Parapet and Pitch-Pan Leaks on a Built-Up Roof
A 30-year-old 4-ply built-up roof with gravel surfacing sits on a 1/4:12 slope over a concrete deck. The parapet is 18 in. above the roof surface. A steel column penetrates the roof, protected by a pitch pan filled with asphalt mastic; the pan is 6 in. above the roof. The base flashing at the parapet is 6 in. high, nailed at the top and covered with a 4-in. lap of siding that stops 2 in. above the roof. During a 2-hour water test, water appears at the interior column base and at the parapet base. The drain is at the low point but the roof ponds 1 in. deep near the drain. The owner wants a spot repair without tear-off.
1. What are the minimum flashing heights and counterflashing requirements for the parapet and pitch pan?
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The details are below common minimums:
- Parapet base flashing. Six inches is marginal. Good practice calls for base flashing at least 8 in. above the roof surface, with the top edge turned into a reglet or covered by counterflashing. The flashing must be continuous and adhered to the wall, not nailed through the top edge where water can enter.
- Counterflashing. Counterflashing should overlap the base flashing at least 4 in. and be set in a reglet at least ½ in. deep, caulked and fastened above the water line. The siding lap stopping 2 in. above the roof is not counterflashing; it leaves the base flashing top exposed and nailed.
- Pitch pan. A 6-in. pan is low for a roof penetration. The pan should extend at least 8 in. above the roof, with a flange sealed to the membrane, and be filled with a compatible pourable sealer reinforced with fabric around the column. The sealant should not be relied on alone.
Ponding raises the water level at the drain, so even a flashing height that looks adequate can be submerged.
2. Diagnose the leak paths at the parapet and column.
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Parapet leak. The base flashing is only 6 in. high and is nailed at its top edge. The nails create holes, and the siding lap stops 2 in. above the roof, so water running down the wall can get behind the flashing. There is no effective counterflashing or reglet. With 1 in. of ponding, the water line is close to the top termination.
Column leak. The pitch pan is 6 in. above the roof and filled with mastic. Asphalt mastic shrinks and cracks with temperature cycling, especially around a steel column that moves at a different rate. Water sits in the pan or behind the mastic and travels down the column flange. The pan flange may also be poorly bonded to the BUR plies.
Ponding at the drain increases hydrostatic pressure at both details and prevents the roof from drying. The water test is valid evidence because it isolated both leak paths.
3. Specify the repair sequence and verification.
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- Remove gravel and cut back flashings at the parapet and column to sound membrane. Do not simply add mastic over the old detail.
- Correct drainage. Add crickets or tapered insulation to eliminate the 1-in. pond at the drain, and verify the drain is clear and the strainer is correct.
- Parapet flashing. Install new base flashing at least 8 in. high, adhered to the wall, with a reglet and new counterflashing overlapping at least 4 in. Seal the reglet and fasten above the water line.
- Column pitch pan. Install a new pan at least 8 in. above the roof with a properly adhered flange, fill with a compatible flexible sealer reinforced with fabric, and detail the column with a water shed.
- Reinforce field plies and re-gravel.
- Verify. Perform a controlled 2-hour water test at the repaired details, inspect the interior during the test, and photograph the flashing heights. Re-test after the first rain.
A spot repair that only re-caulks the pitch pan and the parapet top will not stop water entering behind the flashing.