The short version of the "25% rule": if more than 25% of a roof is damaged or repaired within a year, the whole roof has to be replaced instead of repaired. You will find it quoted all over the internet, and sometimes by roofers standing in a driveway.
Where the 25% Rule Comes From
The 25% rule lives in the Florida Building Code (Existing Building, Section 706.1.1). In Florida, if more than 25% of a roof section gets repaired, replaced, or recovered in any 12-month period, the entire roof system has to be brought up to current code. It came out of hurricane country, and even Florida loosened it in 2022. Newer roofs there can now be repaired past 25% without triggering a full replacement.
Does California Have a 25% Rule?
No. There is no statewide 25% rule in the California building code.
If a roofer points at 25% damage and says "code requires a full replacement," ask them to show you the code section. That is a fair question, and a good roofer will not mind it.
That said, California has its own rules that decide whether your roof can be repaired, and some of them are stricter than people think.
What California Actually Requires
Two layers, max. California's residential code allows at most two layers of roofing. If your roof already has two, the next job is a tear-off. No third layer, period.
The deck has to be sound. If the wood under your roofing is water-soaked or deteriorated, it comes out. This usually gets discovered during tear-off, which is why an honest bid talks about wood repair up front instead of surprising you later.
Wood shake? Plan on a resheet. Shake gets torn off. Roofing over it is off the table in nearly every city. And shakes usually sit on spaced boards with gaps between them, not solid decking, because shake roofs were built to breathe. New shingles need a solid deck under them, so in most cities the job includes new plywood or OSB over those old boards before the new roof goes on. That is the resheet. Budget for it from the start; it is not an extra, it is the job. And most cities around here will not approve new shake going back on anyway, thanks to fire rules, so a shake roof comes off once and comes back as shingle or tile.
The 50% energy trigger. This is the one that catches people. Under Title 24, California's energy code, if you replace or recover more than half your roof, the project generally has to meet current cool-roof standards. The Inland Empire sits in climate zone 10, where those requirements apply to sloped roofs, and the code that took effect January 1, 2026 made them stricter. There are exceptions, but this is why "just patch the other half next year" is not always the money-saver it sounds like.
Your city has a say. Ontario, Rancho Cucamonga, Eastvale, Fontana: each building department runs its own permit process. Small repairs may not need a permit. A reroof does.
Can You Repair More Than 25% of a Roof in California?
Legally? Usually, yes. Code does not stop you at a percentage.
Practically? This is where the 25% idea holds a little truth. Once repairs start covering a quarter to a third of a roof, you are paying repair prices for a roof that still has old-roof problems. At some point, replacement is the better use of the same money. Where that point sits depends on the roof: age, material, and how the rest of it is holding up. I wrote about how we make that call in Repair or Replace.
One more thing: your insurance policy may have its own repair-versus-replace thresholds. That is a contract question, not a building-code question. Read the policy, or have us walk the roof and document what is actually up there, so you are negotiating with photos instead of guesses.
Not Sure Which Side Your Roof Lands On?
We will take a look and tell you straight: repair if repair makes sense, replacement if it does not. The same answer we would give a family member.