Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-55 - State Building Code adoption and amendment of the 2021 edition of the Wildland-Urban Interface Code › Section 51-55-0500 - Special building construction regulations

Current through Register Vol. 24-14, July 15, 2024
Section 501
General.
501.1
General.
Buildings and structures hereafter constructed, modified,
			 or relocated into or within the
wildland-urban interface area
shall meet the construction requirements of Sections 501.4 through 501.8.
EXCEPTIONS:
1. Buildings and structures with fire hazard severity
						  determined in Section 502 and with ignition-resistant construction
						  classification determined in Section 503.
2. Accessory structures not exceeding 200 square feet
						  18.5 m2) in floor area and where located not less
						  than 50 feet (15,240 mm) from buildings or structures containing habitable
						  spaces.
3. Agricultural buildings located not less than 50 feet
						  (15,240 mm) from buildings or structures containing habitable
						  spaces.
501.2
Objective.
This section is not adopted.
501.4
Roof covering.
Roofs shall
			 have a roof assembly that complies with a Class A rating when tested in
			 accordance with ASTM E108 or UL 790. For roof assemblies where the profile
			 allows a space between the roof covering and roof deck, the space at the eave
			 ends shall be fire-stopped to preclude entry of flames or embers or have one
			 layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying
			 with ASTM D3909 installed over the combustible roof deck.
EXCEPTIONS:
1. Class A roof assemblies including those with
						  coverings of brick, masonry, or an exposed concrete roof deck.
2. Class A roof assemblies also include ferrous or
						  copper shingles or sheets, metal sheets and shingles, clay or concrete roof
						  tile or slate installed on noncombustible decks or ferrous, copper or metal
						  sheets installed without a roof deck on noncombustible framing.
3. Class A roof assemblies include minimum 16 oz/sq.
						  ft. (0.0416 kg/m2) copper sheets installed over
						  combustible roof decks.
501.4.1
Roof
			 valleys.
Where provided, valley flashings shall be not less than
			 0.019-inch (0.48 mm) (No. 26 galvanized sheet gage) corrosion-resistant metal
			 installed over a minimum 36-inch-wide (914 mm) underlayment consisting of one
			 layer of 72-pound (32.4 kg) mineral-surfaced, nonperforated cap sheet complying
			 with ASTM D3909 running the full length of the valley.
501.5
Exterior walls and projections
			 other than decks.
Exterior walls and projections other than decks, of
			 buildings, or structures, or
accessory structures
attached to
			 buildings or structures with habitable spaces, shall be constructed with one of
			 the following methods, with materials extending from the top of the foundation
			 to the underside of the roof sheathing:
1.
			 Materials approved for not less than one hour fire-resistance rated
			 construction on the exterior side;
2. Approved noncombustible
			 materials;
3. Heavy timber or log
			 wall construction;
4.
			 Fire-retardant-treated wood on the exterior side. The firere-tardant-treated
			 wood shall be labeled for exterior use and meet the requirements of Section
			 2303.2 of the International Building Code; or
5. Ignition-resistant materials, complying
			 with Section 503.2 on the exterior side.
EXCEPTION:
Unenclosed accessory structures attached to buildings
						  with habitable spaces and projections, such as decks, attached to the first
						  floor of a building, if when the structure is built with building materials at
						  least two inches nominal depth and the area below the unenclosed accessory
						  structure is screened with material with openings no greater than 1/4-inch
						  maximum to prevent accumulation of combustibles and to prevent embers from
						  coming in underneath.
501.6
Decks and appendages.
The
			 material of decks, porches, balconies, and stairs shall be constructed with any
			 of the following materials:
1.
			 Ignition-resistant material that complies with the minimum performance
			 requirement of Section 503.2.
2.
			 Exterior fire-retardant-treated wood.
3. Noncombustible material.
4. Any material that complies with the
			 minimum performance requirements of Section 503.2 when attached exterior wall
			 covering is also either noncombustible or ignition-resistant
			 material.
5. Heavy timber
			 construction consisting of the following:
5.1.
			 Posts shall be a minimum of 6 inches x 6 inches nominal dimension.
5.2. Beams shall be a minimum of 6 inches x 8
			 inches nominal dimension.
5.3.
			 Joists shall be a minimum of 4 inches x 8 inches nominal dimension spaced at no
			 greater than 24 inches on center.
501.6.1
Clearance.
Decks with
			 less than 48 inches of clearance from finished grade to deck joists shall be
			 enclosed with screen material with openings no greater than 1/4-inch maximum to
			 prevent accumulation of combustibles and to prevent embers from coming in
			 underneath.
501.6.2
Walking
			 surfaces.
The walking surface material of decks, porches, balconies, and
			 stairs shall be constructed with one of the following materials:
1. Ignition-resistant material that complies
			 with the performance requirements of Section 503.2.
2. Exterior fire-retardant-treated
			 wood.
3. Noncombustible
			 material.
4. Where the deck, porch,
			 balcony, or stairs are constructed of heavy timber in accordance with Section
			 501.6, natural wood decking products shall be:
4.1. 2-inch nominal dimension lumber;
			 or
4.2. 1 1/4-inch nominal hardwood
			 (i.e., teak, mahogany, or other approved hardwood).
5. Material that complies with the
			 performance requirements of Section 501.6.2.1 when tested in accordance with
			 ASTM E2632 and when attached exterior wall covering is also composed of only
			 noncombustible or ignition-resistant materials.
EXCEPTION:
Wall material shall be permitted to be of any material
						  that otherwise complies with Section 501.5 when the decking surface material
						  complies with the performance requirements of ASTM E84 with a Class B flame
						  spread index.
501.6.2.1
Material in Section 501.6.2,
			 Item 5.
The walking surface material shall be tested in accordance with
			 ASTM E2632 and shall comply with the following condition of acceptance. The
			 ASTM E2632 test shall be conducted on a minimum of three test specimens and the
			 peak heat release rate shall be less than or equal to 25
			 kW/ft2 (269 kW/m2). If
			 any one of the three tests does not meet the conditions of acceptance, three
			 additional tests shall be run. All the additional tests shall meet the
			 condition of acceptance.
501.7
Exterior glazing.
Exterior
			 windows, window walls and glazed doors, windows within exterior doors, and
			 skylights shall be tempered glass, multilayered glazed panels, glass block, or
			 have a fire protection rating of not less than 20 minutes.
501.8
Vents.
Attic ventilation
			 openings, foundation or underfloor vents, or other ventilation openings in
			 vertical exterior walls and vents through roofs shall not exceed 144 square
			 inches (0.0929 m2) each. Such vents shall be covered
			 with noncombustible corrosion-resistant mesh with openings not to exceed 1/4
			 inch (6.4 mm), or shall be designed and approved to prevent flame or ember
			 penetration into the structure.
1. Attic
			 ventilation openings shall not be located in soffits, in eave overhangs,
			 between rafters at eaves, or in other overhang areas. Gable end and dormer
			 vents shall be located not less than 10 feet (3048 mm) from lot lines.
			 Underfloor ventilation openings shall be located as close to grade as possible.