Community: Energy efficiency and durability

Q & A Instructions

[Click map to enlarge]

The web site has a wealth of articles on a wide variety of construction topics. Before posting your question, you may want to check out the articles on this page: How To Do Everything. You just might discover an article there that provides the information you seek.

Please register for a free account or sign in to ask and answer green building questions.

If you want to post a question, the usual rules of courtesy apply:
1. Be nice.
2. If you can't be nice, be polite.
3. If you can't be nice or polite — well, please be brief.

To attach a photo or illustration: Under the box labeled “More explanation,” look for the words “File attachments.” Click that, and you should be able to attach a photo.

Thanks for joining the conversation!

2 Answers

Window sill pan question

Hi all,

I am about to install my windows and will be making my own sloped sill pan. I will be using bevel cedar and screwing on a thin back dam as well. Over this, will go the flashing tap.

Regarding the back dam, should it go behind the window (interior side) or under the end of the window? I would think it would be best practice to have it go behind the window. Only downside I can see is making interior taping more difficult.

Please see pictures on which method I should use.

Thank you!

Asked By Tommy87 | Jun 28 17
6 Answers

Rigid foam on top of studs

I'm currently in zone 5 redoing a brick ranch home. The wall from the outside to inside is brick, plywood, black sheeting, R-11 and drywall. All of the drywall is down and wall cavities are exposed. The customer wants to use R-15 Roxul insulation and add rigid insulation on top of the studs with taped seams and drywall over that. I know some people do that but not sure which type of rigid foam insulation to use in order to prevent moisture inside the wall. I think we would like to use 1" rigid foam to make sure we can attach drywall correctly.

Asked By tkaj | Jun 28 17
3 Answers

Attic insulation advice needed

First off, GBA is a fabulous resource for us, as we plan to build our “final home” in Asheville, NC. Climate zone 4. Our home will be a 26’ x 44’ ranch with a partially exposed, walk out full basement. Standing seam metal roof, scissor trusses, Zip system wall and roof sheathing, stucco exterior, 3’ eaves and gable ends. We will do a LOT of air sealing, greater than required insulation and high quality windows. The mechanicals and ERV will be in the basement (not in the attic).

Asked By Nancy Broadbear | Jun 28 17
5 Answers

Two minisplits in one room

I just had my mini split system installed. I got multiple opinions from the installation contractor regarding the number of indoor units in one room. There is the setup:

Asked By Bryan56 | Jun 27 17
2 Answers

How to vent an insulated shop attic

I'm building a 40x96 shop. Post frame, with interior OSB, taped as an air barrier. The roof will be metal, with cellulose blown in on top of the ceiling OSB. All utilities and lighting will be using conduit, so there will be virtually no penetrations into the ceiling, except for a whole-house fan which will be insulated and sealed from the underside in winter.

There won't be soffit overhangs, so I'm not planning for a vented ridge either. Would gable vents take care of attic venting? Thinking about using two 18x24" vents on each of the north and south gables.

Asked By Adam Emter | Jun 28 17
3 Answers

Insulation for my basement walls


Was wondering if anyone could recommend a type or place to get rigid foam for my basement walls.

The price of rigid foam insulation seems to have skyrocketed. I have 8' ceilings in my basement and about 70 linear feet of concrete wall to insulate. That's 35 2x8 sheets of dow XPS which at $42 a piece is $1600-1700 for r10. Throw Roxul on top of that to get to r24 and now I'm looking at $2500 for just insulation.

Asked By Tim-X | Jun 26 17
3 Answers

Baffles and blocking at eaves (retrofit)

When doing a retrofit application in an attic we typically install 2 baffles for each soffit vent, and then block off below the baffle in order to prevent insulation from falling into the eaves. All other eaves are also blocked with scrap fiberglass so that insulation does not fill the eave.
I am having difficulty explaining to my installers why it is necessary to block the eaves that don't need baffles, or in a home where there are no soffit vents. any good articles etc. to recommend?


Asked By Jeff Classen | Jun 26 17
2 Answers

Insulating bath and range vent ducts

Ant thoughts on whether or not, to insulate bath and range vent ducts that are in the conditioned space between a R40 spray foamed roof deck and the uninsulated drywall ceiling? Thanks.

Asked By Ross Williams | Jun 26 17
3 Answers

Dense-pack retrofit cellulose insulation for basement walls?

I recently had an energy audit done existing 1958-built tri-level in climate zone 5 (Ann Arbor MI). Looking for advice from the GBA experts to sanity-check some of the recommendations before making decisions; I'll try to keep it to one question per post. One recommendation was to add dense-pack cellulose into the existing above-grade and below-grade (finished) walls.

Asked By Phil Ray | Jun 22 17
3 Answers

Interior rigid foam for ceiling

I have been working on a well insulated house in climate zone 3. We installed 38' trusses for the roof, and I have been concerned by some things I have read about the potential for truss uplift, especially with such wide trusses. Right now the trusses look great, and are very flat and level.

Asked By Jason Whitacre | Jun 22 17
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!