Installation Details · FAQ

How does drainage work on a flat commercial roof?

Flat roofs aren’t truly flat. The standard slope is 1/4 inch per foot toward roof drains or scuppers — about 1% slope, which moves water reliably to the drains without being visually noticeable from the ground. Trill installs tapered insulation when needed to create slope on roofs that started life truly flat.

For a 5,000 square foot Madison County commercial building, Trill typically installs four roof drains (one per 1,250 sq ft) with internal piping to grade or to a parapet scupper outlet. Drain placement matters: low points should be at least 6 feet from any HVAC unit (so condensate doesn’t pool around the drain) and 18 inches from any seam or penetration. Proper drainage is the single biggest factor in commercial roof lifespan; standing water cuts membrane life by 30 to 50%.