FREQUENTLY ASKED QUESTIONS
What is an awning?
An awning is an architectural fabric
projection that provides weather protection, identity or decoration
and is wholly supported by the building to which it is attached.
An awning is comprised of lightweight, frame structure over which a
cover is attached. See Architectural
Awning
Specification.
What is a canopy?
A canopy is an architectural projection that
provides weather protection, identity or decoration an is supported by
the building to which it is attached and at the outer end by not less
than one stanchion/upright support post. A canopy is comprised
of a lightweight frame structure over which a cover is attached.
What is a retractable awning?
A retractable awning is a moveable awning that rolls or folds
against a building or other structure by which it is entirely
supported.
Why should I get an awning?
Awnings and canopies are beneficial in both practical and
aesthetic ways providing weather protection by shielding from the
sun, rain, snow, sleet, hail and wind while also distinguishing your
home from the rest on the block.
How do I know what size awning to get?
The size of an awning is determined by its length, width and
projection from the building to which it is attached. Other aspects
of size include clear height (underneath), rise (pitch) of roof and
post of rafter spacing. This information is especially important to
those involved in the planning and review process.
The fit of an awning is determined by the
connection of the awning to the structures (most often a building),
it is important to coordinate the appropriate parts of the awning frame
with structural members in the building so that loads are
distributed properly.
What is a design load?
A design load is a load for which awnings and canopies may need
to be designed. Loads are categorized:
Dead Load - This is what the awning or canopy itself weighs
(including frame, fabric and hardware). This load must always be
included with other design loads since it is always acting on the
structure. For instance, if the design calls for 20 psf snow
load, and the structure it self weighed 2 psf, the the design for
snow should actually account for 22 psf total load.
Wind Load - This load, as well as snow load, are usually
the most critical loads on awnings and canopies. Important aspects
of wind load are:
●
Speed
or Velocity - Basic wind pressure is a function of its
speed. Basic wind pressure (psf) can be computed as the product
of 0.00256 times the square of the wind speed (mph). It can be
readily observed then, for example, that the wind forces on an
awning are four times greater if the wind speed is doubled, and the
forces are nine times greater if the wind speed is tripled. Design
wind speeds are generally shown on maps published in the building
code. Local codes may require higher design wind speeds.
●
Exposure - This is a general category for the amount of
protection from the wind that is afforded by the surrounding
environment. Consult your local building codes for requirements.
●
Gusts - These are short-term
excursions of velocity above the steady design velocity, which must
be accounted for in design.
●
Drag, Lift - Drag is
the wind-induced pressure toward the fabric surface, and lift is the
pressure away from the fabric surface. Wind forces can act in
different directions on an awning system, toward or away from the
fabric surface, depending on various factors. When designing an
awning frame, all these factors must be taken into account.
●
Return Period - This term is used
to describe the time interval that is the basis for determining the
required design wind speed. In most cases the return period is 50
years. That means the required design wind speed is that which has a
0.02 statistical probability of occurring once in 50 years. It has
been determined by loss and safety experts that it is an acceptable
level of risk and have based code design requirements on it.
Snow Load - Required design snow loads
are established by maps published in the building code. Just like it
is for wind sometimes local requirements may be more stringent. But
in many locales there is no requirement for snow load design. Check
with the local department of building and safety.
Some important considerations about designing for snow are:
●
Ground Snow - The beginning point for snow design,
this is the pressure of the designed snow load occurring at ground
level.
●
Exposure - It is the general
category for the amount of protection from the wind that is provided
by the surrounding environment. Consult with your local building
codes for requirements.
●
Flat Roof Snow Load - This is the
design load occurring at the actual roof level, and results from
factoring the ground snow load by a coefficient accounting for
exposure and height. Many times the flat roof snow load can be as
little as 0.6 or 0.7 times the ground snow load. The snow map or
code may indicate a 20 psf ground snow load; the actual design
pressure required for an awning may be as little as 12 psf.
●
Drifting - Building codes require
that the phenomenon of drifting snow be accounted for in the design
of roofs; this includes awnings and canopies. The codes will
describe the procedure for designing with snow drifting in mind.
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