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Roof Drainage System Considerations – Part 2 - September 2020

Mon, Sep 21, 2020

The core of that article stressed the importance of not reducing the size of any type of roof drainage. And not to do anything that can cause the roof to hold more water either during or after a rainfall than it was originally designed to hold. I also discussed how far we should have to go in bringing an existing building, which was built in compliance with the code when built, up to current code. Keep in mind that reroofing a building is a level 1 alteration and has a limited scope. Thankfully, we are not required to resize the drainage system to meet the most current code with each subsequent reroof. But what about some of the less obvious examples? Consider an existing building with parapet walls, internal primary drains and no provisions for secondary (emergency overflow) drainage (see picture 1 above). In these situations, several questions arise. First, is the roofing contractor required to add secondary drainage? I will try to answer that question after we review a few related code sections that apply. Read more


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