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!

0 Answers

Detailing WRB/Roxul/siding in retrofit

I am putting together a plan for a client to add 2" rigid mineral wool as a continuous exterior insulation upgrade. One-story 1974 ranch house, huge 4' overhangs, zone 5 NW Ohio. Existing walls are 2x4 with fiberglass batts and interior poly vapor barrier. Current siding is vertical pine board-and-batten. Already encapsulated crawlspace and insulated foundation walls, air-sealed in attic and blew in more insulation, so doing the walls is Phase 3.

In Green building techniques | Asked By Andy Chappell-Dick | Sep 30 15
10 Answers

Two choices for minisplit sizing

Trying to size a Mitsubishi Hyper Heat Mini Split:

Climate Zone 5A, Zip 01301, Heating Design Temp -2F (approx), second story space, 2 bedrooms and a hallway, 450 sqft floor area, R19 walls, ~R60 ceiling, ~30sqft window area in N and S walls, none on W or E. Don't know what to use for airtightness. 1890 farmhouse with dense pack in the cavities, membrain VB, thin polyiso backer for the vinyl siding that was installed over wood clapboards. I paid attention to airtightness details when I gutted this part of the house. I was estimating "average" tightness.

In Mechanicals | Asked By Brian C | Sep 25 15
49 Answers

PassivHaus Clothes Dryers?

I would like to learn more about how those building to the PassivHaus airtightness guidelines deal with the clothes dryer.

I did some internet research, but couldn't find much information on the CFM rating for clothes dryers. I'm assuming they are rated at 200 - 400 CFM, depending on the size the of the dryer. With the current trend toward bigger appliances, perhaps it's even larger than that . . . I don't know.

For a house built to 0.5 ACH50Pa, does this throw the system off balance? Do clothes dry? Is there enough air exchange?

In PassivHaus | Asked By Daniel Ernst | May 3 10
8 Answers

Polyisocyanurate IKO Enerfoil vs IKO Ener-Air?

I live in Quebec northwest of Montreal where it's next to impossible to buy Polyisocyanurate but a local store ordered it from IKO. After several weeks it finally arrived but it turns out to be IKO Ener-Air. The store owner said I could return the Ener-Air but he can't get me the Enerfoil for some complicated reason. I've already installed 2" EPS foil-faced rigid foam on my concrete block walls and was ready to add 1" Polyiso. So the question is can I use it as is or can I add foil to the IKO Ener-air to make this work ?


In General questions | Asked By domenic montagano | Sep 27 15
2 Answers

Whole house fan with conditioned attic?

We're building a house in the Northeast and the owner is insisting on a whole house fan in addition to central AC.
The attic will be a semi-conditioned space with foam insulation in the rafters. This means no outside air exchange.
Is there a way to put in a whole house fan and vent directly outside?
House is about 3000 sq ft.

In Mechanicals | Asked By Pete Dusenberry | Sep 28 15
4 Answers

Sub slab insulation with Superior Walls

Does anyone have a solution for how to insulate below a basement slab when using Superior Walls for a basement? The closest thing I could find was this link here:


I'm not exactly sure how they dealt with the edge near the walls. Is the gravel base graded at different levels to accommodate the different levels of foam?

Is the loss of R value in the floor near the wall a big enough deal to worry about?

In Energy efficiency and durability | Asked By Brian W | Sep 29 15
4 Answers

What are yourthoughts about studs left undrywalled?

I saw photos on Houzz of exposed interior wall studs - Prentice Architects and HS2 Architecture.
What are your thoughts? The light is attractive. What are your thoughts?

In GBA Pro help | Asked By Mary Schwaba | Sep 29 15
1 Answer

I live in Iowa and i'm want to know if it is necessary to have a vapor burrier on my ceiling if I have roof vents

I'm also considering installing a attic exhaust fan, not sure how to determine the size of fan I need.

In General questions | Asked By chris walker | Sep 28 15
3 Answers

Breaking the thermal bridge on the interior

I had a thought about a possible wall construction that I wanted to gauge with everyone. The primary reason I thought of it was for ease of building for a traditional builder - especially flashing complications and building out around windows if there was exterior rigid insulation. It involves using polyiso on the interior of a 2x6 stud wall. In my mind it allows me to use a thinner layer of rigid insulation with higher r value per inch, placing it on the warm side so it retains its r value in Michigan winters (climate zone 5). And it addresses the thermal bridging issue.

In Energy efficiency and durability | Asked By Brian W | Sep 27 15
0 Answers

Is makeup air needed for propane boiler?

We are building a 2200 sf house with closed cell insulation and heated this propane radiant heat. The plumber says I don't need makeup air. He says the HRV will handle it and I just need to put a louvered door in the mechanical room. Please advise. Thanks!

In Mechanicals | Asked By Peter Whitman | Sep 28 15
Register for a free account and join the conversation

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