What’s a Straw-Bale House? Jerome Brown, owner-builder
Why build with straw bales? • Terrific insulation value -- typically R-40 or better • Typically available locally -- less trucking • Reuses a natural product that farmers otherwise burn: avoids CO 2 pollution • Organic architecture -- a less rigid aesthetic • Federal & state energy tax credits • (Mandated by one’s wife)
Why not build with bales? • More expensive than stick-frame const. • Needs larger concrete foundation (an environmentally nasty material) • Fewer experienced builders: less experience = higher cost • Detail- and labor-intensive technology • Hard to nail things to bale walls (pet peeve)
2 Ways to build with bales: (1) Load-bearing method (approved only for single-story construction) (2) Post and beam/infill method (our choice)
Load-bearing method • Start with a firm foundation (heavy bales) • Build bale walls with internal stiffeners (allthread, re-bar, etc. ), incorporating windowand door-bucks • Top walls with a “box beam” (see later) • Build roof assembly on box beams. Roof load (+ snow load, etc. ) is borne by bales.
Load-bearing straw-bale wall (from Carolyn Roberts’ website, houseofstraw. com)
Post & beam/infill method • Start with a firm foundation • Erect post-&-beam walls; frame window & door openings; top with continuous box beam • Build roof on box beam; roof load is borne by post-&-beam structure • Fill spaces between posts with bales
Our post-and-beam straw-bale house (showing post-&-beam and roof framing) (showing bales, roof, windows & doors complete)
What’s a “box beam”? 3/4” plywood 4 x 4 Insulation (all solidly nailed together) 2 x 4 4 x 10 wall beam
Common objections (& remedies) (1) Fire? (keep out oxygen) (2) Rot? (keep out oxygen and water) (3) Pests? (keep out oxygen) (4) Strength? (attention to detail, same as conventional construction) (5) Weight? (greater than frame wall, needs stout foundation) (6) Costs? (see later)
Keep out Oxygen? • Once bales are tied in place, cover them with plaster skin, inside and out. • Stucco can be used on outside, though lime plaster is better (doesn’t trap moisture). • Lime or earth plaster can be used inside. • Trick is to make this skin as continuous as possible -- no holes/cracks unless absolutely necessary.
Costs? • Generally higher than frame construction: stronger foundation, more labor-intensive, plaster ingredients can be expensive, more details to attend to • Paybacks: dramatically reduced energy costs during (long) life of building; lowmaintenance plaster skins • Tax credits: normally both federal & state
Online References • http: //www. thelaststraw. org/resources/rg 06/ code. html • California Straw Building Association (CASBA) www. strawbuilding. org • Canada Mort. and Housing Corp. reports at www. cmhc-schl. gc. ca (esp. fire-testing) • Andrew Morrison - www. strawbale. com • http: //www. houseofstraw. com/ • Google “straw bale” -- lots of resources
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