rigid foam insulation

[Cooler]

The 2" thick Foamair panels have an R-10 rating.  If I double up on this will it be equal to an R-20?

Also, this is scored to 12" widths.  If my studs are 14" on center then the space between studs is 12½".  Should I use a foam spray to fill in the gaps?

[CLETUS]

The 2" thick Foamair panels have an R-10 rating.  If I double up on this will it be equal to an R-20?

Also, this is scored to 12" widths.  If my studs are 14" on center then the space between studs is 12½".  Should I use a foam spray to fill in the gaps?

I wouldn't use rigid panels in a wall... too much effort plus you need to fill the gaps, I would guess this would make the project more expensive. Also, are you sure your studs are 14"?

[Ninefingers_grapes]

I have 2 inch foam on my celestory roof, 4 x 8 panels (24) in total, sealed with white roofing compound over 'fiercer' glass like material.
I can hear snow flakes hitting the roof in winter,  ice and hail will chase me into a room not under roof.  My buddy in WA (Bellevue) in the early eighties had panels cut to stud spacing from 4 foot thick 4 x 8 'white' blocks of foam,  Some fit tight, some fit loose and some had to be fitted to size.  Even with plastic of the studs before 10 drywall panels he had air leakage.
I had my roof, filled with foam on the inside and some of the 'snowflake' noise went away.
I would try spray foam, but you need a professional to do this, too many horror stories on formaldehyde leaking due to improper mix, improper heat and out of date material.

Good Luck on any means that your do

Steve in SE PR

[Snipe Hunter]

Is fiberglass not an option? It's soooo easy.

[Cooler]

This is for the underside of a 4 season enclosure over what used to be a deck.  The previous owner had built it over a 60 year old Douglas Fir deck.  I had to remove the 2 x 8 under structure piece by piece and replace it with pressure treated.  

I want to insulate it before the winter but I won't have the time to enclose the foam before the cold weather comes.  I thought that I could just put in the foam and enclose it later on.  

I have several projects that have be be done before this one.  

I could put in a single layer now and then add fiberglass bats in the spring.  At that time I intend to put  vinyl soffit to  enclose.

The floor gets icy cold in the winter.  The deck is 10 feet up over the ground.

[cndamm]

Doubling up would get you R20. Filling gaps with spray foam would work. The installed R value is better than R20 due to lack of air infiltration. With 1% moisture the R value of fiberglass is cut in half. I always use foam when I can. My 28x40x10 workshop uses foam and I can easily heat and cool it with a 1 ton mini split.

[K. L. McReynolds]

The 2" thick Foamair panels have an R-10 rating.  If I double up on this will it be equal to an R-20?

Also, this is scored to 12" widths.  If my studs are 14" on center then the space between studs is 12½".  Should I use a foam spray to fill in the gaps?

Gotta be careful which spray foam you use, some varieties can swell too far and break/bend/hurt surrounding materials.

No more difficult than it is to cut the foam, I'd cut/glue sections to fit the gaps.

[Cooler]

Gotta be careful which spray foam you use, some varieties can swell too far and break/bend/hurt surrounding materials.

No more difficult than it is to cut the foam, I'd cut/glue sections to fit the gaps.

The boards come in 48" widths and are scored at 12" and 16" intervals to snap apart.  In the past I've made extremely clean cuts on foam board using my table saw.  I could set the fence and slice through the stuff for a nice snug interference fit.  But I don't think that will work with the scored panels if I cut within a half inch of the score.  

They do make rapid and moderate foam in a spray can.  Mostly I only see the moderate stuff in the big box stores anymore.  The rapid stuff expanded far more and much faster.  And I should note that any excess that gets on a finished surface is nearly impossible to clean off.

[EricU]

when I did my rim joists, I cut the foam shy and put spray foam around it.  A foam gun pays for itself very quickly for that job. Just store it with a can on the gun, even an empty can will do. I don't know if I would go much more than an inch narrower than the stud bay. I put two layers of 2" foam in each cavity, it's relatively cheap and does increase the r value some.

For my walls, I just put the foam up first and then built the wall in front of it.  I used the aluminum faced polyiso.  Yeah, I gave up 2", but the insulation is a lot better.  Wood is not that great of an insulator, and adding another layer of foam may not increase the r value much because of that.  If you can possibly have a continuous sheet of foam, you are a lot better off.  I'm having trouble visualizing your application.  Foam is quite strong in compression, you can build a house on top of it.

[Cooler]

when I did my rim joists, I cut the foam shy and put spray foam around it.  A foam gun pays for itself very quickly for that job.  Just store it with a can on the gun, even an empty can will do.  I don't know if I would go much more than an inch narrower than the stud bay. I put two layers of 2" foam in each cavity, it's relatively cheap and does increase the r value some.

For my walls, I just put the foam up first and then built the wall in front of it.  I used the aluminum faced polyiso.  Yeah, I gave up 2", but the insulation is a lot better.  Wood is not that great of an insulator, and adding another layer of foam may not increase the r value much because of that.  If you can possibly have a continuous sheet of foam, you are a lot better off.  I'm having trouble visualizing your application.  Foam is quite strong in compression, you can build a house on top of it.

My basement used to leak because of the layers of clay in the area.  The water would run down hill along the layer of clay about 2 feet below the surface.  

I had three types of quotes for this job.  One type wanted to cut a moat around the perimeter of the basement floor and add a sump pump.  I was not happy with that type of work.

Another contractor wanted to dig a French drain which would interrupt the flow of water along the clay line.

The final contractor would dig up along the leaking wall, clean the wall and cover it with roofing tar. He also put up 2" foam panels outside the wall.  I'm not sure what that was supposed to do. 

I have since learned that there is a panel that resembles a 2" thick piece of scotchbright scouring pads with a permeable membrane on both sides.  This is supposed to allow water to drain even better than drainage sand.  

In any case it has not leaked in 20 years.  I don't know what the insulation panels outside the wall are accomplishing though.