Flat Roofs in Winnipeg
Published On:  May 19, 2022
flat roof


What is a flat roof and how does it compare to a sloped roof?


Flat roofs have a low slope between 1 and 10 degrees or at least 1/4 inch per foot.  Typical residential roofs, on the other hand, have slopes ranging between 4 inches to 9 inches per foot.

So flat roofs aren’t technically flat but rather low sloped.  Because the slope is small and gradual they appear to be flat to an observer.


What types of flat roofs exist?

There are 3 different types of flat roofs:


1. Built-up Flat Roofs

 Built-up roofing, also called BUR, has been since around the 1840s.  It is made up of alternating layers of reinforcing fabric and bitumen.  It is used in low slope roofing such as commercial flat roofing.  There is also generally an aggregate layer on top such as stone or gravel.  This type of roofing has good waterproofing and also is protected from the elements such as UV due to its aggregate layer.

It can last between 15 – 30 years and may even last up to 40 years if well maintained.


2. Modified Bitumen Flat Roofs

Modified Bitumen was the next advance from Built-Up Roofing and first appeared in commercial and flat roofing around the 1960s.   These membranes are composed of asphalt that is combined with a rubber or plastic membrane.   There are two main varieties APP and SBS.   Modified Bitumen has several advantages over Built-up roofing.  It isn’t as heavy and is easier to repair.  It also has a reasonable life expectancy that can be increased with regular roof maintenance.

Modified bitumen membranes usually come in rolls that are either heat welded or cold-adhered and can sometimes be mechanically attached as well.

Two Types:    SBS and APP

SBS and APP roofs can last between 20-40 years with regular roof maintenance.


3.  Rubber Membrane Flat Roofs

There are 3 main types of rubber roof membranes:

  • EPDM or Ethylene propylene diene monomer is a rubber roofing membrane that usually comes in black.  It can be fully adhered, ballasted, or mechanically attached.  It stands up well to UV radiation and harsh temperatures.    It comes in various thicknesses ranging from .045″ to 0.90″.  EPDM roof membranes can last up to 50 years if properly installed and maintained. Because it is made of rubber, it provides an excellent water proof barrier.

  • TPO or Thermoplastic Polyolefin is a single ply rubber roofing membrane that can be ballasted, mechanically fastened, or chemically adhered.  TPO comes in 10, 12, and 20 foot wide sheets. TPO is generally white but does come in other colors usually at an increased cost.  TPO reflects UV rays and is impact and weather resistant. The seams are hot air welded.   TPO roofs can last up to 30 years if well maintained.

  • PVC or Polyvinyl chloride is a synthetic polymer of plastic.  PVC is a single ply roof membrane that is very strong and durable.  PVC can be installed by heat welding the seams.  It is impervious to chemical and water leaks and provides UV protection.  PVC roofs can last up to 30 years and are relatively easy to repair.

What are the advantages of Flat Roofs?

Flat roofs have a lot of strength and can span large areas without requiring as much material.  They are prevalent in commercial buildings due to these advantages. Another advantage of a flat roof is that it takes less time to install and repair in comparison to a sloped roof.  Flat roofs have less lumber making up the roof deck and are therefore also cheaper to build. 


  • Strength
  • Less time to install
  • cheaper to build than an equivalent sized sloped roof

What are some disadvantages of Flat Roofs?

Flat roofs, due to lack of slope, do not have an attic.  This means there is less space inside.  Due to not having an attic, there is also less space for insulation in a flat roof. Another disadvantage of flat roofs is water drainage is not as good as in a sloped roof.   While flat roofs do have drains, a heavy rain can cause water pooling on a flat roof quicker than it would on a sloped roof.


  • Less space due to lack of an attic
  • Less space for insulation due to lack of an attic
  • Water Drainage is more of a concern than a sloped roof

Why are flat roofs popular in Winnipeg?

In Winnipeg, we get large amounts of snow which a flat roof has no problem handling.  Sloped roofs, on the other hand, can collapse under a very large snow load.   

How long does a Flat Roof last if properly maintained?

As we mentioned earlier, there are at least 3 different kinds of flat roofs.  The type of flat roof will determine its maximum age before replacement should be considered.   Flat roofs generally last between 20-50 years depending on what type of flat roof is installed and how well it is maintained.

What is needed to properly maintain a flat roof?

Firstly any standing water or snow build-up should be removed  as soon as possible to reduce load and water pooling.  Secondly regular roof maintenance should be performed on the roof to keep it in good shape and to address any problems early.  Camco Roofing Limited can provide your business or residence with regular maintenance of your flat roof.

Maintenance Required

  • Removal of built-up snow
  • Removal of pooled water as soon as possible
  • Regular roof maintenance

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