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: 107

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

Tom White posted videos
7 hours ago
Maria Lacey replied to Linda Wigington's discussion Low-cost electricity monitoring: Accuracy & Applications in the group 1000 Home Challenge
"I attempted to use an AZTech device. I have used the Watt Stopper, Watts Up Pro, Kill-A-Watt…"
11 hours ago
Maria Lacey joined David Eggleton's group
Thumbnail

1000 Home Challenge

Linda Wigington distinguished between deep retrofits & deep energy reductions, thus expanding…See More
11 hours ago
Profile IconCynthia Sandherr, James Skeldon, Mathew Castel and 3 more joined Home Energy Pros
14 hours ago
Andy Li replied to David Parker's discussion Energy auditor equipment for sale- blower door, duct tester,combustion analyzer in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Is Minneapolis Duct Blaster still available? send some photos and how much do you ask for? my…"
17 hours ago
Andy Li 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
Hal Skinner replied to Richard Beyer's discussion What's your opinion on the best insulation option for your GREEN attic space?
"Mornin Richard, Maybe 'Options' might be more appropriate here?  We take the path…"
19 hours ago
Richard Beyer posted a discussion
20 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service