Untitled - National Roofing Contractors Association

All curbs, penetrations, roof drains and plumbing pipes
must be in place before installing the roof. Openings tor
curbs cut through the roof membrane after the roof has
been completed can present a serious bitumen drippage
problem when the membrane is constructed of low
softening point bitumen. All curbs should be firmly
fastened to the building structure or to the roof deck betore
roofing material application. Roof drains, vent pipes,
etc. should all be in place prior to roofing and restrained
to prevent damage to the flashings or membrane that
may occur if mechanical devices are installed over the
completed membrane.
Mechanical units mounted on pipe standards beneath
which roofing materials will extend must be mounted to
a height sufficiently above the roof to allow room to install
the roof system and to make repairs beneath the unit.
Heavy loads, such as large mechanical units, should not
be rolled over the completed membrane, as they may
cause damage to the roof. A failure in horizontal shear
between the membrane insulation or deck from these
loads may result in future splitting of the roof. NRCA
recommends that mechanical equipment be installed on
fully enclosed curbs (not on support stands) to eliminate
the need for reroofing under these units when reroofing
becomes necessary in the future.
See the NRCA Construction Details for recommended
mechanical equipment curb, stand and penetration
flashings.
As a final consideration, it should be noted that helicopter
placement of mechanical equipment can cause damage
to the roof system if the helicopter is operated too
close to the roof surface.
IX. PREFORMED ROOF INSULATION
Roof insulation provides both the insulation for the building
and a substrate to which the built-up roofing materials
are applied. Therefore, it must be compatible with,
and should provide support for, the roof membrane.
An ideal roof insulation would have the following theoretical
properties:
. It would be able to withstand the bitumen application
temperatures required for installation of the
roof membrane.
. It would have good physical strength, rigidity and
impact resistance.
. It would be incombustible and would be acceptable
for insurance and building code requirements.
. It would be constructed of materials that will resist
deterioration.
. It would be moisture resistant.
. It would have a low k-value (thermal conductivity)
so that the highest possible A-value (thermal resiStance)
can be obtained in the thinnest possible
piece of a particular insulation.
. The k-value YX>uld remain constant and would not
"drift" higher with age.
. Its surfaces would accommodate secure
attachment.
. It would have dimensional stability under varying
temperature and moisture conditions.
. It would be manufactured so as to be compatible
with the roof membrane.
The qualifications listed above would be present in an
ideal insulation. In practice, however, no single commercial
product contains all of the ideal properties. Thus, the
designer should choose materials with properties best
suited to the specific project.
Roof insulations, when used for the control of heat flow,
should be installed in two layers (when thickness permits)
with all joints offset between the upper and lower
layers. The joints of the insulation should be installed to
provide moderate contact at the joints. The upper layer
should be installed with the long dimension of the insulation
boards placed in a continuous line and the end
joints staggered.
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