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!

3 Answers

Chimney liner needed when converting from tank to tankless water heater?

I am planning to have a tankless water heater installed (not looking for full payback just want continuous water, more floor space, and less natural gas consumption).

I had a couple mechanical contractors come out today to give bids. One mentioned that if I convert to a tankless water heater that I will need to have the chimney lined for my furnace vent pipe. He stated that since they will be removing the vent in the chimney that is for the current water heater, that the furnace will need a liner now to eliminate condensation.

In Mechanicals | Asked By Aaron Phillips | Feb 3 14
1 Answer

Insulation and vapor management for walls against earth

Background: I have cement walls for a walkout basement and concrete slab on grade floor and I am trying to insulate without trapping moisture. I would like vapor permeable insulation and am trying to figure out how to both trap vapor from the outside earth outside, and prevent heat of the inside conditioned space from meeting the cold exterior surfaces. There is exterior drainage and some rigid foam outside the house protecting it but I once say wetness at the base of one wall. The floors are dry.

In General questions | Asked By Chris Campbell | Feb 3 14
4 Answers

Thermal mass question

I'm wondering how much I'll decrease the effectiveness of a 4" slab/ thermal mass by laying a thick underlayment (looks like a yoga mat) over the cement floor and installing a floating 5/16" engineered wood floor over that.

The 4" cement slab is insulated on all 5 sides with 4" of extruded polystyrene foam board.
I've been living in the home while I'm finishing it and I love how its working during these cold snaps.

So, my question is, if I put this floor & underlayment down, will I be decreasing the thermal mass's effectiveness by 30%, 40%, 50% or more? Is there a way to find out?

In General questions | Asked By Michael Belhumeur | Jan 28 14
4 Answers

Cord wood moisture storage

I do weatherization & occasionally run across people who store a cord or more of hardwood in their basements. They usually say that the wood is dry before they bring it in. I am dubious, and believe that this still adds significant moisture load to the house. In winter here, in southern Vermont, it is pretty dry inside, so anything with moisture content is going to release it into the house.

Are there any estimates available about how much moisture a cord of wood in various conditions would bring into a house?

In Energy efficiency and durability | Asked By Bob Rueter | Feb 3 14
1 Answer

Cathedral ceiling insulation method advice

I have a 1970s house with cathedral ceiling in the living room. We tried to get the house insulated up to code and need some advice. One insulation contractor came back with suggesting spraying 2" closed cell form in the cavity and add 8" fiberglass batt to make it R39. He called it a hybrid method. Does this work? Will moisture trap between fiberglass batt and the closed cell form creating condensation?

In Energy efficiency and durability | Asked By doris ng | Feb 3 14
6 Answers

What is the diameter of a 12" mushroom vent?

I know this may sound like a strange question, but I have a contractor who says the the mushroom vents that measure 15" across are called 12" mushroom vents because of how much air flow they actually let in!

In General questions | Asked By Susan Cockrell | Feb 1 14
3 Answers

XPS on exterior walls

I'm considering buying a house built with 2x4 walls and fiberglass batts. I want to install XPS on the exterior walls to add "R" value to the walls and reduce thermal bridging. My question is - is it necessary to remove and reset all the windows and doors to accommodate the additional wall thickness or is there a way to NOT remove the windows and flash them so they don't leak? I need help on this one. Is there a construction detail I could use?

In Green building techniques | Asked By Alan McLennan | Feb 3 14
1 Answer

BPI certification options

I live in Oakland, CA, and am seeking BPI Building Analyst and Envelope certifications. I have three options:

1. Self study plus paid field exams
2. online training plus field exams
3. Classroom instruction

In Energy efficiency and durability | Asked By Michael McVey | Feb 1 14
1 Answer

ERV or HRV in western NY?

Is there agreement yet, whether an ERV or HRV is best for cold winter/hot-humid summer? I am looking for a small one for tight well insulated 1100 sq ft with 80CFM bath exhaust fan,
120 - 300 CFM hood exhaust and a passive make up air vent in each room.

Here ERV is recommended:




In General questions | Asked By nashwaak river | Feb 1 14
1 Answer

Airtightness and mechanical ventilation

What is the limit point, in terms of airtightness, that a residential retrofit needs mechanical ventilation (with heat recovery)?

In PassivHaus | Asked By ilais igoumenidis | Feb 2 14
Register for a free account and join the conversation

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