I would like to re-insulate the crawl space under part of a bedroom because the room is cold in the winter and I don't believe it was ever done properly. The crawl space is under an 8 x20 foot addition that was added on about 34 years ago just before we bought the house. Everything else about the addition reflected shoddy workmanship that I've been correcting since we moved in so I'm not surprised that the crawl space was also subpar.

First let me mention, I've gone through the archives on this site for crawl spaces and have done a fair amount of googling on the subject on the internet. I must confess that I'm finding alot of conflicting opinions and suggestions so I hope someone here can give me some current thinking on the subject.

Here are the details about my crawl space.

- its about 2 feet deep and is essentially above grade which I sense may be important
- the overhead floor joists are 2x8's on 16" centers
- the floor is dirt with what appears to be a thin piece of clear plastic on top of it but it doesn't entirely cover the floor
- the joists have 3 1/2" rolled insulation installed some of which has falling down
- there are 2 metal air vents one on each outside wall
- there's a small covered opening (18" x 16") from my basement to gain access to the crawl space
- its unheated

I'm trying to determine the best way to approach properly and practically insulating this crawl space and whether it is something I can do myself.

I thought it might make sense to pull all the existing fiberglass insulation out and have someone spray foam in between the joists and around the plate and sill areas and remove the metal vents. But I've read conflicting comments about doing this. I'm just looking to make a noticeable improvement in reducing the coolness in the bedroom above the crawl space without creating any problems.

Can anyone with some experience dealing with crawl spaces give me some suggestions on what might make sense.

Thank you.

 

Spray foam would be the best. Spray foam it all and close the
vents. A flash coating on all wood will keep you from needing a
VB.

 

For starters, you could consider finishing the rest of the crawl space's vapor barrier (poly is cheap, and easy to install). And, yes, do correct the insulation situation in the joist spaces. Having foam sprayed could be best (don't know, haven't researched it), but if you want to go on the cheap and don't mind spending some time on your back, rip out what's there and add some R-19 batts, paper-side up. Keeping it tight against the underside of the floor is important, so some sort of bracing or even in-filling with rigid foam might be in order.

And another thing--what does the attic insulation look like in the cold room? If it's less than R-31, beef it up to make it R-31. Heat likes to rise.

Had a house with a similar cold bedroom years ago. After studying things for a while, I added a cold air return for the forced air heat, and the thing turned into a sauna. Had to partially-close the 2 heat registers to keep from getting cooked medium-well.

 

What does "a flash coating on all wood" mean?

 

Means insulate to the r value u want then put a inch of closed
Foam over all the wood so no mold can grow. This will keep you from needing a VB on the ground

 

The attic above this room has R-38 (12" fiberglas insulation) so I'm in good shape there.

 

What you should really be doing, is insulating the crawl space walls and the wooden floor headers around the perimeter. The wall insulation should be brought onto the grade floor for a few feet or run below grade on the wall if the wall is partly below grade. If you do that, there is no need for any floor insulation. In Canada, our government will give us a grant of up to $1000 to do this type of insulation they consider it that important With the walls insulated, you lose a little heat under the foundation wall, but may even gain heat from the earth under your house.

We also had f/g insulation hanging down - we ripped it all out. It wasn't doing any good.

Whether to seal or not seems to not be clear cut. If crawl space is sealed then you will need a vapor barrier over entire dirt floor. Unsealed, if the floor is relatively dry, you can get away with venting in summer and sealing & insulating vents in winter.

We had our crawl space walls sprayed with 3 1/2" or more of closed cell foam. Height varied from about 3ft to 1ft and wall length sprayed was about 125ft. Cost us $1600 (would have been about $1100 for 2")

With this insulation, our unheated crawl space should stay at about 60F throughout winter. Remains to be seen. I have put a temperature sensor down there to find out. So far it is but no really cold weather yet.