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!

8 Answers

How best to install HVAC return duct on outside of house?

Basic facts: 3 level house built on a down slope hillside lot in 1994. HVAC zone one covers main and upper floors. Zone two heats lower floor bedrooms. Equipment room located on lower floor. Climate zone 3c---SF Bay Area home. Large SW facing windows heat up main floor (family room) and upper floor master suite.

Asked By Joe Geesman | Oct 4 16
1 Answer

Can I use rigid styrofoam on top of top plate to minimize thermal bridge from trusses


I was wondering if its suitable to install a truss on top of a sandwich styrofoam between 3/4 ply and the top plate of an exterior wall, Sort of like putting a SIP on flat. Can the SIP support the point load of trusses for lets say a roof needing to support 100 psf?


Asked By Stephane Aucoin | Oct 17 16
1 Answer

Green Bldg Advisor for higher education?

Do you have a program of providing full content of Green Building Advisor to libraries? At a large institution it is not feasible to manage an account with a single ID and password for use by faculty and students. Access by IP address ranges is necessary. Do you provide this type of institutional subscription? For many years your journals Fine Homebuilding and Fine Woodworking have been popular supplements to architectural education. Green Building Advisor could have similar value if access can be feasibly managed.

Henry Pisciotta
Arts & Architecture Librarian

Asked By Henry Pisciotta | Oct 17 16
8 Answers

Adding insulation to floor vs adding insulation to walls

Hi, we have a basement that is partially below grade on two sides and on grade for the rest. The walls are cinder block, and the foundation is a concrete slab with a layer of gravel under it. There are 5 windows that are 35x37, double-pane, with air leaks around them. There is a propane furnace that ducts heated air to ceiling vents in basement rooms and floor registers on the main floor. Three of the rooms in the basement have electric baseboard heaters. The basement and main floor are both 1500 square feet. The only floor covering in the basement are then stick-on vinyl squares.

Asked By John Lambert | Oct 16 16
1 Answer

Room HRV

Just completed exterior renovation on a 200+ colonial. Removed everything from outside air sealed, installed roxul, plywood, taped joints, typar, 1 inch foam board, 3/4" strapping, vertical grain clapboards, etc... I have an ell that the radon level is now slightly elevated because it is so tight. It is basically 20 X 30 and attaches to the main house via a large opening. It has the kitchen and living room in it. It is a slab which I did not do so not sure how leaky it is. I want to install a single HRV and was looking at twinfresh comfo, Mica 60, Mica 150 style through wall units.

Asked By Terry Grube | Oct 17 16
5 Answers

Casting concrete to repair rubble foundation?

I have a crawlspace that leaks air badly in the winter and I would like to insulate (I live in Minneapolis, MN for reference). Upon embarking on the job, I uncovered a rubble foundation that is in need of repair. This foundation is part an old extension to the house and is of much lower quality than the original limestone brick foundation. It also looks as if it has been repaired at least once in its life as there are some random chunks of red brick and glass embedded in the wall which I doubt were original.

Asked By Frank Thorton | Oct 16 16
1 Answer

Separate ERV intake and exhaust or tandem?

We are installing an ERV in a new house and the hvac contractor has suggested using a tandem intake/ exhaust vent that looks like the attached sketch. The ERV installation manual allows this as well as two separate vents with a minimum of 6 ft between them.

These will be installed about 12 feet above ground level. It looks like there is a possibility of cross contamination with the tandem unit. Should I ask for two separate vents?

Any advice will be appreciated.

Asked By Jeremy Turner | Oct 16 16
5 Answers

How to air seal the attic floor to the wall sheathing?

I'm designing a house that will be built near Rochester, NY in zone 5. My primary air barrier will the plywood attic floor and plywood wall sheathing. What's the best way to seal these together? For structural reasons, I would prefer if the sheathing were continuous between the first floor and attic.



Asked By John Ranson | Oct 12 16
8 Answers

Question about adding an outlet in front of foam board insulation

I have a Brick home.
My wall consists of brick then 1x4 frame laying the flat way with 1" foam board in between. Then the entire wall covered in 1" foam board then 1/2" osb then 3/8" drywall.
I want to add an outlet below a light switch that is already installed.
There is not access in the attic and from what I can tell from the basement is the wall is 1.5" on top of the basement wall so I can't drill up through the floor.

Any suggestions would be appreciated

And I do not want to install 2x4 frame just to add an outlet

Asked By Tyler Klingbiel | Oct 16 16
2 Answers

Average cost to finish an attic?

What is the average cost to finish an attic?

Asked By Daniel Mark | Oct 16 16
Register for a free account and join the conversation

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