Appeal 32371

Appeal Summary

Status: Hold for more information

Appeal ID: 32371

Submission Date: 6/25/24 1:13 PM

Hearing Date: 7/3/24

Case #: R-001

Appeal Type: Building

Project Type: Residential

Building/Business Name:

Appeal Involves: Alteration of an existing structure

Proposed use: Single Family Home

Project Address: 3718 NE 11th Ave

Appellant Name: Kenneth Cowan

LUR or Permit Application #: Permit 24-048088-RS

Stories: 2 Occupancy: R-3 Construction Type: V-B

Fire Sprinklers: No

Plans Examiner/Inspector: Roza Malekzadeh

Plan Submitted Option: pdf   [File 1]   [File 2]   [File 3]   [File 4]   [File 5]

Payment Option: electronic

Appeal Information Sheet

Appeal item 1

Code Section

R806.5(6)(6.2)

Requires

(R806.5(6)(6.2))
"Air-permeable insulation only: In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing to a minimum insulation level of R-20 for condensation control."

Code Modification or Alternate Requested

To avoid an unnecessarily thick roof while mitigating moisture from condensation, we request an adoption of the 2021 IRC standards in section 806.5(5.1.2)

"5.1.2. Where air-permeable insulation is installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R-values in Table R806.5 for condensation control." [see attached File 4 for table R806.5]

Proposed Design

To avoid high embodied carbon foam products in this single-family residence full-gut energy retrofit, we propose a roof assembly insulated with mineral wool at the thickness called for in the 2021 IRC for our climate zone 4c.

This is an ‘unvented rafter assembly’ (cathedral ceiling) with interior service cavity and a ventilated metal roof. For the detailed drawing, please refer to attached file 5, or our architectural set, page A4.0/1.

Five measures are taken to maintain safe levels of moisture year-round:

  1. Adequate exterior-to-interior insulation ratio, following Joseph Lstiburek’s guidelines in his 2017 Article for Building Science Corporation “Hybrid Assemblies,” table 1. Our exterior rigid board insulation is R12.6, and 32.6% of the total roof r-value, which exceeds the minimums of r10/20% in 2021 IRC.

https://codes.iccsafe.org/s/IRC2021P2/part-iii-building-planning-and-construction/IRC2021P2-Pt03-Ch08-SecR806.5

https://buildingscience.com/documents/building-science-insights-newsletters/bsi-100-hybrid-assemblies

  1. Drainage/ventilation channels below metal roofing to allow outward drying of condensation.
  2. 3” of Rockwool Comfortboard80 on top of roof sheathing. This material is air and vapor-permeable, water-repellant, does not rot or promote the growth of fungi or mildew, chemically inert; non-corrosive.
  3. Siga Majcoat vapor-permeable weather barrier (34 US perms) to allow outward drying.
  4. Intello Plus air barrier enclosing the entire thermal envelope to limit the transport of moisture-laden air. Low Class II vapor retarder in winter (<0.13 Perm), protects against condensation, and maximum vapor openness in summer (13.2 Perm) to facilitate rapid drying to the interior in summer.

Assembly layers, from exterior to interior:

Standing seam zincalume, 24 guage (sri 65)
Epilay Epistik high temp ice and water shield
1/2" CDX (r-0.55)
3/4" (1x4") strapping for air channels upward to ridge vent
3" Rockwool Comfortboard80 (r-12.6) (32.63% above sheathing- must be minimum 20%)
SIGA Majvest 200 (54 us perm)
(existing) sheathing (r-0.55)
(existing) shiplap
2x8" rafters with 6"(r24) Rockwool Comfortbatts (leaving gap for better outward drying)
3/8" OSB or Zip, seams taped (r-0.41, ~1-5 perm) (Intello in exterior walls)
1/2" strapping/service cavity
gypsum drywall (r-0.5)

Total r-value 38.61

Reason for alternative

The alternate is required to eliminate the negative environmental impact of unnecessary materials (toxic foams or excess mineral wool), and to lower structural risk with improved moisture management using exterior ventilation channels and a vapor-permeable weather barrier to allow better outward drying.

Previously approved similar roof assembly:
Permit # 2009-179584-000-00-RS

Appeal Decision

Request to use the IRC provisions of 806.5(5.1.2): Hold for more information.


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