rivets, etc., shall be of aluminum alloy. Nails shall be barbed and etched. Neoprene or aluminum backed fiber washers shall be provided for all holes for fasteners, b. Workmanship: 1. Application shall be started true to line and care she tt be taken to keep the horizontal and vertical lines of the sheets straight and plumb. Work shall start at the end of the building opposite the prevailing winds and shall proceed across the roof one course at a time, or if preferred, all courses shall be carried across the roof simultaneously, keeping the adjacent lower course at least one sheet ahead of the next upper course. The first sheet shall be applied with the edge turned down at the gable and side and with the edge turned up at the opposite side to be lapped by the next sheet. Roofing shall be laid with corrugations parallel to the roof slope, siding sheets shall be attached with corrugations vertical. Sheets shall be bent along corrugations only. 2. Sidelaps for roofing shall be 1-1/2 corrugations, minimum, and for siding 1 corrugation. End laps shall be 8 inches for roofing and 4 inches for siding. 3. Holes for Fastenings shall be drilled or punched and all holes sealed with washers. Side laps shall be fastened with machine screws or sheet metal screws approximately 15 inches on centers. Sheets shall be secured to sheathing or framing at end laps and intermediate bearings with nails through washers at the crown of alternate corrugations. 4, Protection: Where aluminum overlaps dissimilar metals or masonry, the overlap shall be painted with aluminum pigmented asphalt paint. 8-16. PICTURE SCREENS: Motion picture screens wheve shown on the drawings shall be constructed of asbestoscement sheets complying with Federal Specification No. SS-S-283 for Type I sheets. Sheets shall be of thick- nesses called for in as large sizes as practical. Joints shall be butted and shall occur only over solid bearings. Nails shall be countersunk and nall holes and joints filled with an approved cold water type putty, sanded smooth. All holes for nails through 8-13