Inside a Flat Roof Replacement: Old Drain Box Out, Copper In

The roof before

This is the kind of flat roof Joe sees every week around Philadelphia: a dark, worn surface with patch marks from earlier repairs. Patches can stop a drip for a while, but each one adds another layer, and none of them fix what's underneath.

A big part of this job was the drain box, the metal box at the roof edge where rainwater leaves the roof and runs down into the downspout. When a drain box wears out or isn't sealed right, water can back up at the exact spot where the most water collects. On this roof the old box came out completely instead of getting patched again.

What the crew did

In Joe's own words from his post that day: "We tore out old drain box & installed a copper drain box along with a white granulated roofing system for extra UV protection & new drip edge metal."

• Old drain box out. Torn out completely, not covered over.
• New copper drain box in. Copper is a common choice for drain boxes because it holds up well to standing water and weather. Joe's post on the process says it was "properly sealed & water tight."
• White granulated roofing system. A light-colored cap surface reflects more sun than a dark one, which Joe uses for extra UV protection.
• New drip edge metal. Fresh metal along the roof edge so water drips clear of the wall instead of running behind it.

The drain box, step by step

These are the crew's own photos from the drain box swap. Tap any photo to see it bigger.

The finished roof

The finished roof is bright white, with the new copper drain box sealed in at the edge and new metal along the drip line. Compare it to the before photo at the top of the field guide, or drag the before and after slider on the home page.

Every roof is different. A roof with soft decking, several leak spots or a sagging section may need more work than this one did. Joe looks at your roof first and tells you what it actually needs. If you want the full picture of how a flat roof goes on from the deck up, read how a Philadelphia rowhome flat roof is replaced.