Flat roof??

[travcojim]

What are the pros and cons of the flat roof style of construction?  The roofs that are used in some of the expensive prefab buildings such as the Wee House http://weehouse.com/flash/SFWA_index.html#/weehouses/   and a few of the others like blue sky.   It looks like these styles can be build using the small house plan for much less than the prices they are selling these prefabs for.  Of course alot of that cost is the high grade woods and flooring and so on and so on.  But using the Small House plans would it be possible to use a so called flat roof and build basically the same thing, even a possible compound arrangment with two side by side or even connected by a small covered walkway.
  Just thinking of low cost ways of building...

[MountainDon]

NM and the southwest in general have built flat roof houses for years decades centuries.

Let it be noted that most flat roofs are not genuinely flat. Rather they are very low pitches. Older building I've been on top of here seem to have as low as 1:12, some seem even less... hard to tell sometimes when walking on them. Newer construction uses a little more pitch. They hide the pitch behind parapet walls.

Pros of flat roofs? Some people like the looks.    In some ways simpler to build. I'm not sure you'd save a lot of money building flat/low pitch. For example: compare the roof rafters for a 16 ft wide building. Depending on snow load, pitched rafters (4:12 and up) could possibly be 2x6, whereas flat rafters would have to be 2x10's.

Easier to work on top of and less likelihood of slipping and sliding off. Definite pluses there. Easier for one person to build.

In general flat roofs leak more. The parapets leak. The joint between the roof and the parapet can leak. The service penetrations in the roof can leak. That's the big con. Modern EPDM type materials are better than the old traditional tar and gravel.

Flat roofed building may be more difficult to attain adequate roof/ceiling insulation.

It seems to me that flat roofs cave in under snow loads more often. Maybe they weren't designed/built for the 100 year storm, whatever?

Maybe you can tell I don't like flat roofs, but that is only my opinion. Lots of my neighbors like their homes, flat roofs and all.     YMMV

[hpinson]

I have a flat roof and I dislike it intensely. No matter what, sooner than later it will leak somewhere, especially if, like mine there is any sort of elaborate duct work . Parapets need constant maintenance too. That's all bad in an adobe home.

I'm strongly considering some sort of spray on roofing.  Does any one here have experience with SPF spray-on roofing, or comparable materials?  Durability in comparison to tar / gravel roofing? Lifespan? Insulation? Health concerns?