Flat Roofs: Which Material Should You Choose?

EPDM, TPO, Elastomer, Polyolefin… What do these acronyms and words even mean? And, more importantly, are they good options for your roof?

We decided to put together everything you need to know about flat roofs here, but you can always explore our article on all types of roofing if you want more information. That said, this article will help you make a sound decision for your residential or commercial roofing project. There isn’t a one-size-fits-all option out there, so you’ll need to take a look at the pros and cons for each flat roof material. Even if the price is important, keep in mind that the least costly option might not necessarily be beneficial in the long run. 

Elastomeric or modified bitumen membrane

Elastomeric membranes come in two varieties: traditional and self-adhesive. The former involves using a blowtorch to fuse a base elastomeric membrane to a finishing membrane composed of granules, while the latter uses cold-fusion technology (no blowtorch). Since traditional modified bitumen membranes require the use of a blowtorch, be sure that your contractor is covered for fire damage on their insurance. Moreover, some roofers may try to cut corners by not sealing joins (e.g., near skylights or vents). This can lower the material’s lifespan, so be sure to take the time to find a qualified roofing contractor for your project. 

An elastomeric membrane can also be used for resurfacing, which allows you to lower waste and lessen your environmental impact. Resurfacing consists of heating up the old membrane, pushing in the leftover particles, and installing a new membrane on top.

If you’re planning on building a rooftop terrace, an elastomeric membrane should be your material of choice. It has all the characteristics needed and can be walked on without causing any damage. Its resistance also makes it the top roofing material choice for Canadian residents. 

Pros of an elastomeric membrane:

• Requires little to no maintenance
• Resistant to wear and tear caused by branches or other debris

Cons of an elastomeric membrane:

• Slightly more costly than asphalt and gravel roofing

TPO

Thermoplastic Polyolefin (TPO) is a single-ply roofing membrane that’s applied using hot air welding. It doesn’t need much equipment to install, so many contractors offer it as an option. That said, be sure to take the time to hire a qualified roofer for your project – poor installation can easily cause water infiltration.

Of all the petrol-based roofing solutions, TPO is the least polluting option. Plus, it’s entirely recyclable at the end of its lifetime. TPO is also more aesthetic than other solutions as it’s available in many colours, including white, which reduces the urban heat island effect. However, manufacturing TPO does require more energy. 

Pros of TPO roofing:

• Highly resistant to UV rays, heat, and extreme weather conditions

Cons of TPO roofing:

• Its surface can easily deteriorate
• Not as resistant to extreme cold as other solutions
• Its official lifespan is unknown (fairly new material)
• Easily damaged (perforated)

EPDM

EPDM stands for Ethylene Propylene Diene Monomer. It’s essentially a synthetic rubber! This flat roof material is equally resistant to extreme colds as it is to strong UV rays. It’s also resistant to high humidity levels. Its characteristics are fairly similar to those of the TPO membrane. Though, besides being recyclable, it can be made of fully recycled materials, greatly reducing its environmental impact. 

Pros of EPDM roofing:

• Entirely recyclable
• Highly resistant to UV rays
• Keeps its elasticity in extreme cold

Cons of EPDM roofing: 

• Installation must be done elegantly
• Damages can be difficult to spot
• Easily damaged (perforated)

Tar and gravel

Tar and gravel roofing is a multi-layer roofing solution for your flat roof. It’s basically a sheet of felt that’s soaked in asphalt, and it can help reduce the risk of water infiltration. This kind of roofing can be long-lasting, but it’ll need to be maintained and inspected fairly regularly. For instance, it’s important to make sure that there’s gravel covering up the entire surface so that the felt sheet doesn’t dry out due to sun exposure. Many flat roofs in older Toronto districts use this roofing material. However, more and more people are opting for single-layer flat roof options, and an increasing number of municipalities are banning the use of tar and gravel as a roofing solution. Be sure to consult your city rules and regulations.

It’s easy to tell when you need to get this roofing material replaced. You’ll notice craters starting to appear, dust accumulation, and even exposed felt. When the gravel begins to detach from the surface, a professional will need to coat the roof with a liquid solution and add more gravel. 

Pros of tar and gravel roofing:

• Lower material cost compared to other roofing solutions
• Easy to repair

Cons of tar and gravel roofing: 

• Maintenance is quite tedious
• Proper installation conditions aren’t available (need to consider the weather, the asphalt’s temperature, how thick it is, etc.)
• Limited expansion and contraction (elasticity) capabilities

Why not get a green roof? 

Two kinds of green roofs exist: extensive roofs (without cultivation) and intensive roofs (with cultivation crops). In both cases, you’ll need a drainage system. Extensive roofs are much easier to install as they simply require a thin layer of loam (fertile soil), making the workload lighter. Intensive roofs, on the other hand, need at least 6 inches of soil, making it a lot heavier for contractors. Also, costs associated with intensive roofs are higher as the roof needs to be easy to access, requiring more work to be done (e.g., installing a stairwell, door). You’ll also need a structural engineer to assess and, if necessary, help reinforce your building’s structure to support it.

Although the initial cost of a green roof might be quite high, it’ll be well worth it. You’ll save on heating and cooling costs thanks to the insulation effect created by the soil on the roof. The overall air quality will be improved, too, since the CO2 you exhale will be absorbed by the plants. The best part? Your roofing material is protected by the loam, doubling its lifespan! 

What about a rooftop terrace? 

Putting in a rooftop terrace is also an interesting option, especially if you already put in a green roof! Rooftop terraces are popular in more urban settings, where open land is limited or nonexistent. You can put in a patio set, a pergola, little passageways through your crops, etc. The possibilities are practically endless! Just be sure you hire highly qualified contractors to ensure everything is properly installed and fixed into the structure. Of course, you’ll need to make sure there’s a drainage system in place!

White roofs: What are they all about? 

White roofs are used to offset the urban heat island effect. However, there’s some debate regarding their efficiency. Since white roofs don’t attract the sun’s rays, you’ll likely have higher energy bills in colder months. Another inconvenience would be that, in no time, your white roof is likely to turn grey, losing between 30% and 60% of its sun reflecting capabilities. 

Is covering existing roofing with another material feasible?

Tar and gravel roofing can be covered up with a different kind of flat roof material. The gravel must first be removed, and then MDF sheets need to be installed before covering the surface with the new material. However, doing so isn’t recommended as the humidity stays trapped between the layers and can cause damage. 

How much does it cost to replace a flat roof? 

Below is a table with the average costs to replace a flat roof in both Greater Montreal and the Greater Toronto Area, along with each roofing material’s typical lifespan.

Roof Type	Average Cost –  Montreal	Average Cost –Toronto (GTA)	Lifespan
Elastomeric Membrane	$19 – $23/sq. ft.	$23 – $30/sq. ft.	20 to 30 years
TPO/EPDM	$11 – $14.5/sq. ft.	$13 – $18/sq. ft.	25 to 30 years
Tar & Gravel	$11.35 – $12.60/sq. ft.	$12.55 – $13.85/sq. ft.	15 to 30 years

Replacing a flat roof on a residential building usually averages around $14,500 and $24,000, whereas replacing a flat roof on a commercial building can easily run upward of $120,000 depending on the surface area. Take a look at our roofing cost article for more details. 

Which flat roof material to choose?

Best value for money: Elastomeric membrane

Most eco-friendly: EPDM as it is entirely recyclable

The coolest: a green roof with a terrace

Why you need a qualified roofer for your flat roof

While picking a roofing material is important, you’ll need a reputable contractor to ensure that it’s installed correctly. Avoid water infiltration, installation errors, and other issues by working with our Advisors. They’ll get you up the three quotes from Verified Contractors at no cost or obligation! If you’re ready to get started, Call us or fill out our form.

Happy renovations start here!