This week the class has concentrated on installing the insulation and air barrier in the crawl space of the Zero Energy House. This is quite a significant segment of the assembly because it will block soil gases, keep moisture out of the crawl space, and complete the thermal boundary at the base of the structure. We have no venting in our crawl space which makes it a conditioned air space. This will allow us to install the ducting for the forced air furnace and not insulate it. Since the ducts are already in conditioned air space there is no penalty for any leaks.
When looking at the pictures of the week in progress the assembly process can be seen. First we positioned two inch thick by two foot wide by eight foot long panels of rigid insulation on the crushed rock floor of the crawl space. The gaps between the rigid insulation were then filled with expanding foam to help complete the insulation layer. The insulation was then covered a with 6 mil polyurethane vapor barrier that was fastened to the footing with furring strips around the perimeter of the inside footing.
This was a very productive week and informative in that we demonstrated that there is a definite need for vapor barriers in the crawl space. Before work was started the moisture level in the crawler was very predominant. The moisture level and soil gases were very sensible. The moisture levels were measured at 25% to 35% in the material and an ambient relative humidity at 75%. After installation of insulation and vapor barrier the odor of ground gases was gone and the humidity level was sensibly less. We will continue to test the moisture levels of the air and materials and post them in the coming weeks.
Good bye, and good building,
Dan Smith
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