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

Roof leak argument for open-cell vs. closed-cell under roof deck

I have heard the same general argument used by several insulation installers (even BPI certified ones). They say that the use of open cell foam affords better leak detection protection and drying to the inside when it sprayed under the roof deck rather than closed cell foam.

GBA seems to favor closed cell based on my reading of the site posts. The house is in Zone 4 and has a standing seam metal roof that is about 6 years old. Any additional thoughts?

In Energy efficiency and durability | Asked By Woody McMahon | Mar 31 14
1 Answer

If a home will run on 100% solar electricity, is it still wise to spend extra $$ to make the home LEED or Passive certified?

If a home I plan to build will run on 100% solar electricity from PV panels on its roof, is it still wise to spend extra $$ to make the home LEED or Passivhaus certified?

The house will be in southern Oregon.

In Energy efficiency and durability | Asked By Eddie Bautista | Mar 30 14
1 Answer

Is AquaPEX safe for drinkable water?

I need to replace existing PVC domestic water pipe with a new pipe.
AquaPEX and polypropylene can be considered.

In Green products and materials | Asked By Andrzej Porwit | Mar 30 14
1 Answer

How much rigid insulation on the outside of this house?

Old farm house. Want to add proper amount of rigid insulation over existing clapboards and install wood siding.

In Energy efficiency and durability | Asked By Chuck Everett | Mar 30 14
1 Answer

What method would be best for insulating the exterior of a foundation and still permit the application of stone veneer?

I am wanting to maintain thermal mass inside my envelope so I would like to insulate the exterior of my new foundation. I am considering mineral wool (rock wool) but am not sure about several issues of concern. I am hoping to use the compressed 3" batts for an R10 value but am unsure exactly how to apply.

FIRST: If I apply rock wool to the exterior of the foundation - how should that be done? Should I use some form of furring strip? What could I use that would withstand burial for 30 yrs.
SECOND: If applied on the exterior - what would the pros/cons for insects and termites?

In Green building techniques | Asked By Ralph Hertlein | Mar 30 14
3 Answers

Insulating the roof deck with both closed-cell and open-cell foam?

I am consulting on a home where the HO wants to have the insulation at the roof deck. They are thinking 2” of closed cell followed by 6” of open cell.

The HO put forward this idea.

2" closed cell at the roof first to provide the vapor barrier then followed by 6" of open cell which will be enough to encapsulate the top chord of the roof truss and minimize thermal conduction.

Does anyone have any experience with this type system?

Is there any concern of the two layers of foam de-bonding from one another?

In GBA Pro help | Asked By Mark Parlee | Mar 29 14
1 Answer

Old brick with closed-cell foam on interior - Exterior paint?

I have read a considerable amount about the challenges of insulating brick homes. As I am in an historic district, interior insulation is my only option. From what I have read, closed cell foam is my best bet.

My question is how to best handle bulk water on the exterior of the home. It is a rowhouse with zero overhangs. Presently the front of the house is painted and the rear is exposed brick.

In Energy efficiency and durability | Asked By Wayne Weikel | Mar 28 14
11 Answers

Fireplace vs energy-efficiency

I'm striving for a net zero house in northern CA zone 11, which I think is a zone 3B on the US map. 6 inch blown cellulose walls with 1 " outside foam, R50 blown ceiling; mini-splits on each level. Here's the issue; my wife wants a fireplace for aesthetic reasons; I would prefer a wood stove with glass front as a supplemental heat source. . She's ok with an insert in the fireplace.
Is there technology that will make the insert a supplemental heater and not blow half my heat budget up the chimney when it's not on? Blowers to get more heat output? Your thoughts appreciated.

In Green building techniques | Asked By Michael McKinley | Jan 3 13
3 Answers

Improvement of older windows...

My son's home has a "great room" with lots of window area, including two double doors to a deck (one fixed glass panel and one door), rectangular windows above each door of nearly equal size (same width, slightly shorter), and two triangular windows at apex of ceiling/roof. These are 20+ year old standard thermopane wood windows of the time (seals appear to be intact).

In Energy efficiency and durability | Asked By Howard Gentler | Mar 24 14
3 Answers

Insulate knee walls

Situation: Currently have knee walls with no insulation behind them or the cathedral portion of the ceiling. The rafters are 2x6's. Ventilation is provided from vents installed between the exposed rafter tails. Blown in insulation is currently blocking off the top of the cathedral portion. I live in zone 5.

In Energy efficiency and durability | Asked By Jim Johnston | Mar 28 14
Register for a free account and join the conversation


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