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: 180

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

Photos

Loading…
  • Add Photos
  • View All

Latest Activity

Earth Advantage posted an event
Thumbnail

CakeSystems™ Software Course at Webinar

March 4, 2016 from 9am to 11am
CakeSystems Software training is offered as a self-paced online course of 3-4 hours followed by a…See More
4 hours ago
Anthony Adams posted a blog post

Bonus room attic walls heat load

Hi Everyone...First of all I am 59yr old retired Federal employee. I took HVAC in a trade school 30…See More
7 hours ago
Tom White's video was featured

Multifamily Building Energy Innovation- TrueFlow Capture Box

Video explaining the new tool to help reduce the energy costs of effective ventilation in multifamily buildings.
11 hours ago
Alfie Davis posted a blog post

Utility of a Hardwood Staircase

Everything needs a makeover after a certain time. Your home is one of them.  Sometimes, you…See More
15 hours ago
miguel pace shared a profile on Facebook
20 hours ago
miguel pace liked miguel pace's blog post It is very important to select a fin fan
20 hours ago
Charles Ryan Weitzel posted a discussion

Oil Fired Boiler Being Used as the Heating Source in Two Air Handlers of a Historic Home

I'm not sure this makes any difference, but I've only run into a system like this here, where I…See More
yesterday
Ronald Wallis replied to Jonny Fisher's discussion Minneapolis Blower Doors and Duct Blaster for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"interested in your equipment. Do you have pics? Is equipment compliant with new regulations?"
yesterday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service