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10 Answers

Screws as condensation points

Maybe I'm over thinking again...

When 4" of XPS is held in place with 5.5" screws many screws will end up going through the sheathing (missing the studs).

Another case I am thinking of is when I install a flat roof with 3.5" of polyiso screwed down.
Then a membrane and 1/4" polyiso (special high compression strength polyiso) glued down (R1). So screw heads have R1 protecting from cold - like standing snow. In this case there is about 1 screw per 1 sq ft.

At 1 screw per 1 sq ft, the cross sectional area of the screws is only about 1/3000 of the assembly.

In Green building techniques | Asked By Mark Bartosik | Sep 13 09
5 Answers

Fiber-cement lap siding — Back vent or not?

I'm installing fiber cement lap siding on the second and third floor exterior walls in a hot humid climate, subject to relatively high rain fall and high winds.---8 1/4" x 5/16" with 7" revaeal on wood frame 2x6's on 24" centers, above 20' from ground.

In Energy efficiency and durability | Asked By John Walls | Sep 20 09
2 Answers

Building with concrete block - good or bad?

We are looking at something like the Lite-block made in Houston which can be done by a homeowner. What type of roof should be used with this system - metal beams/roof or standard wooden trusses? Would like info on the ease of building with this material for a homeowner and the green factor.

In Green products and materials | Asked By Doris | Sep 21 09
4 Answers

Old insulation in crawl space

I have an existing crawl space that in the past was a wet and damp space. Now that it has been cleaned , the old insulation seems to be holding the damp musty smell. The crawl space is semi heated with the furnace and duct work in the space. Should we remove the old insulation and put nothing in its place, or should we instal new insulation and if so, what do you recommend?

Thank you
Mark Yuschak

In Green building techniques | Asked By Mark Yuschak | Sep 9 09
1 Answer
4 Answers

I have a customer very concerned about limiting her family's exposure to terpene VOC's.

We're about to build the customer a new, 2-story house. At present, we're intending to build 2x6 wall frame with cavity walls filled with either cellulose or open-cell foam.

Any other observations about terpene sensitivity, or means of encapsulating terpene inside framing lumber would be greatly appreciated.

Also, do you think a typical layer of open cell foam under the roof deck will actually serve to encapsulate the terpenes in roof framing and decking members.


In GBA Pro help | Asked By Dan Fette | Sep 16 09
5 Answers

What is the procedure for de-rating attic insulation?

I am an energy auditor and 90% of the time see attic insulation that looks like the lunar landscape. If blown in insulation levels range from 14" down to 2" or drywall at can lights how do I provide an effective R-value to the space? Oh yes uninsulated attic hatches included.

In General questions | Asked By Bruce Chyka | Jul 17 09
5 Answers

AirTightness without Sprayfoam

I am searching for Airtightness strategies that are achieving 1.5 ACH50 or better.
I am also trying to avoid sprayfoam for a variety of reasons.

If you are achieving good airtightness without spray foam please comment here

or join this discussion at the JLC Building Science Forum
Thank You,
John Brooks

In Energy efficiency and durability | Asked By John Brooks | Sep 9 09
1 Answer

Offgassing & SIPs?

Does anyone have a metric for estimating offgassing of formaldehyde (and other chemicals) from SIPs? A research article I recently found stated that SIPs offgas formaldehyde, toluene, etc.—even through gypsum drywall. I'm in the process of contacting the authors of this paper, as well as querying various manufacturers of "safe" sealants, but I'm wondering if anyone else has leads on solid sources of information (i.e., independent research), especially with regards to the possibility of sealing in the chemicals so they can't offgas into a living space.

In Green products and materials | Asked By Claire Anderson | Sep 14 09
3 Answers

Exterior XPS screws vs glue

So on a prior question I asked about condensation risk on the tips of screws that penetrate the sheathing when fitting 4" of exterior XPS. This applies to both roof (polyiso) and walls (XPS).

I didn't really get an answer to that.

So I am considering hardly using any screws and fully adhering the foam to the sheathing / deck.
This is maybe not so green in that I don't have a no-VOC option for the roof, and the costs go up, and it is more risky since I am not aware of it being done elsewhere in the case of walls (it is normal for roofs).

In Green building techniques | Asked By Mark Bartosik | Sep 14 09
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