Found out my local code requires 1/4 inch per foot slope on flat roofs, not 1/8 like I thought

Was double checking a permit application last month and stumbled on the city code for my area. Turns out I've been under-sloping my last 3 residential flat roof jobs by half. Has anyone else found a local code requirement that surprised them like this?

3 comments

3 Comments

wesley_jones22d ago

Had a buddy who ran into this exact thing last year. He was doing a garage addition for a neighbor and figured he knew the slope rules cold. City inspector showed up, pulled out the tape measure, and told him it was wrong on the spot. Turned out his local code had changed in 2021 but nobody told him. He had to redo the entire underlayment and add another layer of foam to get it to 1/4 inch. Cost him two weekends and a couple hundred in materials. @miller.emery sounds like he learned that lesson the hard way too. These little code surprises are a pain but they save headaches later.

miller.emery22d ago

Had the same thing happen to me a few years back. Changed my mind on it quick once I saw the actual code.

hall.joel22d ago

Read an article from Fine Homebuilding last month that talked about how code updates are happening faster now than they did twenty years ago. They said some cities are adopting new codes every three years instead of every five. Makes it hard for guys who learned the trade a while ago to stay current. That slope thing with the underlayment is one of those changes that seems small but really messes with your whole timeline.

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