Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LEAK DETECTION IN ROOF MEMBRANES
The present invention relates to a system for monitoring roof
membranes for the presence and location of moisture penetration. It has
particular
application to monitoring low-slope and flat roofs of residential and
commercial
buildings for undesired water ingress.
BACKGROUND OF THE INVENTION
The failure to detect, find and correct minor roof deterioration in the
earliest stages is considered the greatest cause of premature roof failure.
This is
particularly true of roofing materials applied on low-slope or flat roofs.
Costly roofing
problems are often the. result of design deficiencies or faulty application of
the roof
system. Even when properly designed and applied, all roofing materials
deteriorate
from exposure to the weather at rates determined largely by the kind of
material and
the conditions of exposure.
Several methods have been used to try and locate roof leaks after they
have occurred. This is becomes a particular problem for inverted roof assembly
membranes (IRMA) roofs where the roof membrane is typically bonded to a
concrete
deck and any leak detection system needs to be located on top of the membrane
which is usually covered with a thin layer of water. The detection system must
then
locate any membrane breach through the water layer to the deck below while
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avoiding other paths to ground formed by roof drain, pipe penetrations, and
metal
fleshings.
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Electric field vector mapping uses a wire loop around the perimeter of
the roof surface to introduce an electric potential between the structural
deck and a
selected roof area which is sprayed with water. The electric field potential
caused by
a conductive path to any roof membrane damage is then located using a
sensitive
voltmeter and a pair of probes. The vector mapping method it limited in its
ability to
locate the ground fault signal when the IRMA roof includes insulation and
heavy
overburden such as a vegetative covering.
A roof leak monitoring system is detailed in U.S. Pat. No. 7,652,481
(Vokey) issued January 26, 2010 to Detec Systems LLC discloses an arrangement
for leak detection on flat roof systems using a gridded system of wire sensors
whereby the X and Y wires that form a grid are alternately operated as an
electric
guard and then as a leak detection sensor measuring the conductivity to ground
at a
membrane breach through the water on the surface of the membrane. The method
relies on the assumption that a breach through the membrane will be located
coincidentally at an intersection of the x and y wires of the common grid
section.
However, where there are two breaches including a first breach close to an x
grid
location only and a second breach at a location next to a y grid location only
can, the
analysis of the voltages can result in an incorrect assessment that there is a
single
breach in the grid sections where the x and y wires of the grid intersect.
An improvement to this arrangement is also shown in US Patent
8,319,508 (Vokey) issued November 27 2012.
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A yet further improvement is shown in Published US application
2014/0361796 which shows that, where a roof deck is used which has no or low
electrical conductivity, a measurement system can be provided where the
current is
detected between a sensor on top of the membrane and a conductive layer
underneath the membrane connecting the deck to the membrane such as an
adhesive.
The disclosure of the above Vokey patents may be referred to for
further details of the subject matter claimed herein.
A more recent roof leak monitoring system is detailed in US Patent No.
8,566,051 issued October 22, 2013, to Gunness which describes a system for
detecting and locating a leak through a membrane that includes a detector
array and
computer. The detector array includes a boundary wire loop, sensors, and
leads.
The boundary wire loop surrounds the area of the membrane to be tested and
generates electrical tension on the surface of the membrane. The sensors are
laid
out in a sensor array and are placed on top of the membrane and within the
boundary wire loop. The sensors are encased in a plastic covered cable or form
individual wires which have open ends for their terminations so as to define a
cable
so that the sensors made by the open terminations form a chain. Each sensor
communicates individually with the computer and the signals from the sensors
are
used by the computer to perform vector mapping that detects and locates leaks
through the membrane. This is an automated form of vector mapping which relies
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on a uniform and continuous covering of water over the membrane to locate
breaches accurately. =
All of the above methods are usually employed to assist in locating roof
leaks on IRMA assemblies.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for
monitoring leaks in a flat or low slope roof construction of the type having
an
impermeable membrane applied over an underlying horizontal support.
According to the present invention there is provided a method of
detecting a leak in a roof where the roof comprises a generally horizontal
roof
support deck with a water impermeable membrane applied onto the upper surface
of
the support deck so as to define an upper surface of the membrane and a lower
surface of the membrane, the method comprising:
applying electrically conductive shielding elements on the upper
surface of the roof membrane in an X and Y grid pattern so as to be in
electrical
communication with any moisture on the upper surface;
the X and Y grid pattern of the electrically conductive shielding
elements providing separation of the membrane into a plurality of zones each
being
bounded on two first sides by two of the electrically conductive shielding
elements
extending in the X direction and being bounded on two second sides by two of
the
electrically conductive shielding elements extending in the Y direction;
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generating an electrical potential difference between the electrically
conductive shielding elements on the upper surface of the membrane and a
conductive component at or adjacent the roof deck on the underside of the
membrane;
5 in each of
the zones locating a respective one of a plurality of sensor
conductors on the upper surface of the membrane;
each of the sensor conductors being separate from the electrically
conductive shielding elements;
while the electrical potential difference is applied between the
electrically conductive shielding elements and the conductive component,
generating
an electrical potential difference between the sensor conductor on the upper
surface
of the membrane and the conductive component on the underside of the membrane
such that, in the presence of a leak located within the zone, current flows
between
the sensor conductor and the conductive component through moisture at the
leak;
and detecting said current flowing between the sensor conductor and
the conductive component through moisture at the leak to determine the
presence of
the leak.
Preferably the method includes operating switches in sequence to
measure and record the current from the sensor conductor in each zone
sequentially. However some or all of the sensors may be operated
simultaneously.
Preferably the potential is applied to all electrically conductive shielding
elements simultaneously. However
the potential may be applied in zones
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surrounding the zone under detection with the conductors in zones in other
areas of
the membrane remote from the zone in detection being left unpowered.
Preferably the method includes connecting the sensor conductor in
each zone to a measurement circuit and switching circuit for generating the
electrical
potential.
Preferably the method includes operating a switching circuit to apply
the electrical potential to the electrically conductive shielding elements so
that the
potential is applied periodically. That is the sensing action may be repeated
periodically during the life of the system to provide a continuous monitoring
action
over many years.
Preferably the detected current is used to provide a value of either the
current flowing or the changes in resistance between the sensor and the
underlying
conductor for analyzing the measured resistance or current in all of the zones
to
identify any leaks in the membrane.
Preferably the sensor conductors are located generally at or adjacent
the center of each of the zones and spaced from the electrically conductive
shielding
elements.
Typically the electrically conductive shielding elements and the sensor
conductors are covered by a layer of aggregate or other roof build up material
applied over the membrane. That is the conductor are permanently located
underneath the material on the roof to provide continuous monitoring over the
life of
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the system. The system herein is particularly advantageous where the membrane
is
not accessible for monitoring by other systems.
Preferably the electrical potential applied to the electrically conductive
shielding elements is .greater than that applied to the sensor conductors by a
difference of the order of one or more volts since this acts to better shield
the
sensing action at the location in the zone. That is any leaks outside the zone
under
= test are supplied with current by the shielding elements rather than by
the sensor
itself and thus any current drawn from the sensor is caused by leaks within
the zone
under test.
As a subsidiary advantage, the electrically conductive shielding
elements can be used for a cathodic protection system in which a supply and
switch
= is provided such that in the off state, when no measurements are being
made, a low
voltage cathodic protection supply is applied between all the electrically
conductive
shielding elements and the conductive component.
In some cases where necessary due to the geometry and arrangement
of the roof structure, a permanent guard wire is placed around conductive roof
penetrations to provide further isolation and avoid false readings.
In some cases the conductive component comprises the roof deck
itself where the deck is formed of a material which is sufficiently
conductive. As an
alternative, the conductive component can comprise a conductive layer between
the
membrane and the roof deck where the roof deck is formed of a non-conductive
material.
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Preferably the electrically conductive shielding elements and the
sensor conductors are bare wires applied by an adhesive to the upper surface
of the
membrane so that the wires are in electrical connection with any moisture on
top of
the membrane.
As an alternative the electrically conductive shielding elements and the
sensor conductors can comprise an exposed conductor such as a strip carried on
an
adhesive tape attached to the membrane.
Thus in general there is provided a method of detecting a leak in a roof
where the roof comprises a generally horizontal roof support deck with a water
impermeable membrane applied onto the upper surface of the support deck which
may have a layer of aggregate or other roof build up material applied over the
membrane, the method comprising:
Applying guard conductors acting as shielding elements on the top
surface of the roof membrane in a grid pattern providing segregation of the
membrane into zones bounded by the X and Y conductors which when joined
together create an electrical guard for each of the zones.
Placing a sensor conductor in the center of each of the zones created
and bounded by the X and Y guard conductors.
Connecting the sensor conductors in each zone to a measurement
circuit and switching circuit for generating an electrical potential between
two
components of the circuit;
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Operating a switching circuit to apply the measurement supply voltage
to the X and Y guard circuits;
by operating switches in sequence to measure and record the current
or resistance to the roof deck through the any breach in the membrane and
analyzing the measured resistance or current in all of the isolated zones to
identify
any leaking areas in the membrane.
To enhance the operation of the guard conductors which are driven
from the same supply that is used for the sensor conductor measurement
circuit, the
voltage to the measurement circuit can be reduced by a volt more thus making
the
guard circuit more attractive to stray currents outside of the grid zone that
is
currently being measured.
The same guard conductors can also be used for a cathodic protection
system in which a secondary cathodic protection supply and switch is provided
such
that in the off state, when no measurements are being made, a low voltage
(usually
about -0.85 to -1.1 Vdc), cathodic protection supply is applied between all
the X and
Y guard conductors and the building ground connected to the rood deck to
inhibit
corrosion and electrolysis.
If needed, a permanent guard wire can be place around conductive
roof penetrations to provide further isolation and avoid false readings.
It will be appreciated that the present invention can be used with roof
systems where the roof is horizontal or generally horizontal which includes
roof
panels which are slightly inclined to the horizontal.
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The present invention overcomes the mentioned limitation and allows
for a non-ambiguous determination of the grid enclosed section where a
membrane
breach has occurred.
5 BRIEF DESCRIPTION OF THE DRAWINGS
= One embpdiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is an illustration of the basic concept and circuit which details
the measurement circuit and the concept of a guard circuit.
10 Figure 2 is a circuit schematic showing the measuring and
control
circuit for multiple zones and shows the microprocessor controlled switching
arrangement.
Figure 3 is a cross-sectional view through a portion of the roof showing
the arrangement of Figure 1.
Figure 4 is a similar view showing a modified arrangement.
Figure 5 is a top plan view of the arrangement Figure 1.
DETAILED DESCRIPTION
Referring now to the drawings, the overall arrangement of the subject
roof membrane moisture detection system can best be seen with reference to
Figures 1 and 2. A roof membrane 31 is illustrated which is applied as a
direct
covering layer over a roof deck 30. The deck is typically of concrete but can
be of
any suitable material that is sufficiently conductive to allow the detection
of a low
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level electrical current travelling through the deck to a measurement ground.
The
membrane is a water impervious material such as thermoplastics and is sealed
at
any joints to provide a continuous water barrier over the roof deck. This
barrier is
intended to provide the leak prevention and any penetration therein caused by
a
puncture or faulty seal or by wear can allow the moisture to penetrate to the
deck
where it can cause damage or can continue into the structure to cause damage
to
internal structures. The membrane is typically covered by a drainage layer 2,
thermal
insulation 3 and a surface covering 4 such as built up roofs with gardens as
shown
schematically in Figure 3.
Referring to Figures 1 and 4, copper conductors 35 and 36, illustrated
as a flat conductor strip adhered to a mounting strip or tape 26, is laid
across the
membrane in a grid like pattern. In approximately the center of each grid a
short
strip of the same copper tape 40 is adhered to the membrane. This short strip
of
tape is the sensor that detects any current 12 that travels from a breach in
the
membrane 31 through a connecting cable 13 to the measurement circuit 11. The
basic measurement circuit is formed by voltage source 7 with one side
connected to
measuring circuit 11, earth ground 9 and the conductive deck 30. The positive
side
the voltage source 7 is connected to the guard conductors 35 and 36, at
connection
14 and to the measuring circuit 11 through dropping diodes 10. The diodes
reduce
the measuring voltage slightly which enhances the effectiveness of the guard
conductors 35, 36.
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While the potential applied between the guard conductors acting as
shielding elements 35, 36 and the roof deck 30 when selected and between the
guard conductors and the roof deck when not selected is typically
substantially the
same, advantages may be obtained by increasing the potential difference across
the
conductors when they are acting as shielding conductors. This can draw in more
of
the current from remote locations which can interfere with proper measurement
at
the selected measurement conductor.
Figure 2 illustrates a larger section of a roof system with four gridded
zones shown. The X and Y guard conductors 35, 36 are connecter to the guard
switch 20 via cable 17. The guard switch applies the full battery potential to
the X
and Y conductors during the measurement. This forms an electrical guard
isolating
the zones 37 from each other. The measuring voltage is also applied to the
zone
switch 21 through diodes 10. The microprocessor control and measurement
circuit
11 selects the zones in sequence and measures any resistance through the
membrane 31 in its isolated section to ground. When all zones are measured,
the
results are compared to earlier readings and any degradation of the resistance
in the
roof deck is noted. At the end of the test cycle the guard switch connects the
grid
conductors 35, 36 to .a low voltage cathodic protection source 19 which
inhibits
corrosion of the copper conductors.
The arrangement as shown in Figure 3 herein thus provides a method
of detecting a leak in a roof with the roof comprises a generally horizontal
roof
support deck 30 with the membrane 31 attached over the upper surface of the
deck
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so as to define an upper surface 32 of the membrane and a lower surface 33 of
the
membrane which is attached preferably by an adhesive layer 34. The
electrically
conductive shielding elements 35 and 36 are applied in the X and Y arrangement
of
a grid pattern and sit directly on or adjacent the upper surface of the
membrane so
as to be in communication with any moisture on top of the membrane generally
contained within the layers covering the membrane as shown in Figure 2. The
grid
pattern of the shielding elements 35, 36 provided a zone 37 bounded on two
sides
by the shielding elements 35 and on the other two sides by the shielding
element 36.
As explained above a potential difference is generated between the
shielding elements 35 and 36 on one side and the conductive component on the
other side or on the side of the membrane, where the conductive component is
defined either by the roof deck 30 itself as shown in Figure 4 or by a
conductive
material within the adhesive layer 34 between the membrane and the deck.
As shown in Figure 5 there is provided a short strip 40 of the conductor
which is arranged out of adjacent the centre of the zone 37 and spaced from
all of
the surrounding conductors. The strip 40 is thus separated from the conductors
and
is not in electrical communication therewith.
As explained previously, while the electrical potential is applied to the
conductors 35 and 36, an electrical potential is applied across the circuit
defined by
the strip 40 and the conductor underlying the membrane through the moisture in
any
leak present within the zone 37. The current in the circuit can be detected
and a
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value provided either for the current itself or for the resistance these
change due to
the presence of the moisture in the leak.
The conductors 35 and 36 act so that any other leaks outside the zone
37 are not detected by the circuit through the conductor 40 since any current
flowing
to those leaks is provided by the conductors 35 or 36 depending upon the
location of
the leak.
In some cases the detection system is used to measure the current in
each other zones independently and sequentially. However it is also possible
that
some more all of the zones may be measured simultaneously using separate
sensing systems.
In the most simple system, all the conductors 35 and 36 are
simultaneously connected to the potential so as to separate the whole membrane
into the separate zones. However it will be appreciated that the membrane may
be
divided into separate areas where the detection of the leaks is carried out
separately
in those separate areas thus requiring only the potential to be applied to the
conductors in that area.
= As set out above, the conductors are 35, 36 and 40 are permanently
located underneath the material on the roof so that they are protected thereby
and
remain in place during the life of the system. Thus the monitoring can be
carried out
periodically during the lifetime of the membrane so as to provide early
indication of
any leak, allowing early remedial action.
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The conductors 40, 35 and 36 when provided in the form of a flat strip
can be directly adhesively attached directly to the membrane. More
conveniently the
conductors can be provided in the form of a tape with the conductor carried on
a
band or tape of a material having a rear adhesive allowing it to be bonded
easily to
5 the membrane.
