Nailbase insulation vs. 2 layers of tuff-r with staggered seams

We are going to be rehabbing a home in CT in which the third floor is part of the living space. We want to get the insulation level up by using either nailbase or 2 layers of 2" tuff-r with staggered seams on top of the deck. We are going to use close cell spray foam with polyisocyanurate insulation to increase insulation and stop bridging on the inside. Has anyone used nailbase over spaced wood slats that use to have a cedar shake roof over it? We believe that the closed cell spray foam underneath would act as a vapor barrier, the slats would provide more that enough support and the hot roof is o.k.  but real-world experience would be much appreciated.

Tags: hot, insulation, nailbase, roof

Views: 426

Attachments:

Reply to This

Replies to This Discussion

I would consider using cellulose insulation blown in between the rafters, rather than spray foam against the skip sheathing. Foam on both sides is risky, in my opinion, and will make any future repairs to the roof structure a real challenge. Since you are addressing thermal bridging above the sheathing I don't see the real advantage to more foam below. Proper air-sealing of the drywall lid will probably be adequate, and I'm assuming you are making plans to correctly control interior moisture load anyway.

 

An alternative would be to install all of the insulation below the roof deck. Install baffles made of rigid foam board between the rafters, with a 1"+ vent space, then install cellulose or possibly foam between the rafters, and follow up with foam board across the bottom. That way you preserve the vented roof. Obviously this approach uses up some of your headroom.

Building assesmblies need to be able to dry in at least 1 direction.  Rigid insualtion on top will limit the drying to the outside so you should allow it to dry inward. I would agree with David and use cellulose. I would not use poly on the inside. Vapor diffuison through the drywall is not a big worry. What is a worry is air leaks carrying moisture in to the ceiling. You should consider and air tight drywall system along with a vapor retarding paint. You will also want to use more than 1 layer of rigid insulation with staggered and taped seams.

 

Do not use batt insualtion. Only use a dense pack material as that performs better than batts and cuts down on air movement close to the point of being an air barrier.  I said close but it is not an air barrier.

RSS

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

Crosbey Archery liked Crosbey Archery's blog post How to improve the air quality in your home ?
yesterday
Crosbey Archery replied to Don Hynek's discussion Testing "Magic Pak" units?? in the group Multifamily Buildings
"second-floor (and higher) units without humping a ladder all the way around the building is a very…"
yesterday
Colin Genge posted events
yesterday
Profile IconJon Turnbaugh, Lights N More and John Kamas joined Home Energy Pros
yesterday
Amber Vignieri posted a blog post

Relay Network Targets Multifamily Housing Upgrades Nationwide

Affordable apartment buildings are home to more than 10 million American households, making them a…See More
yesterday
Tom White's video was featured

Robby Schwarz on Builder Collaboration

Hear Robby Schwarz, of EnergyLogic discuss the value Owens Corning brings to Thrive Home Builders.
yesterday
Crosbey Archery liked Don Hynek's discussion Testing "Magic Pak" units??
yesterday
Crosbey Archery joined Norm Bourassa's group
Thumbnail

Multifamily Buildings

For too long there has been relatively little EE focus on multifamily, but some new programs have…See More
yesterday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service