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!

14 Answers

Who has a favorite heat-pump water heater?

We are now underway with our "pretty good" house here in southern Oregon and I am committed to the hybrid heat pump water heater concept for our 2100 sq ft, three generation house. With four adults and a grandchild in the house, I felt that an 80 gallon unit would be desirable. We plan to locate the HPWH in a centrally located laundry room which is just under 700 cubic feet and have plumbed a floor drain into that room for condensate or tank failure (hope NOT). I had been inclined to go with the GE GeoSpring but I have heard a rumor that GE is going to discontinue manufacture.

In Green products and materials | Asked By Alan Hart-McArthur | Oct 13 16
62 Answers

Another crawl space in the Northwest

Hello all, I have a 1150 sq ft rambler house in Fall City, Washington (near Seattle), zone marine 4c. I am currently in the process of redoing the crawl space. I have pulled the damaged and rodent infested insulation down, and removed the town vapor barrier. It seems I had some rodents that were digging past the foundation and getting into the crawlspace, ruining everything.

In Energy efficiency and durability | Asked By David Meyer | Nov 28 16
2 Answers

What type of horizontal purlin/furring under my metal roof?

I'm agonizing over what to use under my metal roofing. I need something that will lie over my two layers of foamboard to take screws for attachment to rafters and also something to attach my exposed fastener metal panels to.

I'd like to avoid adding another 1.5" using 2x4 but most furring strips I'm finding are total garbage and only come in 8' lengths. Originally, I had planned on using 1/2" OSB or plywood, but that will be very expensive and wont allow me to shim out any sags easily. I wish there was some affordable synthetic material I could use.

In General questions | Asked By Dielectricunion | Oct 13 17
1 Answer

Need some structural advice for my 4x4 loft frame.


Here again, with another question for my tiny house. This time, it has to do with the design for my lofts.

I will have two lofts (one for sleeping and one for storage)..so each loft should never have more than 500 lbs on top of it. My walls are framed with 2x4's and I also attached a few pictures that I dug up for reference. The picture with the 2x4 beam is just a mockup to show the height of the loft. The picture of the underside of the loft is what I am aiming to achieve.

In Energy efficiency and durability | Asked By Grey Wolf | Oct 12 17
1 Answer

Under slab vapor barrier at two levels

I am retro fitting a existing slab on grade barn into a home , in order to accommodate plumbing, the run of the stairs and other , I am raising the floor. 2 to 4 inches of sand will be added followed by 3 inches of reclaimed XPS , then a 4 inch stained concrete finished floor. Typically I would top the foam with a vapor barrier, however there is a vapor barrier under the slab now. So I wonder if having 2 vapor barriers separated by the original concrete , sand , and foam creates a problem. Basically the sand and any moisture in lower concrete never dries out..

In Green building techniques | Asked By scott mangold | Oct 12 17
4 Answers

Tiny house subfloor insulation and moisture management

First, I want to thank you for all of the fantastic information you've put out on this site! The forums alone have been incredibly helpful in planning my tiny house design.

I'm at the point of buying materials and building the subfloor and I'm running into a couple issues that I haven't been able to find answers to here, or anywhere else online.

I have a 24' trailer with steel joists flush with the top of the outer frame. They're on 16" center running the width of the trailer and there's steel flashing underneath the trailer that will let moisture out, but can support insulation.

In Green building techniques | Asked By Eli H | Oct 11 17
8 Answers

Attic and wall insulation

I know these questions are asked continuously and I have read for days to try and answer this myself but I can't find a clear answer.
For several different reasons I won't go into I am leaning towards a polebarn structure for the exterior. I am located in E TN.

In Energy efficiency and durability | Asked By User-6896983 | Oct 11 17
7 Answers

Foam first or last in cold enclosed porch floor?


I have seen this question answered many ways while searching online, so I thought I would pose it here. I know there is another thread on this topic, but it seemed worth posting again.

When insulating an enclosed porch that is not climate controlled, should the layering be: pink foam board affixed to the floor underside, fiberglass batts, plywood for vermin control?

Here's the application:

In Energy efficiency and durability | Asked By JonesyHome | Oct 12 17
2 Answers

Spray foam in unfinished attic?

We are building a home in Zone 6. The room above our three car garage will remain unfinished for some time. Long term intent is to make a guest quarters.

While the room is unfinished (no insulation, no heating or cooling) the insulation folks recommended a thin coat of closed cell foam spray to temper the space somewhat and reduce the swings in temperature.They also tell us that it might avoid condensation. They suggested 1 1/2" foam in ceiling, no insulation in walls. The roof on the house is a shingle roof. The rest of the house has a spray foam "hot" roof.

In Energy efficiency and durability | Asked By Frank Torti | Oct 12 17
4 Answers

Is it advisable to have a furred air space between cedar siding and zip system sheating?

We are designing a house in Westchester County, New York.

In Energy efficiency and durability | Asked By user-6750330 | Oct 4 17
Register for a free account and join the conversation

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