BPI's April Stump the Chump: What’s Wrong with this Picture?

We know, we know. There’s a lot right with this picture, such as the gorgeous view of Lake Tahoe in the background and the awesome powder for skiing. But from a whole-house-as-a-system perspective, what’s wrong with this picture? What is the owner trying to do, and what would be a better solution?

Thanks to our own Larry Zarker, BPI CEO, for sending in this dandy shot. He offers the following Winston Churchill quote to explain what’s going on here: “You can always trust the Americans to get it right, after they have exhausted every other possibility”.

Think you know what the problem is, as well as the solution? Send it to us at lmcdowell@bpi.org.

 

Tags: April, Chump, Stump, building, newsletter, performance, the

Views: 421

Reply to This

Replies to This Discussion

Problem is Ice Dams.  The home most likely had melting of roof snow which then refroze and created ice dams possibly causing water damage or excessive ice buildup at roof edges. This caused the homeowner to install energy intensive heat strips to melt the ice dams and jack their electric bill through the roof during snow events.  

 

This is caused by:

1)      Air leakage from penetrations near exterior wall

2)      Heat sources close to exterior wall such as heating ducts or recessed lighting cans

3)      Insulation in contact with roof sheathing causing thermal bridging to roof deck

4)      Lack of soffit ventilation

 

The solution:

 

1)      Air seal exterior top plate with spray foam. It is also important to air seal any other penetration which is delivering heat to the underside of the roof deck.

2)      If recessed lighting is installed near exterior walls, the cans should be ICAT rated to prevent air flow through the fixture. An inexpensive air tight trim kit may also be purchased to avoid changing out fixture itself. Heating duct boots can be sprayed with 2 part foam to prevent heating of roof deck.

3)      Install soffit ventilation at code recommended level at EVERY BAY that is affected.

4)      Install insulation baffles at all soffit edges in order to provide a path for ventilation and carry away any remaing heat transferred from house and cool roof deck. This also prevents insulation from contacting the roof deck (causing thermal bridging).

 

Since it is often difficult to get full insulation amounts at the soffit edge due to clearance, an optimal solution would involve installing ventilation baffles and using spray foam insulation against the baffle and as far in until a full amount of blown insulation may be used. This solution also seals any air exfiltration through the wall top plate at the same time. 

 

 

Oh, and most likely, this is the north facing roof your looking at, unless you have tons of winter shade on the southern exposure.

Congratulations to Craig Bird of Preston Insulation in Tucson, Arizona for winning last month’s “What’s wrong with this picture?”contest. Craig was not only the first person to send in the correct answer. His answer was far and away the most comprehensive, and dare we say, the most elegant in illustrating what in the world of home performance was wrong with the picture, and what should be done about it.

The picture shows a snow-bound house in front of Lake Tahoe, its roof zig zagged with heat strips.  Says Craig:

“The problem is ice dams.  The home most likely had melting of roof snow which then refroze and created ice dams possibly causing water damage or excessive ice buildup at roof edges. This caused the homeowner to install energy intensive heat strips to melt the ice dams and jack their electric bill through the roof during snow events.  

 

This is caused by:

1)     Air leakage from penetrations near exterior wall

2)     Heat sources close to exterior wall such as heating ducts or recessed lighting cans

3)     Insulation in contact with roof sheathing causing thermal bridging to roof deck

4)     Lack of soffit ventilation

 

The solution:

1)     Air seal exterior top plate with spray foam. It is also important to air seal any other penetration which is delivering heat to the underside of the roof deck.

2)     If recessed lighting is installed near exterior walls, the cans should be ICAT rated to prevent air flow through the fixture. An inexpensive air tight trim kit may also be purchased to avoid changing out fixture itself. Heating duct boots can be sprayed with 2 part foam to prevent heating of roof deck.

3)     Install soffit ventilation at code recommended level at EVERY BAY that is affected.

4)     Install insulation baffles at all soffit edges in order to provide a path for ventilation and carry away any remaining heat transferred from house and cool roof deck. This also prevents insulation from contacting the roof deck (causing thermal bridging).

 

Since it is often difficult to get full insulation amounts at the soffit edge due to clearance, an optimal solution would involve installing ventilation baffles and using spray foam insulation against the baffle and as far in until a full amount of blown insulation may be used. This solution also seals any air exfiltration through the wall top plate at the same time. 

RSS

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

George Matthews commented on George Matthews's event Proof is Possible Tour by the Home Performance Workshop
"Here is the flyer for the Advanced Techniques and Tools in Home Performance Friday October 7th at…"
5 hours ago
George Matthews posted an event

Proof is Possible Tour by the Home Performance Workshop at Truitt and White Lumber Conference Room

October 7, 2016 from 9am to 1pm
Building Energy Performance Testing is sponsoring the Proof is Possible Tour to come to the San…See More
6 hours ago
George Matthews replied to George Matthews's discussion Shortridge 8400 Flowhood for A/C airflow testing in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Here are the pics of the flowhood and airdata manometer"
Saturday
Sarah Holloway posted a photo
Friday
Joe Urycki added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

TEC blower door and UEI combustion analyzer for sale

For sale is one used TEC Minneapolis blower door system: Includes model 3 fan with rings A and B,…See More
Friday
John Nicholas replied to Kevin Emerson's discussion Studies re: radon mitigation and energy efficiency
"The Nay side is well represented with the links already posted. I presented a neutral side, with…"
Friday
Ray Lehman replied to Kevin Emerson's discussion Studies re: radon mitigation and energy efficiency
"Hey John, Thanks for the information.  Very good empirical data. While I agree that running…"
Friday
John Nicholas replied to Kevin Emerson's discussion Studies re: radon mitigation and energy efficiency
"I have no links, just some anecdotal evidence. I had several Blower Door Tests done on my own home.…"
Friday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service