Low Pitch Residential Roof Replacement - Los Angeles Area

Hello, and thanks in advance for the help.

My knowledge and information is based on 5 roof quotes I’ve received over the last 9 months. When I purchased my home in the Los Angeles area, the inspector notified me that I needed to replace the roof. It’s been 12 months since then and we’ve had one decent sized leak. We’re ready to move ahead with replacing the roof.

Today I have a low pitch roof, a low enough pitch where it’s nearly impossible to have a roof with shingles. Total roof sqft is ~3,000 sqft (on a 2,100 sqft house + garage). Currently, I have an asphalt/gravel roof. 3 roofers suggested replacement with modified bitumen, 1 suggested TPO, 1 roofer suggested spray on. Bitumen prices were $22-26k, TPO is $21k, not sure what spray on was. You can’t see the roof well from the street, so while I don’t want it to be hideous, a little ugliness is not the end of the world.

Any suggestions on how to proceed (I’m sure it’s difficult without seeing the roof)? Thanks for your time either way.

What are the details for the Modified Bitumen roofs?

How many plies?

Granulated or smooth cap sheet?

I’m far from an expert so I’m sure knowledgeable flat roofers will educate me. In our area TPO is considered substandard and PVC is the most common flat roof system. TPO has been failing on bigger jobs here after 10-12 years and it is not possible to weld patches unless you adhere to the underside. In our market TPO was used mainly on budget jobs because it was so much cheaper than PVC. Maybe it has improved?


I believe smooth cap sheet, i’m not sure how many plies. I apologize for the lack of information.

Do you have any general thoughts re modified bitumen vs. TPO?

Thanks for this information.

Take it with a grain of salt. My flat roof knowledge is very limited but I’m sure some of the seasoned vets on here will provide good info.

TPO has been crap in the US since the beginning… The sheets are splitting down the middle. I wouldn’t put it on a doghouse, unless I didn’t like the dog!


IMO TPO should be avoided since it is engineered to fail.

Modified Bitumen can be installed in a variety of ways, all correct.

IMO a good Modified Bitumen roof is fiberglass base sheet with 2 layers of modified bitumen installed over it.

The top sheet (cap sheet) can be granulated like shingles or smooth.

If smooth it will need to be coated for protection from the sun.

If granulated the bleedout needs to have granules embedded into it.

Granulated tends to look nicer, the smooth can potentially last longer if it is coated on a regular basis.