Know Your Roof Penetrations
The reasons for roof penetrations are numerous: roof vents, electrical conduit, utility pipes, satellite dishes, HVAC curbs, lightning protection. According to the National Roofing Contractors Association (NRCA), “The most vulnerable part of any roof system is that point at which the horizontal roof deck and a vertical surface join.” While some roofs have more penetrations than others, all penetrations can be a source of leaks if not installed and maintained properly.
Roof penetrations should be flashed in accordance with the roof system manufacturer’s instructions, using material compatible with the roofing membrane. Where possible, flashings should extend a minimum of eight inches above the finished roof surface.
The Trouble with Pitch Pockets
In the past, using pitch pockets (or pitch pans) around penetrations was a common practice, especially on modified bitumen and built-up roofs. This method involved installing a 2-inch high flanged open-top metal box placed around the penetration, mechanically fastening it to the roof and filling it with non-shrink grout. Pourable bituminous or polymeric sealant is added on top and built up (sloped) so water runs down and away from the penetration.
The NRCA has been discouraging the use of pitch pans for almost 20 years. They are a last resort and should only be used when other methods are not practical. The reasons why are many, but the most compelling is that they are a maintenance headache. Over time, the sealant shrinks and dries out, which causes it to crack and pull away from the sides. As soon as the sealant becomes concave, it traps water and leaks are likely. A pitch pocket is one of your roof’s most vulnerable features.
When this happens, don’t just apply more sealant. That will last less time than the original application did. The old sealant needs to be cleaned out and fully removed, the concrete grout checked, and only then filled with more sealant. A weatherproof sheet metal rain hood is a good idea to protect the sealant from the elements.
Today, liquid-applied, fabric-reinforced flashing materials provide a better alternative to pitch pockets in most situations.
When your roof is first installed by a professional roofing contractor, it’s likely the roof penetrations were sealed properly; however, when new penetrations are installed on existing roofs, problems often arise. Here’s why:
- Incompatible materials used to flash penetrations. Improper materials and installation can inadvertently void the roof system manufacturer warranty.
- Pitch pockets used when other flashing methods would provide a better outcome (i.e. easier long-term maintenance, less likelihood of leaks, etc.).
- Penetrations sealed by non-roofing professionals. The satellite installer or plumber isn’t likely to do the job the way your roofer would, especially one who is certified by the manufacturer of your roof system.
What to Do if You Need to Add a Penetration
There are a few basic steps which will improve the quality of waterproofing around new penetrations, reduce the amount of maintenance required, and lower your chance for leaks.
First, put your service contractor in contact with your roofing contractor (someone approved by the roof system manufacturer). The roofing contractor can advise the service contractor on adequate spacing between penetrations (24-inch clearance between walls and curbs and 12 inches between pipes and curbs) and appropriate flashing details. If your roof is currently under warranty, the roofing contractor should notify the roof system manufacturer that new penetrations were added to the roof.
Lastly, schedule the work so the roofing contractor can come in after the subcontractor to seal the penetration. A reputable roofing contractor will ensure that the penetration is sealed according to manufacturer specifications using the recommended practices of the NRCA.