Sealed Crawlspace No Insulation

By adam
July 29, 2013   Comments Off on Sealed Crawlspace No Insulation

Hello folks with vented crawlspaces. The best and most affordable method for increasing comfort, saving money, reducing household moisture, reducing pest infestation, and improving indoor air quality.

The Sealed Crawlspace with No Insulation.

A sealed crawlspace with zero insulation in the floor and zero insulation on the walls will always outperform a vented crawlspace with insulation in the floor system. As it turns out, floor system insulation only contacts about 75% of the floor system at best, the remaining 25% is the wooden joists which remain exposed to environment of the relatively hostile (hot, cold, too wet, too dry, dirty) crawlspace not to mention plumbing pipes, duct-work, equipment, all on the wrong side of the “thermal investment”. When you plug the vents, not only do you stop the temperature and humidity swings of the ambient environment, but you begin to “retain” the energy of any ducts and equipment. An effective “sealed vapor barrier” resists ground-moisture, and retains wasted household energy. Often there is a precipitous drop in the crawlspace humidity and wood moisture content when we plug the vents, and the perimeter is able to retain waste energy from your home. Considering all the features of a bare-minimum-sealed crawlspace, the biggest impact is the air-tightness of the perimeter wall, followed by the air-tightness of the sealed-vapor-barrier.   You can save 15% to 20% on heating and cooling bills simply because the crawlspace has become a comfortable space for the HVAC system to operate in, and the home retains its temperature between cycles as the entire floor system & wires, pipes, & ducts are all “inside”.

Amazing Panorama of Sealed Crawlspace with Lights No Flash
Amazing Panorama of Sealed Crawlspace with Lights No Flash


In crawlspaces where the builder (cheaply) built a pony wall to save on concrete blocks the plain un-insulated wall is the weakest link. Rather than insulate these walls with batts between the studs, again covering only 75% of the wall or less, sometimes much less, we often prefer to insulate the wall in its entirety with PRODEX which also helps to air-seal the pony wall which can be very leaky. In the above photo you can see the call-out to the pony wall. The above crawlspace would perform pretty much the same with or without the insulation in the floor system. This can be proven with the readings from the temperature and humidity monitor. Crawlspaces with vast wall areas that are “framed” and sheathed rather than built solid with CMUs perform worse thermally. rather than 8″ of concrete you have some siding and sheathing to resist the ambient fluctuations. I guess the point here is that even if you have a floor insulated sealed crawlspace or a non-insulated-sealed-crawlspace, it might make sense to wrap the pony-walls around the crawlspace with a product like PRODEX or BLUE BOARD by DOW so that you can illiminate the thermal bridging and provide some air-sealing.