Re-covering roofs offer a sustainable
approach, reducing waste and cost.
Roofs are usually replaced or repaired when roof failure has
occurred. The definition of failure is subjective in that it is the building owner
who decides which and what level of loss of function is unacceptable. An
example of total failure is a roof that has sustained substantial dam- age from
high winds. In economic terms, total failure occurs when the costs of restoring
the roof to a maintainable and serviceable condition outweigh the benefits of
the restoration.
When
roof failure occurs, whatever the cause, the owner is faced with selecting the
appropriate course of action. At one time, the options were limited,
constrained both by the current materials and designs. If the roof failed, you
were faced with the choice of attempting repairs or tearing off and replacing
all, or part of the roof. This is no longer the case. Increasingly, another
option is becoming a viable alternative to complete tear-off and replacement
-re-cover.
REPAIRS
Repairing a roof
is almost always the most desirable option provided that it is economically
viable and the roof can be effectively restored to an acceptable level of
service. If this can be proven to be the least costly alternative based on a
cost/benefit analysis, it is often the most desirable intervention.
RE-ROOFING
Re-roofing
generally involves the tear-off and replacement of the existing roof. Most
roofing professionals believe that com- plete tear-off and replacement is the
preferred re-roofing option as it has several advantages over a partial job.
Tear-off and replacement provide the building owner with several opportunities
that are otherwise unavailable to him or her.
They
include the opportunity to:
·
Implement thermal
upgrading, thereby reducing the building's overall energy costs;
·
Improve the roofs
drainage. There is ample evidence to show that well drained roofs perform
better than poorly drained roofs. Eliminating ponding water will not only extend
the life of the roof, but will also limit the amount of water that could enter
the building should a leak occur;
·
Inspect the deck. A complete tear-off allows the condition of the leak
to be assessed and provides the opportunity to affect any necessary repairs.
RE-COVER
Although
tear-off and replacement is the most desirable option, another increasingly
popular alternative is re-cover.
FM
Global, North America's leading roofing systems testing and approval authority,
defines re-cover as a system where: "The existing roof system is left in
place and new components are installed over it."
The
increasingly popularity of re-cover is due to a number of factors including the
introduction of elastomeric, plastomeric asphalt modified and other membrane
systems with characteristics that lend themselves to re-cover applications.
These are generally lightweight membranes that can be installed in a variety of
ways such as in mechanically fastened assemblies, fully adhered or loosely laid
and ballasted systems.
In addition,
there are a number of economic and practical advantages to be gained by
re-covering a roof as opposed 10 tearing it off and replacing it. Some of these
are:
·
Re-cover avoids
the expense of replacing the existing insulation, provided, of course, that the
insulation is dry and in sound condition;
·
If the bulk of the roofing materials can be left in place, the
difficulties and costs associated with their disposal can be avoided. Labour
costs are reduced since there is less material to move and install;
·
Re-cover minimizes
interruptions and may even allow interior operations to continue normally;
·
Re-cover has lower
overall costs than a tear-off and replacement.
·
Re-cover also
mitigates the risks associated with tearing off the roof and leaving the
building unprotected from the elements until a new waterproof cover can be put
in place.
Remember
that re-covering does not allow for a complete inspection of the deck or other
components of the left-in-place roofing system.
EXTREME CARE
REQUIRED
Before any roof is
re-covered, it is recommended that a series of test cuts be carried out that
will provide information about.; the condition of the existing roof assembly,
including vapour/air barrier and deck. The number -and location of the test
cuts should be in accordance with sound statistical practices so as to provide
a level of confidence acceptable to the owner. All physical testing of
asphaltic built-up roofs should conform to ASTM D 2829-97, Sampling and
Analysis of Built-Up Roofs.
Extreme care and
due diligence must be exercised when a re-cover system is considered so as not
to expose the building owner to unintended liability and costs. The addition of
insulation or additional layers of membrane may, by example, compromise the
fire resistance of the entire assembly. FM Global, by example, cautions against
adding plies to an existing B.U.R.
as this may
change its rating from a Class 1 to an inferior Class 2. Adding insulation
beyond a prescribed maximum may also jeopardize fire ratings. It must also be
remembered that in most instances, super- imposing a new re-cover membrane onto
an existing roof will add to the dead lead of the system. Care must be taken to
ensure that the design load limit is not exceeded. A qualified professional
structural engineer should be engaged to deter- mine the capacity of a
structure to support the new roof before a re-cover system is applied.
During the
installation of a re-cover roof, the existing roof may be subjected to a large
amount of rooftop traffic as materials and equipment is moved across it.
Caution must be taken to prevent damage to the underlying components during
installation. Whichever option—repair, re-roof or re-cover—is selected, the
decision should be made only after careful consideration of all the costs,
benefits and risks inherent with each alternative.
Peter Kallinger is the
technical director of the Canadian Roofing Contractors Association.