This tutorial explains how to diagnose and repair a roof leak caused by a cracked boot around the plumbing vent flashing.
I became aware of a possible leaky roof when I noticed water stain on the drywall ceiling. The water stain occurred during a period of record rainfalls and extensive flooding in the metro Atlanta, Georgia region. My area received about 17 inches of rain in an 8-day period! 17 inches of rain is a lot for an area that would normally less than 4 inches on average in September. With that much rain any roof leak, no matter how small, is likely to be noticed.
Finding the Roof Leak
The main attic is above the room with the water stain on the drywall ceiling. To locate the source of the leak, I got a flashlight and went into the attic. The stain is the corner next to the exterior wall, so I focused my search in that direction. The PVC vent pipe for the basement bathroom plumbing rises through the roof directly above the stain on the ceiling. The vent pipe became an immediate suspect.
Take care to walk only on the wood joists when working in the attic. The ceiling drywall will not support your weight and you can fall through! Move slowly and carefully.
This is the lower end of the vent pipe – it’s covered by blown fiberglass insulation. The dark bits on the insulation are nut shells left by flying squirrels that sometimes get into the attic during the winter. I catch them in a box trap to take them to the park and set them free unharmed. Last winter, when I opened the box trap to set the squirrel free, he ran out and turned around, sat up and stared at me for while before scampering off into the trees. Whether confused or saying “thanks!”, I’m not sure. But I digress.
I moved the insulation away to reveal the bottom of the vent pipe and ceiling drywall. The insulation and paper surface of the drywall were damp. I’m getting close to finding the leak.
A closer look at the vent pipe penetration through the roof revealed daylight shining through around the vent boot flashing. This is the source of the water leak! Rain water is coming in around the vent boot, running down the side of the vent pipe and dripping onto the drywall ceiling. Persistent heavy rains caused enough water to leak inside to be noticed.
On the positive side, the Oriented Strand Board (OSB) roof deck is dry and untouched by the leak. If the roof decking were rotted, the shingles would have to torn up and the rotted section of deck replaced – a major repair effort!
More rain was in the forecast and it might a take a couple of days to get a roofer over to repair the vent flashing. To minimize further water damage, I tied a towel around the pipe just above the horizontal brace. This is only a band aide solution.
Cracked Vent Boot
Now that I know what to look for, a crack or split in the vent boot is clearly visible in this photo (red square). The vent boot must hug the pipe tightly to form a watertight seal. The roof is about 10 years old and the vent boot has cracked from a combination of the UV rays from the sun, weathering, expansion and contraction from the heat and cold.
The 2″ PVC vent pipe with the cracked boot is shown here in perspective to the house. The roof is a steep 10/12 pitch and the house sits on a hillside. A 40 foot ladder is needed to reach vent pipe from the ground. Time to call a professional roofer to make this repair.
This repair is continued in Part 2.
Hope this helps,
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