Flat Roofing

Flat Roofing Systems

BUR (Built-Up Roofing)

Built-Up-Roofing, BUR is a roof that is built with 3 to 5 plies of roofing felts, typically adhered to each other with hot asphalt. This system is often perceived as the standard roof system, and is sometimes referred to as a “Pitch” or “Tar and Gravel” roof. It is still the most common type of roof installed in the Ontario region., although it is steadily losing ground to single ply roofing systems.

The system usually includes a vapour retarder installed over the roof deck, then one or more layers of insulation that is fastened to the deck by hot asphalt, adhesive or mechanical means. Roofing felts are then applied over the insulation with hot asphalt. A gravel and asphalt pour is then installed over the felts. This protects the roof from UV and physical damage, while stabilizing the base felts, and providing ballast to hold the system in place.

Protected Membrane (Inverted)

In this type of installation, the insulation is installed above the roof membrane. The logic being that the roof membrane is kept at a constant temperature, close to that of the building interior. This inhibits accelerated aging, caused by the extreme temperature fluctuations experienced in conventional roof systems.

Inverting the roof also protects the roof membrane from mechanical damage, Ultra Violet radiation and wind uplift.

In this system the roof membrane is installed directly onto the roof deck, gypsum or concrete board is installed over steel decks to provide a solid roof surface.

Extruded Polystyrene insulation is laid loose over the membrane. A layer of filter fabric and ballast is then installed over the insulation to hold the system in place. The ballast can consist of gravel, patio stones, cast in place concrete, etc.

BALLASTED

The ballasted system uses a single ply roof membrane, held in place with gravel. The system usually includes a vapour retarder, with the insulation laid loose, or mechanical fastened to the deck. The roof membrane is than covered with well rounded river stones with a diameter of .75″ to 1.5″

FULLY ADHERED

The fully adhered system uses, like the ballasted system, a single ply membrane. But in this system the membrane is held in place by adhesives. The system usually includes a vapour retarder, with the insulation mechanically fastened to the deck. The roof membrane is than fastened with adhesives to the insulation.

MECHANICALLY FASTENED

The mechanically fastened system uses a single ply membrane, where the membrane is fastened in place with screws and stress plates. This system will include a vapour retarder, insulation which is mechanically fastened to the deck, and a roof membrane mechanically fastened to the roof surface. The fastening can be installed in the seam of the roof membrane (inseam disk system), or a bar may be fastened over top of the membrane and sealed with a cover strip (bar & cover strip system).

TORCH APPLIED

This system is used exclusively with Modified Bitumen roof materials. This is when specially designed propane hand torches are used to heat the modified bitumen membrane just enough to melt its outside layer in order to adhere the membrane.

This product can be installed conventionally as in BUR systems, except the felts are replaced with two plies of modified bitumen. The first ply (base sheet) is usually mopped in with hot asphalt, but may be torched in place. The second ply (cap sheet) is then torched in place over the first. The Cap sheet is usually factory granulated, and needs no further protection.

RECOVER

This is when a new roof is installed directly over an existing roof system. This can be completed successfully provided that any wet materials in the existing roof are replaced, that the roof is relatively smooth, and that the structure can support the extra weight. Typically, any loose gravel or ballast is swept away or scraped from the original roof membrane before the the new roof is installed. This is to reduce the dead weight load and to provide a suitable substrate to adhere or mechanically fasten the new roof membrane

COLD PROCESS

There are two systems that, as the name implies, make use of cold processed bitumen to assemble a roof system.

The Cold Process roof system is essential the same as regular BUR system, except that the hot asphalt is replaced by emulsified cold asphalt. This is brushed, sprayed or squeegeed into place. Specially developed roofing felts are normally used with this system.

In a Resaturated system, an existing BUR roof has all its loose gravel top pour removed with an specially designed industrial wet vacuum cleaner. This provides a clean surface for the installation of the resaturate coating of cold processed asphalt. Again this is brushed or squeegeed into place.

In both Systems a gravel surface layer is then added to stabilize and protect the new roof surface.