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!

7 Answers

Workshop with dwelling above: Heating advice?


Asked By User-6964558 | Dec 12 17
5 Answers

Making sense of the first month of minisplit heating data

I have 4 Fujitsu mini splits (non xlth) hooked up to (2) 24k condensers. They were primarily for AC but I'm trying to reduce usage of my aging 199k/152k steam boiler while the temps are relatively mild (Boston). Right now I'm using a 12K head per condenser, per floor, so 2 total. Dana had some good advice as the min modulation range was about 6200 BTU/hr per unit, and to run both units, so this weather seems to be the sweet spot for efficiency and load.

Asked By Kjmass1 | Dec 12 17
1 Answer

I am looking at installing a FHA propane furnace in series with my geothermal heat pump

I am looking at installing a FHA propane furnace in series with my geothermal heat pump so that I can remove the 20 kW electric backup and be able to install a generator. 1st, does this sound feasible? I see they are coming out with hybrid systems.

A relay on the emergency heat circuit would operate the damper and a limit switch would power the propane furnace thermostat when the damper was completely open.

Asked By TheoAllen | Dec 14 17
12 Answers

Drain Water Heat Recovery

I plan to install a drain water heat recovery unit in my new home. Does anyone know of any guidelines on sizing? For example,there will normally be 2 people in the house, but on occasion that could easily double or more as we have extended stay guests (a week or even more). And we will have a 65 gallon heat pump water heater.

As the DWHR units tend to get pricey due to the copper involved, I want to make sure I get the most bang for the buck.

Asked By Norman Bunn | Dec 11 17
4 Answers

Registry of net-zero homes?

Is there a database or registry for net zero energy homes in US? I tried to ask the question of our HERS rating provider, Resnet, but so far have not heard anything back. HERS index for our home is 35 before PV, and -8 after PV. While we did not live in the house for the whole year yet, it looks like we will likely meet 12 month zero energy balance. I would be glad to call our house net-zero, and be registered/recorded somewhere as such.
On the web, I find the following:
Several organizations offer formal net zero energy certification programs:

Asked By Lucyna de Barbaro | Dec 13 17
1 Answer

What’s my best option for retrofiting rafter bay venting up to a brick chimney?

Hi GBA community!
I'm in the midst of rescuing a friend's roof from poorly installed fiberglass insulation. Here's what I'm up against:
There are 2x8 rafters 2' o.c. on the south side of the house (a saltbox, built in the 1970's, in climate zone 6A). The thermal control layer currently follows the 4' kneewall, presumably but not definitely continuing under the plywood subfloor over to the exterior walls. The rafter bays are completely filled with fiberglass and there are signs of this causing mold to get a foothold. I haven't seen rotted wood yet, but there is staining.

Asked By David Bailey | Dec 14 17
17 Answers

1952 Cape Cod


First-time poster. In the past 2 months, I’ve read a hundred or so GBA articles and comment threads; I’ve been amazed by the expertise and generosity of the community. I’ve also read extensively at buildingscience and finehomebuilding -- I’m new to but very interested in building science. Here’s why:


Asked By Emerson W | Dec 11 17
10 Answers

Brick house insulation


My situation: I have a brick house, that initially had plaster and lathe walls. With the floor joists supported by inner wythe, and the joist ends embedded in the brick. I removed the plaster and restudded the walls with 2x4s.

My concern: On the lower floor, I insulated the stud bays with batt insulation. I thought this was a good thing, however, after reading your article I think I may have been mistaken.  I am beginning work on the second story and don't want to make matters worse.

Asked By 3rd Little Pig | Dec 9 17
5 Answers

Air sealing the cap of a double stud wall

I am currently building a double stud home in NH and am in the process of air sealing all exterior cracks with siga tapes. Since my builder decided to build the interior portion of the double wall after the exterior, we were left with a 4 inch gap between the two walls at the cap. We will be filling the 12 inch cavity with dense pack cellulose, so this gap at the ceiling needs to be blocked off. We decided to fill the gap with strips of plywood which has resulted in cracks on either side of the plywood filler that I'm worried may leak air.

Asked By Chris Roche | Dec 13 17
1 Answer

Window NFRC ratings and airtightness

I've read about NFRC rating. Intuitively, infiltration seems like it should be one of the more important considerations- if the window is leaking air, the U/R value seems secondary.

I'm looking at windows that are NFRC listed. However the NFRC listings on the website do not seem to include infiltration for many windows. You can navigate to the particular window via manufacturer and window type, and from there select the product line, which then brings you to a page with "General Information: and a ratings table.

Asked By C L | Dec 14 17
Register for a free account and join the conversation

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