{"id":2957,"date":"2026-09-09T18:49:16","date_gmt":"2026-09-09T18:49:16","guid":{"rendered":"https:\/\/www.vikkins.com\/?p=2957"},"modified":"2026-09-09T18:49:16","modified_gmt":"2026-09-09T18:49:16","slug":"roof-slope-steel-drainage","status":"publish","type":"post","link":"https:\/\/www.vikkins.com\/fr\/roof-slope-steel-drainage\/","title":{"rendered":"Roof Slope: The Small Number That Decides Whether Your Roof Leaks in Year Ten"},"content":{"rendered":"

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\"Steel
Every profiled steel roof relies on slope to do a job the panel itself cannot do: keep water moving fast enough that it never has time to find its way backward through a lapped seam.<\/figcaption><\/figure>\n

A warehouse roof passes inspection. No leaks, no complaints, nothing on the punch list. Eight years later, water starts coming through at the panel laps \u2014 not during the heaviest storm of the year, but during ordinary rain that the building has handled hundreds of times before.<\/strong><\/p>\n

Nothing failed. No panel cracked, no fastener sheared, no membrane tore. The roof simply did, slowly and consistently for eight years, what a slightly-too-low slope always does: it let water sit at the laps a little longer than it should have, every single time it rained.<\/p>\n

The slope was on the drawing. It met the stated minimum. And it was still wrong \u2014 because the number on the drawing and the number the roof actually has once it is built and loaded are not the same number.<\/p>\n

Why steel roof slope drainage needs more pitch than a membrane roof<\/h2>\n

This is the point most buyers miss, because most general guidance on roof slope comes from membrane roofing \u2014 TPO, EPDM, built-up systems \u2014 where the entire surface is a continuous, sealed sheet. A membrane roof’s minimum slope exists mainly to prevent standing water (ponding) from sitting on the membrane long enough to accelerate UV and thermal degradation. Positive drainage for membrane systems is commonly specified around 2% (roughly 1\/4 inch per foot).<\/p>\n

Profiled steel roofing \u2014 trapezoidal sheet or insulated sandwich panel \u2014 has a second, more urgent failure mode that membrane roofs do not: the side-laps and end-laps between panels.<\/strong> These are not continuous seals. They are overlapping metal edges, sometimes with a sealant bead, relying on geometry and gravity to keep water moving downhill and off the roof before it can find its way sideways or backward under the lap.<\/p>\n

At low slope, three things work against the lap:<\/p>\n