I have designed a house using my mechanical engineering knowledge and lots of research. The house will be built in the Pacific Northwest on the Olympic Peninsula. When discussing my design with contractors in that area, I was constantly questioned about building on a slab. They kept insisting I should build with a crawlspace. I hate crawlspaces. I just can't stand walking around and hearing the slightest thump thump, cold feet, the added expense of a foundation and a floor, and mainly, the lack of thermal mass.

The contractors and builders would state reasons not to build on a slab such as, moisture problems, hard on knees and hips, can't easily re-model and move the kitchen, and lack of insulation. In talking to forward thinking builders, engineers, and from my own knowledge, I realize that none of these are issues. There are a few homes in my area on a slab, which are properly built that work well. I know the owners. Some are passive solar, but more on that later.

So I ask builders in the PNW why they build with a crawlspace, and have yet to get a real answer. One answer I get from builders is, “that’s just the way we build here”. I’m guessing there are several reasons. Could it be a hold over from when concrete was expensive or non-existent and wood was almost free? Could it be that builders can get more money for a crawlspace house? One reason I heard that makes sense is, “We’re building on crawlspaces, making money, so why change?” I even had one builder state that with equivalent houses, one on a slab, the other on a crawlspace, the slab house will be perceived as a “cheaper” house.

My design consists of a perimeter foundation footing, perimeter walls using ICF’s, and first floor walls made of ICF’s. Insulation will be on the very bottom by the perimeter footings, then about 2.5 feet of compacted fill, then the internal cap slab. This is to capture as much insulated thermal mass as possible with this design. Radiant tubing will be down in the insulated earth box and in the slab. When the solar collectors have satisfied the slab, they then pump heat down in the earth box for later use. Such a design will “coast” through a month long power outage with freezing outside temperatures and should only loose a few degrees a week. And with PV panels to power the radiant pump, a power outage will be a thermal non-issue. The house will look normal but be passive solar in that most of the windows will be south facing. No serious calculations were done, just good sound design practices utilized. So what about the summer? With a passive solar design, there will be minimal gain in the summer due to the high sun. And with high thermal mass, the house will be an average of the heat in during the day and heat out during the night. No forced air needed here.

There is a house on the Peninsula, well actually many, poorly designed and placed with large expanses of glass facing west and on a crawlspace. When seen in a summer afternoon, all windows are covered with shades and I’ll be the AC is running. It’s the sun. It’s thermonuclear. This is with the ambient temperature in the 60’s. And because of the low thermal mass, it’s conceivable that the heater might be needed the next morning. Low thermal mass, big temperature swings, and the more active the heating and cooling system will be.

Joe,

I think you're absolutely on the right track, so nice to see someone actually thinking about design here (we're in same area).
Crawlspaces are an archaic practice, they do them because they always have. Do a search on "basement solutions" or similar and you'll see the raft of companies that have sprung up to address the problems that result from crawspaces. You'll find all the technical reasons crawspaces don't work.
Don't listen to them!
Good job on the solar design too.

MG

Well thanks MG about the solar design.

I find that homeowners and builders hardly address proper placement of windows in regards to the sun. Why is that? Do people think passive solar is for hippies? Is it regarded as odd or expensive? I'd bet most people if asked the path of the sun throught the year would not get it right. Passive solar is so simple and in some instances, such as clocking the design on the property, can have no cost at all. There are houses here on the Peninsula on the north side of a hill that receive no sun in the winter. Imagine that.

I know, there's simply no excuse except willful ignorance. I'm constantly amazed at the ugly, useless construction I see around here.

My place is oriented a little southwest, which I guess is not bad, but it kinda drives me nuts. The view would have been fine due south. We're thinking of remodeling to include sustainable elements as well as aesthetic improvements. We might do the crawlspace sealing.
I've been thinking over buying some property near Forks. It sure is nice over there.
Good luck with your project.

Hey, here's the website for Basement Systems, from which I learned all about the crawlspace problem. Maybe you can direct some of the folks who are naysaying you or fill them in yourself. Also for any others with this problem.

Basement Systems

Best, MG

I can't speak to any of the other issues with a slab, but, as an ex-dancer, I will say that the hips and knees issue is very real. If you are at all sensitive in your joints, the hardness of concrete is murder. I like a floor that has some bounce.

I always recommend cork flooring for those that have knee/hip issues. Incorporating a Passive Solar slab in the design phase will eliminate 40-85% of the heating costs of the home for the life cycle of the building. I'm not sure about anyone else, but I'd rather keep that money in my pocket than pay it out for heat.

Here is a quick response in favor of crawlspaces, although slab on grade is also a good practice. I am an architect and I have seen most of our projects change to slab on grade since it is less expensive here in the Baltimore area. I have a crawl space under half of my house and here is what I would loose if it were slab on grade. All of my duct work runs through this crawl space. The crawl space dirt floor is completely covered with 90lb felt and old linoleum flooring. It is clean and dry. The walls are insulated so the space is conditioned (by the inadequate insulation on the ductwork). It makes an excellent storage space as it is high enough to sit in and crawl about. The half of the house is elevated by the crawlspace above grade. To me this is a positive attribute, I want to be above the yard, sidewalk, and street. To people in wheel chairs it is a problem. Slab on grade can be elevated as well. The foundation wall should be adequatley sized to retain a few feet of dirt. Then you have less moisture concerns, although you will still have to build a ramp if you age in place. A comment about builders and what they are accustomed to building... I have found it usually comes down to cost. New practices take a few years to catch on but they are accepted if they save money. The good builders I work with consider the cost of call backs and maintenance and sometimes choose better systems or materials even when they are more expensive. This has become quite a ramble.

We design every house for it's site. If you have a flat lot, a relatively high frost line, want to use radiant heating and your site allows orientation for passive solar techniques then the slab on grade makes perfect sense.

If your site is sloped, your frost line is deeper, trees obscure your access to solar radiation and / or you cannot afford solar panels or radiant heat systems, then a crawl space with a well insulated building envelope makes sense. There really is no one right answer. In your case it sounds like you are doing the right thing.

simple and unique house plans
spreading the word of great home design

Help is coming soon: my spouse is inventing something that will make solar power much more practical. Watch for it.