Crawlspace insulation correctly installed? Floors very cold in winter
I have a a large ventilated crawlspace. It feels dry and there is a vapor barrier on the ground.
The previous owner had R-38 fiberglass batts installed in all the ceiling rim joists and it is held up with netting stapled to the bottom of the joists.
My issues:
1.The batts are not up against the subfloor though, leading to the wood floors feeling very cold in the winter. There is ~10inches of space between the insulation and subfloor.
2. There is no foam board at the rim joists to air seal either
I am getting mixed messages from insulation contractors. Some telling me that the insulation is fine and that I should just add rigid foil-faced polyiso foam insulation to the bottom of the joists and then air seal the rim joists.
Other contractors have said I need to get rid of the air gap and have the fiberglass batts pushed up against the subfloor and hold them with insulation supports; and air seal the rim joists as well.
I am just trying to figure out the best way forward. I am in Central Texas. The fiberglass batts are in very good shape and my crawlspace is very well sealed up, no critters are getting in this space.
Thank you for any insights on what the right way forward is.
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Replies
JBlikesMTB,
The air gap is fine. It does reduce he effectiveness of the batts slightly by allowing convective air-currents, but there is also an argument that it keeps the floor slightly closer to the temperature of the room above.
The problem is thermal bridging at the joists, and the lack of an effective air-barrier. A layer of well sealed foam board solves both. Check your local code though as to whether that foam can be left exposed, or needs protection against fire.
I would think that every spot that the insulation has a leak gives that leak access to the entire space above the insulation. A bad insulation install is essentially an uninsulated floor
IOW an R800000000000 slab of insulation with a 1 inch gap around it with 10 inches above it is an uninsulated floor
That same insulation hard against the floor is a waste of money, but it is not uninsulated
10 inches of space?
pretty tall floor joists
When you say the floor is very cold that is subjective. If you put a thermometer on the floor how much low than the room temp will it read?
I am not a fan of vented crawlspaces. Consider converting it to a conditioned crawlspace. Air seal then insulate the walls and remove the floor insulation. You will need to ensure the crawlspace is connected well enough the it is more or less the same temp and humidity as the rest of your house. If the HVAC equipment is in the crawlspace, it likely leaks enough to condition the space if not you may need to add some vents.
The way I see it fiberglass insulation is useless without an air barrier and most floor leak like sieves. If you want to keep the vented crawlspace and insulated floor consider covering the insulation with an air tight layer of house wrap.
Walta
Another vote for an air sealed crawl. I had NO IDEA how much more comfortable that makes a house until I built one. Unbelievable.
My first suspicion is that air is moving through those air gaps above the batts. The gaps themselves are not a problem, but if they aren't air sealed, then air can FLOW THROUGH those gaps and the resulting convective current can cancel out much, or maybe even all, of the effective insulating value of the batts. A thin layer of polyiso under the joists with seams taped and perimeter air sealed would stop any airflow between the gap and the unconditioned space in the crawl space.
My preference would be to rip out all those batts and to do a crawlspace encapsulation project here. That would mean removing the batts, putting a membrane on the floor and walls, then insulating the walls with rigid foam board. You'd want to insulate and seal the rim joist at this time too. There is a lot of info on GBA about this process.
Bill