Appeal 24911

2019 OSSC Section 602.3 Type III

Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated (FRT) wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.

We would like to consider the use of mineral wool insulation in place of FRT exterior wall framing in Type III construction as an alternate for aerial access road width and sacrificial stud.

The proposed exterior bearing walls in the Type III building will consist of untreated (Non-FRT) wood stud framing with mineral wool insulation friction fit in lieu of the FRT wood framing members per OSSC 602.3.

The proposed 2-hour rated exterior wall design includes the following:
• Two layers of 5/8” thick type-X gypsum wall board on the interior over untreated 2x6 wood stud framing and one layer of plywood sheathing with one to two layers of 5/8” thick type-X gypsum wall board on the outside with either stucco or metal panel as the exterior member.

The proposed design will meet all the requirement of the Portland Code Guide – OSSC/6/#4, except one part of condition #11, the width of the aerial apparatus access space, and condition #4 and #17 for sacrificial stud requirement. The space available on NE 8th Ave, with vehicle parking on each side of the street, will not be able to be 26 ft wide for the 150 ft long space.

For condition #11, aerial apparatus access will be provided on the non-dominant street (NE 8th Ave) across the face of the project site. This is due to overhead power lines running along the main NE Alberta St. The space available for the aerial apparatus will be provided in the street between the vehicles parked on each side of the street. The space between vehicles will be at least 14 ft for the two lanes of traffic. The street will provide more than the length of the required space required for the apparatus.

For conditions #4 and #17, sacrificial studs will not be installed – mineral wool insulation will be provided in exterior walls in lieu of fire-resistant treated wood stud framing and sacrificial studs. All framing details per (0-19) per condition #17 will be followed, with the exception that sacrificial studs will not be provided. The exterior walls will be protected with non-combustible mineral wool insulation as detailed in the wall assemblies shown in Appendix A of the attached report.

Refer to the attached report, stamped by an Oregon Registered Fire Protection Engineer, for the detailed evaluation to justify that the non FRT exterior wall assembly described above will exceed the performance of a traditional FRT wood wall in Type III construction and the use of mineral wool provides protection without the requirement of sacrificial studs. (See Attached White Paper).

Reconsideration Text:

For condition #11, the location of the aerial apparatus access has been revised and will now be provided on the dominant street (NE Alberta St). The existing overhead power and communication lines are being rerouted to provide an unobstructed path for the fire department access. The space available for the aerial apparatus will be provided in the street between the vehicles parked on each side of the street. The clear space available for the aerial apparatus, between vehicles, will be at least 22’-4” for the two lanes of traffic and cover the entire length of the project site along the Alberta St (approximately 98’-8”).

The fire-retardant chemicals typically used have potential long-term environmental impacts. Hence the request for alternate.

The process of pressure-impregnating chemicals into wood to achieve FRT criteria has a negative environmental impact. Additionally, there are concerns regarding health impact to the occupants of the building, from long term exposure to the chemicals used in pressure impregnation. Unlike the chemical FRT process, mineral wool is made from inorganic fiber that does not have adverse impact on the environment or occupant’s health.

The FRT process also reduces the structural strength of wood that must be accounted for in the structural design. The presence of FRT degrades typical wood strength properties, often resulting in increased cracks and splits in the framing over time. This reduction in strength and bearing capacity requires structural members to be oversized and an increase in the overall amount of framing throughout the project.

The attached white paper provides the fire analysis that supports the use of mineral wool (aka Rock Wool) insulation in the wall cavity of untreated wood stud framing as an alternate to FRT wood stud framing permitted by the OSSC. The analysis is based on published temperature data from full scale testing of multiple configurations of fire rated stud walls. The assemblies tested included 1 hour and 2 hour rated assemblies, with and without insulation, insulations included fiberglass and Rock wool types.

The analysis incorporates test data with the fire science fundamentals of gypsum calcification, pyrolysis of wood, and thermal conductivity of materials, accepted by the Society of Fire Protection Engineers, The National Bureau of Standards, and the American Wood Council. These are the accepted industry standards for this type of analysis.

The equivalency analysis included in the white paper is a straight comparison between untreated wood and FRT wood framed wall assemblies, without any benefit from these additional conditions. The analysis documented in the attached white paper concludes that untreated wood framed walls with mineral wool insulation will outperform FRT wood framed walls without such insulation.

Therefore, as detailed in the attached White Paper, the performance of mineral wool filled wood stud framed walls with these additional conditions will far exceed the code intent of FRT wood framing.

This product is within the parameters of our analysis and the proposed wall assembly will exceed the fire performance of an FRT wood framed wall assembly. Code does not prohibit the use of better-quality products than what is mandated. As this proposed assembly exceeds the base code criteria, it will satisfy the code requirements.

This building includes additional protection measures per the Portland Code Guide, except the sacrificial studs and width of the aerial fire apparatus set-up. The set-up area will have the full length available, but the guaranteed width will only be the width of the two-way dedicated roadway of 14 ft. The roof is within 75 ft of the street level in height and the roof is flat, the non-dominant side has equal access to the entire roof. The addition of protection of all exterior walls with mineral wool filled stud cavities provides a fire-resistance rating exceeding the OSSC required minimum, resulting in a higher level of building safety.

After reviewing the attached supporting engineering report, we urge you to approve this appeal request.

Reconsideration Text:

This building includes additional protection measures per the Portland Code Guide, except the sacrificial studs and width of the aerial fire apparatus set-up. The set-up area will have the full length available at the face of the project site, but the guaranteed width will only be the width of the two-way dedicated roadway of 22’-4”. The roof is within 75 ft of the street level in height and the roof is flat. The addition of protection of all exterior walls with mineral wool filled stud cavities provides a fire-resistance rating exceeding the OSSC required minimum, resulting in a higher level of building safety.