Community: Green building techniques

Q & A Instructions

[Click map to enlarge]

The 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

Capillary break sprayed on to footer

We are pouring footers next week and have to make a decision on how to provide a capillary break between footer and foundation wall. Specs in our contract builder call for a liquid applied product to be used, with a $250 allowance for that. The idea was to apply it before drilling in the rebar, then to patch as necessary after rebar is in place.

Now my builder is suggesting that we could instead have the waterproofing contractor spray Tremco Tuff n Dri on the footer after the rebar is in place. He would do this for $250, so it's within budget.

Asked By William Costello | Oct 14 17
1 Answer

Sealing up gaps in OSB exterior sheathing before insulating stud cavities?

My OSB sheathing on the exterior side of my exterior walls has many a gaps varrying from 1/8" to 1/4" as the proper installation instructions require the sheathing to be gapped with a nail to allow expansion due to humidity changes.

So...I'm looking at these gaps (some rather large) and getting ready to stuff mineral wool in. Should I take any time now to a.) caulk or b.) spray foam these gaps? I have a decent house wrap over the sheathing of course but that doesn't stop everything.

Asked By Nicholas C | Oct 13 17
1 Answer

Under slab vapor barrier at two levels

I am retro fitting a existing slab on grade barn into a home , in order to accommodate plumbing, the run of the stairs and other , I am raising the floor. 2 to 4 inches of sand will be added followed by 3 inches of reclaimed XPS , then a 4 inch stained concrete finished floor. Typically I would top the foam with a vapor barrier, however there is a vapor barrier under the slab now. So I wonder if having 2 vapor barriers separated by the original concrete , sand , and foam creates a problem. Basically the sand and any moisture in lower concrete never dries out..

Asked By scott mangold | Oct 12 17
4 Answers

Tiny house subfloor insulation and moisture management

First, I want to thank you for all of the fantastic information you've put out on this site! The forums alone have been incredibly helpful in planning my tiny house design.

I'm at the point of buying materials and building the subfloor and I'm running into a couple issues that I haven't been able to find answers to here, or anywhere else online.

I have a 24' trailer with steel joists flush with the top of the outer frame. They're on 16" center running the width of the trailer and there's steel flashing underneath the trailer that will let moisture out, but can support insulation.

Asked By Eli H | Oct 11 17
23 Answers

Lead paint, old clapboards, honoring history

I purchased an 1860 house in Beacon, NY, with 1820 masonry. The aim is to honor the history of the structure while updating the materials where needed with products free of fossil fuels.

Asked By Gregg Zuman | Oct 9 17
34 Answers

Insulating a low-slope roof

Hi Martin,
We are ready here to go ahead with the insulation of our low-slope roof, and decide to go with closed-cell sprayed foam as you recommended.

We had 3 quotes from local company, and 2 of them proposed to shoot 5-6 inches of foam underneath the 1st deck (in green in the following image), assuming we would remove the interior ceiling.

Asked By Francois Desrochers | Sep 6 17
3 Answers

Attic floor insulation and vapor barrier with phased construction

I'm looking for help on an attic floor assembly. This is new construction where the attic will not be finished right away. It could remain unfinished for 5 years. I want to install the insulation and vapor barrier to perform correctly for both an unfished and finshed attic detail. I want to make sure the assembly is drying to the correct side.

I have attached a pdf to show the assembly.

Asked By Seth Holmen | Oct 9 17
4 Answers

SIP Wall to Gable Corner Question

I am curious to hear if how a design pro might approach a SIP Wall corner at the gable end of a house. I have 2 choices as to whether to run the wall panel long or the gable panel long. Just curious to hear what the advantages to each approach might be. I don't think either approach is structurally any different but there might be a difference that is not readily apparent to me. SIP mfg hasn't been too helpful in elucidating the pros and cons.

Thanks in advance for any thoughts.

Asked By John Brown | Oct 8 17
2 Answers

Has anyone used liquid flashing for window rough openings and still spray foamed and taped the jambs and head of windows?

We are installing European flangeless windows and have used zip liquid flashing for the rough openings. We're planning to use air dam sealant on the interior. The window manufacturer wants us to use air dam on the exterior as well with and air gap between the two beads. Our ZIP Rep has said that the zip tape can be used to tape to the liquid flashing, and it seems less expensive and easier to use for our exterior. But the window manufacturer doesn't like to mix tapes with liquid flashing. Has anyone used liquid flashing and caulk on interior but tapes on exterior?

Asked By Jonathon S | Oct 5 17
6 Answers

HFOs vs. HFCs in spray foam

I am finally ready to insulate my basement with closed cell spray foam. I have the choice between Icynene, Demilec Heatlok HT HFO, or Lapolla Foam Lok 2000-4G.

The latter two brands use HFOs and not HFCs for their blowing agent. I'm not sure which version of Icynene the contractor quoted me for, but he said they weren't using HFOs yet.

Asked By Jimmy Nguyen | Oct 4 17
Register for a free account and join the conversation

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