cost of flat roof vs. peaked?

txmeggieFebruary 8, 2012

Can anyone tell me how the cost of a very good quality flat roof compares with the cost of a traditional but low pitch peaked roof ... a somewhat complex size (i.e. not just one or two rectangles) both on a single story 2800 sf house - all labor and materials considered? Thanks in advance.

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There is no such thing as a good quality flat roof ;) Kidding ... kind of. Just don't believe people when they say flat roofs can be trouble free - having lived in a neighborhood full of them, I would respectfully beg to differ.

You can get the flat roof look with some slope, which I would highly, highly, highly recommend, unless you live in an area that gets no rain.

    Bookmark   February 8, 2012 at 8:16PM
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Don't forget to take into account higher homeowners insurance premiums for a flat roof. Ours was even going to require yearly inspections--yikes! We nixed the flat roof & went with peaked instead.

    Bookmark   February 8, 2012 at 8:37PM
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Flat roof technology has come a long way and they are more problem free than before. I see that you are in Texas so you have hot summers. Do you get any snow? If you do then you need to allow for snow loading.

Most modern flat roofs are now built using EPDM. This is a sort of rubber mat which is use for swiming pools. The seams are sealed and bonded at instalation.

Most flat roofs are not strictly flat but have some pitch somewhere for draining. You do not want a mosquito pond on your roof.

I would recomend having as much pitch on the roof as possible. Often what looks cool about a flat roof visually is the "thin-edge" that "floats" the roof, especially if glass is used so that light is allowed to show underneath it. There are a number of ways to hide the drainage slope so that it looks like a contempoary flat thin roof when you are standing on the ground looking at the house. A view from above would however show the "cheating" and the sloped roof. It depends a bit on the site.

Hope this helps.

Best, Mike.

    Bookmark   February 9, 2012 at 8:20AM
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Good comments so far, thanks, but I am most interested on the COST issue. Can anyone answer that?

    Bookmark   February 9, 2012 at 8:30AM
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You'd be better off getting it figured both ways by someone who is in your area and can see your project up close and personal. If you are in an area where flat roofs are the exception, (most areas are), and they aren't experienced in proper construction, flashing, drainage, using a membrane on a flat roof, it shouldn't be considered. Only seek out reputable, experiencd contractors for your estimates.

    Bookmark   February 9, 2012 at 9:46AM
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Many design decisions should be made on the basis of cost but this is not one of them.

    Bookmark   February 9, 2012 at 10:37AM
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"I am most interested on the COST issue"

Cost is very local, so find some local folks to offer estimates.

That is about all you can do.

EPDM works great, but the major manufacturer does not pursue the residential market, they are interested in commercial applications (it take a lot more material).

Some areas have roofers that specialize in residential EPDM for flat (and almost flat) roofs.

Truly flat requires a lot of attention to drainage and the weight of retained water.
Even a slight pitch eliminates the retained water sealing and weight issues.

    Bookmark   February 9, 2012 at 11:18AM
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In most areas of the country, a flat roof will be more expensive because of the full EPDM membrane needed underneath the entire structure. It will also cost more to you in mistakes from the on the job learning experiences of the contractors you choose. Because of the slower water run, the framing for a flat roof has to carry more weight per square inch than that of any other type other than a tile or slate roof. You can't just decide in the middle of a build to have a flat roof versus a shed or gable, etc. It has to be designed correctly from the beginning as a whole system by a professional.

    Bookmark   February 9, 2012 at 12:17PM
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I think in general that a flat roof will cost more. How much more ... depends. It is sort of like how long is a piece of string.

To give you some idea, I had a modern house designed by my brother. He is an architect. That has flat roofs and it look really stunning. Lots of look no hands overhangs. The cost was 2x the conventional house I eventually built.

I think that anything "non-standard" will cost more. Often significatly more. The "standard" is what everybody else builds in your area. Anything non standard would have to be trucked in, and builders will quote high because it is something that they are not familiar with.

If you really forced me (water boarding etc ...) I would say maybe 50% more. A flat roof if you want clear spans will require steel, glue-lam beams, or TJI wood composite beams. These are all more costly than a peaked roof.

The cheapest clear span flat roof systems are warehouse systems. If you have a Sam's Club, or Costco, or some shopping malls, go there and look up at the roof on the inside. The roof has corrigated steel mat with steel W structured joists. The downside for a house is your roof looks thick because the joists are maybe 2 to three feet in depth. Sometimes the joists can be part of the room, e.g. high grade glue-lam wood beams. These look nice, have a nice finished look like furniture, but cost more. It really depends on the house design, and how much of a clear span you need or want, hence the cost variations can be large. The ultimate clear span beam is a steel I-beams. These are the strongest, look sort of industrial, but can be expensive to install because they are heavy so you need heavy lift like a crane on site.

Many of the houses in Record Houses in Arcitectural Record and Dwell are flat roofed and contempoary. These look great, but they I think cost 50% to 100% more than a "standard" house.

If you want a contempoary look, you can try to find a "pre-fab" house. These have also some along way recently, and I think bang for buck if you can a modern contempoary look may be the cheapest way to go. The reason why is you will have to bring in non-standard stuff anyways, so why not have that built and put together else where, where they know what they are doing, and the cost is cheaper. You then just truck in the sections and assemble on site.

Bes, Mike.

Here is a link that might be useful: My Borther's architect's hotel ... he is a great architect ....

    Bookmark   February 10, 2012 at 11:58AM
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Great advice. Sounds like if I do this, I go for either as low a peaked roof as practical and get my contemporary look from other things, or maybe an almost flat roof.
Stinky tiger - your ID must have a story -- thanks, I do like your brother's work. Thanks all.

    Bookmark   February 10, 2012 at 1:33PM
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