GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Firestop exulation retrofit practical/compliant design

user-1090662 | Posted in Green Products and Materials on

Short version: Do any fiber cement cladding manufacturers honor warranty or otherwise approve mounting on furring strips over exterior fiberglass or mineral wool? Or is there another practical/compliant exterior insulated wall design that resists fire on a tight setback, to the satisfaction of a permitting official?

I have 3x wall studs adjoining a legal nonconforming setback, need 3″ – 4″ exterior insulation to achieve true R-25 or so (Climate Zone 3, annual rainfall 20 inches). I think I will qualify for an expedited variance if exterior insulation plus cladding adds a maximum of 5″or so to wall thickness, and if the design has rational measures to resist fire. That leads to the question, do codes specify the fire rating of alterations that adjoin legal nonconforming setbacks? One way or another, the building department plan checker will want a reason to believe the exterior will be fire resistant on account of the zero lot line, and that the design measures resist moisture and aging. Permitting officials and design professionals in my region see high-end low-R designs for new construction but not retrofits much. I think with the right design I can respond to all parties’ concerns, including neighbors.

I’m open to different designs and materials that address the concerns of fire resistance, long term wall performance, and cost. The setback issue does seems to point to semi-rigid fiberglass or mineral wool under fiber cement cladding, and value engineering seems to point to furring strips. Urethane seems like it could also work for external insulation layer but I’m concerned about cost. Larsen Truss or other truss could also work as a design, or maybe double wall, but all those seem to need expert installation, leading to cost concerns. One more thing, about the practical aspects of getting the job done, any opinions on whether it makes sense to seek bids from industrial insulation contractors, who might adapt their methods to residential– rather than trying to find a residential contractor who likely has never done fire resistant exterior wall insulation before?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. GBA Editor
    Martin Holladay | | #1

    No matter what you decide, I'll all in favor of exultation.

    Exult, o multitudes and heavenly angels -- the firestops shall protect us.

  2. user-729621 | | #2

    it isn't exultation, it is exulation: " jubilation, joy, glee, rejoicing, exultancy" , that is what good design is all about. So thrilled that GBA is going so philosophical! Remember what John Ruskin said about firestops: "Doing is the great thing, for if people resolutely do what is right, they come in time to like doing it."

  3. GBA Editor
    Martin Holladay | | #3

    Lloyd,
    GBA has been philosophically exulting for several years now. We like to have a good time.

  4. user-1090662 | | #4

    Mr. Ruskin is ailing but conveys his good wishes. He continues to advise masonry construction all around. His friend Bill Morris is lately more sympathetic to light-frame raised-floor design and eternit cladding, but was unimpressed with the slag wool--this is no dark satanic mill you're retrofitting, he said. Central heating is for hospitals and all that. BTW I asked Chris Alexander and he liked the lifetime warranty on the fiber cement and the long expected service life of the mineral wool but when he saw the thing about chainsawing some of the eaves, he was so upset he could not focus on the fastener maker's cut sheet. The fact is, these guys appreciate when I bring them their medicinal tinctures but none of them are willing to go to the plan checker with me, although they're all willing to write flowery letters to the heads of zoning, building, and public works on my behalf.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |