Resource for foundation types
As we all know, there are many types of foundations used in residential construction. Most choices seem to be regional. One might be inclined to assume collective wisdom and, without out a lot of thought, decide not to reinvent the wheel. I am not such a one. How do we go about deciding, which foundation type is best for a particular project? What are the variables? We can say soil type but that is too general. What about the soil? And what is our objective? Is it durability or is it to minimize carbon using materials like concrete? I’m looking for resources to become better informed and guidance from the GBA gurus to help direct my search.
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Replies
Too big a subject - I'd start with a couple of good books about foundations.
Hugh,
Start by reading this article: "All About Foundations."
You might also want to read this article in the GBA Encylcopedia: "Foundation Types."
Perfect! Thanks.
Martin has what I'm sure is a pretty solid article here, even if I can't read it at the moment: https://www.greenbuildingadvisor.com/article/all-about-foundations
I'll share what I've gleamed from my time here. Some of these are massive generalizations, and advice will vary by region. If it contains mistakes, correct me.
Slabs are preferred when possible. They are simple to construct, cheap, durable, use less materials, are easy to insulate and seal, are less prone to moisture issues, and are less likely to have homeowners ruin them. Some regions have historically avoided them due to unfavorable soil conditions, but with modern materials and methods slabs can be built on just about any level ground. Some soil types may require post-tensioning. Slabs involve more planning for mechanical rooms, storage, service runs, etc., and will generally use more lot space as a result.
Best practice with basements is not to finish them. They are dark, do not make good living spaces, and are much more likely to encounter water damage or mold problems. Expect water. Nevertheless, they provide a lot of storage space at a low cost, along with plenty of room for mechanical systems. They should be insulated on the outside. Buyers in regions where basements are common might prefer them, even though they make no sense in that region (i.e. my fellow New Englanders, the poor souls).
Crawlspaces should be considered shorter (cheaper) basements, and constructed as such. Do not make a vented crawlspace! Seal it off and make it part of the conditioned space. One benefit crawlspaces have over basements is that the homeowner won't be tempted to finish the space, but it still can be used for services and (some) storage. Downside is that they are less useful.
You can construct a good house on piers if you want, and sometimes the lot might require it. It is probably the "greenest" option, but is relatively uncommon, even for homes featured on this site. Piers cut down on concrete use, and disturb the soil less. Be sure to get the insulating and air sealing details on the floor right. Probably don't use batts, and if you must make sure they are not exposed to windwashing or critters. You'll probably want an engineer for the design.
As a side note, avoid attached garages in all cases, as they reduce air quality.