Community: GBA Pro help

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!

6 Answers

What would you do?

Here's the question: All things being equal, would your recommend to insulate a 2x6 exterior wall with R20 closed cell spray foam insulation at approximately 3" leaving the remaining wall empty or fill the wall with cellulose (or other fluffy type) insulation. For sake of argument, lets stipulate the following:

-From the exterior: wood siding with WRB, Huber zip wall taped, 2x6 frame, board and plaster
-Wall is reasonably air sealed at the exterior sheathing
-Zone 5
-Code R20

Please provide you answer and reason why.


Asked By Bruce Friedman | Aug 9 15
4 Answers

Feedback on 2x8 exterior walls with 2x4 studs to limit thermal bridging

I live in Eastern Washington, Zone 5 A. 100 degrees in the summer to zero in winter with 1-3 ft of snow. I will hopefully be building a home this summer, 2016. I originally looked at SIPs but am convinced that if they are not installed perfectly I may end up with moisture problems later on. My brother suggested 2 X 8 top and bottom plates with 2 X 4 studs, (1/2 inch gap between them to break the thermal bridging), and blown cellulose insulation. Then two separate pieces of 1 inch ridgid foam insulation on the outside.

Asked By Thomas Flanagan | Jul 28 15
1 Answer

I was interested in Air Krete and wonder how good a product it is to have injected inside my exterior walls from outside

I have a 1960s home without much insulation and at first thought some foam might be good. Now

I hear about Air Krete which claims to be a soft and better injected insulation.

Can I get anyone with experience in using this on an older home or any details about its pros and


Anything about what or whether it is a good material to fill the exterior walls of my home.

Thank you for any information. I don't know anyone to contact.

Tom Mc

Asked By Tom McAuliffe | Jul 24 15
1 Answer

Flat roof insulation?

I am converting the sun room to a bedroom
My concern is about the ceiling insulation and ventilation.
the roof is flat and not insulated at all.
The previous owner blocked all air flow from soffit using pieces of wood which also supports the roof.

During the summer time, the asphalt flat will be stressful because of no air flow.

Asked By Mansig yoon | Jul 23 15
6 Answers

On concrete walls that are fully exposed (above grade) for a new residence, should there be an air space?

We are constructing a new dwelling in Climate Zone 4. Site constraint will have one side of the house built in to a hillside, so the exterior wall is retaining, and will be poured concrete. The owner likes the modernist look of exterior concrete walls, so we are planning to use poured concrete walls on the other elevations as well. I am planning on dampproofing the exterior of the retaining sections of wall, and framing the interior with 2x6 studding and insulation, like a finished basement wall condition.

Asked By Jeffrey Lees | Jul 21 15
1 Answer

What type of insulation to use?

We have just started a remodel on an old farmhouse in the Zone 6 region. The old 1 1/2 story farmhouse used 2X4 roof and wall framing with ship lap on both sides of the walls and on the top of the roof. The walls have blown in cellulose and the attic space has blown in fiberglass. The new part will be 2X6 construction and we are matching the roof lines but using 2X8's for the rafters with the ceiling leveling off and 2X8 tie rafters.

Asked By John Berlage | Jul 22 15
69 Answers

Attic is hot after closed-cell spray foam was installed

Finished attic with 4 foot knee wall , duct located in knee wall to support 2 floor,extremely hot, BASF spray tite 2 inches with spray foam wraped around rafter in knee wall but with Sheetrock on ceiling just 2 in foam In cavity . Suggestions to handle heat issue. Richmond Virginia all attic seal very well thinking heat coming from rafters under Sheetrock. Thermal convection coming from rafters. Worked done in the winter, crawl space also done, house built 1994 colonial 2 story with garage with room above with dormer. Also in crawl space does it really need supply vent and return vent

Asked By Mark Hippchen | Jun 27 15
1 Answer

Adding insulation during re-roof: Roxul or foam? Ventilate or not?

Thanks for this great website. I looked, but didn't find an answer to my specific situation so here it is:

Asked By James Hare | Jul 13 15
4 Answers

Has anyone ever seen a span table for old ACTUAL dimension floor joists?

I'm constantly working with 80-100 year old ACTUAL dimension pine floor joists. 2x8 are actually 2x8, the 2x10s actual 2x10s.

Compared to their slimmer decendants, these beefier joists can certainly carry more weight over longer spans. The problem is, inspectors (and many structural engineers, sadly) treat these as nominal framing.

Asked By AARON LUBECK | May 26 09
4 Answers

Vapor barrier for floating cork floor

I live in Peoria, Illinois (Zone 5A). I'm installing a floating cork floor over an upstairs plywood subfloor. Nearly every website I see preaches on the importance of using a vapor barrier under floating floors, but I've also seen vehement advice against it. The planks I'm installing have a thin cork layer on the bottom, so I really shouldn't use a vapor barrier right?

Asked By Yvette Richey | Jul 9 15
Register for a free account and join the conversation

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