DESIGN CRITERIA FOR ROOF WASHDOWN SYSTEM. PHASE 1. FALLOUT REMOVAL STUDIES ON TYPICAL ROOFING SURFACES FOR TWO SIZE RANGES OF PARTICLES (177350 MICRONS AND 350-590 MICRONS)

Abstract : Fallout simulant particles ranging in size from 177 to 350 and 350 to 590 microns were deposited on selected typical roof sections 48 ft long by 8 ft wide to determine the effect of water flow rate, slope, and surface type on washdown effectiveness. More than 90% of the simulant can be removed on composition shingles, aluminum shingles and roll roofing at slopes of 1:12 or steeper with 2 to 3 gallons of water per min per ft of roof width (gpm/ft). It was found that washdown is ineffective on tar and gravel roofing without prior removal of the loose gravel. Washdown on a fiberglass epoxy laminated roof will remove better than 99% of the simulant particles with a water flow rate as low as 1 gal/min/ft.