We meet many Southern California homeowners curious about flat roofs. What exactly is a flat roof, and what are the advantages and disadvantages of flat roofs for Southern California homes?

Our family owned company has 20 years of experience installing all types of flat roofs.  We know the pros and cons of flat roofs for your Southern California home. Understanding more about the types of flat roofs will help you make the best choice when choosing a roofing contractor.

What are flat roofs?

The first thing to know is flat roofs are not actually flat. They have a slope of ¼ to ½ per foot to allow for water drainage. 

There are 5 common types of flat roofs.

  • Built-Up Roofing (BUR). ​​This flat roofing option was the most common before the invention of modified bitumen and membrane roofing. BUR is made of several layers: a bottom layer or two of insulation board, multiple layers of tar or asphalt alternated with layers of roofing felt, and a top layer of gravel.     
  • Modified Bitumen Roofing: (MBR) was developed in the 1960’s and is a lighter alternative to BUR. It typically has three layers and is an asphalt-based material with a top coating of mineral that resembles asphalt shingles.     
  • EPDM (ethylene propylene diene monomer), is a synthetic rubber that is also commonly used as a pond liner. EPDM roofing consists of an insulation layer over which sheets of EPDM rubber are applied. The EPDM membrane can be held in place with river rock or masonry pavers. Alternatively, it can be fastened or glued to the insulation layer.
  • Spray Polyurethane Foam Roof: As the name implies, this roof is made by spraying a layer of high density polyurethane foam. The foam is then coated with a waterproofing elastomeric top coat.
  • Thermoplastic membranes (PVC or TPO) These single layer roofs are typically white or grey in color. Like EPDM rubber roofs, they can be adhered or attached with screws and plates.  

Flat roofs have long been seen on commercial buildings. They are becoming an increasingly popular option for residential roofs.. 

  • Advantages of Flat Roofing

Each type of flat roof has different advantages. 

Bur or Build Up Roofs: 

BUR offers excellent protection against water, UV rays, and inclement weather.

BUR low-maintenance and costs very little to maintain throughout its lifetime.

          It is Typically cheapest flat roofing option. 

The gravel on BUR roofs is an excellent fire retardant

Modified Bitumen Roofing

Peel-and-stick material can be installed by homeowners

Its light-colored mineral surface reflects heat and cuts energy bills

Its price is in the middle of the pack

EPDM Rubber Roof

Homeowner-friendly installation

Relatively light yet highly resistant to scuffs and tears

Leaks are easy to patch

Spray Polyurethane Foam Roof

Low maintenance 

Energy efficient


Thermoplastic membranes PVC or TPO

Flexible membrane withstands punctures, tears, and impact damage.

Resists dirt, debris, algae and bacteria

Easy to install

If you are considering a flat roofing system for your home, you want to be aware of the downsides also. 

Disadvantages of Flat Roofing

  • They don’t last as long, and therefore result in higher cost over the life of your home.
  • Flat roofs require more maintenance, which increases the cost to the homeowner.
  • Because of the low slope, they have reduced drainage, bringing higher risk of water damage.
  • They can be very heavy and therefore require additional support, depending on the type of roof. 

Could flat roofing be a good option for your Southern California home? Contact GreenCal Construction today to discuss your options and get a free quote. 

Get Your Roofing Project Started Today!