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Installing a Vent Stack in Flat Roof Commercial Building St. Thomas Ontario

This week we were in St. Thomas Ontario working at a commercial site with a flat roof. We were at a construction site with a major renovation going on inside this old building that used to be a bank. It’s going renovated and turned into a medical clinic. The renovation contractor contacted Legacy Flat Roofing to install a vent stack in the flat roof as they want to vent a kitchen sink. So in this video we are going to show you the process of installing the vent stack in a single ply flat roof system.

The first step to installing the vent is to clean the surface of the flat roof. A lot of oil, dirt and debris can attach itself to the membrane over the years, which will stop anything bonding with the surface. We use a special membrane cleaner as the surface has to be perfectly clean, then we are going to start drilling through the roof.

The surface on this flat roof is the membrane, light plywood, insulation, and then the metal deck. We cut our hole, cleaned up the area again, and let the cleaning agent flash, or evaporate.

We then apply some adhesive underneath the boot/flange of the drain so that we can ensure a tight seal so the stack stays in place, and doesn’t leak any water. We are going to set the vent stack in place, and most of our waterproofing will be done on the top and outside of the stack. We will use an adhesive around the edge of the metal of the stack, then we will use the alsans around the outside of the stack, which allows us to detail the area how we like so it looks good and is water tight.

We always make sure to apply the alsans very carefully as you don’t want to create a mess, or have the finished product look sloppy. A workaround to make sure it looks nice is to use painters tape to form straight lines. We also cut our reinforcement strips ahead of applying the all sands so it doesn’t get chaotic. To get the best seal we apply alsans , then the reinforcement strips, let it all dry, then apply our final coat of alsans , and remove the tape to let it all set.

Using the multiple methods of adhesion and finishing with the alsans gives it a triple layer of protection. All in all the job turned out great, it’s a clean job and will provide great water proofing for the vent stack.