What climate zone am I in?
Jasonc083
| Posted in Energy Efficiency and Durability on
http://energycode.pnl.gov/EnergyCodeReqs/?state=Massachusetts
My house will be located in bristol county, zip code 02717. Am I climate zone 5 or 4 marine?
I ask because I’m trying to determine what thickness of exterior rigid foam insulation to use.
I’m thinking of using 2×6 walls fiilled with dense packed cellulose, covered with plywood, then tyvek, then 1 inch of xps foam.
Going off this https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing
I’m either ok or under what I need to avoid the dew point issues.
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Jason,
For the purposes of the IECC (which uses the climate zone map developed by the U.S. Department of Energy), all of Massachusetts is in a single climate zone -- namely Climate Zone 5. Our website has the climate zone map on our Q&A page.
In your question, the second link that you provided brings you to an article ("Calculating the Minimum Thickness of Rigid Foam Sheathing") that answers your question about foam thickness. In your climate zone (zone 5), a 2x6 wall needs at least R-7.5 of rigid foam. So 1 inch of XPS isn't enough.
You need at least 1 1/2 inch of XPS.
Ok, thanks for confirming what I thought. The thing that threw me off is that the title of the page in my first link says climate zone 5 and 4 marine. It seems that If i go the route of xps that I will need custom extension jams on all my windows.
is there a way of doing xps without having sunken in windows? I believe I've read something about making them "outies". Does this make putting the windows in a lot more difficult?
Jason,
Assuming this is a new house, rather than an existing house, you can put the windows wherever you want. The GBA detail library includes details for both innie and outie windows.
For more information, see these articles:
‘Innie’ Windows or ‘Outie’ Windows?
How to Install Rigid Foam Sheathing
Climate-wise there's probably an argument that Martha's Vineyard and Nantucket are more akin to zone 4, but anywhere on the mainland MA is climate 5 (even the outer Cape.)
You can get meet the minimum IRC prescriptive levels pretty easily with a layer of 1/4" fan-fold XPS underlayment against the sheathing, followed by 1" of R6.5 low density polyiso.
But better yet would be to go with 2x4 16" o.c. framing and 2" of roofing-iso (or a double layer of 1" foil-faced.) There are multiple vendors of reclaimed roofing iso in MA- search your local craislist for "rigid insulation", and you'll likely find a least one. (There's also The Insulation Depot in Framingham. )With 2" roofing iso you'd have R10-R11 of more rugged higher-density foam on the exterior, and HUGE margin on dew point, and the same or better thermal performance as 1" XPS on 2x6 OVE framing, in a wall 1" thinner than your non-compliant stackup.
I'll have to see if i can do 2x4 walls, I thought code now was for 2x6
MA code is based on IRC 2009, and the code minimum wall-R can be either R20 cavity insulation in 2x6 (no insulating sheathing foam), or R13 cavity fill in 2x4 plus R5 continuous sheathing insulation. After factoring in the thermal bridging either will have a nearly identical "whole-wall-R", of between R13-R15, after the gypsum & siding get added in.
R5 sheathing insulation is sufficient for dew point control on 2x4 construction, but not for 2x6, but there is nothing to keep you from adding even more foam. On deep energy retrofits of existing 2x4 framed homes in MA it's common to add between 3-6" of exterior insulation. The more exterior insulation you have, the warmer the sheathing stays, reducing the mold hazard.
https://www.greenbuildingadvisor.com/video-how-install-rigid-foam-insulation-outside-house
https://www.greenbuildingadvisor.com/video-series-exterior-insulation-retrofit-introduction