Here is your chance!

Thanks to Bo Jespersen, President of The Breathable Home in Manchester, Maine for contributing February's home performance head scratcher.

Bo was stumped after his company was hired to install some spray foam insulation in a second story bedroom side attic.

When Bo arrived, he noticed that the work was exclusively on the north slope of the home, and that the owner had installed three layers of 2" thick rigid foam in-between the rafters, and applied one-part spray foam along the edges (where some stuffed fiberglass was found as well). A small air channel was left between the top of the foam and the bottom of the roof sheathing. The ridge beam was exposed and required ending the rigid foam to the southern slope to make it air tight.

Keep reading...

Tags: BPI, Chump, Newsletter, Stump, the

Views: 189

Replies to This Discussion

The moisture problem with the home in question that Bo Jespersen's company, The Breathable Home is encountering in the Stump the Chump article this month is likely due to warm moist air from inside the house (as described in the article) coming in contact with a cold roof deck.  Frost is probably not even forming.  When this happens, water vapor in the air condenses and causes the described situation where moisture drips down into the room below.
The fix would be to create access to the air gap above the the rigid insulation and completely fill that gap with foam as well as seal the gaps at the top of the rigid insulation near the ridge beam. That would eliminate any possibility of warm moist air from contacting the cold roof sheathing.

The solution to this problem is to prevent warm moist air from contacting a condensing surface.  This is difficult, because it is nearly impossible to create a perfect air barrier – especially one that maintains a seal over time in a climate with large temperature swings and between materials that have different coefficients of thermal expansion. 

One solution would be to pull up the roofing material (singles, slate, whatever), and add rigid insulation underneath, overlapped (2-3in), then add lathe and sheathing (the space between the lathe creates an air channel) and then add the roofing material.   The insulation will need to be thick enough so that the air under the sheathing won't reach the dew point even during the coldest nights.  This option is expensive.  

A cheaper option would be to remove the rigid foam, spray the underside of the roof deck with foam, and then place the rigid board back in while the foam is still nice and gooey, essentially as a continuation of the foam.  That will get rid of the air space where condensation can occur.  It would be nice if the foams had the same thermal expansion coefficients, and there weren’t air bubbles at the interface, but that is probably inevitable.   The risk here is that there isn’t enough vapor permeability through the foam and that any water that gets under the roof deck from roof leaks will stay there.  This is a risk with all under roof deck foam applications, and demands a good job maintaining the roof once the under-deck insulation is installed.    

To just solve the water issue, a ridge vent could be installed and the soffit area could be re-done to create an air channel under the roof deck, but this would mean continued air leakage.  Far from ideal.

RSS

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

Profile IconMichael Capobianco, Lois Bower-Bjornson, Tim Grant and 1 more joined Home Energy Pros
6 hours ago
Evan Mills commented on Tom White's video
Thumbnail

The Impact of Green Buildings on Cognitive Function

"Good to see work like this going on.  Findings seem qualitatively consistent with what…"
14 hours ago
Keith Burrows's blog post was featured

What Happens When Home Performance is Made Visible?

“I don’t know” or “probably not” are the most common responses I hear to the question, “is your…See More
20 hours ago
Sarah Holloway posted a video

Don't Lose Your Marbles. Use DASH!

Are you a growing energy rating business? DASH is everything you need to operate your company.
20 hours ago
Rosie Smith replied to edward knight's discussion Minneapolis duct blaster for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Hi Edward...is this equipment still available?? Thanks, Rosie Smith Fresno,…"
Wednesday
Rosie Smith 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
Wednesday
Jim Gunshinan liked Tom White's discussion Home Energy Reader Survey
Tuesday
Tom White posted a discussion

Home Energy Reader Survey

Home Energy wants to serve you better.  Please …See More
Monday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service