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2 Answers

Should I vent polyiso roof insulation in a Hot/Dry climate?

Hello all. I am helping some friends retrofit their existing roof on a 1960's ranch stryle house. They would like to strip the current roof system and replace it with polyiso foam board (thickness to be determined), and standing seam metal roof system. My question is: should we create a vent between the attachment sheathing and the polyiso, or not. It can get to 110 F in the summer, and down to 15 F in the winter here. Any and all suggestions greatly appreciated

In Green building techniques | Asked By David Bushlow | Mar 2 10
2 Answers


In GBA's current article regarding the safety of foam insulation I see no mention of Icynene. Is this a unique (waterborne) product or just a trade name for a particular type of ureathane? Also, to someone without a chemistry degree, what are the real life risks of any of these products - especially to people highly sensitive to airborne chemicals. Too often I think we rely on the very indusatries that produce and install these products for our information regarding health and safety. Any independent input would be appreciated.

In Energy efficiency and durability | Asked By Brad Brotje | Mar 1 10
23 Answers

Double walls: where to locate the vapor retarder?

My new house will have a double-wall design, similar to what I did in '80, but better.... I think. In my present house I used two, 2x4 walls, insulated, around a 5 1/2" gap, stacked full or fiberglass batts; pretty normal, I guess. What I did NOT like about it, after years of thinking, were all the penetrations in the VR (vapor retarder) by electrical boxes, etc, and all the flipping metal strips over wires that were too close to the sheet rock. On my next house, I am planning on putting the VR on the outside of the inner 2x4 wall to avoid all the prior nuisances.

In Green building techniques | Asked By jklingel | Feb 21 10
2 Answers

Are Gel Fireplaces a safe environmentally friendly alternative?

The manufacturers all claim that these fireplaces are safe, non toxic, and require no venting. Is there any independent sources of information out there to backup those claims? Also I found out that these fireplaces burn one of two types of gel fuels; ethanol or Isopropyl based. Which is preferable?

In Green products and materials | Asked By Peter Schonherr | Feb 26 10
2 Answers

Open-web floor trusses

Wondering if anyone has experience with what I believe are called open-web floor trusses.
I like that they are made from lumber and not OSB. I also like that they have large holes in them.
The few pictures I've seen make them look much larger (deeper) that the average joist.
Is this in fact true?
If so, what is used as a rim joist?
Are there any well-known issues with their use?
I saw a photo of a sagging truss where all the nail plates had peeled back. Scary stuff.

In Green products and materials | Asked By Lucas Durand | Feb 24 10
19 Answers

Foundation options for expansive clay soils??

I am planning to build a super insulated home in the next year or so and would like to avoid using a basement. Our soils here in southern Saskatchewan (9000 HDD) are quite variable when it comes to clay content, but almost all of the homes in the local area (regular concrete basements on wide footers) eventually end up having some problems with foundation movement due to expansive soils. I was really hoping to use a monolithic slab (FPSF frost protected shallow foundation).

In General questions | Asked By Garth Sproule | Feb 15 10
12 Answers

A statement from Icynene

Those following the spirited discussion that followed the posting of "It's OK To Skimp On Insulation" may be interested to learn that a senior representative from Icynene has posted a response.

Paul Duffy, Icynene's vice president for engineering, posted his response today (Feb. 11 at 1:52 pm). Find it here:

In Building Code Questions | Asked By Martin Holladay | Feb 11 10
18 Answers

How do YOU mix the Air in your Home?

In North Texas, the standard is forced air...that's all we know how to do.
Air conditioning is almost mandatory and forced air has been the method.

I have read posts from cold climate folks that use radiant heat or a fireplace as the heat source and they do not even have an air conditioner or duct system.

The forced air systems that we have around here are MONSTERS.
The units are usually large and the duct work looks like an overgrown octopus.

The typical attic is the worst place for these units and the maze of ductwork...

In Mechanicals | Asked By John Brooks | Feb 24 10
7 Answers

Exterior PLYWOOD; is it OK as is?

I just read a couple of lengthy posts here, dealing w/ exterior sheathing leading to condensation problems, and I am confused. Maybe I got lost as the conversation shifted among exterior foam and several slightly tangential posts. Very possible. My concern now is this: Should I drill holes in my exterior plywood, or rely on edge gaps and plywood's permeability to minimize or eliminate condensation?

In Energy efficiency and durability | Asked By jklingel | Feb 23 10
3 Answers

Horizontal skirt of XPS at footer; useless?

This statement "For the cases examined, horizontal skirt insulation (at the footer) has a negligible impact on the annual sensible heating load" comes from the Conclusion section of a report "Analysis of Basement Insulation Alternatives", by Ian Beausoleil-Morrison & Briana Paige Kemery, Mechanical & Aerospace Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K12 5B6. The "skirt" (typically, in Fairbanks, AK) is a two foot wide piece of XPS that is installed horizontally on the outside of the foundation wall, just above the a footer.

In Energy efficiency and durability | Asked By jklingel | Feb 24 10
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