Attaching foamboard insulation under pier and beam, adhesive, nails, screws?

[masraum]

We want (NEED) to insulate under the house. I don't want to use f/g or mineral wool bats. I want to use foamboard. The plan is to attach the foam board under the joists, and tape all of the seams. How do you think I should attach it to the bottom of the joists? I feel like an adhesive of some sort would be the best, quickest way. Whether that's using silicone or latex caulk or construction adhesive, I don't know. I suppose if using a fastener, then some sort of screw with a large washer would be the best/easiest way.

Thoughts?

[lindbhr]

I used 1” foam board to insulate my wooden barn doors. I used foam board glue, but getting it to grab onto the wood was not always easy. I also used 1 5/8” deck screws for some trim pieces and that worked well. Just drive the screw slightly beneath the surface of the foam board. I had spray foam applied under my house, but that is much more costly.

[masraum]

Originally Posted by lindbhr

I used 1” foam board to insulate my wooden barn doors. I used foam board glue, but getting it to grab onto the wood was not always easy. I also used 1 5/8” deck screws for some trim pieces and that worked well. Just drive the screw slightly beneath the surface of the foam board. I had spray foam applied under my house, but that is much more costly.

Thanks.

You're just up the road from me if you're in Brenham, or farther over if you're in Houston. I'm between Columbus and Weimar off of I10.

Someone at some point had done some sprayfoam on the bottom of our house, but I think they must have been drinking because it's a spotty 1/8" - 3/8" layer .

[lindbhr]

Also, those tyvek type one piece suits you can buy at HD are great for crawling under the house. I even reused mine a couple of times.

[masraum]

Originally Posted by lindbhr

Also, those tyvek type one piece suits you can buy at HD are great for crawling under the house. I even reused mine a couple of times.

I've used them in the attic and when spraying paint. I was thinking about getting something like the mechanics overalls, but I'll be the other work as well and don't have to be washed after. Thanks

[expatriot98]

I need to do the same thing and have given some though to the DIY spray foam.

Are you concerned about making a cavity for rodents to live in with the foam board? I don't know if that's even a concern.

[Por_sha911]

Can you run furring strips under the board to hold it up in place and drive a screw through the strip and the board into the floor?

[look 171]

It time to buy yourself a cordless nailing gun"), Steve. I like mechanical fasteners instead of glue because they all seem to fail over time. Use a nail or something to hold them in place between joist, nail up some strips on bottom to keep them there for ever.

[stevej37]

Deck screws with fender washers.

[dad911]

Screws and washers. There is a proper washer for foamboard, plastic and very large:

Foam Board Washer

[masraum]

Originally Posted by expatriot98

I need to do the same thing and have given some though to the DIY spray foam.

Are you concerned about making a cavity for rodents to live in with the foam board? I don't know if that's even a concern.

I've seen some stuff online that talked about termites and spray foam. I hadn't thought to much about rodents and spray foam, but rodents are the main reason that I'm not going with fiberglass or mineral wool. My main issue with spray foam is that you then can't easily get visibility to the foam. If there was some sort of issue, the foam would hold liquid right up against the wood.

In an old house like this (100 yo) I'd prefer to be able to easily dig into stuff if I need to.

[masraum]

Originally Posted by Por_sha911

Can you run furring strips under the board to hold it up in place and drive a screw through the strip and the board into the floor?

Originally Posted by look 171

It time to buy yourself a cordless nailing gun"), Steve. I like mechanical fasteners instead of glue because they all seem to fail over time. Use a nail or something to hold them in place between joist, nail up some strips on bottom to keep them there for ever.

That's exactly why I asked. I was wondering the same.

Originally Posted by stevej37

Deck screws with fender washers.

Originally Posted by dad911

Screws and washers. There is a proper washer for foamboard, plastic and very large:

Foam Board Washer

Lots of more or less the same recommendations. Thanks folks. That's what I needed to know.

[Captain Ahab Jr]

Originally Posted by dad911

Screws and washers. There is a proper washer for foamboard, plastic and very large:

Foam Board Washer

I must have fitted over a 100 boards of insulation on my man cave build project and ^^^^ would be my suggestion too

Be sure to buy a long series pilot drill too

For whatever thickness you decided do it two layers, stagger the joints and tape all joints too with aluminium foil tape

[masraum]

Originally Posted by Captain Ahab Jr

I must have fitted over a 100 boards of insulation on my man cave build project and ^^^^ would be my suggestion too

Be sure to buy a long series pilot drill too

For whatever thickness you decided do it two layers, stagger the joints and tape all joints too with aluminium foil tape

Yes. I was thinking exactly that. If I go with 2 layers, the plan was to alternate the joints, and all joints will be taped with foil tape. Will definitely take your advice.

[masraum]

Originally Posted by expatriot98

I need to do the same thing and have given some though to the DIY spray foam.

Are you concerned about making a cavity for rodents to live in with the foam board? I don't know if that's even a concern.

I found this study online a while back and thought it was interesting.

https://www.lsuagcenter.com/nr/rdonlyres/d33f711d-dc4b-4e4c-9ed6-a97dce9db026/79805/pub3187insulatingraisedfloorslowres.pdf

[Evans, Marv]

I think tension rods between the floor joists might be a good possibility also. They're quick to put up & do a good job of holding it up.

[dad911]

Originally Posted by Evans, Marv

I think tension rods between the floor joists might be a good possibility also. They're quick to put up & do a good job of holding it up.

OP said he didn't want to deal with insulation bats. However, that's what we would typically do(if not using spray insulation). Unfaced insulation between the joists, then a thinner foam board with seams taped to act as a vapor barrier and draft stop.

@masraum - you may want to get some prices on sprayed and conventional insulation installed. I have found insulating is one of the jobs that isn't worth DIY.

[masraum]

Originally Posted by Evans, Marv

I think tension rods between the floor joists might be a good possibility also. They're quick to put up & do a good job of holding it up.

I'm wanting to cover the ends of the floor joists. The wood conducts a lot of heat, so covering the wood will be better for insulation than just putting them in between the joists. And my home needs all of the help that it can get.

[masraum]

Originally Posted by dad911

OP said he didn't want to deal with insulation bats. However, that's what we would typically do(if not using spray insulation). Unfaced insulation between the joists, then a thinner foam board with seams taped to act as a vapor barrier and draft stop.

@masraum - you may want to get some prices on sprayed and conventional insulation installed. I have found insulating is one of the jobs that isn't worth DIY.

Yeah, it's a tough job. Years ago, in our other home I priced out getting more insulation in the attic. Everyone that came out wanted to blow insulation into the attic. I really didn't want sprayed insulation up there. I got some encapsulated Johns Manville rolls. That stuff was fantastic. It was a huge pain in the arse, and a little more expensive, but then it wasn't a nightmare to go into the attic when I was done.

My problem is that I don't trust most folks to do a good job, especially in a situation like this when they assume (probably rightly so) that I won't get under there and check their work.

[cabmandone]

Why don't you just hire someone to come in and spray foam it? Or buy a few kits and spray foam it yourself? (no way in h.ll I'd do that job btw... just hire someone!) OH! and check with your electric company for any credits for insulation too!