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!

5 Answers

Temporary bracing for small trusses

I'm installing standard trusses with a 20' span, 2' overhangs, and a 4:12 pitch for a simple gable roof. The truss drawings indicate that the only permanent bracing needed is sheathing on top and a drywall ceiling directly attached on the bottom, both of which I'll install.

In General questions | Asked By Jeff Cooper | Aug 12 17
1 Answer

Insulating over exterior brick - Do's and Dont's?

Hello, short time lurker, first time poster.

My wife and I bought a small pre-WWII home last fall. Sadly it was built in an era where the very concept of insulation and efficiency were unheard of.

It's a 1.5 story house approximately 1250 sqft. Double brick exterior. My goal is to energy retrofit as much as possible over the next 2-3yrs. That will start with insulating the attic this fall but I need a solution for the walls.

In Energy efficiency and durability | Asked By user-6901433 | Aug 13 17
2 Answers

Flash and Batt - what type of drywall?

Hi Martin:

I have just completed a Flash and Batt insulation in the basement of our home:
installed in 16" 2x8 bays - 2" Dow Corning Foamular and Roxul R22. All seams, foamed, caulked and taped.

Can I use regular drywall on top of this or do I have to use a special Paperless Drywall - I was under the impression that Regular Drywall is actually a vapor barrier and would have the same effect of retaining moisture as 6 mil poly???

Mark Kozlowski
Crawford Bay
British Columbia

In Energy efficiency and durability | Asked By Mark Kozlowski | Aug 13 17
5 Answers

Questions about installing EPS above concrete.

I'm in climate zone 6A, I think. Halifax, Nova Scotia. I've read that the best approach to insulating an existing basement floor is to install a continuous layer of 1" thick EPS foam over the concrete, with taped seams, and two layers of either plywood or OSB on top.

1) If EPS is vapour permeable why use tape to seal the seams?

2) I have existing partition walls that are screwed to the concrete with foam gasket in between, please tell me I don't need to remove them and put the foam under the walls?

In General questions | Asked By Calum Wilde | Aug 12 17
2 Answers

Trying to understand humidity dynamics.

The gym I go to leaves a large box fan on in the locker room 24 hours, presumably so the air movement will dry surfaces (wet floors). I can't imagine they would think it would help with wet clothing left inside the lockers. Accepting that this is inefficient, is it efficacious?

I also know of an archives building that keeps fans on low all the time, with the intent to keep historic articles—especially ones with fabric—from getting mildew. There is a dehumidifier in the room also that keeps humidity below 60%.

In Energy efficiency and durability | Asked By David McNeely | Aug 12 17
8 Answers

550' main water line to house : help me choose a suitable pipe

My driveway is 550' long, and the water meter is at the road. So far I have determined I should be happy with a 1.5" ID pipe, for the flow I am considering. I was all set to pull the trigger on HDPE pipe (NSF rated, 200 PSI), until I read some articles that claim this type of pipe becomes brittle with time when exposed to water disinfectants (read chlorine, chloramine, chlorine dioxide etc.), anything the utility puts in the the great lakes water to make it "safe".

So back to the drawing board. The options:

HDPE CTS 200 PSI pipe

In GBA Pro help | Asked By Mai Tai | Aug 10 17
2 Answers

Need to vent uninsulated crawl space in the Pacific NW?

I own an older house in Seattle which has both a basement and a crawl space. The crawl space has never had vents and has seemed to do fine thus far. However I just completed a basement remodel and the separation between the crawl and the basement is now more robust (insulated and reasonably well air sealed) than it was previously. I had planned to install vents after completing the remodel but after reading some responses on this site, I’m wondering if I really need to?

In General questions | Asked By Marlan Crosier | Aug 11 17
1 Answer

Pole building shop soffit vents a good idea?

I am in climate zone 4C and I'm about to have a pole building built with 2' eaves on a skillion sloped shed roof. I want to have the eaves soffited and the builder suggested using vented metal for this and has stated that it will help vent the building. Someday I will probably insulate the walls and ceiling in this shop. I will have the roof sheathed and I assume when I insulate, I will insulate between the purlins in the ceiling. Will the vented soffit work later when I insulate?

Thanks for any advice you all might have.

In Energy efficiency and durability | Asked By Kail Zuschlag | Aug 11 17
9 Answers

Floor truss spacing and sub-floor options for a "stiff" floor : opinions?

I am currently building a slab on grade home, with 24" deep open web floor trusses (24" selected with the intent of having (2) 20x21" house long chases to run low velocity HVAC ducts, supply and return and avoid bulkheads).

My architect, who is admittedly old school/conservative, specified spacing at 16" OC, with 3/4" ply sub-floor. The house is 30' wide, and the joists are basically designed to take this full span. However, I have a mid width supporting wall/beam in the design, which basically cuts the span in half (max span from wall to exterior wall is 17').

In GBA Pro help | Asked By Mai Tai | Aug 5 17
6 Answers

Peel-and-stick or Tyvek WRB?

Here is my proposed exterior wall assembly:

5/8 Drywall
Vapour barrier (for the building inspector)
2x4 studs at 12" o.c with 3.5" Rockwool batting
5/8" Densglass Drywall sheathing
2" Rockwool boards
cement board open cladding

I was commenting on other threads but thought I'd start a new one. I need the advice of the GBA members.

Question: Considering cost, performance and application, Should I use a SA membrane or Tape the seams of the sheathing and Staple on a WRB?

Self adhering membranes I've looked at:

In Project management | Asked By Jamie B | Aug 11 17
Register for a free account and join the conversation

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