The elimination of the rafters both in labor and material does present some economics.

A roof that is flat is generally surrounded by a curb, has a slight slope to direct water to a drainage point, a downspout or gutters when the there is even a small pitch to the roof, and incorporates a fabricated or made on site waterproof membrane to protect the building from water ingress.

The installation of the protective, waterproof membrane on a flat roof is generally not a project for a home handyman.

The Four Different Types Of Flat Roofs:

There are four main categories of flat roofing. They are:

• Built-Up Roofing (BUR)

• Roll Asphalt

• Single Ply Membrane

• Sprayed Polyurethane Foam (SPF)

Built-Up Roofing:  

BUR (tar and gravel roof) involves layers of tar impregnated roofing felt rolled out on the roof.  Each layer overlaps the previous layer.  In between the deck material and each layer of felt a layer of hot tar is mopped over the surface.  A final layer of crushed gravel holds the roofing to the deck and helps protect it from the suns destructive ultraviolet rays.  Depending on the exact materials used and climate conditions these types of roofs should last from 10 to 30 years.

Roll Asphalt:   

Roll asphalt roofing has been the traditional method for sealing flat roofs for years.  One layer of asphalt impregnated organic or fiberglass felt is laid on the roof and fastened down with galvanized nails and roofing cement.  A final covering of crushed gravel or other mineral product is placed on the surface.  Roll asphalt has a limited life of about 10 years. It is common to find this type of roofing system used on garages and sheds.  It is the most economical roofing system available.

Single Ply Membrane:  

Single ply membranes are a product that must be installed by trained professionals.  Consisting of either a thermoset or thermoplastic membrane they are placed on the roof in a single piece.  With proper care and maintenance a single ply membrane will have an average life of 10 to 15 years.

Sprayed Polyurethane Foam:  

An SPF roof is seamless.  It consists of a layer of foam, covered with a resilient coating which seals and protects the surface.  SPF has been around for over 30 years.  It requires specialized equipment and professional installation.