Garage underway

The garage is underway, though slow as we wait for record rains to pass. Today it looked good and the foundation crew even scheduled a cement truck but had to cancel.

As with the house, we're trying to insulate as much as possible. The traditional slab design uses a perimeter frost wall around the.. uh.. perimeter, which extends below frost line and keeps the foundation from heaving. This is relatively expensive. It required an excavator and a mason crew. The modern alternative is a monolithic pour, but it has heat loss because underneath the perimeter is usually left uninsulated to heat the ground slightly to avoid frost heave.

However, frost only happens when all three of the following are present: Moisture, frost susceptible soils, and freezing weather. We've eliminated two by using well draining gravel under the garage and large roof overhangs with good drainage design around the land. Because of this, we were able to use a unique design and place foam underneath the perimeter footing. This seems odd, foam is supporting the weight of the building. But with standard 25PSI compressive strength foam, you get 3600 pounds of bearing strength per square foot. This is more than the soil is rated at. Just for safety, we used 40PSI foam, which I think is a good idea. Even though we very carefully leveled the perimeter, there may be some small voids underneath the foam.


This is the sectional drawing of the perimeter. I had an engineer check just to be sure.


A rather large looking load of foam insulation. I got some funny looks pulling something twice as tall as my car.


Foundation mostly formed before the rains.


Foam placed, rebar in the perimeter trench and reinforcing mesh not quiet in place


Heat tubes placed. There are two 300 foot runs of 3/4" tube placed 12" apart They're placed a little closer together in front of where the workbenches go for added comfort.