Flat Roof Systems - What Are Your Roofing Options?

While asphalt shingles are still as sought-after as ever, they’re not made for flat roof systems. If you choose a flat roof, consider other, more suitable, roofing options.

In such a case, what are your options to safeguard your flat roof from potential damage stemming from challenging weather conditions?

This article details the materials and systems dedicated to flat roofing, their advantages and drawbacks, including tips for prolonging your roof’s lifespan.

What Are the Best Flat Roof Material Options for Canadian Homes?

Flat Asphalt and Gravel Roof

Source : Soumission Rénovation

An asphalt and gravel roof consists of several layers of asphalt felt (four or five) with overlapping folds to completely coat the roof’s span. And, between each layer, a liquid asphalt is poured. Next, a layer of white or grey gravel is spread to coat and protect the asphalt from UV rays. Without this protective layer, the asphalt would rapidly wear over time.

While an asphalt and gravel roof has a 10–15-year lifespan on average (more in some cases depending on the quality of the installation), the rooftop might need to be replenished with gravel, as needed. Additionally, keep in mind that temperature fluctuations and inclement weather can lead to gravel being knocked loose from certain areas of the roof.

This type of roofing is well-known for preventing water leaks, which means that even small pools of water building up on the surface are unlikely to cause damage. For gravel and asphalt roofing, budget between $7 and $12 per square foot.

Lastly, note that this flat roof system must be installed by professional roofers, especially since handling molten asphalt is rather perilous.

Elastomeric Membrane Roof System

Source : Les Toitures Keven Lebrun inc.

Elastomeric roof membranes consist of two layers: a base sheet (screwed or glued) and a gravel layer (white, light grey, maroon, or green); the latter is the topcoat. 

The importance of adding a granulated finish is to ensure that the whole installation is highly resistant to sunlight, impacts, and tears. The joints are fused with a blowtorch, which forms a tight seal around the entire system.

Note that an elastomeric membrane can also be cold-applied using self-adhesive layers. The membrane, which is particularly resistant to impact and temperature variations due to its high elasticity, benefits from requiring few repairs throughout its lifespan. 

While the membrane will remain water-resistant over its estimated lifespan, it's still vulnerable to stagnant water, which can shave at least 10 years off its expected service life. Also, note that if algae and/or ice found on the surface of the membrane isn’t removed within a reasonable delay, it can damage the membrane’s top layer.

Ideally, the roof drain should be at least 4 inches wide to ensure any water build-up is properly drained. If you’re thinking of investing in an elastomeric membrane, budget between $9.50 and $15 per square foot. 

Pricing is, without a doubt, higher than an asphalt and gravel system (which ranges between $7 and $12 per square foot). However, it’s worth noting that asphalt and gravel covering is far less durable than elastomeric roofing, which lasts between 25 to 40 years. 

Single-Ply Flat Roof Membrane

TPO Membrane

Source: PC Qualité Toits Inc

TPO (thermoplastic polyolefin) is a single-ply reflective coating, reinforced with wear-, tear-, and impact-resistant polyester. The seams are typically fusion-welded with a heat gun, making for a joint that’s stronger than the membrane’s surface.

Additionally, this type of membrane has a glossy finish, making it easy to maintain. It’s widely used in the construction and renovation industry given its numerous advantages.

When it comes to the cost of installing a TPO membrane, it hinges on the roof’s square footage. Budget between $7 and $8 per square foot for smaller spans and up to $12 per square foot for longer spans, as the cutouts and overall work make for a large-scale undertaking. 

For an additional fee, you can also get a manufacturer warranty for workmanship and materials.

*The price points listed include materials and labour.

The Advantages of a TPO Membrane for a Flat Roof 

• Easy installation (lightweight material)

• Very malleable; can mould to a building’s shifting frame

• Extremely durable and resilient to tears, high winds, impacts, bacteria, moisture, and punctures

• If the joints hot-welded, the fusion of the two makes for a homogeneous bond, which makes the joint even stronger than the membrane itself

• Large panels significantly reduce the number of joints (which automatically reduces labour costs)

• Eco-friendly product (TPO membranes are toxic- and hazardous ingredient-free and fully recyclable)

EPDM Membrane

Source: PC Qualité Toits Inc

An EPDM membrane (thermoset rubber) is made of ethylene, propylene, diene, and a monomer, which isn’t always reinforced. Installation-wise, this roofing system is similar to a TPO membrane.

The only difference between the two is that the joints aren’t made the same way. Instead, all joints are glued—the joints are sealed with tape or contact cement. This is why an EPDM membrane can’t be recycled in the same way as TPO roofing. However, its durability—50-year minimum—makes it a particularly sought-after roofing option. 

In terms of its unique characteristics, note that EPDM roofing is rot-resistant, which often makes it the preferred option for green roofs.

Budget between $9 and $12 per square foot for an EPDM membrane (including materials and labour).

The Advantages of an EPDM Membrane

• UV-, fire-, cold-, steam-, and temperature-resistant

• Low maintenance, aside from occasional repairs to rubber membrane seals and bi-yearly inspections (spring and fall)

• High elasticity and flexibility, making it less prone to splits or cracks

• Excellent long-term energy-efficient investment, reducing heating costs during the winter.

The Advantages of a Single-Ply, Flat Roof Membrane

Single-ply membranes have a slew of advantages, including their easy installation and recycling potential. Moreover, they’re competitively priced and represent a 10–15% saving compared to roofing materials combining asphalt and gravel. In other words, single-ply roof systems cost between $7 and $12 per square foot, with an expected lifespan ranging between 15–35 years.

And, since these membranes are retailed in white, reducing heat islands, makes them an environmentally friendly product. Generally speaking, single-ply membranes are designed to withstand the effects of UV rays, snow or rain build-up, and temperature variations. Lastly, such roof coverings are also used to host green and blue roofs.

Re-roofing your house? Check out our article Roofing: Comparing Different Materials.

What Are the Disadvantages of Single-Ply Membranes?

Single-ply membranes have some drawbacks, the first of which is their installation method: Given that it’s a single-ply membrane, installed as a continuous piece of material, it’s more suited to commercial rooftops.

Otherwise, the fabric has to be cut, working around rooftop obstructions, such as vents. Moreover, sealing the joints calls for a skillful hand, as failure to do so will impair the roof’s overall waterproofing properties.

These two types of roof systems are also disadvantageous during the wintertime. Since a TPO membrane is hot-air welded, it’s a little harder to maintain the normally resulting adhesion in freezing temperatures.

As for EPDM membranes, they’re also affected by harsh climes, and the glue or tape used to seal the joints can be negatively impacted by the cold.

For more information, check out our Flat Roof Financial Guide.

Why Should You Never Shingle a Flat Roof? 

Unfortunately, traditional asphalt shingles can’t be used on flat roofs. The gaps between the shingles are at cause, allowing water to infiltrate.

Said risk is rather limited on pitched roofs, given that water naturally runs off. Patrice Desjardins, of PC Qualité Toits, stated that “shingles use gravity as a waterproofing method. The slope has to be significant enough for water to drain in the right direction.” As for a flat roof, water builds up on the rooftop and ends up seeping into the gaps. 

How to Find the Right Roofing Contractor

Source : Dori Construction Inc.

When looking to hire a roofing contractor, it’s essential to take several precautionary measures to guarantee the quality of the service undertaken. “The roof system selected isn’t as important as the company hired to carry out the job. Every roofing system has a unique installation method,” stated Desjardins.

First, check online reviews written about the company you plan to hire. Make sure the comments left are by local, legitimate users. A company’s reputation online can be a good indicator of the business’s reliability and quality of workmanship.

To have a more accurate assessment, it’s recommended to reach out to three different companies, each of which will carry out an independent inspection of your roof. Compare all quotes and make sure each contractor clearly explains the work to be done, without disparaging competitors. This transparency will highlight their professionalism and reinforce the trust established between yourself and the roofing contractor.

Before making your final decision, check whether the company in question is officially registered by checking your local business registry. Doing so will ensure the contractor in question is running and operating legally. Another crucial step consists of verifying whether the roof system manufacturer named in the quote is reputable and reliable. This information is essential for guaranteeing the durability and efficiency of the material used for the roof’s system.

Moreover, make sure the roof system manufacturer offers a product warranty. It’s important to underline that warranties must be purchased with the manufacturer directly or any associated retailers, via the roofing contractor. Without a manufacturer-issued certificate, roof system warranties aren’t valid, except for the workmanship warranty, provided the company is legally registered during the duration of the warranty. If you reside in Quebec, make sure the hired contractor has a valid, RBQ-issued licence.

Lastly, don’t forget to check whether the contractor has valid insurance. Make sure they have the necessary insurance policies, including liability and workplace injury insurance. That way, you’re protected if a jobsite incident or accident occurs, guaranteeing an overall safe collaboration. Adhering to the advice mentioned in this article can help maximize your chances of finding a reliable and skilled contractor to carry out your roofing needs.

For more information about flat roof maintenance, check out our article: 6 Things to Know to Properly Maintain Your Flat Roof.

Looking to build a rooftop deck or garden? Check out these articles: Building a Rooftop Terrace in Canada - How Much Does It Cost? and How to Build a Rooftop Terrace.

Flat Roofing Materials FAQs

Is a flat roof cheaper than a conventional, sloped roof?

In general, a flat roof is cheaper to build than a sloped roof, given that not as much material is needed and the structure itself is rather straightforward. However, flat roofs can incur higher maintenance fees, including water drainage and waterproofing membrane maintenance.

What is the average lifespan of an elastomeric membrane?

An elastomeric membrane roof system lasts between 25 and 40 years, depending on its professional or DIY installation and the maintenance carried out over the years. This type of roof system provides great weatherproofing and can withstand temperature variations.

How much does an elastomeric membrane roof system cost per square foot?

An elastomeric roofing membrane costs between $16 and $19 per square foot, including installation. The total cost depends on the square footage to coat, rooftop accessibility, and prep work necessary.

What is the cheapest way to build a flat roof?

The cheapest way to build a flat roof consists of choosing cost-effective materials, simplifying the design, and minimizing labour costs.

What type of roofing is best for a flat roof?

The best type of roofing for a flat roof depends on various factors like budget, climate, durability, and maintenance requirements.