Built-up Roofing
A. ROOF DECK:
1. Roof deck must be solid sheathing, either plywood or original plank board construction. Any large voids must be replaced or covered with sheetmetal.
2. Installation may be applied directly over rigid insulation board.
3. Overlays are allowed over original built-up roofing if the roof is in reason able condition.
a. New material may be applied directly over smooth surfaced or mineral surfaced cap sheet.
b. Gravel or rock surfaced roofs should be swept clean and covered with minimum 1/2” insulation board material prior to installation of the new roofing.
4. Severe ponding water problems should be corrected. (Puddling of water on flat roofs is acceptable.) Ponding water issues must be evaluated no later than the pre-inspection or the in-progress inspection.
B. BASE SHEET APPLICATION:
1. A slip sheet of Kraft paper or other appropriate material is needed on areas of the deck containing a large amount of residual asphalt.
2. Nail one layer of base sheet over the entire roof area. Ply sheets may not be used as a substitute for a base sheet.
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Base Sheet |
3. “Sprinkle mopping” the base sheet is allowed only over non-nailable decks or instances where nails are not feasible.
4. Nails should be square head, ring shanked type long enough to penetrate 3/4” into or through the deck. Shorter nails may be used to minimize penetra tion of the deck where visible.
5. Nailing pattern is typically 9” along each edge with two rows staggered 18” apart down the middle of the sheet.
C. PLY SHEET APPLICATION:
1. One or more layers of ply sheet should be applied according to the manufacturer’s specification being used. Multiple layers may be achieved by lapping the material shingle fashion.
2. Ply sheets should be solid mopped with hot asphalt. Edge laps should be 2” minimum. End laps should be 4” minimum.
This is a mineral surface, hot mopped cap sheet roofing system
D. SURFACE APPLICATION:
1. Mineral surfaced cap sheet may be solid mopped in with hot asphalt.
2. Gravel may be embedded into a flood coat of hot asphalt sufficient to cover the underlying plies.
3. Plies may also be surfaced with asphalt emulsion, Aluminum coating, or other approved elastomeric coating.
4. Plies must be covered with some approved surfacing. Leaving plies ex posed is not acceptable.
E. ROOF JACKS AND PLUMBING VENTS:
1. May be reused if in serviceable condition. When roofing over an existing roof, flashings should be lifted and installed with the new roofing.
2. Flashings should be set over the base sheet in a layer of plastic cement and nailed down typically with roofing nails that penetrate 3/4” minimum into the deck material. Flashings may also be strip mopped with the plies.
3. The flashing should be primed with an asphalt primer prior to solid mopping the plies to the flashing surface with hot asphalt.
4. Plumbing pipes may be sealed to the flashing with flashing tape, rubber collar, or plastic cement.
F. MISCELLANEOUS FLASHINGS:
1. All vertical angles should receive a cant strip if the curb is 2 or more inches high.
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| A triangular “cant strip” for verticle angle adherence |
2. Penetration flashings may be reused if in serviceable condition.
3. All sheet metal penetration flashings shall be set in plastic cement, nailed securely, primed, and solid mopped into ply system. Strip mopping flashings into the ply system may be acceptable with some manufacturer’s requirements.
4. Angles on gravel roofs should be surfaced with mineral surfaced cap sheet.
5. Top of base flashing should be nailed securely to prevent slippage.
6. Perimeter edges should be finished with sheet metal or 3 course minimum with webbing and plastic cement where applicable.
G. VERTICAL WALL FLASHINGS:
1. Properly surfaced roofing material may be turned up under existing counter flashing and nailed to prevent slippage.
2. If the existing wall was removed, the roofing material may be turned up a minimum 6” into the wall cavity and new stucco or siding installed over the roofing material.
3. Properly surfaced roofing material may be turned up 6” on an existing wall, nailed to prevent slippage, and sealed with a minimum 3 course using plastic cement and webbing.
H. EQUIPMENT SUPPORTS AND BLOCKING:
1. All large equipment blocks and/or sleepers shall be securely mounted to the roof deck and flashed into the roof membrane in an appropriate way.
2. Conduit and pipe blocking should not be sealed to the roofing membrane.
I. BUILDING DEPARTMENT INSPECTIONS:
1. Pre-inspection of roof overlays should be required especially where ponding water is a concern.
2. In-progress inspections should include spot checks of decking, roof application, and flashing installation.
3. Final inspections should be done while the roof is being finished.
