Flat Roof Repair, Coating or Replacement: How to Decide

This page covers houses with flat or low-sloped roofs under the 2025 California codes, in force since January 1, 2026. It doesn't price the work or predict how long a coating or a roof will last, and it can't diagnose a leak at a distance. Which system to choose for a new flat roof is in flat roof options for Los Angeles homes; repair or replacement on a pitched roof is in roof repair or replacement, and the defects of a built-up roof, from blisters to slipping plies, in hot mop roof: repair or replace.

The rest of this page goes through each step, starting with the one most bids skip.

• Infrared imaging (ASTM C1153). A scan at night locates wet insulation in roofs that have insulation above the deck in contact with the waterproofing.
• Electronic leak detection (ASTM D7877). Electrical conductance methods locate leaks in exposed or covered roofing membranes.

Where a house's insulation sits below the deck, between the joists, rather than above it, the useful checks are a core cut or test opening through the roofing, and the ceiling below: a stain, a sag or a soft spot over the same area tells you where water has been. Ask what was checked and where. A bid for a coating that rests on a walk-over alone is a bid that hasn't looked.

Two rules follow a repair:

• The Energy Code doesn't treat it as a re-roof. California's 2025 Energy Code defines a repair as reconstruction or renewal for maintenance, and treats replacing a component that has energy requirements as an alteration instead. Its cool-roof and insulation rules for roofs apply when more than 50% of the roof is replaced.
• A permit depends on the city and the size. The City of Los Angeles draws the line by value (work of $2,500 or less may be exempt, with conditions), Long Beach exempts roofing repairs of up to 100 square feet in 12 months, and Santa Clarita up to 10% of the roof or 200 square feet, whichever is less, in a year. Unincorporated Los Angeles County and Burbank have no roofing item in their exemption lists. The details are in re-roof permit rules across LA-area cities.

1. Not leaking. Coatings may seal some pinholes, but they generally won't find and repair existing leaks; those have to be found and fixed first, and the repairs allowed to dry.
2. Draining. A coating goes only on a roof that drains properly; some coatings are adversely affected by ponding water, so ponding areas are repaired before coating.
3. Dry underneath. All wet roof insulation is removed and replaced before coating.
4. Holding the coating. An adhesion test confirms the coating will stick to the existing surface; a primer may be needed, and the surface has to be clean and completely dry.
5. Not past its life. A coating can help a roof age more slowly, but it can't add life back to a roof already beyond its service life.

Two LA-specific rules apply as well. Under the 2025 Energy Code, the re-roof rule counts "adding a new surface layer on top of the existing exterior surface," so a coating over more than half of a low-sloped roof needs a reflective, CRRC-rated product in climate zones 4 and 6 through 15; whether the insulation part of the rule applies to a coating-only job is a question for the building department. And in the South Coast Air Quality Management District, Rule 1113 limits roof coatings to 50 grams of volatile organic compounds per liter. The coating types and the energy rules are compared in flat roof options for Los Angeles homes, and how acrylic and silicone differ on manufacturers' data sheets in silicone, acrylic or elastomeric roof coating.

A recover is allowed under CRC R908.4 where the new covering's manufacturer allows it, and the same section lists a new coating over an existing low-slope roof among the recovers it permits. It rules a recover out where:

• the existing roof or covering is water-soaked or has deteriorated to the point that it isn't an adequate base;
• the existing covering is slate, clay, cement or asbestos-cement tile;
• the existing roof already has two or more applications of any type of roof covering.

Some agencies go further. Unincorporated Los Angeles County's re-roofing code manual lets the building official keep the old covering only when inspection shows no more than one layer of certain listed types, with a sound deck and framing able to carry the added weight; Long Beach requires a tear-off once a roof has two or more applications. If your roof already has two coverings on it, ask the building department before any bid that leaves them in place.

• The Energy Code, when more than half the roof is replaced. A low-sloped roof needs a reflective surface (aged solar reflectance 0.63 with thermal emittance 0.75, or SRI 75) in climate zones 4 and 6 through 15, unless insulation at the deck is used instead, and R-14 continuous insulation in zones 1, 2, 4 and 8 through 16, with exceptions for roofs already insulated. The details, the exceptions and the stricter local values in unincorporated LA County and Burbank are in flat roof options for Los Angeles homes.
• Insulation between the joists, once the cavities are open. The Energy Commission's 2025 compliance manual treats a roof as altered when the work opens up the space between the framing members, and the code's minimum for ceilings and rafter roofs in an alteration is R-19 between the framing, or an assembly U-factor of 0.054. On a flat roof where deck boards come off, ask whether the bid includes it.
• Slope. On a re-roof, CRC R908.1 doesn't require the 1/4-inch-per-foot minimum slope for a roof that drains positively. A roof that ponds doesn't get that exception, so correcting the slope, with tapered insulation or reframing, belongs in the scope.
• A permit with inspections. The agency, the permit type and the inspections are in re-roof permit rules across LA-area cities, and for the City of Los Angeles in roof permit in Los Angeles.

Water that stands is a drainage problem first. Clear and check the drains, scuppers and overflow outlets, find where the condensate goes, and look at the slope toward the drains. A coating over ponding areas works against the manufacturer's own instruction; a recover or replacement over them carries the problem into the new roof. California's residential code requires a roof drain at each low point unless the roof drains over its edges, and, where a parapet would trap water if the drains back up, an emergency overflow (CRC R903.4 and R903.4.1). The causes of ponding and the fix for each are in ponding water on a flat roof: causes and fixes.

1. What was checked under the surface? A moisture survey, core cuts or test openings, and the ceiling below, and where.
2. What happens to wet areas? How much will be cut out and replaced, and what the bid does if more is found.
3. Repair, coating, recover or replacement, and why? The reason should come from the roof's condition, not from what the company sells.
4. For a coating: the product, its CRRC rating, the adhesion test, the primer if any, and how the leaks and ponding areas are fixed first.
5. For a recover: how many coverings are there now, and whether the new one's manufacturer allows it over what's there.
6. For a replacement: the insulation the Energy Code calls for at your climate zone, insulation between the joists if they're opened, how the slope and drains are corrected, and how the flashings are raised at parapets and doors.
7. The permit, and who warrants what: the agency and permit type, the manufacturer's warranty and the roofer's workmanship warranty, each in writing; what each kind covers is in roof warranties explained.

Cali Energy holds California contractor license #1032379, with C-39 Roofing, B General Building and C-10 Electrical, the classification that covers solar. Our roofing work is on our roofing page.

Code sections, rules and figures on this page come from the primary sources below. Codes, local requirements and product terms change; each was verified October 9, 2026.

1. California Residential Code 2025, Chapter 9, Roof Assemblies (R903.4, R908.1, R908.3, R908.4, R909)
2. California Energy Commission, 2025 Building Energy Efficiency Standards (Title 24, Part 6), CEC-400-2025-010, sections 100.1 (definitions),…
3. California Energy Commission, Single-Family Residential Compliance Manual for the 2025 Standards, CEC-400-2025-005
4. GAF, Liquid-Applied Roofing Manual, version 2.1 (2024)
5. ASTM C1153, Location of Wet Insulation in Roofing Systems Using Infrared Imaging
6. ASTM D7877, Electronic Methods for Detecting and Locating Leaks in Roofing and Waterproofing Membranes
7. South Coast Air Quality Management District, Rule 1113, Architectural Coatings