DESIGN CRITERIA FOR ROOF WASHDOWN. PHASE II. FALLOUT REMOVAL STUDIES ON TYPICAL ROOFING SURFACES FOR THREE SIZE RANGES OF PARTICLES (44 TO 88 MICRONS, 88 TO 177 MICRONS, AND 590 TO 1190 MICRONS)

Abstract : Fallout simulant particles ranging in size from 44 to 88, 88 to 177 and 590 to 1190 microns were deposited at a rate of approximately 2 grams/min/sq ft for a period of 30 min on selected typical roof section 48 ft long by 8 ft wide, to determine the effect of water flow rate, slope, and surface type on washdown effectiveness. A residual mass of less than 10% of the 590 to 1190 microns particles was obtained on aluminum shingles, composition shingles, roll roofing, corrugated metal and fiberglass epoxy laminated roof with a maximum of 3.5 gallons of water per minute per foot of roof width (gpm/ft) at a slope of 1:8 or greater. Thirty-five to forty-five percent of the 88 to 177 microns particles was retained on the corrugated metal at this same slope with a water flow of 3.5 gpm/ft of width. A residual of 5% or less was obtained on roll roofing at a slope of 1:8 or greater with a water flow of 3.5 gpm/ft of width with both the 88 to 177 and the 590 to 1190 microns particles. With the same two particle sizes, a residual of 5% or less was obtained on a fiberglass epoxy laminated roof with a maximum water flow of 1.0 gpm/ft of width at a slope of 1:12 or greater.