Clearing Drains Before the the San Fernando Valley Rains — What Changed This Year
What to do about a flat roof in the Valley in the first forty-eight hours, starting with the camera.
After a storm the useful work happens in the first two days, and most of it is documentation rather than repair. This is what to do about a flat roof in the San Fernando Valley once the wind drops.
What actually matters
Ponding is the beginning of most flat roof failures. Water standing more than forty-eight hours after rain is a defect, not a quirk of the building. It adds load, accelerates breakdown of the membrane, and in this climate leaves a mineral crust that holds the next rainfall in exactly the same place.
What to do in the first forty-eight hours
Document before you touch anything: wide photographs to establish the property, then close photographs of each item of damage, all dated. Drainage does not fail in the storm; it fails in the eight dry months beforehand. A drain that has been dry since April collects grit, leaves and debris, and nobody looks at it until water is coming through a ceiling. A tarp fixed through sound covering creates damage that was not there before.
How the San Fernando Valley changes the answer
Summer is the problem here. The Valley runs ten to fifteen degrees hotter than the coast and holds it for weeks, so a roof surface that reads 90 degrees in Santa Monica is well past 160 in Van Nuys by mid-afternoon. Everything on the roof expands into that heat and contracts again overnight, and it is that daily movement, not the peak temperature, that opens laps and backs fasteners out. Most of the housing went up between 1950 and 1975, which means original decking, undersized ventilation and at least one previous layer that somebody roofed straight over rather than tearing off.
What we look at on an inspection
- Fall across the roof, and any area holding water beyond forty-eight hours
- Drain and scupper clearance, including underneath every strainer
- Membrane condition across the whole field, not only at the edges
- Flashing at every penetration, curb and item of rooftop plant
- Parapet termination and counterflashing along the full perimeter
- Insulation moisture, established by probe rather than by eye
- Evidence and quality of previous patching
Common questions
The damage looks minor. Is it?
Possibly not. Wind damage frequently looks trivial from the ground and turns out to have broken the seal across an entire elevation.
Should I get a tarp on it straight away?
Only once it is photographed, and only if it can be fixed without putting new holes through sound covering. A badly fixed tarp creates damage that was not there before.
The honest summary
Ponding, blocked drainage and failed penetration detail account for nearly every flat roof call we take. If a quote does not mention drainage, it is a quote to recreate the same problem in a new material. In the San Fernando Valley the thing to watch is attic temperature and intake ventilation, because a Valley attic that cannot breathe cooks the underside of the roof as hard as the sun cooks the top.
Free inspection, drone photography where access is difficult, and a written estimate with deck repair priced per sheet. No obligation.