sample of the material into the pan and taking a tester
manner as it is with bound water in soil. Thus, a certain
reading. It may not be possible to obtain 135 PCF dry
background reading will be present even though the roof
material In the pan, however. Any error resultant from
an inadequate compaction of the dry material will be
A roof with wet insulation 4 inches thick will provide a
higher moisture count rate than will a roof with the same
h. This curve IS accurate as long as the same 135
wet insulation, but only 2-inches thick.
PCF is produced in the field. If other weights are desired
for field compaction, then a separate curve should be
Thus, the reading of a moisture tester on a single
produced for each desired field weight. Obviously, It is
location on a roof cannot be used alone as an index of
desirable to attempt to select only one or two appropriate
whether the roof is wet or dry.
field weights to minimize curves and effort
A series of readings over a representative sample of the
The pan can also be set on legs, anything at least two
roof must be taken and readings compared to each other
feet from the ground and five feet from surrounding
to produce a profile which can then be interpreted as a
objects Watch out for the tailgate of a pickup truck due to
the presence of the gasoline tank and spare tire, both
1-32. ROOF MOISTURE TESTING
Starting from a corner, take readings on a 10' grid
pattern over the roof. 1/2 minute readings should be
The soil tester becomes a most useful tool when it is
quite adequate. Record the actual counts Do not bother
used to measure the trapped moisture in a built-up roof.
with computing a ratio and do not attempt to use the soil
It is always difficult to locate a leak and to estimate the
moisture chart to determine actual moisture in
area of roof damaged by a leak Built-up roofs generally
consist of a waterproof membrane sandwiching a thick
layer of insulation between it and the roof structure If
It will be noted that a majority of the readings will fall at
moisture becomes trapped In the insulation, the
some minimum value for this particular roof This will
insulating value is damaged and the roof structure is
correspond to the dry readings. Other readings will be
higher. The highest readings should be further explored
with additional readings taken on 5' grid to establish the
Any attempt to puncture the roof to investigate the
degree of moisture intrusion is undesirable because of
the additional damage the testing introduces. The non-
These highest readings represent the wettest portion of
destructive nature of the tester provides for rapid,
the roof It may be necessary to make a test penetration
accurate determination of roof moisture without
to determine the actual moisture present at this highest
penetration of the roof.
value By observation this can be classified as an
arbitrary "moist", "wet", or "saturated" value.
Readings in between the dry bottom readings and the
moist high readings can be classified proportionately.
All roofs are not constructed alike.
They vary in
Extra readings should be taken around chimneys, vents,
thickness, type of insulation, type of underlying
stairwells, cornices, and other protuberances. Wet areas
construction, and type of waterproof membrane.
should be tracked to their perimeters.
Some will have hydrocarbons associated
1-35. PLOT ROOF MOISTURE PROFILE
construction materials and Insulation, others
little Internal hydrocarbon structure.
On a drawing of the roof, plot the observed values
channel is affected by the internal hydrogen in