Forums
New posts
Search forums
What's new
New posts
New media
New media comments
Latest activity
Classifieds
Media
New media
New comments
Search media
Log in
Register
What's New?
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Navigation
Install the app
Install
More Options
Advertise with us
Contact Us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
The Water Cooler
General Discussion
Spray foam under roof decking.
Search titles only
By:
Reply to Thread
This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Message
<blockquote data-quote="perfor8" data-source="post: 4058297" data-attributes="member: 10088"><p>That's a tough install for anything other than blown-in loose-fill insulation. They make radiant heat barriers (basically just a layer of aluminum foil, although they also make spray-on, paint-like products) to reflect radiated heat. The radiant barriers can be placed above the rafters, in between the rafters, attached to the bottom of the rafters, or above the joists - none of those would be easy with your limited access. "Fluffy" insulation (rock wool, fiberglass, cellulose, etc.) will only be effective for convective heat - and do little for radiated heat. And, you are correct, as the fluffy insulation becomes hot, and the trapped air becomes hot, that hot mass (air has mass and hot masses radiate heat) will radiate heat to your ceiling. My best off-the-cuff solution is to place all the fluffy insulation you can get in there while still maintaining a vent path so hot air can get out. </p><p></p><p>The passive "chimney effect" someone else mentioned is accomplished by having vents located at elevations that are as low (intake) and high (outflow) as possible. Again, difficult with your roof's shallow pitch. Passive ridge vents are an option (plastic spacers that elevate the shingle ridge cap to allow air egress at the ridge). Active venting could be accomplished with solar or otherwise powered fans at the peak, but they'd need adequate vents down low for air intake.</p></blockquote><p></p>
[QUOTE="perfor8, post: 4058297, member: 10088"] That's a tough install for anything other than blown-in loose-fill insulation. They make radiant heat barriers (basically just a layer of aluminum foil, although they also make spray-on, paint-like products) to reflect radiated heat. The radiant barriers can be placed above the rafters, in between the rafters, attached to the bottom of the rafters, or above the joists - none of those would be easy with your limited access. "Fluffy" insulation (rock wool, fiberglass, cellulose, etc.) will only be effective for convective heat - and do little for radiated heat. And, you are correct, as the fluffy insulation becomes hot, and the trapped air becomes hot, that hot mass (air has mass and hot masses radiate heat) will radiate heat to your ceiling. My best off-the-cuff solution is to place all the fluffy insulation you can get in there while still maintaining a vent path so hot air can get out. The passive "chimney effect" someone else mentioned is accomplished by having vents located at elevations that are as low (intake) and high (outflow) as possible. Again, difficult with your roof's shallow pitch. Passive ridge vents are an option (plastic spacers that elevate the shingle ridge cap to allow air egress at the ridge). Active venting could be accomplished with solar or otherwise powered fans at the peak, but they'd need adequate vents down low for air intake. [/QUOTE]
Insert Quotes…
Verification
Post Reply
Forums
The Water Cooler
General Discussion
Spray foam under roof decking.
Search titles only
By:
Top
Bottom