I have been going with a relatively unique (and time-consuming) approach to address two similar situations: vented cathedral ceilings and semi-conditioned attics with HVAC equipment.

I have been combining 3/4" Dow Tuff-R polyiso and R-21 high-density FGB insulation to achieve both an air barrier, a partial radiant barrier, and roughly an R-30 in 2X8 roof rafter assemblies (in older homes in Northern VA).

The 3/4" Dow Tuff-R is set 1" from the sheathing (with a ridge vent retro'd in to the roof, and natural ventilation at the roof-fascia intersection). The edges of the Tuff-R are sealed with closed-cell foam, and the joints taped with Nashua Extreme Weather foil tape. The remainder of the cavity is then filled with R-21 HD batts. Ducts in semi-conditioned attics are often sealed.

With recessed lights in cathedral ceilings, I try to get as much polyiso above the can housing (and swap out bulbs to LEDs), while maintaining an air space beneath the sheathing.

I have come to really appreciate the approach, but I wanted to bounce this off the pros before I continue my love affair with this approach.

Thanks in advance!

Views: 135

Replies to This Discussion

Sounds good at first blush & used similar approach for others (minus leaving can lights) - As an FYI it is R26 technically & I am assuming by radiant barrier this one has the foil facing & it is facing the sheathing?

For the tape, make sure you check with DOW to make sure they approve but that sounds good

How are you getting the 1" gap?

Now the problem I see - even with LEDS, those cans are not rated for foam to be touching them, only items like FG, rock wool, & cellulose should be touching (assuming IC Rating)

Thanks for the reply Sean.

I have been using 1" polyiso sleepers to achieve the 1" air space between the roof sheathing and the polyiso board.

I have indeed been using the foil-faced product.

I will look into the tape and whether Dow approves. Any advice on finding that info out without scouring Dow's entire site?

I will have to look further into the can lights and the issue you raise with foam coming into contact with them.

Look at there spec / installation directions or call there technical support department or regional rep if not listed - generally pretty good at answering questions

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Todd Collins replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"might want to consider vapor permeability.   Need to move the dew point out far enough to…"
1 hour ago
bill lazar replied to robert jones's discussion Should your local weatherization company be required to have someone BPI certified on their staff?
"all this will be clarified soon with the new SWS guidelines mandated by DOE- but just WZ…"
1 hour ago
Glen Gallo replied to Brady Mills's discussion Can someone recommend a whole home water filtration system?
"I was in the business of cleaning up water at one point. We produced spot free pressure washers of…"
3 hours ago
Patrick Michaelyan replied to Casey Gesell's discussion Looking for home improvement companies to join our dealer network!
"Casey I'm in Arlington, VA."
6 hours ago
Patrick Michaelyan replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"Thanks for the input Dennis!"
6 hours ago
Patrick Michaelyan replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"It's about time! I love Hardie products but I had my reservations in the part when installing…"
6 hours ago
Patrick Michaelyan replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"Great, thanks Craig. I read up on Tyvek's Stucco Wrap many moons ago and completely forgot…"
6 hours ago
Dennis Heidner replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"If you are using Hardie on a building,   James Hardie recently released a note that says in…"
7 hours ago

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service