I'm in the early planning stages of building my dream green home. I've been working on a solid plan for a little over a year now and have considered a tire home, underground home, and a straw bale home. After looking at 'final' projects straw bale won out in a land slide. The looks of the home are beautiful and still retains all the green features I am looking for. My question is about the roof. I understand the simple stuff like the color of the room matters, it only makes sense that a back roof will be hot while a light colored room will be cool.
But what do you make the roof out of? What is the material you use? I want to know everything from what is the supporting structure made out of to what goes on top of that and finally what is the final covering made out of? It seems everywhere I look it talks about the wall of the home being straw with a earth plaster but very few references to what to make the roof out of or choices when it comes to making a roof? Can you guys put together a simple guilde to the best ways to make a green room including what they are made of and the insulation you use on them.
Thanks,
Gregg Webster
Iowa City, IA
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Hey Gregg!
That's a pretty long laundry list you're asking for?! First I must answer a question, with a question. You didn't mention if you are planning to build via Post & Beam, or load baring?
Followed by: "There's more than one way to skin a cat." Meaning, there are several choices of how one can proceed with the roofing structure. My best suggestion is to first research several books on the topic. Build It With Bales, II (Matts Myhrman) is a good basic primer. But there are several others' with greater detail and more advanced techniques. "The Serious Straw Bale," comes to mind.
In general. If building load baring, one builds a box beam across the top course of bales. On which rests the truss members. Those can be off site, pre-manufactured or with use of an accurate jig, handmade on site.. Over the truss work, rests the decking material. Which varies in composition from one area of the country to the next. Some use OSB (chip board), some exterior grade plywood. And in rare cases actual dimensional lumber (1"x8"). The choice of actual roofing material depends on several factors. Are you going to collect/harvest rain water for domestic use? If so, the perferred is a standing seam metal roof with finish coat approved for such. Although a real fire danger, one could use untreated cedar shake shingles. Asphalt composition shingles are the cheapest, most common but not to be used for water collection/harvesting.
If you are planning on going the P&B route? You might consider timber frame mortise & tennon, for the "bones" of your SB home. Even though larger, timber framing actually uses less lumber material than does one built from diamensional milled lumber, with much less embodied energy. If you have plans for an interior exposed vaulted ceiling? This might be worth considering, with the beams left exposed..
Another alternative consideration? Is a all-in-one system called a SIPs panel. Basically two layers of OSB board sandwiching a central core of insulating foam (6 - 8" thick). Provides interior finish surface, insulation and decking material all in one. Usually manufactured in 8' x 24' panels; are structural in design requiring fewer beams or diamensional lumber. But not what one would consider a DIYer's method. The panels are hydraulically hoist lifted and placed.
Regarding the insulation, if a standard truss system and flat interior ceiling is being planned? One can use the newer generation of expanding foam, batt insulation or blown loose cellulose fiber. I'm intrigued by the new blue-jeans material insulation, personally. But, there are several organic natural choices that aren't that pink stuff... Just remember, you want your ceiling/attic insulation to come as close to that of the bales walls as possible. Somewhere in the R30 to R40 range..
My last mentions before I button my yap.. Do not neglect, providing wide enough eves/overhang of your roof to provide adeqate shelter from rain washing down the exterior wall surfaces. Eighteen to twenty-four inches, is considered the minimual. If using a standard truss system? Do not neglect installing "hurricane clips" to attach the truss work to the box beam. A bead of construction adheasive between the trusses and decking also helps in ensuring a storm doesn't blow the hat off of your home. Some storm studies have shown that attaching the decking material with screws instead of nails, provides somewhere in the neighborhood of a 20% increase in structural integrity, even over ring-shank nails. Also if building a load baring SB, use a system that ties the box beam to the foundation!! (there are several choices).
Well, that should make things' about as clear as mud?? I hope at least that answers more, than it brings questions to mind.
Happy Bales to You!
Regards, Mark aka: Spuds
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