Q&A: A Forum for Green Building Experts and Beginners

Q & A Instructions

[Click map to enlarge]

The GBAGreenBuildingAdvisor.com 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!

1 Answer

Roof insulation / decking combination

Hello, I live in Winnipeg MB, Canada (Zone 7, North of North Dakota).

I am insulating my garage ceiling to R22+ (standard pink fibreglass between 2x8 ceiling joists). I am also looking to insulate my garage roof to keep some of the heat from the summer out of the attic space in which I will store some things that i do not want subjected to high attic temperatures (I also expect this will help keep the garage cooler as well since the attic will be only about as hot as the outside air at most.

I intent to layer the system as follows:
1. OSB as the roof decking

In Energy efficiency and durability | Asked By Mike Gagne | Sep 14 14
5 Answers

Zone 4B - 2012 IBC and SHGC

The new 2012 IBC adoption in my future building area will mandate that windows can only have a maximum of 0.40 SHGC, including the south facing windows. I am trying to achieve a Passive House design but the low SHGC mandate makes it more difficult. I am going with Intus uPVC triple pane windows. Originally I was going to go with the 0.49 SHGC for the south elevation but now I have to go with the 0.37 SHGC. The building department will NOT budge on this factor and will not allow any windows > 0.40 SHGC.

In Building Code Questions | Asked By Peter L | Sep 13 14
4 Answers

Inset 2x6 sill plate

We're in the final phases of house plans for our new build in Illinois(5A). I'm very interested in adding 2" of XPS foam, but not so excited about it extending beyond our basement foundation wall. Would it be acceptable to inset a 2x6 treated sill so that the foam does not extend beyond the 8" basement foundation wall?

I've attached a drawing to help explain...

Thanks a bunch - I really appreciate all the advice I've learned on this site!

In Green building techniques | Asked By Craig Harper | Sep 14 14
5 Answers

If I have a 5 1/2 in. square framing bay and the exact same 5 1/2 inch square batt, does it matter which way I install it?

Does fiberglass work directionally? Or does it matter?

In Energy efficiency and durability | Asked By rich graves | Sep 13 14
2 Answers

So. Calif. — Adding insulation to existing walls that have fiberglass batts

I have a solidly built building - wood frame stucco walls. Built in 1960, (I helped) with rolls of pink fiberglass in the walls and attic. It is no longer effective against the heat.
What can we do to add wall insulation. I have had the walls of other homes insulated with blown in cellulose with success, but there was no existing insulation in those situations. Will blown in work with the old fiberglass in the wall cavity?
Is there a better option?
Thank you.

In General questions | Asked By Kay Park | Sep 13 14
3 Answers

Insulating interior AND exterior basement walls OK?


In Energy efficiency and durability | Asked By Nikola Kolarich | Sep 12 14
4 Answers

Ventilation above foam on roof application?

Just looking for others' opinions. Zone 5. 200-year-old colonial. Skinning existing old board sheathing with 1/2" plywood. Ice and water whole thing as air barrier. Adding 3 inches polyiso, 2.75 inches EPS on top.

Was planning to vertically run 2x4 every 16 inches securing through everything with Trufast 9" screws. Then install 1/2 in. plywood as roof nailing deck.

Is it overkill to ventilate this in this manner? Is it still necessary to tape each layer of foam sheathing if I do have this ventilation in place?

Appreciate others thoughts.

In Energy efficiency and durability | Asked By terry grube | Sep 10 14
0 Answers

Beware the dual-hose portable AC / heat pump

For years I've wondered if a dual-hose portable heat pump/air conditioner could be a poor man's ductless minisplit heat pump. The advantage, as my logic went, was that I didn't have to drill any holes or charge any refrigerant.


I bought a 14kbtu portable heat pump (Edgestar AP14001HS Portable Air Conditioner) ($400-$700)

I did some primitive temperature and airflow measurements.

I was impressed by the overall quality and the 11.2 EER, but what I found was very disturbing.

In Mechanicals | Asked By Kevin Dickson, MSME | Sep 12 14
11 Answers

I need help choosing the correct minisplit and heat pump for my studio

I have two proposals to install a single unit mini-split with an outdoor condenser for my studio building. The building has a 24 x 32' foot print. The walls are 10' high, with a cathedral ceiling that is 16' high at the ridge. Walls are 2 x 6 (at least) with fiberglass batts. Roof rafters are 2 x10" (I think) with fiberglass batts between, and then either 1 or 2" rigid foam insulation skimming it (under the sheetrock). Building is tight. Floor also has fiberglass and rigid foam board between the 2 x 12" joists.

In Mechanicals | Asked By DANIEL GOTTSEGEN | Sep 10 14
30 Answers

When roofs do rot, which side does the rot start on? worth using copper-borate treatment as preventative?

When roofs do rot with closed cell foam underneath, which side does the rot start on?

Is it worth using a copper-borate treatment as preventative?

Zone 6. There will be 4" 2lb closed cell foam on the underside of the sheathing. tar-paper on top. Attic space will be living space. not expecting to have any rot issues but....I'm thinking a belt-suspenders approach here. considering spraying whichever side is prone to rot in this situation with a copper borate solution as a preventative.

thank you.

In General questions | Asked By eric Mikkelsen | Sep 8 14
Register for a free account and join the conversation

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