Preparing the site for our modular Passive House
Sitework began in mid-July. Everything is now ready for the arrival of the modules on August 11.
One of the ways we controlled costs on the project was to eliminate the conditioned crawl space, which on a passive house can be a very large expense, with the insulation of walls and footings just as is required in a passive house basement. As described in the previous blog, we opted to make the first floor framing the edge of our building envelope so everything below that is of standard construction.
One issue we ran into in the design phase was the confict between the Building Science Corporation’s recommendations for an insulated floor first floor assembly over a crawl space, the building code’s requirements for crawl spaces, and passive house requirements. The issue is warm moist air in summertime getting into the floor assembly and condensing when in contact with the relatively cold floor structure.
BSC would prefer we have a completely closed crawl space protected from below by a sturdy vapor barrier. This would keep moist summer air out of the crawl. They then recommend completely insulating and sealing the underside of the joists to remove any chance of condensation there. They also recommend monitoring the sealed crawl space for moisture and having a dehumidifier located there in case of any moisture build up.
All fine, but the building code requires sealed crawl spaces to be ventilated with air from the interior of the house. That of course would completely erase all the airtightness we are struggling to achieve.
What we decided to do was follow BSC recommendations completely, but to create a “ventilated crawl space” as defined by code, placing the minimum number of ventilation louvers in the exterior walls of the crawl space. Since we are allowed to make these louvers operable, we will simply keep them closed up, making the crawl effectively a sealed crawl space.
Here are some pictures of the progress…