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Rigid foam board in Newfoundland

I live just outside St. Johns Newfoundland and will be building a new house this coming spring. I will be using 2x6 for framing. In the cavities I will install Roxul R -24. ½ spruce plywood covered by building wrap. Next I plan on installing 2 inches of Owens Corning ridged foam, tape seams. Next 1x4 strapping, rainscreen on 16 centers for attaching 6 inch spruce clapboard. My question is 2 inches enough to keep the wall warm where I live. Average winter temperature is 0C but it can get colder. Also can be quite damp with horizontal rain due to high winds.

Asked by paul fowler
Posted Sat, 01/12/2013 - 08:39
Edited Sat, 01/12/2013 - 14:40

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2 Answers

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1.
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owens corning = XPS ??
will it be covered or use as your water shield same time ?

How many sq ft of wall ext walls ?

If temp doesn't go too far below 0c and if it doesn't go there often,
i'd say that you in business with 2" of XPS ( R10? ) and the Roxul 24
You won't probably get R24 from the Roxul because of the thermal bridge from the 2X6,
but the exterior foam will cut the bridge and and you will probably get near R20 with this ..
additiona R10 of foam i'd say you will be at neat R30 all around!!
that's a pretty good insulated wall for a moderate temperature as you get !

Not too sure about the rain screen exterior, somebody else will probably help you much more on that matter than me ! :)

Move the building warp outside of the foam i'd say ..keep the foam as dry as possible
if possible for you to flash the wrap properly at this position

personally i try to use water shield as far as possible without compromising its integrity

Could also use 2 layers of tyvek if you want to be 100% safe about water management.

high winds always = water problems
water problems always = $$$$

so better more than just enough protection

Answered by Jin Kazama
Posted Sun, 01/13/2013 - 01:17

2.
Helpful? 0

Paul,
If you can choose a U.S. climate zone that is similar to your climate zone in Newfoundland, then you can answer your question by consulting the simple table in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

If you aren't sure which climate zone to choose, and you want to be sure of your decision, you can perform your own dew-point calculations by following the instructions in this article: Are Dew-Point Calculations Really Necessary?

Answered by Martin Holladay, GBA Advisor
Posted Sun, 01/13/2013 - 07:25

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