Should I repair my San Francisco roof or replace it?

Is it the roof, the parapet or the drain?

Many San Francisco leaks start at the edges of a flat roof: parapet caps, scuppers, drains that clog with leaves and grit, and the joint where a pitched front meets the flat back. Those can often be repaired. When the membrane itself is brittle, blistered or split in several places, patching starts to cost more than it saves.

When does a San Francisco roof cross the line?

• The membrane is past the life InterNACHI lists for its type (modified bitumen about 20 years, built-up about 30) (InterNACHI).
• Water pools for days after rain across large areas, not just at one drain.
• A roofer finds wet insulation or soft decking in more than one spot.
• The roof already has two or more layers, so the code won't allow another one on top (CRC R908).

Does an old Victorian roof change the answer?

Steep Victorian and Edwardian gables often outlast the flat sections behind them, but their valleys, bay-window roofs and cornice flashing fail first. A good assessment looks at each roof plane separately; replacing the flat roof now and the steep front later is a common split.

What does the city allow for repairs vs. replacement?

DBI's online reroof permit covers replacing the roof covering without structural work. If rotten decking turns up, replacing it needs an over-the-counter building permit (SF.gov).