laminarflow
Mechanical
- Nov 23, 2001
- 25
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.
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.
