Adding a Penetration to Your Commercial Roof: What You Need to Know

July 13, 2020

You’re adding new manufacturing processing pipes, coax cable, a plumbing vent, or a new HVAC unit; a roof modification is inevitable. Sealing the new penetrations properly means the difference between endless maintenance and a watertight roof. There are three different approaches your roofing contractor can take to flash the penetration and some essential steps you should follow.

Premanufactured Flashing (aka Boots)

The more information and notice you provide the roofing contractor before they arrive on site, the greater the odds are that they’ll come prepared with premanufactured boots to use.

This cone-shaped flashing looks more like a witch’s hat than an actual boot. Most are seamless to create a watertight seal and slide down over a pipe before being heat-welded or sealed to the field of the roof. Without the need to fabricate the flashing, the process of sealing the penetration is faster, resulting in less labor and expense.

Field Wrap Flashing

When premade flashing is not available or cannot be used (e.g. there’s a continuous pipe, penetrations are too tall, it’s an odd shape, etc.), a boot can be made from non-reinforced membrane. This field fabrication process involves the following general steps:

  1. Heat weld one to two pieces of detail membrane to the roof around the base of the penetration and ½- to 1-inch up the penetration.
  2. Using adhesive, apply a vertical piece of detail membrane around the penetration’s circumference (heat welding where it overlaps) with a ½-inch minimum coming down onto the roof surface.
  3. Caulk the field wrap flashing with sealant around the top of the penetration and add a worm gear clamp. Field fabrication is sometimes called the “caulk and band” method for this reason.

The finished flashing should be a minimum of eight inches in height above the field of the roof. This method is more labor intensive but an ideal option for most hard-to-flash penetrations.

Pitch Pans

Only as a last resort, are pitch pans (or pitch pockets) used around penetrations. What was once a common practice, is now a method that is best avoided whenever possible. Most manufacturers make pre-made pitch pans that can be purchased and welded directly to the membrane. Clad metal (weldable) is another option for a custom pitch pan. These are all filled 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 reason roofing contractors avoid using pitch pans unless necessary, is the maintenance they require. In time the sealant shrinks and dries out; this causes it to crack and pull away from the sides. Once the sealant becomes concave, it traps water and leaks are likely.

Steps to Take

There are five things you need to do when installing a new penetration on your commercial/industrial roof.

  1. Notify the roof system manufacturer so the work is warrantied. Manufacturers may complete an inspection to ensure alterations were done properly.
  2. Hire a roofing contractor that is licensed by the roof system manufacturer of the system you have installed.
  3. Put your roofing contractor in contact with the HVAC installer, cable company, etc. Together they can discuss the location of the penetration and appropriate flashing details.
  4. Plan ahead. Schedule the work when both contractors are available.
  5. Let your roofing contractor do the roofing work to ensure a watertight seal.

A professional roofing contractor knows how to work safely on the roof and will complete the flashing detail according to manufacturer specifications and the National Roofing Contractors Association’s repair manual. Your HVAC tech might create twice the work for your roofing contractor if they remove the roof membrane. With careful scheduling and sequencing of the work by both parties, your new penetration will be installed properly.

To schedule roofing service, contact D. C. Taylor Co. at 319.363.2073 today.

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