Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Spray Foam Insulation


RIKIL's Avatar
Member

Join Date: Dec 2008
Posts: 53
CO

08-02-09, 04:27 PM   #1  
Spray Foam Insulation

I am looking at getting some spray foam insulation in my house and the only thing I am really hung up on is the R value. I have been reading and the R value is anywhere from 3.5 to 6 per inch. For the areas where I am wanting to put this, I have 2x4 studs (which I know are actually 1.5x3.5"). In doing the math, if I were to get 3.5" of spray foam insulation I would only get 12.5 to 21 of an R value when using the different types of spray foam.

I just don't think this is worth it but I also think I am missing something.

Am I seeing this right? Are teh R values that low?

RIKIL

 
Sponsored Links
airman.1994's Avatar
Member

Join Date: Dec 2005
Posts: 5,581
VA

08-02-09, 06:41 PM   #2  
Closed cell can be above 7. You will be air sealing as well as having a VB. Just remember you will have to have a HRV to bring in fresh air to the home.

 
Bud9051's Avatar
Member

Join Date: Oct 2008
Posts: 9,772
ME

08-02-09, 06:52 PM   #3  
The range stated is about correct, depending upon the material selected. Do you already have insulation in the walls? If so, your gains will be minimal for the effort and costs of removing what is there and then installing foam. A more beneficial approach is to add a complete layer of rigid foam over the inside or outside. A complete layer will cover the framing material and reduce the thermal bridging. I'll attach a link below for reading.

Are you doing any other work in conjunction with this upgrade, like remodeling inside where the walls are exposed anyway. Or replacing siding where it would be easy to add a couple of inches of foam board. let us know where you are so we can estimate the r-value needed.

One extra word about well installed rigid or sprayed in foam. The final results are often better than the r-value would suggest due to air sealing properties of the installation. Since we know air sealing is important, it is possible to achieve significant improvement by just air sealing. The point is, yes the spray in foam will air seal, but you can do much of that yourself for less. If you have no insulation in the walls now, consider blown in cellulose. I'll give you the whys if interested.

Welcome To Home Energy Magazine Online

PS R=5 or 6 per inch is generally considered reasonable.

Bud

 
RIKIL's Avatar
Member

Join Date: Dec 2008
Posts: 53
CO

08-03-09, 08:01 AM   #4  
Posted By: Bud9051 The range stated is about correct, depending upon the material selected. Do you already have insulation in the walls? If so, your gains will be minimal for the effort and costs of removing what is there and then installing foam. A more beneficial approach is to add a complete layer of rigid foam over the inside or outside. A complete layer will cover the framing material and reduce the thermal bridging. I'll attach a link below for reading.

Are you doing any other work in conjunction with this upgrade, like remodeling inside where the walls are exposed anyway. Or replacing siding where it would be easy to add a couple of inches of foam board. let us know where you are so we can estimate the r-value needed.

One extra word about well installed rigid or sprayed in foam. The final results are often better than the r-value would suggest due to air sealing properties of the installation. Since we know air sealing is important, it is possible to achieve significant improvement by just air sealing. The point is, yes the spray in foam will air seal, but you can do much of that yourself for less. If you have no insulation in the walls now, consider blown in cellulose. I'll give you the whys if interested.

Welcome To Home Energy Magazine Online

PS R=5 or 6 per inch is generally considered reasonable.

Bud
The insulation in my attic is old and has been flattened, so I am sure it is in need of replacement. That will probably be ~1000 sq ft. I also have an unfinished basement that I would like to put the spray foam in, that might be another 1000 sq ft.

 
Bud9051's Avatar
Member

Join Date: Oct 2008
Posts: 9,772
ME

08-03-09, 09:09 AM   #5  
You mentioned 2x4 studs, so I assumed walls. For ceilings, your options are different. Again, where are you? We don't need your street address, but some indication of your climate area.

Have you priced spray foam in your area? It can be $1.00 to $2.00 per board foot (one foot square, 1 inch thick). That would be $4,000 to $8,000 for your project (just 2 inches thick). PLUS, you can't leave spray foam exposed. In a ceiling or basement it needs to be covered with an approved fire barrier, typically 1/2" sheetrock. But you will need to check with your local code office to see what they want.

More details and glad to help.

Bud

 
RIKIL's Avatar
Member

Join Date: Dec 2008
Posts: 53
CO

08-04-09, 06:55 AM   #6  
Posted By: Bud9051 You mentioned 2x4 studs, so I assumed walls. For ceilings, your options are different. Again, where are you? We don't need your street address, but some indication of your climate area.

Have you priced spray foam in your area? It can be $1.00 to $2.00 per board foot (one foot square, 1 inch thick). That would be $4,000 to $8,000 for your project (just 2 inches thick). PLUS, you can't leave spray foam exposed. In a ceiling or basement it needs to be covered with an approved fire barrier, typically 1/2" sheetrock. But you will need to check with your local code office to see what they want.

More details and glad to help.

Bud
I am in southern Colorado. The walls I mentioned would be in a basement and eventually covered with sheet rock. As for the attic, I will need to see what to cover it with.

I talked to a friend who is having it done in his garage, he is getting 2400 sq ft (2" thick I think) for $3800.

Would be nice if I could do it myself and save some $$ but I heard it is a pain and I should leave it up to the pros.

 
mlac52's Avatar
Member

Join Date: Jul 2009
Posts: 16

08-09-09, 06:48 AM   #7  
Posted By: RIKIL I am in southern Colorado. The walls I mentioned would be in a basement and eventually covered with sheet rock. As for the attic, I will need to see what to cover it with.

I talked to a friend who is having it done in his garage, he is getting 2400 sq ft (2" thick I think) for $3800.

Would be nice if I could do it myself and save some $$ but I heard it is a pain and I should leave it up to the pros.

Is your friend installing open cell or closed cell spray foam?
I dont think you can install closed cell do it yourself spray foam for the price you friend is getting it done for. I just spay foamed under my floor between the floor joist with closed cell spray foam. The do it yourslef kits is not that hard to use, Its a little messy. keeping the tank temp right is the main thing. other than that its like spray painting. also dont expect the do it yourself kits to cover the advertised square footage, allow at least 20% watse per kit. Overall im happy with the spray foam its great at stopping air leaks.

 
Search this Thread