Welcome, my name is XXXXX XXXXX X will do my best to help you with your issue.You have AC vents in your crawl space?
no they are in the attic
If I understand what you're saying you feel cold air coming out of the ventilation openings to your crawl space when the AC is on, is that correct? and your AC air handler is in the attic and there is no duct work in the crawl space?
yes.. what is..is the air in the house escaping through the floor into the crawlspace and coming out the vents
Then you're best bet would be to insulate the floor of the living space
yes how and with what i get so many conflicting answer as what is the best way
There are 2 viable options. Either spray foam which would also seal air leaks or rigid foam sheets attached to the bottom of the floor joist and butted tightly together to also seal air leaks
what about moisture problems..should i close vents off? should i sheet foam between the joist?
It's usually best to leave the vents open but if there is a significant temp difference between the crawl space and outside closing the vents may be a good idea. It's also a good idea to put a vapor barrier on the ground if the crawl space has a dirt floor. If you insulate (sheets on the bottom of joist not in between) you'll reduce the temp difference. Sheets on the bottom of the joists will make a tight seal, in between joists won't
what kind of foam sheets do you recommend
well crawlspace gets cooled by the ac coming thru the floor
Rigid Dow styrofoam is one option but there are others. Not the foil faced sheets. Only the plain styrofoam sheets are tongue and groove. Once the unsulation is installed the AC should get into the crawl space
and installed perpendiculer to the joist?
so there is an air space between the sheet and main floor
yes perpendicular is easier
yes there is a dead air space
which provides some additional insulation value
and i wont have a moisture problem on house side of sheets
No, since the air won't circulate there
what thickness of foam?
and how to i hold up the foam sheets
1" is adequate. Are the floor joists pressure treated?
Be sure the seams are butted tight
The use coated deck screws made for treated wood just to be safe and put a washer behind the head of each screw so it doesn't pull through the foam
keeping your sheets tight together and tight to the outside walls is important to keep air from infiltrating
do you have any more questions?
no not yet thanks so much for your insight