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: 70

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

Colin Genge commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Pressurize the house to +25 Pa. Use smoke on the registers to identify leakage to outdoors then use…"
8 hours ago
Tim Reynolds replied to Alan Gindt's discussion Minneapolis Blower Door, Pressure Pan, and Bacharach CO 3 For Sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"I was wondering if you would sell the pressure pan by itself and for how much? Thanks -Tim"
17 hours ago
Profile IconTim Reynolds and angela hines joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
17 hours ago
Profile IconAllen Rathey, Kevin Love, Shannon Kahl and 1 more joined Home Energy Pros
18 hours ago
angela hines replied to Alan Gindt's discussion Minneapolis Blower Door, Pressure Pan, and Bacharach CO 3 For Sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"What is the price for them together? What is the price just for the blower door set?"
yesterday
Alan Gindt replied to Alan Gindt's discussion Minneapolis Blower Door, Pressure Pan, and Bacharach CO 3 For Sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Yes"
yesterday
Anna Jursik's blog post was featured
yesterday
Everblue posted a status
"New Energy Auditor Jobs posted on our Massachusetts Job Board! Check them out: http://www.everblue.edu/hiring/job-board/massachusetts"
yesterday
Everblue posted events
yesterday
angela hines replied to Brooke Ingram's discussion 3 full sets of testing equipment available for sale! in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Hi is the Minneapolis blower door set still available?"
yesterday
angela hines replied to David Allen's discussion Like new! Great Deal! Minneapolis Blower Door system, Duct Blaster and Flir i-7 Infrared Camera for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"I am interested in the blower door and camera. Are they still available? If so i will buy. Please…"
yesterday
angela hines replied to Alan Gindt's discussion Minneapolis Blower Door, Pressure Pan, and Bacharach CO 3 For Sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Is this still for sale? I am interested and would want to buy."
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service