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

What is the R-value of blown in cellulose at different densities?

for a 2x4 wall
1-2 pcf = ? R-value
3-4 pcf =
5-6 pcf =
7-8 pcf =

for a 2x6 wall
1-2 pcf =
3-4 pcf =
5-6 pcf =
7-8 pcf =

What I really want to know is if there is a density where the R-value begins to decrease because it is too dense.

In Green products and materials | Asked By Tim Leasure | Jan 30 16
13 Answers

We are planning to re-roof our house with metal

I am not a builder, so please bear with me. Our house is in Northwest Florida, a red brick ranch style built in 1960. We currently have GAF Timberline shingles that were installed in 2000 and they are failing. We are planning to re-roof with white Galvalume snap-lock panels, the kind with the tabs on the panel with slots.

In Energy efficiency and durability | Asked By Donald Nelson | Jan 28 16
7 Answers

Evaluating HVAC schemes for retrofit?

I've been planning a major retrofit to our 100 year old farmhouse and its coming down to crunch time. No surprise here, but the HVAC system has been the most challenging. I'm hoping that the astute staff and readers of GBA can offer fresh critiques and/or alternatives to the proposed scheme.

In Mechanicals | Asked By Edward Odgers | Jan 26 16
6 Answers

Ventilation strategy

help with ventilation strategy.

My house will be tight, but unfortunately there are 3 leaky wood burning fireplaces. I will do my best to seal these dampers, but they are staying... So essentially I believe these holes will be the leakiest place. I have lived with soot smell in my last house weeks after I had a fire, simply because of negative pressure in the house.

So i guess in this scenario I am a fan of supply ventilation.

In General questions | Asked By Dean Sandbo | Jan 27 16
4 Answers

Cathedral ceiling ventilation baffle

I have a 12/12 roof over an attic that I am making into a storage room. I added 1/2" plywood onto the joists to make a rough floor. On one half of the roof a second roof was built over it at about 10/12 to extend the roof out over a porch. All three "roofs" meet at the ridge. I am building ventilation baffles between the rafters with 1x1's as the spacers and 5.5mm underlayment plywood as the baffle panels. The sheathing is old 1" boards on the rafters with 1/2" OSB over that on the single roof side. On the double roof side it is 1" boards throughout with OSB only along the upper 24" or so.

In General questions | Asked By Doug G | Jan 28 16
7 Answers

Cathedral ceiling venting?


Just looking for a little help with my Ceiling. I built a new log home this summer and made a mistake with my cathedral roof. I was told by a relative to use a new method of 1" of spray foam and roxul R30, the 1" of spray foam would be enough to not need to vent the roof.

In General questions | Asked By John Hunt | Jan 24 16
46 Answers

How to install bathroom exhausts in an airtight house?

I am in the planning stage of my new home build. I am planning on using advance framing techniques with 2x6 studs, 2" polyiso rigid foam on the exterior, open cell spray foam in the wall and unvented roof.

After all that effort and extra expense Im suppose to place 4, 6" holes in my wall for my bathroom exhaust fans with nothing more than a meta flap to keep air from coming back in? Same for my dryer's exhaust. Seems like a lot of air intrusion points.

In Green building techniques | Asked By Jeffrey Savage | Jan 7 16
8 Answers

How to properly insulate a vented crawl space?

From the articles I've read on this website I know most people prefer a basement, slab on grade, or a sealed crawl space to a vented crawl space. Unfortunately a basement isn't an option due to high ground water and apparently in Idaho (where the new build is taking place) the vented crawl spaces out perform the sealed crawl. There aren't any slab on grade homes in the area and our builder isn't familiar with them, so we are trying to avoid it if possible.

In Energy efficiency and durability | Asked By David Voros | Jan 28 16
6 Answers

Access to crawl space through masonry stem wall

My small, one-story, wood-framed house will be built on a masonry stem wall three courses (24") high that will support a raised wood floor. My locale requires continuous rebar along the top course, so the top course will be bond-beam blocks. I need to install an access opening through the stem wall (through the interior floor is not an option), and code requires at least a 16" x 24" opening.

In General questions | Asked By Jeff Cooper | Jan 28 16
2 Answers

Long electrical wiring home runs


In General questions | Asked By C. Maglio | Jan 28 16
Register for a free account and join the conversation

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