The best flat roof material for a house is the one that fits how that particular roof is used: a white TPO or PVC membrane for a sunny roof over living space, modified bitumen (often self-adhered or cold-applied) for a small porch or addition roof that meets a shingle roof, a protected PVC or multi-ply membrane under a roof deck, and anything but EPDM near kitchen exhaust. On a house, the details around that material decide how long it lasts as much as the material itself. For advice on your roof, call NEMA Roofing at 866-631-3366.
Match the material to the roof
Most homes have one of a few kinds of flat or low-slope roof. Each one points toward a different choice.
| Roof on your house | What usually fits | Why |
|---|---|---|
| Main roof of a modern or mid-century home, over bedrooms or living space | White TPO or PVC, or a light coated or granulated modified bitumen cap sheet | Keeps heat off the rooms below; a reroof in climate zones 4 and 6 to 15 (the coast from Santa Barbara to Oxnard, and the San Fernando Valley) must meet cool-roof values anyway |
| Porch, patio cover, garage or addition joined to a shingle or tile roof | Modified bitumen, often self-adhered or cold-applied | Small areas with many edges and a joint to the pitched roof; an asphalt-based sheet laps and flashes well with shingle underlayment, and needs no open flame |
| Roof deck or balcony over living space | PVC or a multi-ply membrane rated for use under pavers or decking | The membrane is covered and hard to reach, so it must be the most reliable layer; pavers on pedestals protect it and lift out for inspection |
| Roof near a kitchen exhaust or grill vent | A membrane rated for grease, not EPDM | The U.S. Department of Defense’s roofing criteria state EPDM is not resistant to grease and oil |
| Roof with many skylights, vents and pipes | A system with prefabricated or liquid flashings for its penetrations | Every opening is a joint to flash, so clean, factory-made flashings reduce the places water can get in |
How each system is built, and how the main types compare, is in our flat roofing systems guide; the look and wear of each top surface is covered in flat roof surface finishes.
Why torch-free methods matter on a house
Some modified bitumen sheets are applied by melting them with a propane torch. On a house that raises a fire question, because most homes are wood-framed and the roof edges, parapets and wall framing near the torch are combustible. The Defense Department’s criteria (UFC 3-110-03), written for military buildings, go as far as prohibiting torch application over combustible decks and structures, and require a two-hour fire watch after the last torch is out even on noncombustible ones. For a home, ask which application method is proposed. Self-adhered and cold-applied modified bitumen, and heat-welded TPO and PVC (hot air, no open flame), avoid the question.
Coast, valley or hillside: how location changes the choice
- Near the ocean. Salt air is hard on metal, not on membranes. According to the UFC, steel with an aluminum-zinc coating holds up less well where salt spray reaches it directly, and different metals should not be combined; on a home near the beach, ask what the edge metal, scuppers and flashings are made of.
- Inland valleys. Heat is the main stress. The NOAA 1991-2020 normals for the Pierce College station in Woodland Hills show about 115 days a year at 90 degrees or above. A reflective surface, good insulation and a membrane that tolerates daily expansion and contraction matter most there, and Woodland Hills and Tarzana (climate zone 9) fall under the cool-roof values on a reroof.
- Hillside fire zones. In the City of Los Angeles, the building department requires a Class A roof covering within Very High Fire Hazard Severity Zones on re-roofing work; other cities and the counties set their own fire-zone rules, so check yours. On a flat roof the rating belongs to the whole assembly, so confirm the membrane, cover board, insulation and deck together are listed Class A.
What makes a home flat roof last, whatever the material
- Slope that drains. California’s Residential Code calls for a design slope of at least 1/4 inch per foot for membrane roofs (CRC R905.9.1 to R905.13.1). Standing water shortens every membrane’s life.
- Flashing at every change of slope. The code requires flashing where the roof meets a wall and wherever the slope or direction changes (CRC R903.2.1): the joint between a flat porch roof and the main pitched roof is a common leak point.
- A firm base. A cover board over the insulation resists dents from foot traffic and hail; the UFC requires cover boards on all low-slope systems except ballasted ones.
- Enough thickness. Thicker sheets tolerate wear better. For comparison, the UFC sets minimums of 60 mils for PVC and 72 mils for TPO on military roofs; ask what thickness is proposed for yours.
- Walk pads to equipment such as air conditioners, so service visits do not wear a path into the roof.
How long each material lasts is covered in flat roof lifespan by material, and whether a flat roof is cheaper than a pitched one over time in flat roof vs pitched roof cost.
Choosing a flat roof with NEMA Roofing
NEMA Roofing installs and repairs flat roofs on houses through our flat roofing services. Homeowners anywhere in Santa Barbara, Ventura, Los Angeles, Riverside or San Bernardino counties are served by our crews from five locations: Santa Barbara, Oxnard, Woodland Hills, Tarzana and Downey (see all service areas). To talk through the right material for your home’s roof, call 866-631-3366.
