Foundation Type: Walkout Basement or Slab on Grade
Hello! I’m looking at building a home in athe next few years and am wondering if I should go with a slab on grade or walkout basement foundation? I’m leaning towards slab on grade for cost as well as for the thermal mass properties it would provide. I would aim to build a single pitch structure with a second story on the higher side of the house.
However, I’m wondering if the walkout basement would still be worth the investment. Our land slopes down slightly, making grading an easier task. It would be nice to have a second floor built from the foundation alone, as well as more space overall. However, I wonder if it’s worth it to sacrifice the thermal mass and if it is easier to build on a slab vs. walkout, as well as the overall costs.
Thoughts and ideas welcome, thanks!
Colin
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The effect that thermal mass has on a house is almost always greatly exaggerated. If you have very high temperature swings between day and night and don't want to use a lot of insulation, then it can have a small effect, but it's generally best to ignore it.
Below-grade space tends to be less expensive to build than above-grade space, but to keep it from feeling like a basement requires some extra effort in design and decorating. Most basements are not made to keep moisture out, but they should be, and it's not hard to do, but it does take more materials and effort than most contractors are used to doing.
It's usually easier to build on a slab, but if you have to bring in a lot of fill, that can get expensive, and it can be hard to make it blend in.
Gotcha. I'll be at 9,000 ft in the mountains, forgot to mention that. I've heard slab on grade can be tricky when the frost level is that deep.
It can be. It really depends on how deep your frost penetrates. You can use a frost walls and backfill to create a raised slab, or you can use a frost-protected shallow foundation system that uses exterior foam insulation to keep frost at bay.
For what it’s worth, I live in a slab on grade now and it’ll be the last time. There are too many problems that can’t be reminded later when the arrive, if they arrive. Plumbing always involves removing finished surfaces, cracked tiles, cold feet, and if you don’t do some type of frost protected shallow foundation at your elevation, there’s a significant amount of heat loss to the ground, let along the heave.
If you can swing the 40k extra to do a full 9’ basement, I think you’d be doing yourself a forever favor.
Thanks for that info. When you say cold feet, are you referring to hold the floor feels as a slab on grade? From what you've saying, it sounds like it's not worth the thermal mass properties based on heat loss?
Consider a "shallow frost protected foundation" if you go slab on grade.