- Urban and suburban areas, heavily
wooded areas, or other terrain with numerous, closely spaced
obstructions the size of single-family dwellings or larger.
- Open terrain with scattered
obstructions having heights less than 30 feet, including
flat, open country and grasslands.
- Flat, unobstructed areas directly
exposed to wind blowing over a large body of water.
Wind speeds can range from gale force
(39-72 mph) to hurricane (73 mph and over) to tornadoes
(usually immeasurable). Wind damage to a roofing
system can sometimes go undetected until it is too late.
Damage can range from a loose membrane in a corner to the
complete loss of an entire system.
The
location, height and the historical wind-speed data on a
specific location can together provide solid information for
designing and appropriate roofing system. The proper
mechanical fastening of items such as the roof insulation,
metal components, and in some cases the actual roof membrane
itself, become increasingly important. The number of
fasteners and fastening pattern for the roof insulation can
vary from manufacturer to manufacturer. It is
extremely important to be sure that the number of fasteners
and the pattern by which they are installed is adequate for
the conditions. Wood nailers can be added to provide
the proper attachment for associated metal components.
A secure perimeter detail is the first
line of defense against imposing wind forces. Roof
membranes in almost all cases required attachment at the
perimeter; whether these systems are single ply membranes,
fully adhered with adhesives, or cold process, built-up roof
membranes. The number of fasteners are typically
increased, fastening patterns are modified at corners and
perimeter walls, and ballast is increased. By
considering these factors ahead of time, a serious loss can
be prevented.
Rain
The amount of rain that is anticipated is
another factor to consider. A building located in the
Pacific Northwest, typically a rainy climate, should
obviously be looked at differently than a building in
Arizona, typically an arid climate. Positive drainage
is a key component to the performance of any roof system.
Without positive drainage, a roof can begin to prematurely
degrade, as surfacing and coatings can quickly erode away.
If a roof has a history of ponding water,
additional measures should be taken to alleviate the
situation. On an existing structure with minimal slope
to drain, tapered roof insulation is an excellent solution.
In some cases, the simple installation of additional rooftop
drainage is enough to solve the problem. In the case
of new construction, providing structural slope for water to
drain is the optimal way to go. This option ensures
positive drainage for the present and the future.
Hail
Hail is one of nature’s surprises.
When it is least expected, a hailstorm can wreak havoc on a
multitude of different roofing systems. Hail is
generally concentrated in the mid-section of the United
States, although it can occur almost anywhere with the right
atmospheric conditions. The surfacing of a roofing
system that experiences numerous hailstorms becomes the
primary defense against damage. Additionally, the type
of roof insulation board under a non-aggregate single-ply,
modified bitumen, and built-up membranes, allows the system
to be more susceptible to impact damage. In the case
of existing roof systems, larger hailstones have been known
to actually break blisters in a roof system. Gravel
and ballast surfaced roofing systems historically provide
the best protection against a hailstorm.
Temperature
The temperatures that roofing systems are
exposed to can dramatically affect the performance of a
roofing system. Cold temperatures cause a system to
contract, while hot temperatures cause the system to expand.
Thermal shock of a roofing system can lead to a number of
different problems. Thermal shock occurs when sudden
environmental temperature changes cause a roof membrane to
rapidly expand or contract. Built-up roof membranes
have been known to split for hundreds of feet when this
phenomenon occurs. Certain types of single-ply
membranes have experienced craze cracking throughout an
entire system.
An aging membrane that simply cannot
accept the rapid change of temperature sometimes has this
type of occurrence. With cold temperatures and areas
susceptible to thermal shock, incorporating materials
designed for low temperature flexibility is important.
These materials include modified felts for built-up roofs,
cold-process adhesives and modified asphalt. It is
also important to properly plan expansion or contraction
joints into both new structures and existing roof systems.
An expansion joint is a joint that goes through the entire
structure and a control joint extends from the roof deck up
through the roof system. Both of these joint types
allow for movement within the roofing system with the intent
to minimize potential problems. Roofing systems
exposed to hot temperatures and constant sun are all
together different.
Sunlight
The exposure to ultraviolet rays can
cause a system to lose its flexibility properties and
prematurely age. It is an important factor in these
situations to consider a surfacing alternative that will in
fact lower the surface temperature of the roofing system and
protect the underlying components. In comparison, you
most likely would use a sun block for your skin if you
planned to spend a week Hawaii. Installing a roof
membrane surfacing that reflects and protects is also
important to the longevity of the overall system.
A few of the options that are available
are white or aluminized reflective coatings. There are
roofing membranes that have the choice of numerous surfacing
options. There are also a number of manufactured
membranes, white granulated modified bitumen membranes and
even aluminum foil-surfaced flashing membranes.
Manufacturers have even designed specific coating that, in
addition to their reflective properties, also provide
increased fire-resistance capabilities to allow an entire
system to achieve the desired fire rating.
The opportunity exists early on in the
roofing system design process to take into consideration the
climate, natural forces and building specifics. If
these items are not fully considered, then the roofing
system could be destined for premature catastrophic failure.
Be sure that whoever you choose, whether it is a roof
consultant or another design professional, that they
consider the specifics of climate conditions in your area
and how they relate to your building.