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!

6 Answers

100-year-old single-pane windows, storm windows with low-e, or interior panels?

1. Is Low-E a good choice for all windows, or should it be selected for certain windows according to their location?

2. Is there any unbiased performance data available for storm windows? In particular Larson windows? I have found an interior panel (link below) that claims a U-value of .29 and has achieved Energy Star recognition. Can a Single pane, low-e storm window do a better job? I think it's worth noting that a single pane storm being mounted on the outside of a 100 year old window frame may reduce drafts entering the window frame area more than an interior panel.

In Energy efficiency and durability | Asked By b l | Oct 29 14
1 Answer


I recently purchased a 1930's brick and aluminum-sided two-family home in Teaneck, NJ. The insulation in the upstairs apartment is very old and dilapidated and lining the roof. The outside walls in both apartments are not insulated, it would seem. I would like some ideas about insulation. Can call me, too, 646-245-3801.



In Energy efficiency and durability | Asked By Janice Thill | Oct 29 14
5 Answers

Want to reduce indoor humidity in a cool, humid environment. Outdoor humidity >70% most of the year. Would an ERV be useful?

I live in a fairly new, well sealed house on the west coast of Canada. Ventilating indoor moisture most of the year is difficult as the outdoor humidity rarely goes below 50% and in spring and fall, usually in the 80-90% range, with temperatures averaging 40-60 F. I am researching ERVs, but unless they can reduce the humidity of the incoming air significantly, ventilation is only going to increase indoor humidity. Lots of condensation on the windows during fall, winter and spring. Air quality in the house is good.

In General questions | Asked By Bill Readings | Oct 26 14
2 Answers

Vapor retarder location


In Green building techniques | Asked By Ryan Lambert | Oct 29 14
11 Answers

Can I use R-15 rock wool batts in a REMOTE wall with R-20 exterior foam?

I have read many articles on this site (thank you) and am currently using some of what I have learned in my house construction in Ridgway CO. For reasons I need not go into, the house has two wall systems – the north and west walls are built from ICFs. The south and east walls will be 2x4 studs, plywood sheathing, Tyvek and two layers of taped exterior foam with an R value of 20.

In Energy efficiency and durability | Asked By Gary Dick | Oct 28 14
11 Answers

Minisplit - One indoor unit for two adjacent rooms?

Do any of the minisplit manufacturers offer a wall mounted indoor unit that will service two adjacent rooms? I'm considering a minisplit to replace the gas furnace and a/c in my 1300 sq. ft. single level home in zone 3A (mixed-humid). Without a shared indoor unit on the common wall between two bedrooms, I might need five indoor units. The multizone minisplits seem to jump from 4 to 8 zones and the price jumps too. I understand the technical problems with one wall unit serving two rooms, but have any of the manufacturers solved them.

In Mechanicals | Asked By Steve Robertson | Oct 23 14
101 Answers

Water - The Wonder and the Danger

We live on a watery planet. 70% of the earth's surface is water (the same percentage of water in our bodies). It is the font and sustainer of life (SETI looks for water on other planets as the sine qua non of life). So why have our modern "green" building practices turned it into a monster? And how can we stop fighting it and turn it back into an ally?

In Energy efficiency and durability | Asked By Robert Riversong | Nov 28 10
3 Answers

If I don't cool my home on summer, should I think like I'm in a cold climate when I design my wall assembly?

In regards to vapor difussion, in a mixed-humid climate, where no AC will be used in summer, should a Cold Climate wall assembly design work just fine?

In other words, does the special concerns we have to consider when designing a mixed-humid wall assembly, have to do with being able to work succesfully and withstand both heating and cooling seasons? What if I don't have a cooling season (No AC in my home), should I just use a cold-climate approach?

This is for Pucon, Chile, which has a climate like US's 4-C, or Marine.


In General questions | Asked By Jose Castro | Oct 28 14
4 Answers

Installing ductless minisplit over refrigerator

Building an 800sf 2 story house, main floor is 400sf open floor plan. Would there be any problems if I were to install the ductless mini split head above the refrigerator?

I was thinking of mounting it on the front of the soffit so it would be flush or slightly proud of the front of the fridge, allowing it to spread air down without hitting the fridge. It would also be further from the coils on the back of the fridge. I read that it should be 7-10" below the ceiling.

In Mechanicals | Asked By Tom Frisch | Oct 28 14
1 Answer

Rim joist thermal barrier

The rim joist in my unfinished basement is insulated with 3 inches of rigid polyiso along with one part spray foam to air seal around the edges. My understanding is that building code exempts up to 3 1/4 inches of spray foam in this area from the thermal barrier requirement, but that this exclusion does not apply to rigid foam boards.

In Building Code Questions | Asked By Michael Lee | Oct 27 14
Register for a free account and join the conversation

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