Crawl Space Venting

Anyone that has a crawl space knows that you may or may not need a crawl space vent. The problem is that I've seen both used when they shouldn't have been.

The vent is needed (and required by code in many municipalities) when the crawl space has been separated from the building envelope. This means that the shared wall is insulated, the floor above the crawl is insulated and all pipework is insulated. This vent allows the earth to vent naturally outside of the confined space and reduce humidity and potential moisture issues. Vents should never be used when the crawl is inside the building envelope...

Today was one of those days when HZG was asked to view a home's "cold room" problem. The room was an addition over a newly built crawl space. I went into the crawl and saw insulation board on the perimeter (R10 foam board...good), no insulation on the floor (good), insulation on the heat runs (why?) and 2 wide open vents. Hmmm...the builder couldn't decide if the crawl was in or out.

I prefer (if at all possible) that crawls be brought into the living envelope. No matter how well you insulate a floor and duct work, it's elevated and subjected to the cold when the crawl is treated as outside. I rarely ever have seen a vented crawl space that was warm in the room above.

Back to the story...HZG recommended to the home owners that they have 2 masonry blocks installed where the vents were, insulate the new area and then remove the wrap from the heat runs. There are two schools of thought with the wrap - yes, by wrapping the heat will be warmer at the registers; however the radiant heat loss as it travels under the floor is lost. Since the floor is exposed, I would trade degrees of heat at the register for more warmth across the floor as it travels.