I am looking at a job in my area. Vented vs unvented crawl space. The client’s ( Dental Practice ) main concern is to reduce their AC cost $ 800.00 in the sumer. Presently , the existing crawl space is approx. 4000 sq. Ft. with a dividing cnd. block wall creating two spaces of 1500 & 2500 sq. ft.

Presently, their is no floor insulation or a grade vapor barrier. Also , their are min. wall vents. The floor system consist of 12” open trusses . Hence, not creating a good situation for a typ. batt insulation application due to the open truss design and the inability to completly insulate the floor joist system.

I have been reading about ventless crawl spaces and am thinking this might be the way to go.

What I am propsosing is to install a 10 mm plastiic vapor barrier at grade. Spraying the aprox. 6″ tall cnd. block walls with 2″ of closed cell foam ( r 10 ), hence , closing off the existing wall vents. Also penetrating the existing duct hvac duct work and providing (3) 4 “x 12″ air supply’s. One in the smaller area and two in the larger area to ” pressurize the crawl space” .

Will this lower the moisture levels in the crawl space enough to show a significant diff. and result in a lower energy bill during the warmer months.

Also, are their any potential long term dangers going with a ventless crawl space design as explained.

I appreciate your any comments concerning this project.
Thankyou, Gerry

How is the high Radon level explained for the sealed crawlspaces? What is the source for the radon? If the crawlspace is “sealed” and crawlspace air is force supplied or power vented one would think the radon levels would be less.