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!

9 Answers

Antique house #1: Cedar Roof

I will likely be taking on a crazy project in the next few months - buying an old house in Rhode Island, and improving it, on speculation.

The general scheme is to
--Do minimal work on the older (about 325 years) portion of the house,
--Expand/rebuild the newer (about 115 years) section with modern kitchen, baths, windows, etc.
-- Remove ugly garage, breezeway, and dormer.

In General questions | Asked By curtis betts | Sep 30 15
1 Answer

Is R-13 x 2 greater than R-21 (for a 2x6 wall)?

Two layers of R13 batt insulation is cheaper than one layer of R21 batt (for a 2x6 wall). Can I place 2 layers of R13 in the wall and achieve a greater R value than one layer of R21?

One other note: Unfortunately the R13 is faced. Would two faced layers cause a problem?

Location-Southern California-92705

In Energy efficiency and durability | Asked By Keith Messick | Oct 8 15
8 Answers

Is makeup air needed for a propane boiler?

We are building a 2200 s.f. house with closed cell insulation and heated with propane radiant heat. The plumber says I don't need makeup air. He says the HRV will handle it and I just need to put a louvered door in the mechanical room. Please advise. Thanks!

In Mechanicals | Asked By Peter | Sep 28 15
24 Answers

Anyone familiar with Insultex house wrap?

I was wondering if anyone had any thoughts on this house wrap - http://www.insultexhousewrap.com/

They appear to be making some exaggerated claims and I am not certain that the R-value claimed would be possible.

Any thoughts?

In Green products and materials | Asked By Marcus Sheffer | Jul 31 15
7 Answers

Insulating a pole barn

Hi. I am interested in building a small (20'x20') eco friendly pole building as a "tiny house". I like the idea of a pole building because it avoids the use of concrete for the foundation. I plan on using perlite bags beneath an earthen floor as the "sub-slab" insulation. For the walls and ceilings, I would like to use cellulose. I have not been able to find any details online for appropriately insulating and air sealing pole buildings. What resources I have found generally ignore thermal bridging entirely, for instance.

I would like to achieve R-40 walls and an R-60 roof.

In Green building techniques | Asked By Steven Gubkin | Sep 30 15
1 Answer

If you install a dedicated recirculation line, can you have it run on demand? Or does it have to run continuously?


I'm trying to figure out the benefits/drawbacks of installing a Dedicated Recirculation Line versus an Demand- Initiated Recirculating System. I've already read Martin Holladay's great article in Fine Home Building.

Clearly, the demand-initiated systems are better suited for retrofits since they use the existing cold water line (at least the D'mand one I'm familiar with). And the Dedicated Recirculation Line is better for new construction due to the cost of installing additional plumbing back to the water heater.

In General questions | Asked By Whitney | Sep 30 15
2 Answers

I live in Iowa and I want to know if it is necessary to have a vapor burrier on my ceiling if I have roof vents

I'm also considering installing an attic exhaust fan, not sure how to determine the size of fan I need.

In General questions | Asked By Chris | Sep 28 15
1 Answer

Detailing WRB/Roxul/siding in retrofit

I am putting together a plan for a client to add 2" rigid mineral wool as a continuous exterior insulation upgrade. One-story 1974 ranch house, huge 4' overhangs, zone 5 NW Ohio. Existing walls are 2x4 with fiberglass batts and interior poly vapor barrier. Current siding is vertical pine board-and-batten. Already encapsulated crawlspace and insulated foundation walls, air-sealed in attic and blew in more insulation, so doing the walls is Phase 3.

In Green building techniques | Asked By Andy Chappell-Dick | Sep 30 15
3 Answers

Crawlspace foundation with wing insulation as well as vertical exterior insulation?

Hi. In northern New York state, climate zone 6. Preparing to build a 20 x 30 second home for a client that will be insulated but not heated for the foreseeable future. Some day it might be used year round.

Crawlspace foundation with footings to frost depth. We are planning to insulate the stem walls on the exterior with 2" XPS. A slab is planned at level of footing. We are contemplating skipping the sub-slab insulation of 2" XPS and adding wing horizontal wing insulation instead--in addition to the vertical stem wall insulation.

In Energy efficiency and durability | Asked By Jon Brown | Oct 1 15
1 Answer

Polyiso along ceiling under truss chords

New build in climate zone 5. My plan is to establish my air barrier on the outside with zip sheathing and liquid flashing, and want to continue the air barrier across my ceiling (below a vented attic with blown cellulose). I thought about continuing the zip panels across the ceiling attached under the truss chords and tape them from the inside. I want to have options for drywall and tongue and groove wood for different rooms. I also thought about running polyiso boards in the same manner, maybe in two layers with staggered and taped seams. Any thoughts on this option?

In Energy efficiency and durability | Asked By Brian W | Oct 1 15
Register for a free account and join the conversation

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