Appeal 32395

Appeal Summary

Status: Decision Rendered over 32371 (7/3/24) for more info

Appeal ID: 32395

Submission Date: 7/11/24 2:55 PM

Hearing Date: 7/24/24

Case #: R-001

Appeal Type: Building

Project Type: Residential

Building/Business Name:

Appeal Involves: Alteration of an existing structure,Reconsideration of appeal

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: VB

Fire Sprinklers: No

Plans Examiner/Inspector: Roza Malekzadeh

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

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 adoption of the 2021 IRC standards in section 806.5(5.1.2)

Proposed Design

RECONSIDERATION TEXT:

We used Ubakus (2D-FE modeling based on the Glaser method) to generate hygrothermal simulations for Winter and Summer performance. Ubakus is not as precise as a very expensive WUFI analysis, but it is widely accepted in calculating overall u-value and condensation amounts.

Through this analysis, we decided to make two changes to miss the dewpoint by a much wider margin:

  1. fill the rafter cavities with 7.5” of Comfortbatt (to increase total R-value)
  2. add a layer of Intello Plus vapor permeable membrane inside the service cavity (which is a more reliable vapor retarder than OSB)

In this roof assembly, the relative humidity will not reach 100% saturation (dewpoint), so zero condensate will form.

MODEL ASSUMPTIONS:

We used Portland OR design temperatures and humidities based on 2021 ASHRAE (https://ashrae-meteo.info/v2.0/) for Portland.

Outdoor climate:
Winter -5c / 23f, 60%RH
Summer 38c / 100.4f, 20%RH

Indoor climate:
Winter Heating 20c / 68f, 50%RH
Summer Cooling 24c / 75f, 35%RH

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)
SIGA Majvest 200 (54 us perm)
(existing) sheathing (r-0.55)
(existing) shiplap
2x8" rafters with 7.5" (r30) Rockwool Comfortbatts
3/8" OSB (r-0.41, ~1-5 perm)
Intello Plus vapor retarder
1/2" strapping/service cavity
gypsum drywall (r-0.5)

Total r-value 44.61

Attachments–
Roof - 3718 NE 11th Ave - Portland OR Summer
Roof - 3718 NE 11th Ave - Portland OR Winter
Roof Assembly Detail (revised)

Reason for alternative

The alternative 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 # 09-179584-RS

Appeal Decision

Request to use the IRC provisions of 806.5(5.1.2) based on the dew point analysis: Granted as proposed.

"The Administrative Appeal Board finds that the information submitted by the appellant demonstrates that the approved modifications or alternate methods are consistent with the intent of the code; do not lessen health, safety, accessibility, life, fire safety or structural requirements; and that special conditions unique to this project make strict application of those code sections impractical.

Pursuant to City Code Chapter 24.10, you may appeal this decision to the Building Code Board of Appeal within 90 calendar days of the date this decision is published. For information on the appeals process, go to www.portlandoregon.gov/bds/appealsinfo, call (503) 823-6251 or come to the Development Services Center."