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

ERV or regular bath fan?

I am currently doing a 420sqft extension on the back of my house that includes a bathroom. All of the outside walls have been sealed on the inside with spray foamed at all of the seams, and the outside has been wrapped in Tyvek and 1/2 foam before vinyl siding. All of the drywall in the extension will be sealed with gaskets per ADA. The whole house including the extension is insulated with Roxul mineral wool. The original part of the house is not sealed per ADA, but is wrapped in Tyvek paper and .5 foam - I believe the seams are untaped. The house is heated and cooled with mini splits.

In Energy efficiency and durability | Asked By Kevin Schramm | Dec 8 14
1 Answer

New Home Build


I'm a long time reader. I've learned a great deal from reading these forums. We're building a new home real soon. Hopefully, we will be in this home a long time, and energy efficiency is important to me. I'm sure I'll have many more questions, but I'd appreciate any advice on the following to start.

Our home is 2,500 sf. It's basically a rectangular, two-story, shape. We are zone 4a.

In Energy efficiency and durability | Asked By C. Maglio | Dec 8 14
9 Answers

Ceiling air / vapor barrier... Is this a bad idea?

I'm still struggling with my ceiling air / vapor seal challenge. I'm adding R50 cellulose above my upstairs ceiling. I'm also trying to get the house air and vapor tight. In Minneapolis it's always either way too dry in winter or too humid in the summer.

In Green building techniques | Asked By Ryan Griffin | Dec 4 14
6 Answers

I can't find out how amps are converted to volts

As I said in an earlier thread I am making a solar powered usb charger. My solar panels have more than enough amps for the charge but the volts are behind at 7.71 and needs to be at 12. So my question is this: How are amps converted and how many amps WILL BE converted to supply the needed 4.3 volts more?
This is by far my favorite solar site.

In General questions | Asked By Shaye Miller | Dec 6 14
9 Answers

Noise from PEX/PVC drain pipes

We are at the stage of starting the framing for the new construction home in Pittsburgh. It is also a Passive House duplex. Our architect specified cast iron for domestic water drainage pipes (from shower and toilet, etc.), mostly on the account that these result in most quiet interior. For delivery of the water within the house, PEX is planned. Then we heard that iron pipes are more susceptible to clogging. Is some compromise, where pipes close to dining/living room are cast iron, and PEX elsewhere an OK option?

In General questions | Asked By Lucyna de Barbaro | Dec 6 14
7 Answers

Proper installation of 2 adjacent outdoor mini-split units?

We just finished a major renovation project that included sprayfoaming, all new windows, and one new Fujitsu Halcyon mini-split on each of the three levels. The temps are now dropping here in Maine, so we're finally getting a chance to experience the heating capabilities after a ton of research I did on this site and others (we do have backup electric heated floors and a propane fireplace ducted to the lower and upper levels as supplemental heat sources for brutally cold times).

In GBA Pro help | Asked By Phil Knutel | Dec 6 14
11 Answers

Vapor permeability of polyiso

Attached is a picture of foil-faced polyiso which as a bunch of holes in it. The holes were made with a wall paper removal tool which puts holes in the paper to allow liquid stripper to get behind the paper. I welcome comments on this approach to see of foil faced polyiso could be modified to allow vapor permeability thru the sheet if holes were done on both sides.

In Green products and materials | Asked By Dirk Gently | Mar 18 14
8 Answers

Span tables for dead loads above 20 PSF.

Does anyone know where I can find span tables or equations to calculate dead loads in excess of 20 PSF?

Every table I've found including IRC, AF & PA show dead loads of only 10 or 20 PSF. I'm looking to see my options for a pour over a subfloor I'm designing for an addition. I do plan on having a Structural Engineer double check my math and stamp the drawings, I just would prefer not to pay them and extra $500-600 to pretend like it took them all day to do a set of calculations for the floor joist, girder, and columns.

Thanks for any help in advance!

In Building Code Questions | Asked By Michael McArdle | Dec 6 14
6 Answers

Insulating a pier foundation floor in a marine climate

What's the best practice floor insulation assembly for a structure built on a very low pier foundation in a cold and wet marine climate?

I'm rebuilding a very small, very poorly-built, addition in south coastal BC (Canada). The addition rotted out, in part due to poorly managed roof runoff.

The climate here is damp year-round, with 50%-100% humidity. Temperatures go much above 60 F for eight months of the year. Winter means nine feet of rain with temperatures in the 40s (F) while summer means a few weeks of temperatures in the upper 70s (F).

In Energy efficiency and durability | Asked By Joe Smith | Dec 4 14
3 Answers

Plywood in the framing exposed to the elements for ~5-6 weeks?

Our new construction is in Pittsburgh, PA, mixed humid climate, quite rainy. We also usually have sleet and some snow in winters. The framing is to start 12/8/14. Windows and EIFS systems won't be installed until about mid-January or possibly later. Do we need to wrap the house in the Tyvek for the period before EIFS system can be applied? We thought of pre-treating plywood with liquid-applied weather barrier used in EIFS, but that can only happen at 40F and above and we won't have scaffolding/tenting until mid-January. The estimated cost for Tyvek is $800.

In General questions | Asked By Lucyna de Barbaro | Dec 6 14
Register for a free account and join the conversation

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