Flashing Roof Openings (1973)

[Music] It's often necessary to penetrate the roof of an industrial plant or commercial building to add equipment supports, vent stacks, piping, or other projections. Flashing, if properly installed, can effectively seal these openings against leakage that may damage costly equipment, inventory, or other contents of the building or cause deterioration of the roofing system. When it's necessary to penetrate a roof, first locate the center of the opening by drilling a hole through the roof from the underside. Chip away the slag from around the opening, taking care not to damage the roof membrane. A tight bond between the flashing and the roof cannot be obtained unless loose material is cleared away. Flashing should not be installed unless the roof surface is completely dry. Lay out the opening using the center mark as a guide. The flashing may be fabricated either round or square and properly installed. Either shape will seal the roof against leakage. Now cut the opening to the desired size using a suitable blade long enough to penetrate the roof membrane, the insulation, and the roof deck support. Do not disturb the roof membrane outside the opening. The area around the opening must be clean and dry. Roof coatings may not adhere properly to the roof membrane if it is damp or dusty. Trow on a coat of plastic roof cement covering an area slightly wider than the flashing flange. Now, position the metal flashing, seating it firmly in the plastic cement. The flashing flange should be at least 4 in wide. The bolts used to secure the flange to the roof must be long enough to penetrate the thickest part of the roof deck. Nuts can be threaded on the bolts by reaching through the opening. Space the bolts close enough to eliminate any uneven surface of the flange. Bolts are usually placed about 3 in apart. After all the bolts have been tightened, t a layer of plastic roof cement on the flashing flange overlapping the roof membrane. Before the first layer of roofing felt is put down, brush or swab on a generous portion of roof coating wide enough to accept the roofing felt. The first layer of felt is positioned around the flashing and pressed firmly into the coating. Before positioning the next sheet, coat the felt where the pieces overlap. The four overlapping pieces of felt surrounding the flashing make up the first layer, bonding the flashing flange to the roof membrane. Seal the layer of roofing felt by trling plastic cement around the flashing at all seams where the felt overlaps and around the edge where the felt meets the roof membrane. In preparation for the second layer of felt, cover the entire area with roof coating, overlapping onto the roof membrane. The second layer of felt should extend 6 to 10 in past the first layer. The second layer of roofing felt is positioned around the flashing on top of the first layer and firmly pressed into the roof coating. Again, four overlapping sections of felt make up the second layer. Seal with plastic cement around the flashing and all overlapping seams. Once again, cover the entire area with coating overlapping onto the roof membrane. The top layer of felt will extend 6 to 10 in past the first two layers. The third layer of felt is installed using the same procedures. Coating between sheets, sealing with plastic cement, and coating the entire area. Once the flashing has been sealed around the roof opening, the most important part of the job has been completed. Any accumulation of roof water is now prevented from entering the opening. Replace any slag that was previously removed to restore the roof surface. It is recommended that roof flashings be at least 8 in high to cover most roof weather conditions. An equipment support column should be isolated from the roof and flashing. This allows for vibration, expansion, and contraction without disturbing the roof seal. The cap or cover must fit tightly around the projection and overlap the flashing to prevent water from entering the opening. Accurately mark the cap at the column flanges. Lay out the flange width and flange depth and cut the slots with a metal saw or shear. Position the two parts of the cap to maintain adequate clearance for isolation from the flashing. Secure the cap to the column using bolts, rivets, or sheet metal screws. The seams are made weathertight with caulking compound. An alternate method of attaching a cap to the column is by welding. Heavier gauge metal is fitted around the column and welded in place. A sturdy, maintenance-free installation is the result. Clean the welded areas and finish with a rustresistant paint. The roof opening and flashing can be the same for most any projection penetrating the roof. The cap which overlaps the flashing will vary with the shape of the equipment. Fasten the cap around the vent stack. Attach the draw band to secure the cap to the stack. Draw the band up tight. The top of the draw band is rolled out slightly to provide a cavity for the cocking compound. Caulk the opening around the draw band and any exposed seams around the cap. Piping runs through the roof may utilize the same type of flashed opening. It's a good practice to pitch the piping down from the flashing so the water runs away from the roof opening. A one piece cap can be utilized for this application. Clearance slots are cut into the cap to fit loosely around the pipes. Attach the cap to the flashing with sheet metal screws. In some instances, it is impractical to shield the flashing with a cap because of an irregular shape or unusual angle of penetration. Pitch pockets or pans by their design cannot be expected to be continuously watertight. They require frequent inspection and maintenance. Where necessary to use a pitch pan, the depth should be at least 4 in. Openings in the bottom of the pan should be cockked with okum or other material. Fill the pan to a depth of about 1 in with gypsum plaster paras or quick setting mortar mix. This prevents the hot pitch from running through the pan. When the plaster base is dry, pour the pan almost full with hot pitch. When the pitch has cooled, it may be topped off with a layer of plastic roof cement sloping down to the edge of the pan. By following the suggested methods of flashing roof openings, equipment supports, piping, and other projections can be installed through the roof without the nuisance and expense of water damage. [Music]