Behind many common roof problems lie errors in design,
materials and maintenance, Each type of failure causation -
blisters, splits and punctures, to name a few - typically
result from a specific cause. Poor design, for example, can
lead to splits, and debris can cause punctures. Poor
workmanship and material failures can lead to a shortened
roofing life – and costly remedies.
Why Roofs Fail
Blisters are the most common roofing problem. They occur
when a gas, usually water vapor, is trapped within the
roofing system either between the plies or between the plies
and the insulation. Solar heat causes the gas to expand
which creates a pressure within the system that pushes the
The most common splits occur when a metal accessory is
flashed with a membrane material. As the temperature
changes, metals and membranes expand and contract at very
Open laps in the field membrane and in flashings, are
another problem. Open laps are commonly carelessness and
nonconformance with the specifications. Open laps in
built-up and modified bitumen systems can occur when the
bitumen is applied too cold. In single-ply membranes, open
laps are usually caused by improper surface preparation and
deficient adhesive application.
The most preventable failure symptom, punctures usually
occur because of carelessness on the part of people visiting
the roof: HVAC technicians, window washers, painters,
maintenance staff, smokers and tenants.
Another common failure location is penetrations. Of
particular concern are pitch pans. If a penetration is not
thoroughly cleaned of asphalt before installing pourable
sealers, the sealer will not adhere to the penetration.
Wrinkles can occur both in the flashings and within the
membrane itself. The opening left at the end of the wrinkle
is called a “fish mouth” – and an invite for easy water
Failures at flashings commonly occur due to improper
fastening, lapping and sealing.
Surfacing on membranes usually provide protection from
ultraviolet radiation and damage from traffic on the roof.
When the surfacing gets displaced or worn off, this
protection no longer applies.
Fasteners must provide adequate wind lift resistance,
especially in coastal areas. In mechanically attached
roofing systems, wind and thermal forces can cause movement
on the fasteners, leaving unsealed holes for water entry.
Mr. Albers is an expert witness in a court of law, but
is not an attorney. If you have legal questions related
to any of these topics, please consult an Attorney.