Dow Protected Membrane Roof EN - Manual (Page 18)

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1 8
Finding Leaks
in a PMR
THE ISSUE
Is it more difficult to locate a
leak with a PMR or conventional
roof assembly?
DISCUSSION
Building upon years of in-field
experience, the majority of roof
leaks in PMR systems occur at
flashing as opposed to the inte-
rior field area. The field area is
protected from physical abuse,
UV attack and thermal cycling –
all factors that are the primary
causes of roof failures – by both
the insulation and ballast over
the membrane. However, some-
times interior field leaks do
occur.
Concrete decks: For PMR
installations on concrete decks,
generally the membrane is fully
adhered to the deck. This simpli-
fies leak detection because the
leak is localized. For example,
the leak in the interior will be
exactly where the hole in the
membrane is located. If the
membrane is not adhered, the
water can run under the mem-
brane for many feet before
entering the building – just like
in a conventional roof.
Steel decks: For PMR installa-
tions on steel decks, a layer of
insulation or other substrate
(e.g., drywall) is placed first to
provide a base for the mem-
brane – exactly the same as in a
conventional roof. The same
type of leak detection effort is
required for both PMR and con-
ventional roofs on steel decks.
Wood decks: On wood decks
with a PMR installation, the
membrane is typically a felt
layer and two or three plies
mopped on top. In a conven-
tional installation, the insulation
is fastened to the deck and then
the membrane is applied. Both
of these approaches will allow
the water to run to the deck
joints prior to entering the
building.
CONCLUSION
Not only do PMR assemblies
have fewer leaks in the first
place, PMR assemblies over
concrete decks with bonded
membranes have definite advan-
tages when isolating any leaks
that do occur. Both conventional
and PMR roofs over steel or
wood decks require the same
leak detection strategies. In
addition, because PMR roofs are
easier to repair and typically all
of the original materials can be
reused (ballast and insulation),
this environmentally friendly
feature can save money.
Low Temperature
Applications
THE ISSUE
PMR assemblies should
not be used in low temperature
applications because of the
potential adverse effect on the
STYROFOAM
™ Brand Extruded
Polystyrene Foam Insulation.
DISCUSSION
In a low temperature applica-
tion (e.g., freezers), the interior
space has a low temperature and
low water vapour pressure
(humidity). In contrast, the
warm outside temperature and
higher water vapour pressure
causes a vapour drive toward the
interior space. Unless addressed,
this vapour can condense in the
insulation and lower the R-value
(RSI) of the system. It can also
condense on the membrane and
freeze, gradually forming a layer
of thick ice.
Typically in low temperature
applications, the membrane is
placed on the “warm side” – or
the exterior in a conventional
roofing application.
CONCLUSION
In low temperature applications
(e.g., freezers), a conventional
roof may offer performance
benefits.
Conditions, Issues and Ratings
S P E C I A L C O N D I T I O N S A N D I S S U E S