New Flat Roof Installation in Los Angeles
New low-slope roofs for additions, ADUs, garages, patio covers, and new buildings by a licensed C-39 roofing contractor across Los Angeles County. Estimates are free.
- Licensed, bonded & insured
- CSLB #1119699 (C-39)
- BBB Accredited, A rating
Low-Slope Roof Installation on New Construction
Flat roof installation on this page means a new low-slope roof on a structure that has never had one: a room addition, an ADU, a garage, a solid patio cover, or a new commercial building. Because the roof starts from a bare deck and a set of plans, the slope, drains, edges, and every roof opening can be settled before any roofing goes on.
We install new flat roofs across Los Angeles County, working from the approved plans and the project’s inspection schedule, and we coordinate with the general contractor when there is one. Replacing a worn flat roof on an existing building is a different job, covered on our flat roof replacement page. For leaks on an existing roof, see flat roof repair.
For torch-down and other modified bitumen systems, Overhead Roofing is a Polyglass Premio Select Contractor (#9272).
1/4 inch per foot
Pitch under 2:12
Class A roof assembly
CSLB #1119699 (C-39)
Flat Roofs on Additions, ADUs, Garages, and Patio Covers
Each kind of new structure brings its own roof details:
Room additions
A flat roof addition usually meets the house at a sloped roof or a stucco wall, and that junction needs flashing, and sometimes a cricket, so water does not collect against it. Under the Energy Code, an addition is treated much like new construction, so the roof has to match the energy documents in the approved plans.
ADUs
The Energy Commission’s ADU guide treats a detached ADU built from the ground up as a newly constructed building, and an attached ADU or a converted garage as an addition. A newly built detached ADU generally needs a solar PV system, so the ADU roof should leave room for the array and plan how its mounts will be flashed.
Garages and carports
Garage roofs are often framed nearly level, and water that stays on a roof wears it out. A flat roof for a garage needs the slope the code requires, a planned edge for the water to leave by, and a gutter or scupper at that edge. If anyone will walk on it to reach equipment, the surface has to take foot traffic.
Solid patio covers
A flat roof patio cover attached to the house is a small low-slope roof with a long joint against the wall. The ledger board along that wall needs flashing that sheds water away from the house, and the cover should slope away from the wall toward a gutter along its outer edge.
New commercial buildings
New commercial roofs bring roof drains, overflow drains or scuppers where parapets would trap water, rooftop units on curbs, and edge metal that has to be designed and tested for wind under the California Building Code. Our commercial roofing page covers that work in more detail.
Slope, Drainage, and Roof Openings on New Flat Roofs
The California Residential Code sets a minimum design slope of 1/4 inch per foot for modified bitumen, single-ply, built-up, and liquid-applied roofs. Unless a roof is sloped to drain over its edges, it needs a roof drain at each low point, and where parapets surround the roof, overflow drains or scuppers give water a way off if the main drains clog.
On new work, slope is easiest to build into the framing, with joists set at a pitch or tapered framing on top of them. Tapered insulation is the other option, and it can also supply insulation the energy plans call for.
Every pipe, vent, skylight curb, and equipment curb that goes through the roof should be in place, or at least located, before the membrane goes on. Openings cut later by other trades are a common source of leaks on new flat roofs, so ask that any later penetration be flashed by the roofer.
Choosing a Flat Roof System for New Construction
The right system depends on the structure, who walks on the roof, and what sits next to it:
| Project | System that usually fits | Why |
|---|---|---|
| Garage, carport, or small addition | Torch-down modified bitumen with a mineral cap sheet | Stands up to foot traffic, is simple to patch, and suits small roofs with lots of edges |
| Roof beside wood siding or trim | Self-adhered modified bitumen | Goes on without an open flame near combustible materials |
| Large, simple commercial roof | TPO single-ply | A white membrane with heat-welded seams suits big, open roof areas |
| Deck or balcony over living space | A walkable waterproofing system | Standard roof membranes are not made for furniture and daily foot traffic |
Where a cool roof is required, the product chosen must carry a CRRC rating that meets the rule.
Modified bitumen roof installation on a new wood deck starts with a base sheet nailed to the deck, and the cap sheet is then torched or adhered over that base. Torch-down roof installation never puts the flame directly on the wood. For TPO details, see our TPO roofing page.
Call (877) 557-7778 any time, or use the form below. Office hours are Sunday through Friday, 8 a.m. to 5 p.m.
Energy Code, Fire Rating, and Permits for New Low-Slope Roofs
Cool roof rules. California’s Energy Code defines a low-slope roof as one with a pitch under 2:12. For homes and additions over 300 square feet, the state’s prescriptive cool roof values for new low-slope roofs apply in climate zones 13 and 15, which do not include Los Angeles County. The City of Los Angeles is different. Its cool roof ordinance covers new homes and additions, except additions under 500 square feet of new roof, or under half the total roof area if that is larger. Your project’s energy documents list what the roof must meet.
Fire rating. Where the California Wildland-Urban Interface Code applies (the fire hazard severity zones it covers, including every Very High zone), a new roof has to be a Class A assembly. The rating belongs to the assembly, so the membrane, the layers under it, and the deck must be a tested combination.
Permits. On new construction, the roof is part of the project’s building permit, issued by LADBS in the City of Los Angeles, by each city’s own building department elsewhere, and, for unincorporated areas, by LA County Public Works. We schedule the roof around the inspections set for the project.
Scheduling the Roofer on an Addition or ADU
A new flat roof goes on at a set point in the build, and a few things keep it on track:
- A finished deck. Roofing starts after the framing and sheathing are done and any inspection your building department requires for them has passed.
- Settled edge details. Wood nailers, fascia, and gutter or scupper locations are decided first, because the edge metal fastens to them.
- Penetrations in place. Plumbing vents, exhaust fans, skylight curbs, and equipment curbs are easiest to flash when they go in before the roof.
- Dry weather for the membrane. Torch-down and TPO need a dry deck, so a deck finished during the November-to-March rainy season may need temporary protection until the roof goes on.
- Protection afterward. Trades working on the finished roof should use walk pads or plywood over the membrane and report any damage.
What Goes Into a Flat Roof Installation Estimate
We price new flat roofs from the plans and a site visit, and we don’t publish set prices. Flat roof installation cost depends mostly on these factors:
- Roof area, shape, and the number of edges and corners
- The roof system and any cool roof or fire rating it must meet
- How the slope is created, in the framing or with tapered insulation
- Drains, scuppers, gutters, and edge metal
- The number of curbs and penetrations to flash
- Tie-ins to an existing roof or wall
- Height, access, and how materials get onto the roof
You get a free written estimate, and our roofing cost guide walks through the price ranges that public sources report for the region.
Our Reviews
Get an Estimate for a New Flat Roof
Send us the roof plan or a sketch with the roof size, tell us what is being built and where, and let us know your schedule. Call (877) 557-7778. Our license is CSLB #1119699 (C-39); we are bonded and insured, and estimates are free.
Get Your Free Estimate
Please fill out the form below, or call: (877) 557-7778
Please fill out the form below, or call:
(877) 557-7778
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We specialize in helping LA homeowners and business owners protect their most valuable assets with dependable roofing solutions that last. Our licensed contractors are standing by, ready to inspect your roof, answer your questions, and provide a clear action plan all at no cost to you.
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Questions About New Flat Roof Installation
How much slope does a new flat roof need?
The California Residential Code requires a design slope of at least 1/4 inch per foot for modified bitumen, single-ply, and built-up roofs. That is the minimum. The goal is a roof that drains within 48 hours after rain, which is how the roofing industry defines positive drainage. On new work, the slope is easiest to build into the framing.
Do I need a cool roof on a new ADU or addition in Los Angeles?
It depends on where the house is. Within Los Angeles city limits, a local cool roof ordinance applies to new homes and to additions above its size threshold. Elsewhere in the county, the state’s prescriptive cool roof rule for new low-slope residential roofs covers climate zones 13 and 15, which are outside Los Angeles County. Your project’s energy documents state what the roof must meet.
Can a new flat roof tie into my existing shingle or tile roof?
Yes, and that joint is the part to plan carefully. Where the new flat roof meets the old sloped roof, the existing shingles or tiles are opened up so the flashing and membrane can run under them, and a cricket may be needed to move water away from the joint. Brittle roofing at that spot may need a small repair first.
Can solar panels go on a new flat roof?
Yes. Newly built homes and detached ADUs generally need solar PV under California’s Energy Code, so plan the array along with the roof. Mounts that pass through the membrane need flashing made for that roof system, and ballasted racks need a surface and framing that can carry the weight. Tell us where the array will go before flat roof installation starts.
Do you install flat roofs in Santa Monica, Culver City, and Pasadena?
Yes. We build new flat roofs all over Los Angeles County, from Santa Monica and Culver City to Pasadena and the San Fernando Valley, and we take projects in Orange and Ventura counties too. Each of those cities has its own building department, so permits and inspections come from the city where the project is, and the Los Angeles cool roof ordinance applies only inside city limits.
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