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!

15 Answers

Houston home

A would appreciate advice on a home about to be constructed in Houston, TX.

What would be best materials to use for:

1. Exterior walls. Would R19 walls be considered good?
2. Attic (Insulation underneath the roof or on top of ceiling)? Is Foam insulation recommended, if so what would work best?
3. Roof: would a metal roof be a good idea?
4. HVAC. Are minisplits recommended? Would supplemental heating be required if a heat pump is installed?

In GBA Pro help | Asked By Venkat Y | Jul 21 16
3 Answers

Net zero is not expensive?

I'm having a home built and am trying to go net zero with PV and an all electric home. The solar guy and some contractors are very surprised when I say it can be done with 4 kw of panels and fairly standard construction and heating system. I'd like to run my numbers by the wise advisers here and you can tell me if I'm wrong.

In Mechanicals | Asked By Brad H | Jul 20 16
56 Answers

Transoms and Ductless Minisplits


I am trying to heat and cool my second floor with one 12,000 btu ductless minisplit. I have heard that this is possible if I keep the bedroom doors open during the day to facilitate circulation of the hot or cool air.

However, does it get uncomfortable quickly in the night when the doors are closed. If so, I was thinking of putting in operable transoms over the doors. The only problem is they are kind of expensive (~$275 from transomsdirect.com). Attached is my floor plan. I will be putting ceiling fans in each bedroom so maybe the transoms would be overkill?

In Green building techniques | Asked By Jimmy Nguyen | Mar 10 16
0 Answers

You told someone that they could patch open cell foam insulation with

You told someone that they could patch open cell foam insulation with spray insulation from the hdw store. The spray "stuff" that I am familiar with is of the closed cell variety. Is it that to which you are referring? Please advise, as I have some holes that need repairing.

In Green products and materials | Asked By Kenneth Sayers | Jul 21 16
10 Answers

What is the best way to attach the sub-slab vapor barrier to the walls?

In regards to laying the 6 mil poly vapor barrier down prior to pouring the concrete slab...

Should the poly wrap up the side walls higher than the concrete floor level, and then be attached to the walls with caulk & furring strips that are anchored to the walls with Ramset nails?

- or-

Should the poly just barely wrap up the side wall, and be taped to the wall (with Tyvek tape or similar) so that the poly and tape are encased in concrete after the floor pour?

-or perhaps this connection is unimportant, as the slab will get caulked on this slab-to-wall joint

In Energy efficiency and durability | Asked By Adam Peterson | Jul 20 16
1 Answer

Does Low-e glazing affect plant growth?

There seems to be an ongoing discussion about this subject and not a final conclusion yet, I imagined maybe somebody on this forum could know better.

In Green products and materials | Asked By Jose Castro | Jul 21 16
10 Answers

R-35 wall assembly for a 4C Marine climate zone

I am about to build on a 85" rainfall, 6000 HDD and no cooling system (I can withstand a little heat in summer)

I'm thinking of (from outside in)
* 1" wood siding
* 1" of air gap with 1x3" furring
* asphalt paper as WRB and air barrier
* 3" 2pcf EPS as R10 sheathing,
* A 10" double frame wall filled with a total * of R-24 polyester insulation
* asphalt paper as air barrier and vapor retarder
* 3-4" interior wood finish

(see attached image)

In Green building techniques | Asked By Jose Castro | Oct 29 14
8 Answers

Dehumidifier: running too much OR poor energy efficiency?

I just installed a 30 pint dehumidifier in the basement of my single story 900sqft house.

It uses about 4kWh per day to maintain a set-point of 55%, as measured by a Kill-a-watt.

I'm in Chicago, Zone 5.

My electricity bill without the dehumidifier from March-April was about 200 kWh/month.

Last month, with the dehumidifier turned on midway through saw a usage of 240kWh/month. A/C has not been used yet.

How can I determine if that 4kWh energy usage is due to it just running too much (e.g., too small for conditions?) or if the equipment just takes too much energy to run?

In General questions | Asked By Jeff Watson | Jun 6 16
33 Answers

Dehumidification vs. ventilation in an existing house

I have done significant air sealing of our 1930s cape cod house in Virginia (climate zone 4) and it only recently dawned on me through reading various GBA blog posts that this air sealing is probably the cause of our high indoor winter humidity levels (ranging from 55% to 70%)

I understand that adding ventilation is the correct way to go, and the bathroom exhaust fan approach seems the most cost effective. However, before doing this I have a few questions.

In Energy efficiency and durability | Asked By Timothy Godshall | Jan 4 15
7 Answers

How to choose someone for an energy audit?


I am looking to do an energy audit of my house. What should I look for in regarding selecting a company/individual - certifications, etc. What qualities would a good auditor have - what questions should I ask and what should they be asking of me - utility bill history, etc.


In Energy efficiency and durability | Asked By Joe Watson | Jun 8 16
Register for a free account and join the conversation

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