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2 Answers

Sharing the radon stack

I have a 4" PVC stack going from below the slab and through the roof to provide passive ventilation of radon from below the slab (potential radon—not yet measured). Is there any reason I can't tie into it with the bathroom ventilation duct? I like minimizing roof penetrations.

The duct would tie to a Y that points upward; between that, the draft created by the stack itself, and the damper on the fan, I see no risk of ozone entering the house. Any problems?


Asked By David McNeely | May 3 17
17 Answers

Addressing the ping pong issue

Zone 4A. Hip roof necessitates unventilated attic, therefore spray foam insulation against the bottom of the roof deck.

Joe Lstiburek is saying that the source of humidity in this kind of assembly is from the interior, and he describes a “ping pong effect” that results in moisture accumulating at the ridge. His solution is to use closed cell foam or condition the attic (below Climate Zone 5).

Would it not work to spray a layer of cc foam against the sheathing, followed by open cell foam to make up the required insulation value?

Asked By David McNeely | May 2 17
11 Answers

Building a new home in Climate Zone 5 — Need insulation help

We are building a new home in zone 5 (Michigan) and I would like your recommendations on how you would insulate the walls and roof/attic space.

The home is 3500 sqft with 2750 on the main floor and 750 upstairs. The main living space (kitchen, dinning, living room) is open concept with a cathedral ceiling. Other areas have a more traditional attic space.

The basement will be unfinished and we will use 2" rigid foam under the slab and on the walls. (unless you tell me differently)

Walls are 2x6 construction.

Asked By NKoenig | Mar 26 17
3 Answers

Fiberglass-backed polyiso got wet, now moldy on surface: to keep or not to keep? Remediation?

A few months ago I chatted back an forth with Mr. Martin Holladay about my project... I have progressed on it since then, but have ran into an unforeseen problem. Let me bring you up to speed:

I am building an apartment underneath a lean-to roof coming off of a post-frame shop building in climate 3. I purchased some used poly-iso foam boards to use as insulation on the underside of the existing metal roof. At this time I have reached this point (Layers shown from top to bottom):

Metal roof
2x4 purlins (with subsequent 1.5" air gap)

Asked By John Peeper | Apr 23 17
7 Answers

2/3 1/3 insulation rule in roof

Old build with flat wood deck on 2x13s. 4 inches Batt in joist space.(R12) 2 inch air space above batt insulation under wood deck No external vents into air space Adding polyiso on top of deck R 28. Before adding the polyiso can/should we put a separator sheet or vapour barrier on top of the wood as there is more than 2/3 the insulating value above the deck There is a poly vb above the drywall ceiling below e joists.

Asked By UBSC | Apr 19 17
4 Answers

We are building a house in Hanover, N.H.

Based on discussions from GBA, we are adding 2 1/2" XPS to the exterior of the sheathing. What is not clear is what (if any) treatment occurs near the ground level -- i.e., on the bottom edge of the 4x8' panel of XPS.

If left exposed, is it susceptible to rodents, bee nests, etc? The siding will be Hardiboard.

Asked By Frank Torti | Apr 17 17
2 Answers

Insulation and air sealing around exposed rafters and beams

Our new build project with have exposed 4x8" Douglas Fir Beams cantilevering over the front and rear elevations of the property with a low-slope "warm" shed style roof. I've previously posted on the roof assembly and comfortable with our approach there.

I know that cantilevered beams penetrating the assembly is far from ideal, but it is what is so I am trying to come up with the best solution with some input from your kind selves. I can't seem to find anything in the articles so I've purely come up with the below based on a best guess.

Asked By Quinn Sievewright | Apr 11 17
26 Answers

Mold/ventilation problems in an old passive solar house

I just tried to post a long comment on the vapor retarder/barrier article and was blocked for spam so I'm trying again here. I'm under contract for purchasing a 1979 passive solar house in Southern Maine (near Sebago Lake, but at higher elevation). The house needs a lot of work, which we were expecting, but on top of all that they unfortunately found moderate to high mold growth on the roof sheathing and rafters, along with improper insulation/ventilation practices.

Asked By Movintomaine | Apr 9 17
7 Answers

Too late for outie windows?

I framed and wrapped my house planning on innie windows. Walls will be standard construction with 6” exterior foam. Actually…I installed all the windows that way as well. With that behind me, I am feeling like the structural and performance benefits I based this choice on are overblown, and I’d like to change to outie windows. My rough openings are sized for the windows – not the windows plus extensions. I am trying to determine a way to build rough opening extensions that attach outside the sheathing.

Asked By Jim Tyler | Apr 10 17
20 Answers

Mold on the north side of the sheating in my attic

First let me apologize for the longwinded question. I purchased a house a while back it was an as-is purchase. We knew a fire had occurred several years back and seen what was presumed to be smoke damage in the attic.

The house had been re-wired, new sheetrock throughout kitchen etc. When we purchased the house the return air (duct work in crawl space) was not hooked up and this was one of the first things corrected.

Asked By Dysd | Apr 7 17
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