Conditioned Crawls- Verdict-There is No Better Way

I¬†am still amazed at how many times in our industry I hear “building experts”talk about the need for vents in a crawl spaces.¬† That statement is as out of date as”seat belts in cars do not save lives”- it is simply not true.

A little background on why vents were ever put in crawls.¬† 70+ years ago we were building houses with no wall insulation and no HVAC system.¬† Most of these homes also had balloon framing.¬† The vents let air under the house, it moved up the walls, and out of the attic.¬† The process provided a natural cooling effect on the home.¬† It also kept moisture out of the wall assembly in a time when house wraps did not exist.¬† Since warm air always moves to cold air, when we heated these homes, warm inside air would push towards the open wall cavity.¬† Cool air would drop down the wall cavity and exit the building.¬† Again, this air movement in the walls would remove all the moisture created by burning fossil fuels (mostly wood).¬† In the 1970’s we started craming insulation into the wall cavities and introducing HVAC systems in the majority of homes.¬† We left the vents in crawls- so what happens?¬† The cool air that enters under the home in the winter no longer passed up the walls.¬† The moist, humid air in the summer no longer passed up the walls.¬† Instead, the air lingered under the home causing duct work condensation, high moisture content, and decreased home efficiency.¬†

For these same 70+ years basements have been a big part of the American home building industry.¬† We certainly never put vents in an in ground basement.¬† Basements have always been efficient from an energy savings stand point.¬† So why not use that same technology when building a crawl space?¬† Why not create a “mini-basement” instead of a vented crawl?

This “mini basement” is more commonly know as the conditioned crawl.¬† Here is how it works.¬† A sealed vapor barrier (6mil or 10 mil) is placed under the house.¬† All seams are glued, columns are wrapped, and it is attached to the walls up to six inches (100% coverage). ¬†Spray foam is installed from band board (framing on top of block) down to ground level.¬† The crawl access door is insulated and sealed against air infiltration.¬† Positive pressure is introduced to the crawl through natural duct leakage or by putting a small supply in the crawl.¬† No insulation is placed in the floor.¬† The temperature of the earth averages 55 degrees- you use this to help heat and cool your home.¬† Imagine pumping 72 degree air (your HVAC)¬†through that space as compared to a 20 degree crawl space in the dead of winter.¬† Moist, humid air under the home in the summer is eliminated.¬† This space provides energy savings upwards of 35% when compared to a¬†conventional vented crawl!

Building science proves this system is the only way to insulate a crawl space.¬† “Green” building programs recognize conditioned crawls as the best way to insulate under your home.¬† The 2012 IRC Building Code (not adopted until 2014)¬†calls for all duct work to be placed in a conditioned space.¬† This body of experts recognizes the importance of HVAC equipment to be placed in a friendly environment.¬† Will this be the death of the vented crawl?¬† Will this change the minds of those that think crawls must have vents?¬† Only time will tell- Science has spoken.

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