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!

0 Answers

Inadvertant trap in mini-split line set?

I'm finishing the installation of my mini split line sets and realized I may have introduce a "trap" into the line set due to the way I had to route it.

The main line set runs from the compressor to the branch box in the attic. From the branch box, the line sets run down into one stud bay, in a 180 degree bend, through a stud, and pointing back up into another stud bay. This 180 degree bend is my concern.

In Mechanicals | Asked By Mike M | Jul 28 17
4 Answers

Ceiling Vapor Barrier

I am in the process of building a 12 inch double stud wall assembly with dense pack cellulose insulation. I am planning on wrapping the inside wall with a smart vapor barrier of either Siga Majrex or Intello Plus. I have heard Siga's Majrex is a superior product in that Intello has had some issues with trapping moisture from fall months when the barrier is mostly open, due to the transition into winter when the perm rate shrinks and the water has not had enough time to transmit out of the wall cavity. (This is advice I received from a retailer of Siga so I am taking it with a grain of salt)

In General questions | Asked By Chris Roche | Jul 27 17
2 Answers

Rigid foam over existing drywall?

I'm planning on converting half my garage to living space, and I would like to add three inches of rigid foam insulation and another layer of drywall over the existing drywall.

The walls are 2x4 on 16" centers with fiberglass batt insulation, plywood sheathing (or possibly OSB), house wrap, and vinyl cladding. Can you think of any reason why this technique might pose a problem in my northeastern climate?

In Green building techniques | Asked By Ben C. | Jul 27 17
2 Answers

Choosing between Mitsu and Fujitsu mini split, need advice

I'm debating between two contractors. One sells mitsubishi mini splits and the other sells fujitsu

I'm heating a finished room over my garage which is about 750 sqft and has awful(!) insulation in the roof. The Fujitsu guy said that an 18K unit should suffice but I've plugged numbers into a sizing calculator and I'm pretty sure that I need a 24K unit (~26K BTU heating required per the online calculator I used)

In Energy efficiency and durability | Asked By maquino | Jul 27 17
2 Answers

Hardwood floor in basement on concrete - new house

I’m building a house in CT and I have a question for the forum.

In (under) my basement, I have virgin dirt, 12” of stone, 2-3” of spray foam insulation, then 4” of concrete slab. I am looking to put down ¾” hardwood flooring, and have been given different pieces of advice on what to do.

I was told that I could put down another vapor barrier (6 mil plastic) and then ¾” plywood nailed to the slab, and then the hardwood on top.

I’m worried that if I put the poly on top of the concrete, then I will create a moisture trap around the concrete.

What would you do?

In General questions | Asked By MillerConstr | Jul 27 17
1 Answer

I have just had a SIP panel building constructed and concerned about a bathroom tile install.

I have just had a SIP panel building constructed and concerned about a bathroom tile install.
Master shower tile wall will be attached to Durock. ...
Should I put air space between Durock and OSB SIP wall? or possibly ice and water? or should we just attach Durock to OSB ?

SIP panel company is EPS - They had no strong opinion.

Thank you - Howard from Sturbridge MA

In Green building techniques | Asked By Howard Kelley | Jul 28 17
9 Answers

Best method for air sealing an existing tongue-and-groove (wood) ceiling? Sheetrock is out.

The Home is located in Zone 4 NC. Question #1 Any problems using closed cell spray foam on any

large cracks , in attic at ceiling plane. Then using blown in cellulose ?

Question # 2

Any best method for securing tongue and groove ceiling to prevent cellulose from pushing down ceiling ? Netting etc.

Question # 3

Thought of using Reclaimed Commercial Roofing foam board Fiberglass faced , using cut and cobble

at attic joist bays. Leaving small air gap from tongue and groove ceiling. My thought was it would

In General questions | Asked By Greenconfusion | Apr 13 17
3 Answers

How to insulate the 'attic' of a 4' x 14' bump-out with hip roof.

This 100 year old house will be getting exterior insulation (3" SPF is current plan). The attic was insulated with SPF with venting for the underside of the roof deck. Intend to tie-in the attic SPF with the wall SPF therefore the soffits were removed.

There are 3 bump-outs that could compromise the continuous layer of of SPF that we plan to add. The largest is 4x14 (exterior wall size) and has a hip roof. It is currently insulated with pink fiberglass; seen from the eves. Likely done 20+ years ago when the last shingles were installed.

In GBA Pro help | Asked By TIM LANGE | Jul 27 17
1 Answer

Hulstrunk's 100 Year Envelope

I am building a single story addition with a vented cathedral ceiling. I will be using double stud walls, parallel chord trusses and dense pack cellulose. I would like to avoid the use of foam.

I am wondering if any builders are using Bill Hulstrunk's 100-year envelope design.


In Green building techniques | Asked By user-6882359 | Jul 28 17
11 Answers

Curious on thoughts about insulation on a new house.

Will be building a house in southern ontario, cold in the winter hot in the summer. Been reading up on insulation techniques, as i like the idea of thermal bridging but hate the idea of trapping moisture in the walls as i have seen some ugly things over the years in renovations and what moisture can do. Im unwilling to put foam board on the outside and vapor barrier on the inside. Just seems wrong. So here is my thought. Build the walls, apply a one inch foam straight to the studs with a layer of plywood fastened overtop with tyvek.

In General questions | Asked By user-6782048 | Jul 25 17
Register for a free account and join the conversation

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