Partially “earth bermed” foundation
I recently toured a small home on the outskirts of town in Southwest New Mexico, CZ4B. One detail that I liked was how one corner of the house was built into the hillside. A bedroom was located in this back corner of the house (southwest corner of a simple rectangular design). I would guess that three or four feet of the exterior walls at this corner were below grade. A retaining wall jutting out from the south wall created a patio connected to the living area with French doors. The foundation was like a slab-on-grade but with brick rather than concrete.
Since then I’ve been looking for construction details for building into a hillside, being that our property also slopes from the southwest down toward the northeast. I would think that this would help with cooling demands in the summer and make for less cladding to protect from our intense year-round sunshine.
Unfortunately, searching for “earth bermed” and “earth sheltered” on GBA only brings up references to Earthship homes and other such far out dwellings. Not helpful to me, as my priorities and plans do NOT include a reliance on passive solar heating, thermal mass, earth tubes, etc.
Is there some other term I should be using to find construction details for building into a hillside where only a small portion of the exterior walls are below grade?
The foundation I have in mind is a concrete stem wall and slab-on-grade insulated on the interior of the stem wall and below the slab. Would this foundation allow the house to be at-grade at one corner and dug in at the opposite corner?
Thanks,
Aaron
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Replies
Just to clarify, in which zone are you planning to build? Most places in NM are very dry, but if you're building elsewhere where they have more water, it will likely make less sense.
We are in zone 4B, at 6500 ft elevation. This is a fairly dry, high-elevation location in NM. Annual rainfall is 16 inches.
Aaron,
What you are describing sounds like a daylight basement. It's pretty common on sloped sites. The detailing should be the same whether you have an0ther storey above or not.
^ What Malcolm said. Also known as a 'walkout basement'.
My first thought was walkout basement. If you want to consider taking more advantage of the earth's insulating abilities, check out passive annual heat storage (PAHS) designs, also called Umbrella Houses. They may be too far out for you but they have some interesting science involved. Here's one Q+A about it: https://www.greenbuildingadvisor.com/question/new-earth-sheltered-pahs-construction.
Walkout basements are very common in my area, so much so that owners of hilly building sites advertise that there are "many walkout sites available".
You basically build a normal footing all the way around, but only a "real" foundation wall on the side built into the hill. The side that is open is typically framed normally.
Bill
I thank everyone who responded. I see now that regardless of whether the concrete wall is full height or partial height with a stud wall above, the foundation is built and insulated as a basement.
I came across the photo below in another GBA Q&A post from awhile back, but no source was given for the image. Does this image look familiar to anyone? Would this be a wise detail (with possible changes to foam type/thickness to meet my climate zone requirements)?
Aaron
Aaron,
That shows the detail Martin describes in this blog: https://www.greenbuildingadvisor.com/article/how-to-insulate-a-basement-wall