Return to the Renewable Energy Forum | Post a Follow-Up

What insulation is best?

Posted by shelly_k (My Page) on
Tue, Jul 8, 08 at 12:33

Right now we have the spray foam stuff in our attic and the regular roll stuff in our walls. Our walls are 2x6 and we live in South Dakota (i.e. cold climate). Is this sufficient? Or should we do the spray foam stuff in the walls as well? We originally had that in the bid and then changed it because people have told us if we get good windows and doors, the roll stuff will be sufficient.

Follow-Up Postings:

RE: What insulation is best?

sounds like you are in the middle of building. those peole are stupid. the fiberglass bats are actualy not that great, they allow alot of air infiltration. foaming the walls full would be the best, yes more expensive but the way fuel prices are going.......
second best would be compressesd cellulose insulation.

i know i could kick my self for allowimg my contractor to talk me out of foam 7 years ago.

i hope you are puting in triple pane windows

there is a ton od info at build it

good luck

Here is a link that might be useful: there is a ton od info at build it

RE: What insulation is best?

I try to discourage people from foaming the underside of their roof deck as much as I can. Regardless of the foam installers saying their foam is 'open cell', I have yet to see a sample that allows water to run through it.....go to a home show with a bottle of water and try it yourself. The problem as I see it is that down the road your roof will leak...they all do, that's why roofers continue to have employment. When it does leak, with a waterproof layer of foam under it, the water will remained trapped against the foam, rotting your roof deck and even the trusses before you realize anything is wrong. When a foam company can show me foam that water will pass through, I'll change my opinion.

RE: What insulation is best?


With 2x6 construction the nominal space is 5.5". Fiberglass insulation at 5." is an R21 or R3.8 per inch. Expanded Polyisocyanurate would be aprox R33 or R6 per inch. The added bonus for spraying insulation is that it virtually eliminates all infiltration air through the structure. Eliminating Infiltration is the best way to cut your heating costs. Sioux Falls, South Dakota winter design temp is -16 and when that air enters the structure, you have to heat it to +68 desgrees.

I'd go with sprayed insulation unless you plan on having a stucco finish, stucco tends to trap water vapor and condense on the sheathing rotting it.

Hope that helps,

Dan Martyn

RE: What insulation is best?

Designer you have any comments regarding my concern about leaking roof water getting trapped above the expanded polyisocyanurate foam? I've handled sample blocks of that stuff and water doesn't seem to penetrate it at all. It also seems to form a strong bond with the roof decking and trusses (pushed as a hurricane benefit here in FL) so water would not just flow across the top side of it down to the eaves. I really think there are going to be serious issues down the road as the roofs above this stuff begin to leak....

RE: What insulation is best?

People using sprayed in foam for the entire house should be thinking about installing air make up due to the house being too air tight. I know of a couple of people that had to install these and they run about $4,000. My state doesn't require air makeup but I have been told some do.

RE: What insulation is best?

Faom is the best But where you live straw is better and having much thicker walls. new low e glass and argon filled double or triple windows is great. Your windows and doors are just a big hole to let in cold air get them sealed to fix that problem

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Renewable Energy Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here