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!

4 Answers

Zip wall R-6 sheathing plus spray foam or batt

So, I have just framed an addition... 2x6 walls, with zip sheathing with attached r6 insulation. I am in zone 3... Just wondering whether to just fill the cavities with batt or go with open cell spray foam... Having the zip wall taped off well, with good window install, how much benefit I would gain by going with spray foam... The costs are really adding up on my project, just hoping that there wouldn't be a huge negative with going with the batts. Your thoughts?

In General questions | Asked By Dean Sandbo | Apr 21 16
1 Answer

Update on polyiso as a WRB?

Martin did an article on Using Rigid Foam As a Water-Resistive Barrier back in Sep 2010. In it he brought up the possibility that polyiso might shrink over time, so might not be reliable as a WRB even though rated for WRB use. Hoping that 5.5 years later there is enough new information for an update on best practices and practicality of utilizing exterior polyiso as a WRB.


Mitch Costa

In GBA Pro help | Asked By Mitchell Costa | Apr 22 16
4 Answers

To ventilate or not to ventilate?

Greetings all,

I am in the planning process for a new post frame (pole shed) building that will be used primarily as a wood shop. Planning to start construction within the next month.

The building will be insulated (R50 attic floor and R22 walls) and heated in winter - northern boundary of zone 6. When not in use, the building will be kept mid 40's. Warm up to working temps will be air-tight wood stove drawing outside combustion air.

In Energy efficiency and durability | Asked By Greg Smith | Apr 21 16
7 Answers

Is thermal bridging through a solid wood door a big deal?

We are going to be renovating our 1888 home to "pretty good" standards. I wasn't planning on doing anything to the original solid wood front door besides refinishing, squaring up and rehanging (but I'll pay attention to air sealing as much as possible - we are striving for <1.0 ACH). I am not so concerned about the energy losses caused by the thermal bridge but am a little concerned about creating a condition that causes the door to deteriorate (due to moisture or other reasons).

What, if anything, could happen to the door?

In Green building techniques | Asked By Alok Khuntia | Apr 20 16
13 Answers

USA New Wall & Swedish platform framing


I recently came across Greg La Vardera’s website http://blog.lamidesign.com

Although I have read much on energy efficient wall types here, I haven’t noticed any comments on the USA New Wall. I am interested in other peoples opinion on this construction and how it compares to other energy efficient wall types. (I am thinking about the Building Science Corp s list of walls and how they score relative to each other -http://www.buildingscience.com/resources/high-r-value-wall-assemblies )

In General questions | Asked By Mitchell Daniels | Nov 12 13
15 Answers

Run furnace blower or HRV?

We are building a home is southeastern Michigan. It will have 3 110cfm bath fans (one in basement bathroom) and one 80 cfm bath fan (toilet room) and a 400 cfm hood range. I am concerned about air quality, as we a building a very tight house. Our HVAC contractor has said that he can simply program the furnace to run the blower every 1/2 hour to bring in more air which would be filtered. I believe he will also have a scuttle installed on the furnace. What are your thoughts? Most of the HVAC professionals I have talked to say that HRV systems don't work that well anyways. Thank you!

In Green building techniques | Asked By Carolyn Farrow | Apr 20 16
36 Answers

Where is the excess humidity coming from? No obvious sources

I always read about optimal (relative) humidity being somewhere within the 30%-50% range.

I started monitoring the humidity in my single story brick house over winter it appears it's always in the upper 40% range. I am curious why it is so high. This is an old 2-wydthe brick house in Zone 5.

Sample readings:
- Basement: 52% @ 59deg, DP: 41deg
- Main floor: 47% @ 68deg, DP: 47deg
- Outside: 60% @ 33deg, DP: 22deg

Usual suspects:
- 2 people, gone during business hours
- bathroom fan vented outside through the roof, always in use during showers

In General questions | Asked By Jeff Watson | Apr 4 16
5 Answers

Brick steel lintel size

Does anyone has a reliable chart or table for brick lintel length on each side of a brick wall opening? I've contacted brick suppliers and contractors, and apparently is all done by the way is always been done, and I hear 20 different answers.

In General questions | Asked By Armando Cobo | Apr 21 16
1 Answer

Part 2: How best to insulate a 1935 small Cape; is blown in cellulose OK?

Part 2 of my question - Is it ok to blow in dense pack cellulose to the walls of a 1935 small Cape without having a "moisture barrier"? A friend suggested because of the heat/cold differential, there might be condensation, which could moisten the cellulose and eventually damage the frame. The MassSave people say this is unlikely- only in case of ice-dam water damage, for example, would the dense pack cellulose get wet-enough to matter. Thanks very much for your previous comment.

In Energy efficiency and durability | Asked By Miriam Chernoff | Apr 21 16
2 Answers

Okay to dry out cellulose wet for 10 days to use in an attic?

My insulation sprayed damp cellulose into the wall cavities, scooped up the waste, and put it in about a dozen plastic trash bags so I could dry it out and use it in my attic. (I know many installers put the waste back in the machine, but he was wary of doing so because of stray nails that could damage his machine, even though I had a clean job site.)

In Green building techniques | Asked By Michael Bluejay | Apr 21 16
Register for a free account and join the conversation

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