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

Cupping shingles on brand new roof?

Hi everyone,

In General questions | Asked By Tony Johnson | Sep 27 14
8 Answers

Is continuous polyiso over plywood and concrete wall OK?

I have a 200-year-old timber-frame Cape in western Massachusetts. Last year we had Mass Save insulate the roof and three side walls with dense-packed cellulose. Unfortunately the fourth wall was an addition (70's or 80's) and already had fiberglass so the program couldn't do anything to improve it.

We are ready to tackle this final wall. Since the inside is finished we won't be removing the fiberglass but will be adding rigid foam to the outside.

From outside in our details will be:

  • 1 x 10 Ship Lap Siding (Vertical)
In Plans Review | Asked By Jamie Malcolm-Brown | Sep 30 14
2 Answers

Window & door header insulation options - Zone 5

2x6 stud walls, and the header’s have an inside and outside vertical 2x8, with the 2.5” center is empty. The outside sheathing is 1” polyiso with a foil (no OSB or plywood). I want to fill the headers before the windows are installed this week. Drying is to the inside, so no inside VB, and permeability is important. I was thinking 1.5” R6 Roxul ComfortBoard IS or 2” R8 EPS foam. I tried window/door spray foam, but the 2.5” gap was too large, and the foam just falls out to the floor. Am I overthinking this, and I can just stuff it with pink fiberglass?


In GBA Pro help | Asked By Jeff Conners | Sep 29 14
7 Answers

Proper Approach to Insulation Under Add-On Porch

We are moving into a house that has an enclosed porch area off the rear of the house. We assume it was once an open area that was later enclosed. It is now used as a pantry. Above the enclosure is a porch for the second level. The main home is solid brick (built 1910) and the porch enclosure appears to be wood framing with vinyl siding. It sits about 2 feet off the ground - e.g. you could walk under and see underneath to the joists. We haven't moved in but during the inspection I looked under and realized there was no insulation between the joists.

In Energy efficiency and durability | Asked By Historical Work | Nov 24 12
4 Answers

Finishing concrete floor (slab on grade)

The finished first floor of our house will be the slab (8"+ monolithic) and we'll be doing the work ourselves. I'm pretty sure we're going to use EcoProCote products to prep/stain/seal the floor because we've seen good reviews and reports of people using it:

Has anyone had experience using the EcoProCote products? Good? Bad? Alternatives?

In Green building techniques | Asked By Brian Post | Sep 29 14
2 Answers

How do you calculate the net free area of an attic vent?

How does a manufacturer of vents determine the Net Free Vent Area of a vent that they put on the market?

In Building Code Questions | Asked By George Sherry | Sep 27 14
4 Answers

Improving R-value of 2x4 wall in renovation with interior foam board

Hi gang,

Doing a renovation in MA, USA, and I need a little help... There's a 2x4 wall that needs insulating, and I'm not redoing the exterior of the building. It would be easiest for me to get the wall dense-packed with cellulose, then go over the whole thing with 2" foil faced foam... but I have a couple questions...

In Energy efficiency and durability | Asked By Eric Nash | Sep 23 14
1 Answer

Lawyers, Engineers and Builders Oh MY!

A place to debate or kill some time

In General questions | Asked By aj builder, Upstate NY Zone 6a | Sep 27 14
6 Answers

Flash and Batt in Reverse - Modular

Working on a modular residential project in CZ 6. In modular construction though, the batt is installed on the exterior facing edge of sheathing and closed-cell spray foam on the interior facing edge of the gypsum (serving as vapor barrier). Would this flash and batt insulation in reverse cause any problems with moisture transfer?

Also, if we could, does it make sense to add an inch of Poly iso or Roxul on the outside of the sheathing as a thermal break to the outside to increase R value and add a thermal break?

In Green building techniques | Asked By Chris Parker | Sep 26 14
3 Answers

Old house with no sheathing/vapor barrier

I have an old house with no sheathing or vapor barrier, just clad siding on top of studs. I have the interior gutted and I am set to add batt insulation and new drywall back as it was originally. Should I add felt on top of the insulation and under sheetrock as a vapor barrier...still allowing the wall assembly to dry to the outside? or will it condesate on felt in summer and rot studs/etc.

ps I am in SC...really hot/humid.

In Energy efficiency and durability | Asked By charles elrod | Sep 25 14
Register for a free account and join the conversation

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