toe-nailed" through For info on "Gringo Grip", through stud call Slra\v Bale Building partition-wall bales into exterior-wall into 2"X4" bales Systems at 1-800-734-8091. stake
Adobe Or Cob Side View
Not illustrated, is the technique of building threaded rod with bend on one the straw-bale partition wall and exterior bale end, plywood washer on other wall simultaneously, knitting the two together
bent expanded metal lath attached by having some of the bales in the partition to wooden stakes in bale wall and wall extend into the exterior wall. Model it extended into earth wall with dominoes, or the equivalent, before as above, except strip of lath doing it! incorporated and pegged into straw-bale wall during stacking r
Letting the Walls Compress Page 88
Insulating Floors Bales on gravel between supports Under Slabs • foamboard (of a type that can withstand the loading without compressing) • pumice (provides an R-value of about 2.2 per inch [RSI-value of 15.2 per meter])
Bales"
foam board concrete slab repeated bracing^ rT-TT^T^'f~1 ' 'I' T- VrTV leveling guide
gravel/sand vapor barrier as needed spiked 2"X4" [5X10 cm] set and leveled in concrete """P6* between bale See The Last Straw, Issue 6, page 14, for photos of a slab & concrete ^"~>s. \> subfloor being poured over bales, an^ARCHIBIO (1995d) for how-to. Jl ~T \ r • 'l///, ' £ : t ^^ -,~~ \vapor S//, & , ^ J< If barrier Graver^ Between Floor Joists/Supports * See The Last Straw. Issue 12, p. 22, on this example from Mongolia. • fiberglass • cotton A wet ground surface under a raised floor ••- • cellulose, especially dense-packed may contribute to "rising damp" (water vapor • integral insulation and structural floor in outside air) that could condense within, (described, with access information for a and lower the R/RSI-value of, the suspended panel with a strawboard core, on page 80). insulation. Strategies to prevent this include providing as much ventilation as possible for the "crawl space" and covering the ground Bales or flakes between raised joists under the building with a layer of plastic air/vapor f~ flooring sheeting, held down and protected by a layer barrier "* subflooring of sand. Good perimeter drainage is also needed to insure that the sand stays dry. In cold climates, warm, moist inside air TJI joist must not be allowed to move downward board supports screen basket through the floor materials. (See the diagram Well-Ventilated to the left, and CMHC 1994.) The danger lies Crawl Space in the possibility that the water vapor will condense, creating liquid water that will air/vapor sand damage the floor joists and reduce the R/RSI- barrier soil value of the insulation.