Filling in an Old Crawlspace with Geofoam
I am demolishing a house and plan on building new one. The lot is a narrow city lot, therefore, there’s not much flexibility for the placement of the new house. I would very much like to use a FPSF, however, some of the new house’s footprint would extend into the existing/old house’s footprint which was a shallow crawl space. The other portion of the footprint would be on virgin soil. I am in zone 6, in the northern lower peninsula of Michigan. The original house was on a three block crawlspace and the footing’s depth is <24″, code is 42′ below grade. I was wondering if it is possible to excavate down to virgin soil where the old house’s crawlspace was and fill in with geofoam. There is an EPS manufacturer approximately 200 south of me who specializes in geofoam. I should also mention that only the perimeter was dug out for the footing and block work. The floor joists just cleared the soil below. The inspector seemed to think the footing and three block high foundation were constructed after the house was already built. I have completely removed this portion of the house so only the blocks and footing are left.
I want to build a very energy efficient house and I’m trying to avoid a lot of excavation work. I’m leaning towards an ICF or ICCF structure and going 1 1/2 or two stories.
Any advice will be appreciated. Thank you
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Replies
Hi John,
I’m giving your question a bump. Geofoam is not a product that comes up often on GBA, so I look forward to hearing from readers who have used it—and whether the application you have in mind is something they have done. Here’s the only mention of the material I could find on this site after a quick search: Geofoam for Load-Bearing Applications.There are two links to product information that might interest you.
John, I'm not sure I fully understand your situation but is there a reason you wouldn't backfill with gravel and go with a conventional raft-slab system? Geofoam (marketing term for higher-density EPS) has good compressive strength and in some cases it can be cheaper than soil, but I don't see what it would gain you in this case other than increasing your embodied carbon emissions.
They use it for highway construction. I am sure your idea would work. Our local manufacture has lots of information on their web site. Have you contacted your source directly? Like a lot of building component manufacturers, technical support is part of the product.
As a alternative, have you investigated flowable fill?
Thank you for the replies. I spoke with a salesperson from the Mono Slab EZ Form and posed a the question as to whether or not compacted fill can be used on a portion of a FPSF. He responded that it is a relative common place in cities. I then asked about using geofoam and he stated that that would work as well. I will definitely study the links shared by Kiley. In addition, I know the GO Logic used a flowable fill on their GO Home. The GO Home video showing the discussion of the home's FPSF might have been my first video exposure related to FPSF. As far as the raft-slab goes, one of the raft slab's edge beam would be almost completely within the former crawlspace area. So it appears to me, as Michael suggested, it might be a overkill with the EPS and not an environmentally sound solution. So I will look into all suggestions, Thanks again.
I worked on a commercial building where the finish floor elevation of a tenant space in a strip mall was raised with 36” of geofoam.
We removed the slab floor, excavated to the footings like we were digging a crawl space, installed two layers of the geofoam to get to a 36” depth, and then placed 12” of granular fill over the top. This was capped with a new 6” concrete floor.
The geofoam was specified because of a concern that the foundations would fail of the neighboring buildings from the weight of soil fill. We had no problem driving 73,000# dump trucks over the foam once it was covered with 8” of granular fill.