John A. D’Annunzio
When properly completed the
determination of moisture content utilizes advanced technological equipment,
laboratory testing and scientific equations.
The process has advanced to the point where analysis can be objective
and reliable. This phase of the industry
has advanced from the days of the ‘educated’ toe and subjective claims of how
the system felt as it was walked across.
Standard Moisture Analysis Procedures
Proper analysis includes a
combination of both non-destructive and destructive methods of testing. Investigations completed using only one of
these methods are insufficient and lack creditability. The equipment used to conduct non-destructive
tests provides analysis (a snapshot) of the overall roof conditions of large
expansive areas in a quick and efficient manner. Destructive testing – coupled with
gravimetric tests – are required to verify the conditions observed by the moisture
analysis equipment.
There are three types of
non-destructive testing equipment:
- Impedance or Capacitance
- Infrared
- Nuclear
Impedance or capacitance moisture
testing is conducted using a variety of small hand held meters that – when set
over the roof membrane – emit low frequency electronic signals from rubber
electrodes located at the base of the instrument. These types of meters typically determine if
a specific roof area is either wet or dry.
They do not have the capacity to measure the percentage of moisture
present. Dry readings are projected at points where the electrodes are
insulated from one another and there is not a complete electrical circuit. The electrical conductance is greater at wet
areas, which provides a complete electrical circuit.
Impedance testing can be
conducted in a pattern or at various points throughout the roof area. A higher number of readings provide more
cohesive moisture determination. The
testing cannot be completed over wet or ponded areas and modified instruments
are typically required for EPDM roof systems.
Infrared thermography is conducted
with the use of an infrared camera. An
infrared camera detects the temperature of the areas within a roof system and
identifies temperature differentials throughout the area. Infrared scanning is most effective after
sunset because as the air temperature decreases the dry insulation allows the
roof to cool quickly. In areas where
moisture is present – insulation or membrane – take longer to cool due to a
large thermal mass that is developed in these areas.
Thermal mass or ‘hot spots’ are not always an indication
of moisture presence. They can be
illustrated at under deck heating or cooling vents, venting of hot fumes,
moisture on the roof surface (ponded water), or at points of heavy gravel
application. Most infrared cameras
require clear weather conditions for an external period prior to and during the
testing. This typically includes no
recent or current precipitation, heavy cloud cover or windy conditions. Any – or all – of these conditions could
distort the infrared findings.
Nuclear thermography is conducted
using a nuclear scanning meter that emits neutrons from a radiation source from
the scanning meter down through the roof assembly. The emitted neutrons that encounter hydrogen
atoms in the roof assembly are slowed down and bounced back to the counting
detector within the scanning meter.
Higher levels of slowed neutrons are recorded at wet areas because water
contains a significant amount of hydrogen atoms. The recorded reading is an average of the
total roof assembly.
Generally, nuclear scanning can
be completed to depths as much as seven inches and testing can be conducted in
areas of ponded water. Testing is
conducted over the entire roof area by sectioning the roof into grids (5’x 5’
or 10’ x 10’) and recording the readings at each of these locations.
Moisture Verification
After visually inspecting all of
the roof areas, making notes of all of the conditions, defects and problems it
is important to find out the true conditions of the roof system. This is done by extracting a test sample or
core cut from the roof area. Core cuts
are conducted in a roof analysis because each of the moisture analysis methods
has their limitations, and thorough diagnosis of a roof system requires core
cuts. Moisture identified by
non-destructive moisture testing is relative and must be quantified by a
combination of physical core cuts and gravimetric analysis.
The extraction process of core
cuts is similar if the sample is to determine construction or condition of the
roof system. The differences are in the
type of forensic testing that is conducted on the test samples. In the moisture analysis procedure the core
cuts are extracted to determine both the construction and condition of the
existing roof system. For these
purposes, the core cuts can be completed in the following manner for all types
of roof systems:
1. Identify the appropriate location of the test cut. The proper area should be representative of
the entire roof area construction. Do
not take a test cut at a previously repaired area.
2. Take one test cut per moisture
representative in each roof area. A test
cut should be extracted from those areas determined to be dry, and areas found
to have varying levels of moisture presence; low, medium, or high. Facilities
with multiple roof areas and/or multiple roof systems require test cuts from
each roof area.
3. Identify the location(s) of the test
cut(s) on the roof plan.
4. Use a 12” x 12” template and measure the
area to be cut at 12” x 12”.
5. Following the established 12” x 12” pattern cut the
membrane, any insulation(s) and underlayment(s) to the structural
deck. Single ply systems can be cut
with scissors. Bituminous roof
systems require a box cutter knife or hatchet.
6. Remove all roof system components, (membrane,
insulation, and underlayment) from
the opening.
Photograph the system components and structural deck
substrate.
8. Record system construction components identifying the
method of attachment of each
component, including:
1.
deck type
2.
underlayment (if used)
3.
insulation type, thickness and condition (each layer)
4.
method of insulation attachment (each layer)
5.
membrane type, thickness and condition
6.
method of membrane attachment
7.
type of surfacing and method of attachment
The core samples should be placed
in a watertight container and immediately transported to an approved testing
facility for gravimetric testing.
Gravimetric testing is conducted
by separating each roof assembly component
