Tar And Gravel Roof ? - Model Railroader Magazine

markpierce

Living under a flat roof makes me want to change building regulations that would prohibit them.  Such roofs are always "itching" for a leak, especially "bathtub" roofs like the Wells Fargo building (where the roof is below the level of the walls.).

Mark,

Actually flat roofs work very well. As noted they are not really flat but have a slight pitch in one or more directions.

Flat roofs do require waterproof coatings such as hot applied tar or tar and gravel.

In fact, skylights work better and are less likely to leak in a flat roof than in a sloped shingle roof.

The prefered covering for flat roofs today is EPDM rubber membrane. A UV resistant rubber sheet, 45 mils or 60 mils thick that is simply laid out over plywood or insulating foam. On small applications it is glued down. On large applications it is attached at its edges and allowed to float.

EPDM lasts 25-35 years and is easily spot repaired in the rare case of a leak. It's whats on all those big box stores in the shopping centers.

But many older hot tar built up roofs and tar and gravel roofs remain in service all over the country.

The gravel actaually protects the tar from the sun and controls the water runoff rate. These roofs usually last about 15-20 years before needing recoating.

Built up hot tar roofs, where tar paper and hot tar are applied in about three layers of each, last about 7-10 years and than need a new "top coat" of hot tar. After about 40 years they usually need to be stipped off and redone from scratch.

For more than 100 years all the row house in all the east coast cities have had hot tar flat roofs, they work just fine. Even in snowy Boston, hot Charleston as well as Baltimore and Phily which can see both extremes. It was 100 in Baltimore yestersay, and this past winter we had 60" of snow in 10 days. Not one flat roof colapsed, and its likely more shingle roofs had ice dam leaks than flat roofs that leaked in that snow.

As a residential designer I have designed lots of flat roofs for clients over the years - never had a complaint yet.

Sheldon