Why is my roof leaking after heavy rain in Van Nuys
Why is my roof leaking after heavy rain in Van Nuys has a short answer and a longer one. The short answer is that concentrated winter rain finds the weakest detail on an ageing roof. The longer answer — which detail, and why now — is what this guide covers, with the first-hour steps and the checks that actually find the entry point.
The short answer: heavy rain finds weak details
Van Nuys rain is concentrated: 13.42 inches a year, February wettest at 3.79 inches, July at 0.00 inches (NOAA 1991–2020, Van Nuys Airport). A roof that survives months of dry heat can leak in the first heavy storm of winter, because rain tests valleys, flashing and penetrations all at once, while heat has been ageing shingles, sealant and underlayment all summer.
The dated benchmark is 4 February 2024, when 4.30 inches fell in one day. A leak that appears only in heavy rain, and not in light rain, usually points to a capacity or detailing failure — a valley, a flashing step, a gutter or downspout — rather than a hole in the field.
The six most common causes after rain
Valley failure, where debris or worn valley material lets water under the covering. Flashing failure at chimneys, walls, skylights and vents, where sealant has dried or a step has lifted. Penetration failure at pipe boots and vents, a small detail with an outsized leak record. Ridge and cap damage from Santa Ana wind, opened up before the rain arrives. Gutter and downspout blockage, where overflow runs back onto fascia and the roof edge. And underlayment ageing, especially under sound tile, where the covering looks fine and the layer beneath it has failed.
In every case, the stain inside is rarely directly below the entry point. Water travels along the deck, along rafters, and along flashing before it drops through a ceiling, which is why patching above the stain so often fails.
What to do in the first hour, and what not to do
Inside, move belongings clear, catch the drip, and note where the stain is and when it started. Photograph the stain and, from the ground, any visible roof damage, with dates. Keep clear of electrical fittings where water is entering, and do not go onto a wet roof.
Do not coat a large area in sealant, do not assume the field above the stain is the problem, and do not accept a full-replacement verdict before the roof has been walked and the entry point traced. A written scope after inspection should name the failed detail, the repair, and the permit route where one applies: A permit is required — confirm the repair-vs-re-roof line with LADBS for your scope. Van Nuys is in the City of Los Angeles, so permits run through LADBS, not the County.
Related pages: roof leak repair and roof inspection and Roofing in Van Nuys. To discuss your roof, see contact or call (818) 474-8963.
A few answers before you start
Heavy rain tests valleys, flashing, penetrations and drainage capacity all at once. A failure that light rain does not reach can appear only in a heavy storm.
Rarely directly. Water travels along the deck and flashing before it shows inside, which is why tracing, not patching above the stain, matters.
Move belongings clear, catch the drip, note dates, photograph from the ground and inside, keep clear of wet electrical fittings, and call (818) 474-8963 to discuss inspection and a written scope.
Get your Van Nuys roof leak fixed before the next storm
Call (818) 474-8963 to describe what you are seeing, or see contact for the address. Scope is discussed in writing before work starts.