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How to insulate crawl space?

I own a 1950's split level in PA. The house has a crawl space beneath the entire first floor. Half of the crawl space is original to house and has dirt floor. The other half was built as part of an addition and has a cement floor. In addition, the house has forced hot air and there is a lot of ductwork running between the joists in the crawl space.

I've read a lot of other posts regarding this subject on TOH but I'm still not sure if I should insulate the walls or the floor. Based on what I've read it seems like I should insulate the floor but the ductwork would prevent me from getting good coverage. That leads me to believe that I should insulate the walls and put down 6 mil plastic on the dirt floor.

As for ventilation, there is an old drafty window at one end of the crawl space and a small door to the laundry room at the other end. Nothing else other than that.

Canuk, you seem to have a lot of expertise in this area. Any suggestions?

Re: How to insulate crawl space?

You definitely want to put down the vapor barrier. I would check into having the floor spray foamed. This would get into all the nooks and crannies around the duct work. If that is not feasible perhaps you could use rigid foam panels on the underside of the joists. If the floor is really cold you are going to feel colder than the room actually is and are likely to turn up the thermostat. If the money is there insulating the walls will be a big help as well. Hope this helps you out.


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