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!

35 Answers

Choosing a wall assembly: discussion

I really tried to not ask this question since I'm aware that it has been discussed a ton, and I have read a ton on the subject. And even if I've accepted the fact that there's no clear answer, I still have to choose a wall assembly - double wall, 2x6+4"foam, SIP, or some hybrid. Around R40 (I have 12" to work with)

The top priority here is actually budget and ease of construction/quality control.

I've gone through many articles from BSC and GBA amongst many other case studies. This is how my thought process went:

Asked By Bernard Lam | Sep 27 16
11 Answers

Most efficient use of 3/4" polyiso on exterior (polyiso is foil faced on both sides)

My home is standard built- 2x3's 16" oc w/craft faced fiberglass ins not very well installed( gaps,etc.). I have enough 3/4" f f polyiso to cover it. FH's recent articles indicate Roxul batts would be best way to insulate, but I already have the foam.

Asked By Victor Brown | Sep 29 16
6 Answers

Basement – Best way to eliminate musty smell / mildew/ mold etc

I am new to the forum. Thank you for your suggestions.
Purchased a lake house last year. The basement (see attached picture) is musty.
Looking for suggestions / products to redesign the room and clear the air.

My thoughts were to:
Purchase a dehumidifier
Purchase fan(s) to circulate air internally
Install a fan with a timer in the back wall between the 2 room to circulate air

Do I need:
a dehumidifier
a combination of fans to circulate the air
to exhaust bad air to the outside / bring fresh air inside

Here are some facts:
Total SF = 682

Asked By D Moye | Sep 30 16
1 Answer

second WRB with Zip and rigid foam?

I'm replacing the siding (wood clapboard) on my house and part of the process involved replacing the old sheathing (1x hemlock 125+ years old). I used Zip OSB for the new sheathing and will be adding 2 inches of rigid foam (XPS) and 1x strapping for a rain screen. My question is, should I place a second WRB, such as 15# felt, on the outside of the foam, under the strapping? I hadn't planned on it until now, as I was relying on the Zip as the WRB but it seems like it would be nice to have a WRB to keep the foam dry from the outside.

Asked By Michael White | Oct 1 16
7 Answers

Single versus double header for energy efficient framing.

There are two headers that I could use for a short span in a 2x6 wall: one 2x10, or two 2x6's. With the 2x10, I would fill the open space with cellulose on the inside. With the 2x6's, I would sandwich in a 2.5" layer of rigid foam. Since code would require the 2x10 header to be boxed in with 2x6 plates, it seems like the doubled 2x6 header will present less of a thermal bridge and use less wood.

Am I missing anything? I've seen a number of sources suggest single member headers to improve efficiency, but the code requirement for extra plates seems to make them worse.


Asked By John Ranson | Sep 30 16
4 Answers

Mitsubishi remote thermostat and warranty

Hello All,

I have been lurking for awhile, as I usually find my answers through searches, but having a new Mitsubishi Hyper Heat system installed, I thought of a question for which I can't find an answer.

I had it installed by a Diamond contractor (primarily for the warranty coverage aspects), and the inside units have the usual handheld remotes.

Asked By Wayne Yamamoto | Sep 30 16
9 Answers

Minisplit Design for Whole House

Hello, first of all thank you GBA for all of your articles, I have read many and found them to very helpful and interesting.

I am renovating my house (in Tampa, FL) and installing a new AC system, I will be installing minisplits most likely DIY, but will also talk with installers. I want to see what GBA users recommendations are for how I should design my system.

Asked By Jimmy Black | Sep 29 16
2 Answers

Heat pumps and traditional heating

We are about to install a Fujitsu minisplit heat pump for our cooling and heating needs in our 100 year old 2000 sq foot row-home in Montreal Canada, (zone 8 million). We currently have electric hot water radiator heating.

I am curious how I manage to keep the two units from "fighting" each other over who gets to heat the house. I know that when the depths of winter arrive, the heat pump alone will not be able to heat our home.

Is it simply a matter of setting the thermostat for our main heating system a degree lower than the minisplit?

Asked By Sean Lewkiw | Sep 30 16
2 Answers

Can I install 3/8" T-1-11 clear siding over existing 5/8" T-1-11 siding to create a board and batten look?

My house is currently sheathed in 5/8" T-1-11 siding. I'd like to add another layer of 3/8" clear (no grooves) T-1-11 siding over that and then add 2" battens to create a board and batten siding look. Is this a good idea or a recipe for disaster? I live in Maui on the dry side of the island and get a lot of sun on the south and west sides of my house.

Thanks and Aloha,

Asked By Bruce Lowrey | Sep 29 16
1 Answer

EPS foam for loadbearing applications "Geofoam"

I found a bit of info today that I thought I ought to share. There is actually a standard for EPS used in structural applications (like under a footer). The standard I usually see is ASTM C578, which specs "Type I", "Type II", etc. There's a second standard, ASTM D6817, which gives a requirement for compressive resistance at 1% deformation, the maximum safe pressure for long term loads.

I found one manufacturer's nice little cross reference between the standards at http://www.styrotech.com/downloads/EPS-DataSheet-ASTM-D6817.pdf

Asked By John Ranson | Sep 30 16
Register for a free account and join the conversation

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