Flat Roofs Leak

I am often called in to evaluate a leaking flat roof and consider the redesign of the roof to one with a sloped surface. To-date, I have never found such a design to be necessary or cost effective. What I have found in these leaking roofs were signs of multiple poor quality patches using a variety of roofing "goop" all of which was applied in an unprofessional manner.

So, based upon my experience, flat roofs leak because they were improperly installed and (even more likely) poorly maintained. While it is undoubtedly true the sloped surfaces shed water more easily than flat surfaces, flat roofs built to standard practices of the trades are reliable and less expensive to build than sloped roofs. Flat roofs do require some greater maintenance than sloped roofs, but their total life cycle costs are still lower than that of sloped roofs.

Flat roofs have some disadvantages. They are not ideal in areas of heavy snows. They are more difficult to vent. They usually don't allow for easy access to the attic area.

It is also important to understand that most flat roofs and roofing surfaces were not built or designed as decks, i.e. walkable surfaces.

See:The Sound Roof and Decks