- (1) Concrete used for footings and foundations must have a minimum compressive strength of two thousand pounds per square inch (psi). Concrete must be mixed and delivered in accordance with the requirements of ASTM C94 (Ready-Mix Concrete), or may be field mixed. Field mixed concrete will be subject to independent compressive strength testing and special inspection.
- (2) Concrete footings must be placed on firm, undisturbed soil.
- (3) Concrete footings must be continuous, be a minimum of twelve inches wide by six inches thick, be reinforced with a minimum of two No. 4 continuous rebar, and be at least eighteen inches below finished grade measured from the bottom of the footing.
- (4) Concrete foundations must be a minimum of six inches thick, be reinforced with a minimum of one continuous horizontal No. 4 rebar within twelve inches from the top, and one continuous horizontal No. 4 rebar near mid-height, be reinforced vertically with No. 4 at forty-eight inches on center, extend at least six inches above the finished grade, and have a total height of not greater than forty-eight inches.
- (5) Concrete foundation stem walls that are formed by a thickened concrete slab edge as part of a slab on grade floor must be reinforced with one piece of No. 4 rebar in the upper part and one piece of No. 4 rebar in the lower part of the foundation. The concrete floor will be reinforced according to WAC 246-359-430. The thickened concrete slab edge must extend at least eighteen inches below finished grade, be at least twelve inches in width, and provide a slab height of at least six inches above finished grade.
- (6) Where the walls are of wood construction, the treated foundation plates or sills must be bolted to the foundation or foundation wall with not less than one-half inch nominal diameter steel bolts embedded at least seven inches into the concrete and spaced not more than seventy-two inches apart. There must be a minimum of two bolts per piece with one bolt located within twelve inches of each end of each piece. A properly sized nut and washer must be tightened on each bolt to secure the place.
[Statutory Authority: Chapter 70.114A RCW and RCW 43.70.334 through 43.70.340. WSR 15-13-091, § 246-359-180, filed 6/15/15, effective 1/1/16. Statutory Authority: RCW 70.114A.081. WSR 99-03-065, § 246-359-180, filed 1/18/99, effective 2/18/99.]