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: 212

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

Latest Activity

Jonathan Beers posted a discussion

MGE hiring for my job

I'm retiring next spring, and MGE is hiring:…See More
14 hours ago
Summer Reyes's blog post was featured

Equipment We Use: Detecting Water With Infrared Cameras

You know water is somewhere on the property, you can smell the mildew, but can't determine the…See More
15 hours ago
Profile IconGlenn Hourahan and Joseph Frasier joined Home Energy Pros Forum
15 hours ago
Alfredo Baccari added a discussion to the group Job Board
Thumbnail

HERS or/and BPI Energy Inspector in SF Bay Area (SAN JOSE, CA).

ELEM3NTS is a leading energy efficient consulting company specializing in residential homes. We…See More
17 hours ago
Alfredo Baccari joined Diane Chojnowski's group
Thumbnail

Job Board

This group is for posting jobs related to all aspects of the home performance industry including…See More
17 hours ago
David Byrnes's blog post was featured

Strategies for Hiring and Interviewing for Home Performance Professionals

Hire slow and fire fast.  It’s a phrase that experienced managers and human resources professionals…See More
20 hours ago
Dara Bowser replied to Don Fugler's discussion joining ducts in the group HVAC
"Good to hear you have clean dryer ducts Don. The dryer duct issues that we run into are…"
yesterday
Don Fugler replied to Don Fugler's discussion joining ducts in the group HVAC
"David, If the IMC mandates metal dryer duct and prohibits metal screws, they must be accepting…"
yesterday

Photos

  • Add Photos
  • View All

© 2017   Created by Home Performance Coalition (HPC)   Powered by

Badges  |  Report an Issue  |  Terms of Service