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, Building, Chump, Newsletter, Performance, Stump

Views: 160

Replies to This Discussion

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

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

R Higgins replied to William Fisher's discussion Can tankless water heaters provide hot water even when the groundwater is fairly cold?
"I have that problem, 45 to 50 degree ground water, in summer, not that we have much of a…"
8 hours ago
R Higgins replied to Larry Schaffert's discussion How to correctly insulate exterior wall in a 1900 house?
"I'd suggest trying to replicate the existing conditions as much as possible in your rebuild,…"
9 hours ago
Bryan Pringle replied to Bryan Pringle's discussion Dense packed cellulose in basement?
"I am getting a lot of "bad idea" push back on this.  I fully understand that…"
20 hours ago
Greg Mitchell commented on Larry Ralph Jr's blog post Top 7 Worst Crawl Space Repairs
"Spray Foam should be used in crawlspaces.   To learn about closed cell foam in crawlspaces…"
21 hours ago
Jerry Lawrence posted events
yesterday
Morgan M Audetat replied to Bryan Pringle's discussion Dense packed cellulose in basement?
"Right you are. You have to ask: what will the cellulose contribute.  Here in Minneapolis we…"
yesterday
Morgan M Audetat replied to Tony Hicks's discussion Slab-on-grade Insulation
"All slabs float. We have been installing radiant floors on various slab constructions since the…"
yesterday
Tony Hicks replied to Tony Hicks's discussion Slab-on-grade Insulation
"2" XPS foam. I'd love an R-20. Having foam thick enough to get an R-20 would be…"
yesterday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service