|
For many low-slope roofing systems,
Madsen Roof Company recommends and
installs Built-up Roof membranes.
Composed of alternating layers of
bitumen (asphalt or coal tar) and
reinforcement fabrics (felts), built-up
roofs afford quality moisture resistance
and protect from the extreme winter
and summer condition of Northern California.
Traditionally, bituminous membranes
have been installed in multiple-ply
configurations, with three to six
layers bitumen applied between layers
(plies) of reinforcing fabric to compose
the "built-up" membrane.
Hot Asphalt built-up roof membranes
may be used on slopes varying from
approximately 1/8 inch per foot (1%)
to approximately 6 inches per foot
(50%) depending upon the type of asphalt
selected. However, for hot asphalt
built-up roofs, decay resistant or
preservative-treated wood nailers
are required on inclines exceeding
2 inches per foot (17%). This is to
help secure insulation and roof membrane
plies to non-nailable decks or to
roof decks with rigid insulation.
Asphalt and coal tar are the principal
bitumens used for roofing purposes.
They are versatile materials whose
waterproofing properties are desirable
for use in the construction of vapor
retarders and built-up roof membranes.
Other properties make asphalt a good
material for adhering certain types
of insulations and adhering some polymer
modified membrane sheets. Asphalts
are derived from petroleum or crude
oil. Coal tars are by-products of
processing coal into coke for the
production of steel and iron.
Chemically, asphalt and coal tar are quite different bitumens and technically incompatible when mixed. For roofing purposes, asphalts are graded into four categories or types, and coal tar into two, according to the temperatures at which they soften. Unfortunately, asphalts are not graded according to viscosity, only softening point temperature. Work at ASTM is ongoing with the hope that roofing asphalts will also be graded by viscosity.
Type I
Asphalt is relatively susceptible
to flow at roof temperature, it has
good adhesive and self-healing properties.
Type 1 asphalt can be used in aggregate-surfaced
roofs on slopes of up to 1/4 inch
per foot (2%).
Type II
Asphalt is moderately susceptible to flow at roof temperatures. It can be used on roofs with slopes up to 1/4 inch per foot (4%).
Type III
Asphalt is relatively non-susceptible
to flow at roof temperatures. It can
be used on roofs with slopes up to
3 inches per foot (25%).
Type IV
Asphalt is relatively non-susceptible to flow at roof temperatures, which makes it useful in areas where year-round temperatures are relatively high. Type IV asphalt can be used on roofs with slopes up to 6 inches per foot (50%).
|
