If roof walkways are installed in a square or
right angle configuration, look for diagonal “short cuts”
between adjoining walkways.
Although most roof membranes
provide outstanding resistance to natural weathering, their
durability can be adversely affected by contact with many
organic substances, including oils, fats and organic solvents.
Because exposure to these types of contaminants will cause many
roofing membranes to lose strength and resiliency, periodic
inspection is very important to assure that any damage is
identified and addressed quickly.
Frequently, air conditioning
units will leak oil, or oil may be spilled during periodic
maintenance. Also, grease from cooking exhausts can accumulate,
especially if filters are not cleaned frequently.
To identify such problems,
look for membrane swelling. Some single-ply membranes, such as
EPDM or TPO, will exhibit swelling or buckling of the membrane.
This is an indication that the membrane has absorbed the
contaminant and that fundamental physical properties of the
membrane have been compromised.
A membrane that has swelled or
cracked should be replaced.
If contamination, especially
from cooking exhausts, is considered to be chronic, a redundant
layer of roofing membrane should be applied around the exhaust
vent and the roof surface area typically affected by grease
deposits.
A number of proprietary grease
traps are available which can be placed around exhaust units to
absorb fats and grease.
Typically, these units will
require periodic maintenance to function properly.
These units can be installed
by any contractor competent in sheet metal work, but the
installation should be coordinated with a licensed roofing
contractor.
Drainage Problems
Ponding or standing water can
cause problems for both asphalt and single-ply roofing systems.
Because asphalt compounds are not inherently resistant to the
sun’s rays, most modified bitumen and built-up roofing membranes
use a layer of factory-applied granules, a field-applied liquid
coating or a layer of roofing gravel to protect the membrane
from ultraviolet degradation. Under constant exposure to
standing water, however, granule and gravel coatings will tend
to wash off and liquid coatings may blister and peel. Once this
important coating is removed, the underlying asphalt membrane
may begin to degrade due to direct exposure to sunlight.
Although single-ply roof
membranes provide excellent resistance to water and sunlight,
the potential for damage to the roof is also significant when
water is allowed to stand on a roof. A small cut or puncture in
the roof membrane may cause little damage on a well-drained roof
surface, but the same puncture located in an impacted drainage
area can produce extensive damage to the roof insulation, roof
deck and building contents.
Although effective roof
drainage can be achieved through a variety of methods, all roofs
should be designed and maintained to provide a consistent and
effective path for water to completely drain off and away from
the roof surface within 24 to 48 hours of a rain storm.
Effective drainage must also accommodate build-ups of snow and
ice that may typically occur during winter months.
Because most horizontal
structural members deflect in the center of the span, ponded
areas are located frequently along the mid-span of these framing
members. Heavy rooftop units can frequently cause deck
deflection and create a ponding area around the unit.
Roof Drainage Components
Typical roof drainage
components include: a) roof drains, b) wall scuppers, c)gutters
and downspouts.
Although improper roof
drainage can best be observed immediately after a rain storm,
most impacted drainage conditions will leave “tell-tale”
indications even after standing water has evaporated.
Debris frequently accumulates
in ponding areas. Because water eventually evaporates from
impacted areas, a concentric pattern of debris or dirt is a good
indication of a ponding condition.
Discoloration of curbs and
walls may be due to a build-up of snow or ice, or it may be an
indication that water may “back up” during very severe rain
storms. When necessary, roof drains can be added to remove water
from impacted areas.
If it is not economically
possible to re-work an impacted drainage area, the potential for
damage can be reduced by the application of redundant layer of
membrane and flashing, in order to reduce the possibility of
cutting or puncture. ❑
