Energy code compliance: continuous insulation
In reference to my last outreach (you guys are great, and thanks for all your thoughts to date!!) it’s come to my attention that our local building department may consider our improvements as “alterations and renovations” and require that we comply with NYS Energy Code.
Before I ask my question, let me say that I have a hard time understanding why there would be legislation that disincentivizes residential homeowners from improving existing homes even if they don’t meet the minimums of the energy code.
That said we need to prepare for how these changes may impact our building plans (not to mention our retirement plans). According to our location in US climate zone 4/Westchester the wall insulation should be R13/5. As currently planned we’ll be at ~R14 with 4″ dense-pack cellulose (frame is nominal 4″ old-growth lumber). But we’ll need to determine which continuous insulation approach to take. Since we need to stretch our dollars, I think we should limit the search to a single product that addresses all the following. I’ve love to hear what you would recommend:
1) is R5 in the smallest package
2) insulation combined with a WRB if that exists
3) will let moisture that accumulates in the cellulose dry to the outside
4) can be fastened to the existing T&G (probably 16 oc) and have vinyl siding nailed directly to it.
thanks in advance!
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IMO it's not possible to meet all 5 items with one product. However, I think you could get close by using standard building wrap with exterior rockwool (ex, Roxul Comfortboard 80). You'd have to ask them but I think with the proper fastener you can attach vinyl siding through to the sheathing behind the rockwool.
thank you!
Hi Jim,
I'm sure you will continue to get good advice here from GBA members, but at this point, I would recommend that you speak with a local professional or take a step back and start researching building science topics and wall assemblies from the beginning. I say this only because I don't want to see you make costly mistakes and your post shows some misunderstandings (unless you just made some accidental errors or I'm not understanding something about your project, in which case, please disregard my comments.)
You wrote that you want an insulation that "combines the waterproof vapor barrier..." and that "will let moisture that accumulates in the cellulose dry to the outside." Vapor barriers include plastic sheeting and foil faced insulation and don't allow drying. Vapor retarders include paints and polystyrene insulations and allow varying degrees of drying (there are different classes of vapor retarders).
What I think you are asking about is a water-resistive barrier (WRB) that keeps rain and snow melt out of the assembly but allows vapor to pass. The Henry product is a water barrier and air barrier, not a vapor barrier. If you instead use insulation for your WRB, for example, you need to understand the permeance of the given type of insulation you choose, at the specified thickness needed, to know if there is any outward drying potential for your wall assembly.
Vinyl siding installation over exterior insulation depends on the siding manufacturers installation instructions, not necessarily on the type of insulation, though the thickness will come into play. Though many builders install vinyl over thicker insulation or on furring strips, I believe that most vinyl siding manufacturers limit insulation behind their products to 1 inch and want a flat surface behind the siding. Definitely double check this info with the siding manufacturer and specific product you choose.
Also, no insulation includes a proven method for waterproofing around windows and doors. That requires an assembly of flashings integrated with the WRB and getting water management details right is perhaps the most important aspect of the work you are about to do. The second most important thing is air sealing.
Here are a bunch of article I would recommend for you:
Vapor Retarders and Vapor Barriers
Calculating the Minimum Thickness of Rigid Foam Sheathing
How to Install Rigid Foam Sheathing
Installing Windows in Foam Sheathed Walls
Brian, thanks. I appreciate your insights and yes, I am a student of this mystical art of building science. I corrected my post but thankfully the GBA members knew where I was coming from.
We all are Jim! Good luck with the project...
You might want to consider ZIP-R for this as it seems to meet most of your requirements. I'm not sure how it compares in cost to other methods, but to me, it seems like this simplest method for adding exterior insulation with an integrated WRB.
+1 on this being closest to your request. But don't be surprised if it is more expensive than some alternatives.
THANK YOU!
>" But don't be surprised if it is more expensive than some alternatives."
NO KIDDING!
The lower-cost way to go is to install 3/4" thick foil faced polyisocyanurate (R5), seams taped with an appropriately rated foil tape, lapping the window flashing to the exterior side foil. Check with the vinyl siding manufacturer's installation spec, but with most you're allowed get away with using longer fasteners with foam thicknesses up to 1".
The only part that would fail completely is the drying toward the exterior bit. If that's truly important due low-perm interior finishes, using 1" graphite-loaded EPS will get you there:
https://www.achfoam.com/ACH/media/ACH/docs/Foam-Control%20Max/Foam-Control-MAX-TechData.pdf?ext=.pdf
https://www.insulfoam.com/wp-content/uploads/2014/04/15000-Insulfoam-Platinum-Brochure_REV3-17.pdf
Products using metalized facers it needs to be perforated to hit north of 2 perms:
https://www.amvicsystem.com/wp-content/uploads/2019/08/Amvic-Perforated-SB-Product-Data-Sheet.pdf
https://buildwithhalo.com/
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I believe your codes department is incorrect. You'll need to read Sections R501 and R503 of the NYS Residential Code. It's available free on-line at https://codes.iccsafe.org/category/New%20York . You also need to read the NYS supplement found at https://www.dos.ny.gov/dcea/CodeUpdate.html. I don't find anything that requires you to comply with codes for new construction. You may have to hire an architect (or a lawyer!) well versed in this code to present your case. There is an appeal process to the state. I've run into many code officers in New York who are lost in the code.
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R503.1 General. Alterations to any building or structure shall comply with the requirements of the code for new construction.
Is there any amendment hidden in the supplement that over rules R503.1? I didn't see one. How is the code official incorrect?
You may be able to apply for a modification to the State Board if your schedule allows...
The codes people don't allow cut and paste so see image below. It is very specific regarding obligations for improving walls and roofs. Note that new construction does not require 13/5 in walls. There are other ways to meet code.