Hi All, new to posting. I am planning on building an SIP house this spring using a frost protected slab on grade here in central Wyoming. I am planning on a Rumford fireplace in the great room, and was wonding about how to approach the foundation on the fireplace. Should it be a stand alone (separate from the slab) footing, or should I just increase the thickness of the slab under the fireplace? If it is just a thickened slab, how do I treat the insulation under the slab in that area?
thanks
steve
Replies
Welcome Steve. I've built some frost protected houses down in Laramie that had ICF walls and slab on grade foundations.
Especially in central Wyoming (Casper?) ICF walls have a big advantage over SIPs in that they block out the wind noise. Hopefully you've at least considered them.
As for the foundation, I'd generally recommend separating the footer or you may get cracks in the surrounding concrete as things settle out. If are building on the clays that turn to gumbo mud it's extra important since the soils don't provide idea load bearing capacity.
On the other hand, if you are using an extra thick slab throughout to take advantage of daytime solar gain (passive solar), and properly reinforce the slab for the loads, then you're probably better off using a monolithic slab.
Shallow frost protected foundations work great in the Wyoming plains. We'd simply scrape off any plant material and the 1" of topsoil and the excavating was done. After the slab was poured we'd hire a backhoe opperator to scrape dirt from various parts of the lot and pile it up around the house so the bottom of the footers were 2' from grade. The foundation has to stay dry or it'll sink in the mud and having the house slightly raised is about the easiest way to do it.
Definitely plan for a perimiter drain. Those shallow foundations just don't handle wet conditions unless built on soil that drains well, so the perimiter drain is cheap insurance. If you raise the house a bit, the perimiter drain can simply gravity drain so it's low cost/low maintenance.
Around Laramie, some fairly simple passive solar stategies are working very well. We built highly insulated shells with simple passive solar setups and the temps inside stay surprisingly warm with no heat (50's in below zero weather). If they are still in business, Built Green Technologies in Laramie would be a great resourse for this kind of thing if you're interested. They also are very familar with radiant heat systems in high performance shells.
Good luck
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Hello IdahoDon!I live in Lander. I just helped my Dad put up an ICF basement on his SIP house. To be honest, I was kinda part time generaling while my dad was in Wisconsin. I cant say a lot about the experience except that it turned me against the use of ICFs at least below grade and where I was not in 100% control!The ground here is not gumbo, but not far from it. I planned on scraping off the organics and hauling in a bunch of structural fill and gravel to proved the platform for the slab.thanks for your quick advice.steve
LVHS class of '85. Go Tigers! Had a chance to backpack into the Stough Creek basin last summer after being away for many years.
You're right about ICFs--have to do them well or not at all. Lander has a great climate for SIPs since there isn't as much wind.
It's a shame to lose all that thermal mass under the stove. I'll bet you can do as others have suggested and insulate under the footer. Dow's rigid Styrofoam is rated for something like 24 or 29 lbs/sqin (over 3000 lbs/sqft).
Beer was created so carpenters wouldn't rule the world.
Thanks again IdahoDon!I started packing into Stough Creek in 65 with my parents. Did that for a few years until high school got in the way. I moved here in 2005. Last year in April we had 120 mph winds at my place up Squaw Creek! So, once in a while it does get a bit breezy!steve
OK, I stand corrected! 3000 lb/sqft!
Check out this linK.. More Impressive yet!
""http://www.dow.com/styrofoam/na/pro-us/products/highload_100.htm"" A bit more info on the other products compressive strength.
""http://www.dow.com/styrofoam/na/pro-us/applications/slabs.htm
Edited 1/17/2007 11:52 am ET by dovetail97128
Great Info! thanks
steve
Wow, 100 psi (14,400 psf). Now that's some serious foam.
Beer was created so carpenters wouldn't rule the world.
Don,
We used the 60# when we built the thermally isolated footings in 1979. I had my doubts at the time but it has been standing for almost 30 yrs. now and last I talked to the owners the house has no settling problems.
It was a passive solar house and has several 12' tall CMU with fully grouted cells with stone veneer on them in it, plus CIP 8" x 10' perimeter walls on 3 sides. Everything sitting on the foam under the footings.
Most soils around here are considered to be about 2500 psf for bearing and footings are designed for that, so the foam @ 60# has almost 3 1/2 x the needed capacity .
Even a large fireplace footing will probably have a footing designed for much less psf bearing than the foam can handle. Sounds scary.. but the numbers work .
It does sound strange at first, but the idea of foam under the footers starts to make more sense especially with ICF's.
Beer was created so carpenters wouldn't rule the world.
You might check to see what the PSI or PSF load is going to be on the footing. Could be that you can lay the foam under the footing.
XEPS foam has a crush strength that exceeds most footing loads and a lot of soils bearing capacities.. I built an entire solar house that was thermally isolated by building the footing forms out of 2" XEPS . We just built "U" shaped forms from the stuff then poured into them.
I would still pour the slap separate though , helps keep cracking under control a bit better is my experience.
Yes , it was all Engineered and approved by the BI.
Thanks Dovetail!I guess the thing that was bothering me the most was if I have this fireplace footer that is quite deeper than the slab and footers for the building, how do I insulate it without producting some kind of a water trap since it will now be the low spot in the area?steve
Just make sure you have your #'s checked to be sure that the compressive strength is above what is needed for the footer.
Not an expert, but it seems to me insulating under a fireplace footer is of little value and worse is asking for major settling if you intent to build a real brick or stone fireplace. You can disperse the load of a 20 ton fireplace on a footer, but not on a piece of foam insulation. Sorry if I am in error or misunderstand your intentions.
Thanks!Yes, what i was wondering is how (or as you so nicely put it) WHY put insulation under the footer for the fireplace. It is in fact intended to be stone about 22' high so there is a considerable weight involved.steve
you do not have to use insulation under the slab for FPSF.
Are you saying that you will not be using any footings? What sort of soils prep do you plan? ICFs on top of slab?????
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Thanks Piffin. I have done a bit of a review of a number of sources for FPSF, and it appears that there are 2 schools 1-insulate under the slab and out from the thickened edge, and 2- only insulate out from the thickened edge. I cant quite understand the desire to not inulate under the slab unless you desire heat loss?!? So, I was planning on putting 2" xps under the whole thing, thus the question of what to do with a thick footer under the fireplace.steve
I would footer the fireplace separately from the slab and no insulation under it.Just wanted to be sure you understood the options first before answering.
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Thats what I have gotten from the crew posting here! Thanks againsteve
I would add to the others good advice - make a nice deep cut around the perimeter of your fireplace and chimney with a diamond blade - just to prevent cracks there - I did something similar with a 14K lb masonry heater on a slab - no cracks to date. The slab was thickened to 12" w/ a 6" rebar grid under the heater.
Thanks Brian!I am thinking that the best bet is to do as suggested and at least provide the ability for things to move without affecting the whole slab with a cut.thanks againsteve