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

Rooftop rigid insulation and solar panels

We are in the design phase of a modest story and a half house in SE Minnesota, zone 6. My builder suggested room in attic trusses for our upper floor, as well as a few inches of closed cell foam on the interior against the roof deck, followed by fiberglass or cellulose. I realized that may not be enough to control moisture in a cold climate and am debating getting a quote on 4 inches vs looking into rigid foam on the outside of the roof deck. One detail that makes it interesting is we are looking at a bonus room above the garage as well. We plan on using metal roofing of some sort.

In Green building techniques | Asked By Jeffrey O'Donnell | Sep 8 17
2 Answers

Installing a t-stat floor probe in an existing concrete slab?

Hello friends! Quick question here...

We are working on a remodel in a house with an existing in-floor radiant heating system. However, the house did not have a thermostat with a floor probe installed when the slab was poured.

We pulled up the laminate flooring, and polished the concrete slab, and would like to install a new t-stat with a floor sensor.

In General questions | Asked By Benjamin Wooten | Sep 8 17
3 Answers

"Thermoply" applications ?

"Thermo-ply" is an interesting material, less than 1/8" thick and sold as a structural sheathing that can replace OSB as an air barrier etc. I'm considering it as my main air barrier in my thick walls, as a web in Larsen like trusses, under my roof trusses both to support the cellulose above and as the air barrier over a service cavity' and as "tie" plates and around window & door openings for my double wall. My walls will have the primary air barrier on the outer face of an inner 2x4 wall with 2x4 top and bottom plates and an outer wall made of Larsen like trusses for studs.

In Plans Review | Asked By Jerry Liebler | Sep 12 17
29 Answers

More insulation on top of 3" or 4" foam?

If I spray 3 or 4" closed cell foam insulation in the attic (2nd floor), should I also include bat insulation to add to the R value? For example adding R15 Comfort Batt (Roxul) on top of the R21 or R28 from the Foam that I would get?

Do people do this? is this wise?

I'm in zone 5 and will live in this space. Would like to achieve air tightness with foam + the high R values that are recommended.

Foam installers are trying to convince me that 3" or 4" closed cell is more than enough and nothing else is needed.

Would love some advice.

In Energy efficiency and durability | Asked By eldarchik | Sep 7 17
12 Answers

Knauff JetSpray Insulation

Does anyone have experience with Knauff JetSpray mineral wool insulation. The demos look very impressive, as does the R-value, but I can't find any mention of cost or of anyone's experience using it.

In Energy efficiency and durability | Asked By Norman Bunn | Aug 5 17
7 Answers

Passivhaus total energy usage standard

One of the Passivhaus standards is that total energy usage including appliances cannot exceed 11.1 kwh per sq. ft. per year. If I have a 2800 square foot house, then if my total kwh usage is under 31,080 (11.1 x 2800) that is pretty good right?

Seems like that's a pretty low bar. Or am I misinterpreting?


In PassivHaus | Asked By Jimmy Nguyen | May 11 17
9 Answers

Open bedroom windows in a tight house

A general question. We are in the process of building an energy efficient house that will be tight and well insulated. My wife and I over the past 34 years have lived in Minnesota and now Montana. We have year around slept with a bedroom window open, including winter. I have been planning on having Panasonic bathroom fans regularly exhausting the house.

In General questions | Asked By Jay Erickson | Sep 10 17
10 Answers

Phantom Load - Ductless Minisplit


I have an LG ductless minisplit system. The condenser is an LG LMU480HV. There are 8 indoor units (6 wall units, 2 ceiling mounts) connected to the condenser. The system was installed and powered up in January 2017.

In Energy efficiency and durability | Asked By Jimmy Nguyen | Sep 7 17
7 Answers

Sizing a minisplit for supplemental heat

I've been asked to quote a mini-split for a ~832 SF yoga studio that's part of a larger physical therapy/gym complex in a recently renovated low-rise commercial building. The yoga studio has only one exterior (south-facing) wall with large windows; the other three walls adjoin spaces that are conditioned year-round.

Exterior surfaces [wall (185 sf net) , roof (853 sf) & slab floor (32lf exposed)] appear to be insulated; windows (85sf) and skylights (30 sf) are modern double pane. Maximum occupancy is reported at 15 people.

In Mechanicals | Asked By Jon Harrod | Sep 11 17
3 Answers

What heat source should I use for radiant floor in barn?

I had a PEX radiant floor system installed when we poured the floor of my workshop in our barn. The workshop area (with concrete) is 60 X 40 and the rest of the barn (with dirt floor) is 60 X 80. I've put up a wall, and will install a ceiling and insulation in due time to contain the heat in the workshop as best as possible. I have 60 solar panels on the roof and I would like the heat system to be electric for obvious reasons. I don't have a water line to the barn yet, but may have one in future. I'd prefer a closed system, I think, to not use well water.

In Mechanicals | Asked By greenfarmer22 | Sep 11 17
Register for a free account and join the conversation

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