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

Affordable backfill without sacrificing drainage?

My upslope lot results in one wall of the first floor performing as a retaining wall, with retaining walls extending some distance beyond on each side. About a 10% upslope behind the retaining wall as well. I will create a swale some distance above the house to direct most water away, but I still want to build in protection from potentially significant water during heavy rains.

In GBA Pro help | Asked By David McNeely | Mar 8 16
16 Answers

Make up air strategy

This is for a home being constructed in zone 7/8 Colorado mountains. The home will be built with attention to air tightness and will be blower door tested, an ERV will be installed. Heating system will be a direct vented propane boiler with in floor radiant and an indirect water heater.

The house will have a 600 CFM range hood and two electric clothes dryers, these appliances will need make up air provided in order to operate correctly without depressurizing the house.

In Mechanicals | Asked By Chris Armstrong | Feb 26 16
4 Answers

Flash & batt of conditioned attic

Hey Folks.

I'm building a new home in Zone 4 (Nashville, tn). It has a conditioned attic with mechanicals. I'm looking for the most cost effective, yet durable, way to insulate it r-38 or better.

My plan is to spray foam then follow up with a batt after furring 2x10 rafters with 2x4's. I can spray 3 inches of open cell for less than half the cost of 2 inches of closed cell. I'm thinking the OC is the way to go. OC is about $1,800 and CC is about $4,000.

In Green building techniques | Asked By C. Maglio | Oct 25 15
2 Answers

Does attic rafter vent size matter?

We are in NW Missouri between 5A and 5B. This is part of an addition with 24" centers. The insulation company installed some rafter vents but not all. What they did install is smaller than the rafter span. I am putting rafter vents in the rafters that do not have any and air sealing the recommended areas. Should I replace the smaller rafter vents with bigger ones, too, or will it make a big difference? Thank you for the input. Pictures attached.

In Green building techniques | Asked By Becky Parrish | Mar 9 16
3 Answers

PWF insulation with double wall - where to put the vapour barrier?

I have a log house that sits on a permanent wood foundation of 2x6 on 12" centers with R12 fiberglass insulation and interior vapor barrier. I'm in zone 7 or Canadian zone 2. To complicate things further I'm off grid with just solar. For heat we use wood and I've just installed a propane furnace to a) move air and b) heat the basement. There's also a pellet stove in the basement, but expensive and energy intensive. We haven't fully experimented with the furnace for heating the basement, but should do ok as want to put two bedrooms down there.

In Energy efficiency and durability | Asked By Derek Schmidt | Mar 9 16
18 Answers

Perennial cathedral ceiling ice dam issue meets hot roof twist

Martin Holladay, I can imagine you grinding your teeth at yet another tongue and groove cathedral ceiling issue! I thought I could be smarter than the problem. #fail

Background: of our design http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/designing-hv...

Problem: double-walled stovepipe penetrating cathedral ceiling / hot roof appears to be source of heat leak, spurring ice dam and interior condensation on cathedral room walls. (see photos)

In General questions | Asked By Randy Bunney | Feb 28 16
5 Answers

High humidity after a dehumidifier was installed

We have always had Humidity issues in our home. It was built in the 1930s, completed a complete removal 5 years ago. Roof is metal with spray foam insulation. The home contains an attic. Home is only 1,500 square feet. After installing new AC unit with standalone dehumidifier, Humidity still remains 55%+. Never has reached and stayed at 50% and has not gone lower. the dehumidifier just keeps running and running. The Cooling/heating company who did the install is very well known and does. Great work in the area.

In General questions | Asked By Erica Sayers | Mar 9 16
7 Answers

Not sure what to do with basement insulation plan

We had planned to use 1" XPS over the slab of our walk out basement and then finishing. We will also be using 2" XPS on the concrete walls. We had planned to seal all joints between the rigid foam, put 3/4" TG plywood over the floor XPS and then frame and install laminate. However, we have run into some headroom issues and the fact that one wall is load bearing and we have the issue of the stairs when run in the middle of the basement (not sure if these should rest on rigid foam). So, now we are thinking of just doing XPS on the walls.

In Green building techniques | Asked By Carolyn Farrow | Mar 8 16
16 Answers

Best type and location of air barrier

I'm in Zone 4A. I have seen much focus on using the interior drywall as the air barrier layer. This seems impractical, 1) air clearly flows easily in walls of homes here and that would essentially negate the value of the insulation, so stopping the flow (inside/outside) with drywall does little to stop the flow of heat & moisture with that air as it bypasses the insulation. 2) over the life of a home many penetrations to the drywall will occur and these will not likely be consistently sealed, ending your airtightness.

In Energy efficiency and durability | Asked By David Adams | Mar 8 16
2 Answers

Andersen 400 vs Pella 350

I am building a new home this summer and can say that windows are the most difficult thing that I've ever shopped for. Our home will be ICF to the eaves and spray foam in the attic. I intend on making sure it is well sealed and as energy efficient as possible within reason. I'm hoping to get some passive solar on the south facing wall, which is where most of the windows are located. I've been studying and pricing windows for a couple months now and have it down to two selections.

In General questions | Asked By Shawn Henson | Mar 7 16
Register for a free account and join the conversation


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