Mr. Lstiburek has written some thought provoking information on house construction. Much of what I have read [in Builder’s Guide to Cold Climates] deals with proper control of moisture in a building’s ‘envelope’, or the part that you live in and heat/cool.
One of his big no-no’s is venting a crawlspace…. namely to never vent one, instead to insulate the outer perimeter [leaving the floor joists over same uninsulated], and to include it in the building heating and cooling envelope.
I am paraphrasing, and he would probably do so differently [in many pages] but what interests me is that he calls for: “Fire-rated insulation on the exterior crawlspace walls”
How does one achieve this, since rigid foam is not fire-rated when exposed.
a link to this conversation:
http://www.goodcents.com/web/to_vent_or_not_to_vent.asp
the existing thinking that supports venting a crawlspace:
http://www.hmteam.com/around11.html
Replies
Pablo,
"One of his big no-no's is venting a crawlspace.... namely to never vent one, instead to insulate the outer perimeter [leaving the floor joists over same uninsulated], and to include it in the building heating and cooling envelope."
Never say never......
There's a lot of real estate in this hemisphere that has gasses, mold and such that you wouldn't want to incorporate into your living space.
Never forget that you're reading one man's opinion not facts that can be applied everywhere.
Gabe
Hi,
Being Canadian, a Northern Canadian at that, I agree and do build in the manner you stated. Unless its a full basement situation where, of-course, some different rules apply.
Anyways..To your question. I find it un-likeky that any reputable builder would leave exposed rigid insualtion anywhere. The uv will destroy it and yes it is a fire hazard. Usually a quick coat of stucco wire and a bare minimum brown coat of stucco will take care of most of you fire rating comcerns. Remember though to keep the stucco out of the dirt. A band of PWF plywood takes care of that. Paint matches it all up and finishes the project.
Maybe I helped? Maybe I didn't.
Goodluck
The application of rigid foam that I speak of would happen on the inside of the crawlspace, over top of continuous vapor barrier that covers the floor. Over the vapor barrier I have put down 4" of gravel and poured a 3" concrete slab.
I like the stucco idea, it just sounds like a lot of work and material. Covering the foam with sheetrock seems like it could get nasty after many years.
I did some reading further since my post and Lsitiburek calls for "foil-faced isocyanurate". I plan on giving my building materials supplier a call Monday to see if they sell this.
here is the link to this reading, scroll down to 'Cautions / Notes':
http://www.buildingscience.com/housesthatwork/cold/default.htm
"Many production builders want to meet Energy Star minimums while still controlling costs. Wall insulation systems that are good from a moisture and mold perspective cannot be left uncovered because of fire rating. Covering the insulation with thermal protection (gypsum board, cement board or plywood) adds considerable expense). The cheapest acceptable option is to cover the upper 4 feet of the basement wall with foil-faced isocyanurate. This insulation is fire rated for exposed use but does not allow the concrete to dry to the interior............"
Thermax, made by Celotex, is ASTM rated foam with a fiberglass/foil facing that supposedly (at least in my area), meets the 30 minute fire rating and can be applied without further coverings. It is hideously expensive (I think something like $17 for 1/2", 4x8 sheet).
Jason,
Nice call on the Thermax! The material is exactly as you say......ANSI approved for remaining exposed. Celotex has recently been bought by DOW, and their 800 line Rep was very up to date on the product. There are a number of similar products in the line [Tuff-R, Super Tuff-R] that are not made to be left exposed, but basically use the same materials.
Bottom line, and bad news so far, is that Thermax is very hard to come by, the two yards that DOW referred me to are 100 and 200 miles away. I am not needing enough to special order a case [100 sheets of 1" or 50 of 2"] so I may be back to GO.
Any ideas on how to get a hold of this would be great.
Thanks for the right stuff though!
Pablo...I had the same problem, but I just went to my local yard (which has offices all over the state), and they got it in Detroit, which then got transferred to Mt. Pleasant, which got transferred, etc., etc. Bascially, I can get just about anything through the local guys...as long as I'm willing to wait. But I'd get a price first...expensive stuff it is!
Jason,
That is where I am......my local guy will get it, and it will take some time and $22/ sheet. A local [and reputable] builder dropped by to see the progress yesterday, and said he did not feel there was any problem with the un-foiled stuff being left exposed.
The Dow Rep said the same thing, that it should be ok.
Anyway, I am on my way, and appreciate your head's up!
/P