Built-up Roof Components:
Only used when stipulates in the project specifications. In a reroofing situation The Uniform Building Code requires that the new roof has the same insuation characteristics as the roof that is being replaced, therefore if the previous roof was insulated the new roof should also haveat least the same degree of insulation may be used as a seperator betweenold new systems. There are several alternative methods of fastening roof insulation depending on wind uplift requirements.
Highly recommended in all reroof situations when insulation is not used. A slip sheet is placed between the deck and the first ply is mechanically fastened to the deck, the slip sheet is secured in place simultaneously. The slip sheet often consists of a rosin coated paper. It's function is to isolatethe deck from the new membrane so the membrane assembly "floats" above the deck. Awell known fact is that some roofing problems, notably "splitting", occur because the membrane is partially or completely adhered to the deck. As the deck, particularly those constructed of plywood, deflects or adjusts to building movement, the attached membrane it is less capable of absorbing the movement and splitting will occur. The investment in a slip sheet under a built-up system pays for itself many times over.
The number of layers in a built-up roof vary according to specification. Often the sequence consists of a base ply, one or more intermediate plies, and a surfacing ply.
A typical base ply is an impervious sheet of asphault impregnated fiberglass weighing about 28 pounds per 100 square feet.
This is often a fiberglass sheet imprenated with asphault weighing approximately 11 pounds per 100 square feet. Its porous construction allows asphault, applied during membrane installation, to permeate the ply and anchor it securely to the base sheet beneath.
There are several options for surfacing a built-up roof. A popular choice, known as a Cap Sheet, is usually thick ply (72 pounds or more per square feet) with a granulated surface applied during the manufacturing process. Another option is the use of an intermediate ply sheet to which a flood coat of asphalt has been applied. Granules or rock are broadcast into the asphalt while it is still soft. There are several other options that may be considered.
Asphalt can be specified in versions of hot applied or cold process. Hot asphalt comes in several grades formulated according to the slope of the roof. It is heated to its proper equivicious temperature (450° to 550° F) before spreading by machine or hand mopping techniques as indicated in the project specification. Asphalt is the adhesive and warterproofing element of a built-up roof system.
Cold asphalt uses a spray method of application. The benefits of a cold system include the ability to spend more time on intricate hand-detailed work at flashings and the reduced exposure of the roofing craftsman to burn injuries.
The term "tar" is often used interchangeably with asphalt. Tar and pitch (coal tar pitch) are synonymous and is derived from the coking process of the fossil fuels. Asphault, on the other hand is derived from the distillation process of oil.
Tar preceded asphalt as the waterproofing element of old built-up roofs. It is an element that s out of favor today because it carries a higher price and harsh irritants that effect workers during installation. Tar has a lower softening point than most asphalt and therefore is not conducive for use on sloped roofs.