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

Why did the beam at the top of my cathedral ceiling just start sweating after 5 years?

This spring the beam at the top of my cathedral celing just started sweating after 5 years of being dry all year. It started about a month or 2 ago,~ April.
The beam is actually a box beam covering an LVL. The roof, walls & gable end are insulated with open cell foam. The ceiling doesn't get wet only the beam.
No water entering during rain storms. We've never had a moisture problem actually we use a humidifier in the winter. We have a hot air geothermal heating system so the humidifier in the system can't maintain the correct moisture level.

In General questions | Asked By TheoAllen | May 30 18
3 Answers

Chimney downdrafting

I have a 1940’s home that is insulated well with new windows, and we find we get a pretty strong downdraft down the chimney when it rains or there is a pressure disturbance. I’m sure the flue door isn’t that great but there is a aluminum cap on top.

I’ve been keeping a window cracked in the hopes it pulls air from there instead although now in the summer that doesn’t seem like a great idea. I’ve seen balloons you inflate but I can’t imagine those defy physics of air pressure and temperature drops.

In General questions | Asked By Kjmass1 | Jun 1 18
1 Answer

Insulating the exterior of my stemwalls

Insulating the exterior of my stemwalls: The question is, should it drain between the stemwall and insulation, or outside between?

Stem wall-damp proof-drain-insulation or Stem wall-damp proof-insulation -drain?

In General questions | Asked By Mike Hall | Jun 2 18
13 Answers

Vented roof in the Pacific Northwest

I was interested in the brief thread started by Malcolm Taylor, referring to condensation problems for vented roofs in the Pacific Northwest:

http://www.greenbuildingadvisor.com/community/forum/general-questions/99...

It looks like there has been a flurry of research, mainly done by RDH, but I haven't seen much follow-up.

http://www.rdh.com/re-thinking-ventilated-attics-how-to-stop-mold-growth...

In Energy efficiency and durability | Asked By John Prospect | Jun 1 18
8 Answers

Metal roof on uneven strapping / purlins

My simple gable roof is built with trusses covered by OSB then underlayment then 2x4 strapping/purlins. The top chords of some of the trusses seem to be slightly bowed, because if I lay a straightedge from peak to eave, along some of those lines one or more of the purlins is up to 1/2" higher than the others. The roof has a 4:12 pitch and covers a 20' width and 48' length.

To install Classic Rib exposed-fastener panels, how much variation in the purlin height is tolerable?

In General questions | Asked By Jeff Cooper | May 31 18
2 Answers

Anybody know what kind of blown-in insulation this is?

My attic floor was insulated with about 3-4 inches of this material, which I have never seen before. My first hypothesis based on weight and texture is finely shredded redwood bark, but I have never heard of that material's being used as insulation. The attic was probably insulated between 1970 and 1995.

Does anybody know what this is?

In Energy efficiency and durability | Asked By frasca | Jun 2 18
1 Answer

Dehumidifier recommendation

What brand/model dehumidifier with pump do you recommend?

We just had our 1000sqft conditioned basement inspected for mold and were recommended to install a dehumidifier. We are in CZ4 humid. Thank you.

In General questions | Asked By FrankFulton | Jun 2 18
4 Answers

Insulate top of basement footing?

We have removed the slab from our basement and will be adding sub-slab insulation before pouring new concrete. I would like to preserve as much ceiling height as possible while still having a dry and comfortable basement. There will be a layer of 2 3/8" EPS (R-10) under the entire slab that is even with the top of the footing. A dimpled membrane will be placed on the interior concrete block walls and lapped over the top of the footing to direct any water to the interior drain tile. Concrete will be poured directly up against the the interior drainage membrane.

In Energy efficiency and durability | Asked By Andy Freeman | Jun 1 18
2 Answers

Can polystyrene foam be used as a thermal break on inside of exterior osb sheating?

I am in zone 5 and building with 2x6 framing that will be filled with 5.5 inches of open cell spray. I know that 1/2" is too thin for the exterior but have not seen any comments about putting it on the interior side of the osb . Thaks, Ohio Mike%

In Energy efficiency and durability | Asked By user-7030272 | Jun 1 18
8 Answers

Vapor barrier over/ under scribed sleepers on concrete slab

We have an out of level slab by over 1-1/2". We plan on gluing and screwing scribed sleepers to the concrete, applying a 6 mil poly vapor barrier over the sleepers and then screwing plywood to the sleepers and installing engineered flooring material. There is foam and a vapor barrier under the slab. My question is if I put another vapor barrier over the sleepers... will this trap moisture since there is one already under the slab?

In GBA Pro help | Asked By marc rubin | Jun 1 18
Register for a free account and join the conversation


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