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

Is this a reasonable solar bid? — and other questions

Howdy folks,
I got my first solar bid today, from Consolidated Solar Technologies. For a 3.2 kW ground-mount array in Albuquerque, New Mexico, the total cost before the federal tax credit is $16,300, and $11,410 after the credit. This works out to $3.56/watt.

One thing I worry about is that their calculator shows a higher projected output than PVWatts does. Their tool showed 6,500 kWh yearly, but PVWatts shows 5,844 kWh. This is supposed to be a net-zero-enabling array, so I don't want to underproduce. I'm using 6,500 kWh for my yearly usage

In Energy efficiency and durability | Asked By Nate G | Dec 5 16
2 Answers

Insulation options to add R-value

I had the opportunity to reroof this spring and add exterior rigid foam. I used foil faced polyiso 2.75" thick. Due to time and money constraints I applied a single layer taped and foamed. Through fastened wth .5" OSB cut into 3" strips. A new OSB deck was installed and asphalt shingle roof on top of that.

In Energy efficiency and durability | Asked By David Mosijchuk | Nov 23 16
3 Answers

Batt insulation

I'm in the process of buying a home (Metro New Orleans, Zone 2A, very warm and moist) for my daughter and noticed the attic insulation was installed with the Kraft paper facing up. That problem is being corrected by the seller, but now I wonder if the wall insulation was installed incorrectly as well. When given an opportunity to re-inspect this coming Monday I will be removing electrical covers and other things to see if the insulation problem continues with the outside or exterior walls.

In General questions | Asked By Bill Stretzinger | Dec 6 16
9 Answers

Can this assembly work for a flat unvented wood roof in Atlanta, GA (Zone 3)?

Hi all, I am building a flat un-vented wood roof in Atlanta, Ga (Zone 3) and I want to make sure I am doing it correctly. The assembly that I have so far is:

-TPO roofing
- 1/4" exterior grade drywall cover board
- 2.5" Tapered insulation
- 4" Rigid tapered Insulation
- 2" Rigid Insulation
- Waterproof Coating on osb / or peel and stick waterproof membrane
- 5/8" osb
- 2x10" beams (all at the same height)
- 2" closed cell spray on foam insulation
- 1 layer 5/8" type x Drywall
- Resilient channels
- 1 more layer 5/8" type x drywall

In Energy efficiency and durability | Asked By A Patel | Dec 6 16
6 Answers

Exterior foam application and window details

Im in Phoenix about 6 months away from starting my build. I was thinking about upgrading my exterior foam from 1.5" to 3" EPS. The window detailing is where my question lies. I've read the articles here, but we will be using mostly EFIS for our exterior cladding (with some stone veneer). My thought was to nail the window to the exterior after the OSB and Tyvek stucco wrap just like you would without using foam. Then add the 3" of EPS right up to the edge of the window and just add the EFIS to the 3" return created. For the stone veneer we will just frame out the window the 3 inches.

In Green building techniques | Asked By Jeffrey Savage | Dec 6 16
5 Answers

Interior walls acting like exterior walls

New construction in zone 5. We have 3 interior walls that we have to build up still where the vaulted ceiling meets the flat(see pic). We are planning unvented on the vaulted side (3" closed cell, and fill the rest with cellulose, but just blown in cellulose on the flat ceilings. How would you recommend I build and insulate this wall? I figure I need to treat it like an exterior wall, so drywall, studs filled with fluffy and 3" of rigid foam?(that is what we are doing for our other exterior walls). Thank you in advance.

In Energy efficiency and durability | Asked By Michael Brackett | Nov 29 16
3 Answers

Insulated impact-resistant windows

I have a house in Florida (climate zone 2a) with windows facing west. We replaced all windows and sliding doors with white aluminum frame impact rated, insulated, low e glass with grey tint. The specifics on the windows are: Insulated, large missile, Low-E = Windoor GR2, grey tint, 3/4"
NFRC ratings: U factor =0.61, CR = 16, SHGC = 0.23, VT = 0.29

In Energy efficiency and durability | Asked By Pamela Greacen | Dec 6 16
9 Answers

How do I determine the size of a ductless minisplit?

How do I determine the size of a ductless mini-split Heating and Cooling for my new to me Cottage type home built in 1925.

It is 36 feet wide by 26 feet deep. It is an open ceiling type to the roof rafters about 12ft high at the center peak with R-19 insulation, the walls are R-13, Two inside rooms/divider walls with no ceilings (open concept).

The two side outside walks and the front wall get no sun there Is total of 9 double pain windows on these walls the back wall 30ft long has 10 single pain wood frame windows that slide open from right to left.

In General questions | Asked By Mitchell Thompson | Nov 1 16
7 Answers

Is this a valid way to measure heat load?

Our manual J calculation said that the heat load of the house is about 30K at about 65 degree delta T. (It was more precise than that but I don't have the report handy, so I am going from memory.) I am hoping to confirm that the actual load is not too far away from that before we get into really cold weather.

In Mechanicals | Asked By Reid Baldwin | Dec 5 16
14 Answers

How to employ a mixing valve in a closed loop radiant heat system

We are just wrapping up the new roof on my project house and now its [past] time to turn our attention to HVAC - or, more specifically this time of year, Heating! This 1975 house came with radiant heat ceilings as the only source of heat. Recently we have been having night time lows in the teens and daytime highs here in Northern Nevada zone 5 at 5000 feet are usually in the 40's. I have done some preliminary calcs on heat gain/loss, and plan on doing a full Manual J model before laying out any cash for components.

In Energy efficiency and durability | Asked By Roger Smith | Dec 1 16
Register for a free account and join the conversation


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