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5 Answers

Smart vapor retarder over open-cell SPF on underside of roof in Zone 4 (Washington, DC)?

I am having open-cell foam installed under several attic roof areas (collar attic, knee wall.areas, etc.) I have seen lots of statements about the need for a vapor retarder in Zones 5 and higher, as well as the general advice in any zone to add a supply and return (this would be complicated to install this, because it is not simply one big attic space and in any event our heat is from radiators, not forced air ducts).

Asked By Elizabeth Hilder | May 5 16
1 Answer

Mini-split vs Forced air and attic insulation

So hopefully a simple question. I'm building a home and have not decided if I should use mini-split or traditional HVAC.

If I use HVAC, I was going to close-cell spray the attic.
Do i need to do this if I'm running mini-splits?

The house is 2400 sq ft so it would have a multi-zones. I presume the refrigerant lines would be running in the attic. do I need to worry about loss there that would warrant spending the cash on spray foam on the attic? Or could I go with traditionally insulated attic since I would have no ducts.

Couldn't I just insulate the lines?

Thanks as always!

Asked By Mike W | May 6 16
15 Answers

Can someone explain the science behind a mid-wall vapor barrier on a double stud wall?

In order to save money, I've switched my wall assembly last minute from using exterior rock wool board to a double stud wall construction. I would like to speak with my county inspector about using this approach to make sure I don't have problems during construction. I'm struggling to understand how I'm going to explain how a vapor barrier on the back side of the inside wall is a good idea.

I'm in climate zone 5, and here is my intended wall assembly:

From inside-to-out:
Insulweb netting (affixed to stud to hold cellulose)

Asked By Adam Peterson | May 4 16
12 Answers

How does efficiency in a mini-split vary over various operating levels?

It is my understanding that a SEER rating is determined by simulating the operation of a particular make/model air conditioner over a hypothetical season, presumably assuming various temperature and humidity levels throughout the year.

Asked By david jensen | May 3 16
5 Answers

Improvement on the Lstiburek Ideal Double Stud?

Hi all. Please see the attached PDF of a variation on Joe Lstiburek's Ideal Double Stud Wall design (http://www.greenbuildingadvisor.com/articles/dept/building-science/lstib...).

I am trying to go for something a bit quicker and less labour intensive to build, but that is still very vapour open to the exterior (and occasionally interior) to overcome the usual double stud wall shortcomings.

Please fire away with critiques. The main problems I see are:

Asked By Burke Stoller | May 6 16
15 Answers

Exterior rigid foam and re-siding project

I'm seeking input and opinion. I'm looking to re-side with the dread vinyl (need the low maintenance for my two story house). My 40 year old post and bean house has interior sheetrock, 3.5" of fiberglass batt insulation with kraft paper, rough cut full 2x4 studs on 24" centers, plywood sheathing (I think 5/8"), paper (a mix of Tyvek and felt), and cedar shingles. Shingles and paper will of course be removed, sheathing inspected in the process. I'm in zone 6.

Asked By Howard Gentler | May 2 16
3 Answers

Insulating behind tower/tub

I upgraded my membership to GBA pro and poked around some on the strategies & detail pages. For drawing 5-01008 is that essentially the "cut and cobble" method leaving a 3/8 gap around the inner most layer of XPS.

Would this be enough R -value for Zone 6b assuming I were to use 2'' XPS for the first and second layer or would I be better served using 2'' and say 1'' for the inner most layer that requires the 3/8 channel?
Is this detail to be used around the entire perimeter of the shower/tub?

Asked By M S | May 5 16
15 Answers

Comfortboard pricing - Triple $ per R vs foamboard??

Hi all,

Asked By Keith H | Apr 21 16
3 Answers

XPS brands: Dow; Owens Corning; Pactiv/Kingspan?

I would appreciate feedback on the brands of XPS relative to one another.

I'll be installing a double exterior layer next week. Right now I can buy 3/4" sheets of the Pactiv/Kingspan XPS sold by Lowes for $13.57 a sheet (4x8).

Has anyone had any negative experience with the Pactiv/Kingspan foam?


Asked By Bill Daugherty | May 5 16
1 Answer

Is a double housewrap OK?

I'm building in CZ6 and we will be getting started later than expected due to red tape (I won't use red tape to seam seal since it appears to cause delays :-)

Due to starting later than expected, I may end up having to use a liquid applied Tyvek on my OSB to get me through the winter, if I am not able to get the exterior insulation and siding on before the snow flies and it gets too cold.

Asked By Steve Wilson | May 5 16
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