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Community and Q&A

Flat roof advice needed

Howard Road | Posted in General Questions on

I’m building a carport and breezeway in southeastern Michigan and I’m struggling with construction methodology and products for the proposed flat roof.

Flat roof? I know…Martin’s Ten Rules…But… I would like to use all this roof real estate. This roof will cover a substantial portion of my small urban lot and I think, in the future, this could be valuable space. A Small Deck, a Modular Green Roof, Potted Gardens, Solar Panels…

Lots of options show up when you search flat roofs on the internet. Overhangs & Gutters seem logical to me and would be similar to standard residential sloped roofs. Built-Up Curbs & Scuppers are common on commercial buildings. Built-Up Curbs & Scuppers seem more complex and expensive to me, would they allow for a wider variety of future uses?

I’m finding that EPDM and Torch Down Rolled Roofing are the most commonly referenced systems. I’m not thrilled with the prospect of having a black roof baking in the sun right outside my house.

Angled Sleepers or Sloped Rigid Insulation? Sleepers would seem to promote better drying. Insulation is said to provide a softer and more forgiving base for the roofing. A little Insulation would be nice, but these are unconditioned spaces.

Any thoughts or recommendations would be very much appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    If you are struggling with a design issue, and you feel stymied, the usual approach is to hire an architect. That might be a good idea in your case.

    A few points:
    1. If you prefer light-colored roofing rather than dark roofing, you can choose a white PVC membrane roofing.

    2. There is no need to install insulation in a carport roof.

    3. In most cases, a roof with a gentle slope is preferable to a truly flat roof.

  2. Peter L | | #2

    A flat roof in Michigan? Wow, you will curse the day you made the decision to install a flat roof. I've seen plenty of flat roofs fail and cause nightmares and this is in southern Arizona where they don't get snow and rainfall is measured in less than 4 inches per year.

    Flat roofs are a constant maintenance and in Michigan you will have snow and ice, heavy rains, and a flat roof is just asking for trouble. What happens when you get hit with a blizzard and 2 feet of snow is sitting on the roof? Will you go up there and shovel it off?

    Asking how to install a flat roof in Michigan is like asking how to go over Niagara Falls in a barrel. There is no right answer because the question should never be asked in the first place.

  3. Howard Road | | #3

    Thanks Martin,

    I have consulted several architects in my area. They have varied opinions and none of them is recommending specific products. I was hoping for some wisdom from the group, from people who have installed these systems / products and have first hand experience.

  4. Howard Road | | #4

    Peter L,

    I know...I know...But this space is valuable and I'm surrounded by all types of buildings with flat roofs. So I will not be the only crazy person in my area with a flat roof.

    I will have direct access to this roof via a sliding door from my second floor so if I was overly concerned about snow load I could easily shovel it. The roof structure will be designed for snow load so I'm not too worried about that issue.

    All roofs leak, especially flat roofs...I know. This roof is over a carport and breezeway so any leaks will not be a disaster.


  5. Expert Member
    Malcolm Taylor | | #5

    For the last hundred years, at least half of all the houses in many major cities, like New York or Montreal, have been built with flat roofs. Whether you are keen on the idea or not, it can be and is done successfully all the time.

  6. Stephen E | | #6

    Think the most logical approach is the simple one in your case. In Michigan the main purpose of the carport/breezeway would to keep snow off the car and damaging hail. Why have a roof at all? Make a upper deck and be done with it. The deck done right would be mostly water tight.

    Saves a lot of money and gets you valuable space right away.


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