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!


1 Answer

What's best method of converting a "semi-vented" crawl space with a rat slab w/no vapor barrier into an unvented crawl space?

Wondering how best to handle the crawl space of a tri-level in upstate NY (built in late 70's). The house is "semi-vented" (2 vents on the east wall half covered by mulch & soil on the exterior and 2 vents going into a garage on the south wall that have been blocked off with wood). Entrance to the crawl space is provided by 2 common doors from the lower level. The house is heated with hot water baseboard, and currently has fiberglass insulation between the joists... which plays out just like you'd think - the insulation is very wet throughout the crawl space.

In Green building techniques | Asked By Stephen Mager | Sep 9 14
1 Answer

Insulating an unvented low-slope roof

Been reading through many articles throughout the web discussing the varied approaches to insulalting different roof types in varied climates with various materials. that said I cant seem to find (or may have overlooked) approached to insulating my roof.

I live in Washington DC and here's what I have:

Flat roof comprising of (bottom to top):
2 x 8's;
Plywood strips;
2 x materials ripped to provide slope, laid on top of the plywood strips and installed to create a valley in each corner of the roof;
5/8" CDX;
2" thick Isoboard;

In Energy efficiency and durability | Asked By Alexander Brace | Sep 9 14
3 Answers

I need to show that 4" of EPS is weather resistant

I am working with a product from South Africa called Imison.
Web page: http://imison.com/

The core is 4" thick type 1 EPS panels that meet ESR1946/ASTM C578. I understand that 4" wide EPS is waterproof/weather resistant due to it's permeability rating and should satisfy the IBC in regards to being a water resistant barrier however I do not know how to prove it.

I need to prove that the 4" of EPS resist water, however if water does get in it can diffuse out.

In Energy efficiency and durability | Asked By Daniel Sterns | Sep 9 14
12 Answers

What is a capillary break between the footing and foundation wall?

Your details show a caplillary break between the footing and foundation walls. What is it? Is it continuous?

In GBA Pro help | Asked By Arthur Ratner, AIA | Jun 23 09
2 Answers

Vented crawl space insulation, Southern California

I'm in the early stages of rebuilding my house, which happens to have a ventilated crawl space. I believe I'm in climate zone 3B, and my project manager is encouraging me to simply use fiberglass batt between the floor joists to achieve the required R-13 insulation.

In Energy efficiency and durability | Asked By Mike Simanyi | Sep 8 14
12 Answers

Rainscreen siding with a very large gap

Reading about rainscreen siding systems it seems that the recommended gaps are typically 1/2" to 3/4" between the housewrap and and the back of the siding. Is there any reason why one couldn't do a very large gap using thicker furring material? Maybe around 3" or 4" between the siding and the sheathing for architectural reasons on a remodel? Would there be problems with having that large of a gap?

In Green building techniques | Asked By Kevin Hardy | Jul 26 14
5 Answers

Foam, cellulose, sealing, or none of the above? Benefits outweigh risks?

Hi – I'm a homeowner who has spent a ton of time reading a few dozen threads here (invaluable), other posts/articles elsewhere and have arrived at a crossroads…open to advice and/or questions I should be thinking about to help me arrive at a decision. I can provide as many details as needed on my energy audit, house location/construction/details, monthly energy expenses, etc. if necessary.

It boils down to this (Note: no need to use attic for storage/living space)-
1. Use blown-in cellulose in attic, lots of air sealing, CC foam in cantilevers/rim joist
Pro:

In Energy efficiency and durability | Asked By George G | Sep 8 14
21 Answers

Roxul for crawlspace stemwall? And a related detail.

Basic question: Is Roxul Comfortboard a suitable substitute for the usual interior rigid foam insulation in retrofitting a crawlspace? (House in zone 5, crawlspace floor is about a foot below outside grade, walls are CMU. drainage is very good. I do plan to use cut'n'cobble XPS in the rim joist area, to ensure good air seal. Homeowner very opposed to foam if it's not necessary, which has led me to look into Roxul.)

In Green building techniques | Asked By Andy Chappell-Dick | Sep 4 14
39 Answers

High levels of carbon dioxide in house

My house has high levels of CO2 / carbon dioxide, every room is between 1100 ppm to 1200 ppm according to an air quality test I had. There are only 2 grown occupants and it's a 1000 sq. ft. brick house. No pets or plants, gas stove / furnace / water heater.

The basement was the only area that had between 900-1,000 ppm of CO2. I've read ASHRAE likes to see under 1000 ppm of CO2. We do have headaches & drowsiness but aren't sure if it's strictly from CO2. For reference, our CO (carbon monoxide) numbers were all under 2 ppm.

In General questions | Asked By Jeff Watson | Mar 9 14
4 Answers

Why doesn't RESNET put more weight on air sealing in their proprietary formula for determining the HERS Index of a new home?

I recently was granted a HERS rating of 40 for my new ENERGY STAR Vers 3.1 home without renewables. The blower door test was CFM@50 Pascals = 95 and ACH50 = 0.27. My HERS Rater told me that the blower door test data has a minimal affect on the overall RESNET HERS rating. In my opinion and that of many professionals, air infiltration is the single most important factor affecting the energy efficiency of a new home. A new home with high R values for the walls and ceiling may be very energy inefficient if its air sealing is poor.

In Energy efficiency and durability | Asked By JOSEPH POLAND | Sep 7 14
Register for a free account and join the conversation


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