26 September 2006
Built-up Roof (BUR) Membranes.
BUR systems have broad applicability for dependable low slope roof systems with low
service life cost. Consider this roof system unless it can be shown that it fails to meet
important design criteria. Positive attributes of BUR membranes include:
a. Durability with long service life
c. Easily modified for additional penetrations after the initial construction
d. Low maintenance
e. Well-understood maintenance procedures.
However, the success of this roofing system is based upon sound installation
techniques accompanied by suitable quality control. More information on quality control
Cant Strips. Provide cant strips for all built-up roof systems.
Fiberglass Mat Material
. BUR systems must use fiberglass mat felt
material and no less than three-ply or as limited by the UFGS.
Coal Tar Bitumen. Use coal tar bitumen with caution due to the smell
and caustic effect of fumes during construction. Do not use coal tar pitch on slopes
Roof Vents. On BUR membrane systems, moisture relief vents have
proven to be of no value in drying wet materials, and their effectiveness for pressure
relief is questionable. Ventilating base sheets are required on all wet fill decks.
Types of BUR Membrane Surfacing. The three types of top surfacings
for BUR membranes are smooth, mineral surfaced cap sheet, and aggregate.
Smooth Surface BUR Systems. Smooth surface BUR systems using
coatings for protection tend to have a shorter service life than cap sheet or aggregate
surfaced membranes. The most common coatings for smooth surface BUR systems
are hot- and cold-applied, asphalt-based emulsions which may include aluminum or
effect. Smooth surface BUR systems require re-coating at two- to 10-year intervals
depending on the type and quality of the coating, which significantly increases the life-
Mineral Surface Cap Sheet BUR Systems. These surfacings are
mineral surfaced cap sheets embedded into hot or cold liquid applied asphalt. The
surface granules are not organic; therefore, the surfaces last longer without
maintenance than coatings used with smooth surface BUR systems. This fact tends to