Attic insulation. Cost and decision?

[kingquad]

+1 on Highbeam's comments.

I had an estimate to add to the existing 12" shredded fiberglass insulation, over-blowing with cellulose to reach R-45 which was less then $900 for 1200 s.f.. I haven't yet proceeded only because I have a little more work to complete in the attic prior to pulling the trigger.

Also, cellulose has been shown to act as an infiltration (air) barrier, so air sealing isn't necessary. However, I will likely crawl through and use fire rated spray foam to seal wiring and piping penetrations myself, but I'm sort of a belt and suspenders person anyhow.

Lastly, cellulose is treated with a borate salt, and doesn't support a flame, so fire proofing is unnecessary.

I will recommend air sealing/insulating the floor joists with spray foam. Perfect application.

Cheers!

Unless you're talking about dense pack cellulose, that is not true. It's not as bad as fiberglass, but it doesn't act as an air barrier.

 

[kingquad]

There's a lot of good free info about this all over the web. The Finehomebuilding site is a good place to start. I'll also second the recommendation for the Bruce Harley book. I think every home owner should have a copy, even if you're not a DIY'er. Lots of very good info in there. Just make sure you get the second edition.

 

[Tramontana]

Technically you are correct, cellulose is not an air barrier, but it does slow air movement.

From the Greenbuildingadvisor;

Because of the fiber characteristics and high density of blown cellulose insulation (3 to 3.5 pcf compared to mineral wool or fiberglass batts at less than 1 pcf), it is very effective at preventing internal convection and has been recognized as an effective fire-stop by third-party testing and code officials. While it may not meet the strict requirements for an air barrier material (0.02 l/sec-m2 or 0.004 cfm/sf @75Pa), it will significantly enhance the air-resistance of an assembly over other fibrous cavity insulations, maintain its rated R-value by preventing internal convection and dramatically reduce the flammability of a building structure.

 

[johnny1720]

I bought the atticat stuff from home depot, fluffy pink fiberglass blown in stuff. I paid about a grand to get 32 of the bags and a buddy helped me install it. It took two hours. I had a quote for 3k to spray foam my kitchen walls so I didnt even get a quote on the attic. I wished I could step back in time and get another quote on the foam. I could have bought the DIY spray foam kit and done my kitchen for $600 then put fiberglass over it. The atticat stuff is great but the foam is superior in so many ways.

 

[Shane N]

Why did they quote you for open cell foam? I don't see any reason to use that instead of closed cell.