Q&A: A Forum for Green Building Experts and Beginners

[Click map to enlarge]

Please register for a free account or sign in to ask and answer green building questions.

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!


9 Answers

Comparing Window performance

I am trying to compare apples to apples on various triple window brands. When folks here quote the U value of a window I assume they are talking about Uw (whole window). I was told by a vendor that that value varies with the size of the window. What window size are people assuming when they say the U is a certain value?

In Energy efficiency and durability | Asked By Elizabeth Kormos | Feb 14 12
3 Answers

Drylock and basement insulation retro-fit

A follow up question after reading "RR-1108: Hybrid Foundation Insulation Retrofits: Measure Guidelines." As detailed in one of the alternatives in that article, for my basement retro-fit I am planning on using foam panels installed directly to the foudation walls, as the first step towards coverting the basement to conditioned space (playroom). I will likely use foam panels or plywood with a bubble mat (like dry-core) for the floors.

In General questions | Asked By Rick D | Feb 14 12
6 Answers

Efficient HVAC for small apartment

I have a 500 sq ft garage apt with 20+ year old central electric heat and AC that I want to upgrade to a more efficient system. Since it has two rooms and ductwork, I'm thinking a mini-split is not the best option. I now have natural gas and could put in a 95% efficient gas heater (more efficient than electric heat of any kind I think). A 1 ton AC unit seems like a good option for cooling but I can't find one, only a single stage 1.5 ton unit which is overkill. My nephew is an HVAC installer in Texas and he has recommended a 2 stage 2 ton unit that will act as 1.25 ton in lower stage.

In Energy efficiency and durability | Asked By Dorothy Prowell | Feb 14 12
2 Answers

Is there a problem with too much attic ventilation?

As I finalize the soffit & vent design for my new home, I'm coming up with some out of balance numbers.

The attic area is ~4200 sq ft (this include space over garage). Garage will be insulated and drywalled, preped for heat but not heated at first. Using 150:1 I come up with an NFA req of 28 sq ft or 4032 sq in.

Half of the roof has a 8:12 pitch, the other half 6.5:12

Due to the roof configuration, I'm planning on using ventilated ceiling treatment, such as invisivent) on the porch ceilings to add to the middle roof intake ("true soffits are minimal here).

In Energy efficiency and durability | Asked By Jim Orasky | Feb 14 12
11 Answers

Fighting the inspector- double stud wall NOT "ci"!

This is how great building officials can be. I am working on getting my project qualified with the HERs raters and Energy Star programs to qualify for new construction rebates from local utility companies. However the inspector is claiming a double stud wall does not comply with IECC 2009 since it does not have r5 ci / 13 cavity as well as r5 ci at the box sills. I am trying to explain to him the double stud wall achieves the same thing ci does, not to mention my walls are roughly r40 overall.

In Building Code Questions | Asked By Jesse Lizer | Feb 13 12
4 Answers

Geothermal considering heating and cooling

so I've read a few threads here discussing geothermal (ground source heat pump) but they all seem to focus on the heating only. I have a limited yard and consider the ditching of the AC unit a big win. Is there research looking into the efficiency of geothermal vs AC unit? and comparing the entire HVAC system? Also, since I know that it's a split at best with a good heating unit, has there been much looking into split unit systems?

In Mechanicals | Asked By Michael Lutkenhouse | Feb 13 12
3 Answers

Basement retrofit--is a waterproof membrane necessary between foundation and sill?

In "BSI-041 Rubble Foundations note" Dr. Joe describes a recipe for fixing old leaky basements. Among other things, he recommends jacking up the foundation and inserting a waterproof membrane between the sill and the foundation in order to break capillary moisture transport. Which makes sense to me. But in a different recent publication from BSC titled "RR-1107 Final Retrofit Pilot Community Evaluation Report," only one of the six deep energy retrofits described has that feature.

In Green building techniques | Asked By Bennett Sandler | Feb 12 12
6 Answers

Interior foundation drainage plane

Question for the experts. I've been thinking about the ramifications of installing rigid or spray foam insulation directly to the interior foundation wall of a basement. Over the past 15 years I have built approx. 60 custom homes and I can think of 5 foundations that developed some type of leak after construction was complete. All leaks were easily fixed from the interior side. Two were tie leaks and three were hairline foundation cracks. One of the tie leaks showed up when a customer installed a lawn sprinkler system and a sprinkler head soaked a planting bed along the foundation wall.

In Energy efficiency and durability | Asked By Bruce Miller | Feb 12 12
5 Answers

Best economical way to seal a tongue & groove ceiling with rigid foam

My son's house has the notoriously leaky tongue & groove ceiling with fiberglass batt insulation. Our plan is to pull up the fiberglass batts and foam seal in rigid foam between the joists. Because finances are an issue, we will probably do it in steps and have to re-use the fiberglass over top. Then when it is complete, we will add blown in cellulose on top.
What would be the minimum thickness and best type of rigid foam to use for this?
When re-using the fiberglass, do we leave the paper facing on, or should it be removed?

Is this a sound plan? Any suggestions are welcome.

In Energy efficiency and durability | Asked By Jayne Masternak | Feb 11 12
2 Answers

Prefab soffit insulation baffles

Is anyone aware of a prefab soffit insulation baffle that offers a 2" chute opening? Fine Homebuilding had a recent article in which Joe Lstiburek indicated that a 2" airspace in the vent chute should be the minimum as opposed to 1" per code for best performance. A product from AccuVent was shown in the article, but it doesn't achieve that 2" opening. Are there any prefab alternatives available that do? If not, is there one that gets close? Thanks.

In Green products and materials | Asked By Milan Jurich | Feb 11 12
Register for a free account and join the conversation


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