Q&A: A Forum for Green Building Experts and Beginners

[Click map to enlarge]

Please register for a free account or sign in to ask and answer green building questions.

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!

8 Answers

Will I have a dew point problem in the wall cavity?

I'm a contractor living in Southwestern NH and designed an insulation envelope for a house. From inside to the outside it consists off 1/2" plaster, 2x4 with 3-1/2" R-13 blown-in cellulose, 1/2" CDX plywood and a 5-1/2" polyurethane SIPS R-32. The SIPS has 1/2" blue board, 4-1/2" of urethane foam and 1/2" OSB. All seams in the panel will be drilled and foamed.

Does the cellulose move the dew point into the 2x4 cavity?

The total R value of the wall is R-45.

In Energy efficiency and durability | Asked By James Everard | Jun 7 12
1 Answer

Follow-up question about the roof

I just posted a question about the wall cavity. I should have asked about the roof which consists of 2x12's 24" O.C. with 11-1/4" blown-in cellulose R-40+ then 1/2" CDX and over that 5-1/2" SIPS R-32.
Over the SIPS I'm going to 1" strapping vertically and than 1/2" CDX to create a cold roof. I'll have over a R-70.

My concern is with insulation in the framing cavity I might be letting the dew point move closer to the heated side of the house.

I live in Southwestern NH.

In Energy efficiency and durability | Asked By James Everard | Jun 7 12
4 Answers

Installed Cost of Solar Hot Air Panels

I'm doing a little research, to get myself more up to speed on lesser known technologies such as solar hot air panels. Does anyone have experience or knowledge of how much these systems can go for professionally installed? I know there are DIY-ers out there making them, but I'm interested in a price range for a good quality installation, and I'm not sure by what means they are priced (ie solar panels are priced by the watt/kilowatt). Any thoughts?

In Green products and materials | Asked By Mike LaCrosse | Jun 7 12
8 Answers

How to best use fiberglass batts for insulating a suspended concrete slab

I live in western Wyoming, zone 7. I am building into my uninsulated barn to add a bedroom and mudroom onto my house. The barn is on an existing uninsulated slab. We want to suspend another concrete slab on joists with hydronic heating in the suspended slab.

In General questions | Asked By Justine Wysong | Jun 7 12
3 Answers

Icynene over exising drywall cathedral ceiling?

I had convinced myself to remove all the drywall from my cathedral ceiling, have closed cell spray foam applied to R15 against the roof sheathing, re-install the R35 fiberglass batts, and then have new drywall installed. I just read something interesting on the Icynene web site:

In Energy efficiency and durability | Asked By Vertume Dufault | Jun 6 12
2 Answers

We are modeling a net zero house in REMrate. The house scores a -6 HERS yet it still uses 3.1 MMBtu more than it produces?

Isn't a 0 HERS supposed to reflect a net zero house?

In Energy efficiency and durability | Asked By Kent Mitchell | Jun 6 12
4 Answers

How much AC tonnage do I need for a 6,700-sq.-ft. house?

I am building a 6700 sqft house in Brownsville, Texas. The house is not the usual wood frame but is being built from Areated Autoclaved Concrete also called Hebel Blocks. This is a very efficient insulating material. The inside walls are 6" thick and the perimeter walls 8. The ceiling heights vary from 10' to 18'. The living room has 6 windows that at 9'x6' and 2 windows 9'x2.5'. The rafters will received 6" open cell spray foam.

In General questions | Asked By Omar Jalil | Jun 6 12
21 Answers

Vapor-open exterior sheathing

In building up a list of vapor open exterior sheathings to recommend for cold climates (with the goal of creating walls that can dry to the outside and can accomplish the recommended 5:1 outside to inside perm ratio), I've found myself a bit stumped by how to measure the permeance of traditional diagonal 1x white pine sheathing.

In Green products and materials | Asked By Jesse Thompson | Jul 30 10
0 Answers

HRV/ERV and placement of intake


I was contemplating adding mechanical ventilation to my home in the Boston area. I've got a couple of questions I was hoping all you experts could help me with:

1) HRV Vs. ERV: Reading through the posts on HRV/ERV, I am still confused as to what would be the appropriate choice for my geographic location (Boston, MA). Some say HRV and others point to an ERV. We don't have an issue with moisture on the windows in the winter and during the summer the house "feels" humid for only short periods. Any thoughts on a choice here?

In General questions | Asked By Allan Wood | Jun 6 12
7 Answers

Wall assembly review?

Hello, again, GBAers.

I'm in the planning stages of a ~1850 sq. ft. PassivHaus-compliant home in Salt Lake City (5B) [1]. After reading Martin Holladay's post on the Belgian PassivHaus home rendered uninhabitable [2], I am hoping to get some feedback on my wall assembly design [3].



[1] http://1010-design.blogspot.com/2012/02/more-detail.html
[2] http://www.greenbuildingadvisor.com/blogs/dept/musings/belgian-passivhau...
[3] http://1010-design.blogspot.com/2012/06/wall-assembly.html

In Energy efficiency and durability | Asked By Jan Nielsen | Jun 5 12
Register for a free account and join the conversation

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