How should I add Insulation to my concrete crawl space walls and floor?
bwsct
| Posted in Energy, Heating & Insulation on
Hi,
I just bought my first house in Connecticut. Climate zone 5. The family room is over a crawl space and the room is very cold. The crawl space floor is concrete with no insulation along the foundation walls or the floor. There is an unfinished basement connected to the crawlspace with no venting to the outside other than basement windows which remain closed. The flooring in the family room is wood.
How can I best insulate the crawlspace so the room above isn’t so cold at all times?
Should I put down a vapor barrier on the floor even though its concrete and dry?
Should the floor be spray foamed by a professional? Is there any risk in moisture getting between the foam and the floor?
Thanks for any advice.
Replies
Current thinking on crawlspaces is that the easiest way to make them work is to consider them part of the conditioned space--so that means you need to insulate all outside walls, close any vents in the crawl space, and then provide a minimum airflow from your heat/AC to warm the room.
If the house was built in the last 30+ years, there should be a moisture barrier under the slab (which if I understand you correctly) is also present in the crawlspace area.
Adding insulation on the walls of a basement and crawl space also typically mean that you need to cover it to meet code, so drywall over top. There is one rigid foam product from Dow that can be left uncovered--Thermax, but you may have to argue the point with your local building inspector. Here's the Dow brochure:
http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_097d/0901b8038097d511.pdf?filepath=styrofoam/pdfs/noreg/179-07259.pdf&fromPage=GetDoc
Trying to insulate the entire crawl space is a losing proposition. UNLESS, you plan to dig it out eventually for a full basement.
Did a church parsonage last year - simply shoved unfaced FG batts up between the joists and held up with lath (or other scrap wood)
Has worked well in PNW.
6 years ago did same to an ADU, good results there also. That unit I know there is a vapor barrier under the floor, the parsonage I believe there is a tarpaper layer under the oak flooring. With the bottom of unfaced insulation not enclosed, should be no moisture problem even without a VB under flooring.
Depending upon your code, there could also be a requirement for a return, er, I mean a 'transfer grill' in the floor of your house that basically equalizes the positive/negative pressure from the two levels. Not saying I agree with that, just that it MAY be code in your AO.
Also, the Dow product mentioned above meets the flame spread and smoke development requirements. Educate your inspector to the ICC-ES Legacy reports where Dow did all the testing and proved it met.
The crawlspace has a concrete floor. I'd be surprised if there is a vapor barrier since the house was built in 1953. I've attached a picture.
You're right, probably no vapor barrier, so it would be a good idea to add it--but I don't know a procedure. Otherwise you get stack effect vapor coming up through the concrete, made better or worse depending on the insulation in your ceilings.
I'm facing a similar issue with the crawl, but in our house (1963) they didn't pour the rat slab or leave the dirt level, so it is a nightmare to think about remediation. I will use the Thermax on the outside walls (it uses a channel to sit in, a 'T' piece between sheets and they make a matching tape so you can get a nice job). Not sure about the floor yet--worst case I will cover it with poly as best I can...
The problem with jumkhound's suggestion is that it is very hard to get a decent job in the joist cavities around plumbing, ducts etc--and if you use fiberglass bats you have made a perfect nesting place for any rodents that make their way inside.