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!

1 Answer

Miscellaneous Insulation Questions

Hi all,

I posted my first question last night after months and months of reading. Now that I'm over that hurdle, I thought I'd ask a few more about a house I'm building for my family in CZ 4A.

In General questions | Asked By David Baca | Jan 1 13
4 Answers

If we use spray foam on the inside of our attic, should we also use rigid foam on the roof?

If we use spray foam on the inside of our attic, should we also use rigid foam on the roof? This is being built in Upper MI.

We had an estimate for spray foam and along with spray foam. The company states it would then put 1" rigid foam on the outside of the roof. Is this normal practice, as I thought you insulate one side, not both? It is an A-frame with cathedral ceilings.

Must be vented by code, insulated to r-49 on roof, R21 in walls. spray foam was to 39 with 1 inch rigid foam on exterior roof. We are planning on putting 4 inches of rigid foam on outside walls.

In General questions | Asked By gary mccaslin | Jan 1 13
4 Answers

Open Cell roof deck or attic floor

Done my research, open cell foam is my preferred choice. Building a 3,300 sf house in Fort Worth TX. Pitch of roof is steep 12@12. House is single story. Considering the following two foam options, would appreciate feedback. Additional info, going with two a/c units (4 and 2 ton, both units are two stage. Also using erv air exchange to supply fresh air.

In Energy efficiency and durability | Asked By Jeff Bailey | Dec 29 12
2 Answers

Using a heater to raise the bathroom air temperature: a moisture question

In my home I use a small, electric kickspace heater to raise the temperature in the bathroom during showering. The elevated air temperature allows for the air to hold more of the moisture and raises the window glass temperature, reducing condensation on that glass.

In General questions | Asked By todd Stanley | Dec 31 12
6 Answers

Wall Assembly-Very Cold Climate Zone 7

I live in northern Maine and will be building a passive solar home. I want to achieve r-50+. Here's a rundown on my proposed wall assembly with three thoughts in mind; 1. high thermal resistance, air tightness, economical as possible. Any ideas/suggestions would be appreciated.

Pine board cladding
Drainage plane
WRB housewrap (ie. Tyvek)
3/4" fiberboard
2x4 outer stud wall (3.5" Roxul insulation) 24" OC
5.5" (or 7.25"?) cavity (Roxul insulation)-chase for electrical
Primary air barrier attached to inner wall (taped OSB treated with liquid vapor barrier)

In PassivHaus | Asked By Matthew Michaud | Dec 29 12
3 Answers

Surface bonding with epoxy


This question is too long. Sorry. Blame it on brain dumps.

I've grown up with farming where many times you don't have what you need, and have to make do. And later in life, I found out I am Autistic, which explains why it is hard to find engineering positions (I have an M.Eng. in materials science and engineering).

In Building Code Questions | Asked By Gordon Haverland | Dec 30 12
0 Answers

Cost Effective Building Options for High Performance Homes

I have observed a number of questions asked in this category and read many GBA articles on the topic. I have also heard of lumber shortages from super storm Sandy and challenges from snow storms and previous ice storms. Here are some ideas from our building project (agreenhearth dot com) and experience:

In Green building techniques | Asked By Patrick Walshe | Dec 31 12
44 Answers

13 reasons why foam fails?

Jetson Green just reprinted some blog content from 475 Home Building Performance, here is the Jetson Green post:
and here is the original from 475:

In Green products and materials | Asked By Adrienne Burt | Dec 18 12
5 Answers

Connecting a bath fan intake to a duct

My bath fan spot is in a bad place. Thinking about connecting it to a duct rather than having it sit directly above the bathroom. Any watch outs in doing this?

In Mechanicals | Asked By stephen edge | Dec 30 12
4 Answers

Raised-frame floor above slab

I understand the importance of super insulating the underside of a slab with large amounts of XPS foam, especially in my very cold climate (northern Maine). I have run across a unique foundation design of a passive house in Falmouth, MA, by architect Steven Baczek (http://www.deapgroup.com/Falmouth_PH.html). It involves insulating ABOVE the slab, essentially leaving the slab out of the conditioned space. His design involves 4" of XPS rigid foam resting on top of the slab, followed by 2x8 16" OC boards spanning the slab, resting on a 2x4 strut. 3/4" T+G subfloor covers the 2x8s.

In GBA Pro help | Asked By Matthew Michaud | Dec 30 12
Register for a free account and join the conversation

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