Canadian Contractor

From commercial pilot to general contractor: (9) 'Roofer madness'

"I've taken quite a bit of ribbing over our decision to build a house with a flat roof... But the technology is proven."

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July 22, 2014 by Robert Koci

I have taken quite a bit of ribbing over our decision to build a house with a flat roof.

“You’ll end up with a swimming pool over your head!”

“It will leak, and then you’ll be sorry.”

“It will collapse the first winter under the snow loads.”

Ironically, most of these conversations take place in shopping malls and offices that have flat roofs.


You can't beat a low, flat roof line for a clean modern look.

You can’t beat a low, flat roof line for a clean modern look.

Truth is, flat roofs are not flat. They have very subtle slopes that allow the water, whether rain or melted snow water, to flow off. And the technology is proven. Flat roofs are by far the most common roof seen in commercial buildings, although not so with residential buildings in this part of the country. Why is that? Maybe it’s aesthetics, maybe it’s the relative simplicity of building a sloped roof, or maybe it’s just habit.


In our case, my wife and I chose a flat roof for aesthetics. We want a low, modern building with horizontal lines. A flat roof adds greatly to that look. Our architect had no problem with our request. In fact, most of his work is designing commercial buildings, so he was in his zone. That our roof trusses and deck would be wood rather than steel really only mattered when it came to the number of trusses and their depth. The engineering is well established either way.


Brian Audia of A&G Roofing inspects one of the 8 roof drains installed in the valleys of the flat roof deck.

Brian Audia of A&G Roofing inspects one of the 8 roof drains installed in the valleys of the flat roof deck.

My wife and I don’t like the look of eavestroughs, so our roof design is a series of inverted slopes with large capacity roof drains in the valleys, eight in total. They are all connected to large downpipes that run vertically inside the building through an architectural void feature, and then under the foundations and away from the house. The result is a parapet of only 12”, and no awkward-looking eaves.


The roof deck itself is covered in a commercial-grade material used on major big box and chain restaurant roofs all over North America. It took a week to install and seal the seams, fit the corners, and install mushroom caps and boots for the various stacks and vents that, like the roof drains, run through the architectural void space to the basement.


We had essentially two insulation and deck-shaping options, both common with commercial roof structures: either install shaped rigid foam insulation above the deck and under the membrane to form drainage valleys, or spray foam insulation under the roof deck, using angled roof trusses so that the deck itself would form the drainage valleys. We chose the latter, given the added benefit of spraying insulation foam into all the nooks and crannies around the roof trusses and roof deck edges. The costs were about equal either way.


Is a flat roof cheaper than a conventional sloped roof? I really doubt it when compared to an asphalt tile roof with typical slopes and dormers. But compared to the same sloped roof with, say, cedar shakes? Probably pretty close. I call our roof the ‘leather seat’ option; it’s special, and makes our roof line very unique and appealing.


My chief carpenter (and long-time friend) thinks my flat roof is ‘Roofer Madness.’ So for a bit of fun, I’ll invite him over in February and see how nervous he gets. One of us will be wrong!


Robert Koci

Robert Koci

Rob Koci is the publisher of Canadian Contractor magazine. Tel. 647-407-0754
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5 Comments » for From commercial pilot to general contractor: (9) 'Roofer madness'
  1. Well let’s hope the membrane makes at god seal, as getting water into a spray foam flat rof is naty.
    It may take a long time to show up,but the hot da mp environment soom breeds mold and will rot out tigs

    • John Bleasby says:

      Thanks for the warning Claude. Of course, a leak in any roof/insulation system will cause all kinds of problems down the road. One thing I failed to mention in my story this week was the fact that the material manufacturer themselves will perform their own inspection of the entire installation job on my house and, upon their approval, will issue a 15 year warranty covering all material and workmanship. In my previous experience with other roofers and roofing systems (ex. cedar shakes, flat roofs that were tarred) this was not the case. Also, it is highly recommended that only a roofer with extensive experience with commercial flat roofs and this system in particular be selected. I appreciate your feedback. Do you have any particular examples of problems that you could describe to help other readers?

      • Steve says:

        Does the warranty cover material and Labour?

        If it is just materials, they prorate it based on how much you used the roof before it failed.

        If it fails 10 year in on a 15 year warranty. You will get 1/3 of the material costs. Assuming the company is still around.

        With a flat roof most of the cost are is in the labour not materials. Not sure if you considered this in the warranty.

        • John Bleasby says:

          Good comments! Yes, the coverage is for labour AND material. The company is a major corporation, so one must assume they will survive the warranty period. My understanding is that any/all repairs required will be wholly covered by the warranty. But certainly your points are important for any purchaser of any roof system warranty/guarantee to investigate.

  2. Marten Burghgraef says:

    It is one thing to cover their own products and material. The problem is the damage it causes to other materials, insulation, drywall, paint, etc. Looks like you are using some type of rubber roof. Don’t walk on it. My experiences have been nothing but negative on this type of roof. But that was a long time ago, perhaps better now.