ASTM D7954/D7954M-22a

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Designation: D7954/D7954M − 22 D7954/D7954M − 22a
Standard Practice for
Moisture Surveying of Roofing and Waterproofing Systems
Using Nondestructive Electrical Impedance Scanners
This standard is issued under the fixed designation D7954/D7954M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice applies to techniques that use nondestructive electrical impedance (EI) scanners to locate moisture and evaluate
the comparative moisture content within insulated low-slope roofing and waterproofing systems.
1.2 This practice is applicable to roofing and waterproofing systems wherein insulation is placed above the deck and positioned
underneath and in contact with electrically nonconductive single-ply or built-up roofing and waterproofing membranes and systems
such as coal tar, asphalt, modified bitumen, thermoplastics, spray polyurethane foam, and similar electrically nonconductive
membrane materials. This practice is also applicable to roofing and waterproofing systems without insulation placed above
moisture absorbing decks such as wood, concrete, or gypsum, that are in contact with single-ply or built-up roofing and
waterproofing membranes as described above.
1.3 This practice is applicable to roofing and waterproofing systems incorporating electrically nonconductive rigid board
insulation made from materials such as organic fibers, perlite, cork, fiberglass, wood-fiber, polyisocyanurate, polystyrene, phenolic
foam, composite boards, gypsum substrate boards, and other electrically nonconductive roofing and waterproofing systems such
as spray-applied polyurethane foam.
1.4 This practice is not appropriate for all combinations of materials used in roofing and waterproofing systems.
1.4.1 Metal and other electrically conductive surface coverings and near-surface embedded metallic components are not suitable
for surveying with impedance scanners because of the electrical conductivity of these materials.
1.4.2 This practice is not appropriate for use with black EPDM, any membranes containing black EPDM, or black EPDM coatings
because black EPDM gives false positive readings.
1.4.3 Aluminum foil on top-faced insulation, roofing, or waterproofing membranes gives a false positive reading and is not
suitable for surveying with impedance scanners; however, liquid-applied aluminum pigmented emulsified asphalt-based coatings
shall not normally affect impedance scanner readings.
1.4.3.1 This practice is not appropriate for use with aluminium foil faced modified bitumen membranes, as the electrical
conductivity of the aluminium foil surface can give false positive readings.
1.4.4 While their overburden remains in place, this practice is not appropriate for use with inverted roof membrane assemblies
This practice is under the jurisdiction of ASTM Committee D08 on Roofing and Waterproofing and is the direct responsibility of Subcommittee D08.20 on Roofing
Membrane Systems.
Current edition approved April 15, 2022May 1, 2022. Published May 2022. Originally approved in 2014. Last previous edition approved in 20212022 as
D7954/D7954M – 15a (2021).D7954/D7954M – 22. DOI: 10.1520/D7954_D7954M-22.10.1520/D7954_D7954M-22A.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7954/D7954M − 22a
(IRMAs) or protected roof assemblies (PRMAs), which contain above the deck waterproof membrane and overburden that may
include insulation, drainage components, pavers, aggregate, ballast, vegetation, or combinations thereof, because the impedance
scanner will not differentiate between above and below the membrane moisture.
1.4.5 See A1.4 for some cautionary notes on roofing anomalies and limitations that affect the impedance test practice.
1.5 Moisture scanners using impedance-based technology are classified as EI scanners.
NOTE 1—The term capacitance is sometimes used when describing impedance scanners. Capacitance scanners are purely capacitive as they do not have
a resistive component. Impedance scanners combine both capacitance and resistance for testing; thus, they are well suited to the measurement of different
types of materials and constructions found in roofing and waterproofing systems as the combination of both components allows for a more versatile
testing, calibration, and measurement arrangement.
1.6 This practice also addresses necessary verification of impedance data involving invasive test procedures using core samples.
1.7 This practice addresses two generally accepted scanning techniques for conducting moisture surveys using electrical
impedance scanners:
1.7.1 Technique A—Continuous systematic scanning and recording (see 8.2), and
1.7.2 Technique B—Grid format scanning and recording (see 8.3).
1.8 This practice addresses some meteorological conditions and limitations for performing impedance inspections.
1.9 This practice addresses the effect of the roofing or waterproofing construction, material differences, and exterior surface
conditions on the moisture inspections.
1.10 This practice addresses operating procedures, operator qualifications, operating methods, scanning, surveying, and recording
techniques.
1.11 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated
in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values
from the two systems may result in nonconformance with the standard.
1.12 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Caution should be taken when accessing, walking, or using scanning equipment on the roofing
or waterproofing surfaces, or elevated locations, when using ladders, and when raising and lowering equipment to elevated
locations.
1.13 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C1616 Test Method for Determining the Moisture Content of Organic and Inorganic Insulation Materials by Weight
D1079 Terminology Relating to Roofing and Waterproofing
D7438 Practice for Field Calibration and Application of Hand-Held Moisture Meters
E2586 Practice for Calculating and Using Basic Statistics
F2659 Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor
Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D7954/D7954M − 22a
NOTE 2—See A1.3 for other referenced documents.
3. Terminology
3.1 For definitions of terms used in this practice, refer to Terminology D1079.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 comparative moisture, content, n—qualitative characterization of moisture content in relative terms (that is, low, medium,
and high levels of moisture).
3.2.2 core sample, n—small specimen of insulation and membrane having a minimum of 2 in. [50 mm] diameter obtained by
cutting through these components down to the deck and removing them from the roofing section under test.
3.2.2.1 Discussion—
Core samples are used to verify the membrane and insulation composition and ascertain information on their condition.
3.2.3 detect or detection, v or n—for the purpose of impedance scanning, the condition at which there is a consistent indication
that an elevated level of impedance reading is present within the roofing or waterproofing system.
3.2.4 false-positive, adj—reading that indicates that elevated moisture is present when it is not.
3.2.4.1 Discussion—
For example, a false positive in roofing for impedance scanning may be returned when some other electrically conductive material
is present in the roofing system.
3.2.5 gravimetric analysis, n—determination of moisture content by weight of a material by comparing wet weight to oven dry
weight expressed as a percentage.
3.2.6 moisture content, MC, n—mass of moisture per unit mass of dry material.
3.2.6.1 Discussion—
The moisture content is usually expressed as a percentage by weight and determined gravimetrically.
3.2.7 roof assembly, n—assembly of interacting roof components including the roof deck, air or vapor retarder, insulation and
membrane, or primary roof covering designed to weatherproof a structure.
3.2.8 roof section, n—portion of a roof that is separated from adjacent portions by walls or expansion joints with no changes in
the components throughout the section.
4. Summary of Practice
4.1 This practice covers a procedure in which a specifically developed nondestructive electronic impedance (EI) based moisture
scanner is used in conjunction with interpretive data and invasive verification practices to detect and evaluate the moisture
conditions within low-sloped roofing and waterproofing systems by nondestructively measuring the electrical alternating current
(ac) impedance.
4.2 This practice is intended to be used in conjunction with the impedance scanner manufacturer’s operation instructions and
guides.
5. Significance and Use
5.1 Excess moisture trapped in roofing or waterproofing systems can adversely affect performance and lead to premature failure
of roofing or waterproofing systems and its components. It also reduces thermal resistance, resulting in reduced energy efficiency
and inflated energy costs. Impedance scans can be effective in identifying concealed and entrapped moisture within roofing or
waterproofing systems.
5.2 This practice is intended to be used at various stages of the roofing and waterproofing system’s life such as: during or at
completion of installation of roofing or waterproofing system to determine if there was moisture intrusion into the roofing or
D7954/D7954M − 22a
waterproofing system or underlying materials; at regular intervals as part of a preventative maintenance program; and to aid in
condition assessment, or before replacement or repair work, or combinations thereof, to assist in determining the extent of work
and replacement materials.
5.3 This practice alone does not determine the cause of moisture infiltration into roofing or waterproofing systems; however, it can
be used to help tracing excess moisture to the point of ingress.
6. Apparatus
6.1 EI Scanner—This apparatus shall be specifically developed to detect and evaluate nondestructively comparative moisture
conditions within roofing and waterproofing systems.
6.1.1 Principles of Operation—The EI of a material varies in proportion with the material’s moisture content. The EI of materials
such as those listed in 1.2 and 1.3 in the roofing or waterproofing system directly under the footprint of the scanner is measured
by creating an alternating electric field that penetrates the materials under test. The small alternating current (ac) flowing through
this field is inversely proportional with the impedance of these moisture-absorbing materials. The instrument determines the
current’s amplitude and converts this value to a comparative moisture value.
6.1.1.1 The depth of the signal penetration varies depending on the sensitivity and signal strength settings of the scanner as well
as the composition of materials, thickness, and moisture content of the roofing or waterproofing system under test.
6.1.2 Apparatus Requirements:
6.1.2.1 The moisture scanner shall be capable of sending signals nondestructively into the materials below the surfacing and the
scanner.
FIG. 1 Typical Nondestructive Moisture Scanner
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6.1.2.2 The moisture scanner shall have integrated adjustable calibration ability for the differing composition, thickness, density
of materials, and moisture conditions that can be encountered in roofing or waterproofing assemblies.
6.1.2.3 The moisture scanner shall have a display giving comparative readings of moisture conditions of materials found in roofing
and waterproofing systems.
6.2 Scanner Types—Two types of impedance scanners are commercially available:
6.2.1 Handheld scanner designed to be used for point readings on a grid system, and
6.2.2 Mobile-wheeled scanner, which can be rolled across the roofing or waterproofing to obtain continuous readings as the
scanner moves over the surface.
NOTE 3—See A1.1 and A1.2 for examples of typical handheld and mobile-wheeled types of impedance scanners.
7. Operator Qualifications and Referenced Materials
7.1 The operator shall:
7.1.1 Be familiar with the use of the impedance scanner;
7.1.2 Have knowledge of and available for reference at the roof site a copy of the manufacturer’s operating and calibration
instructions for the impedance scanner used;
7.1.3 Have knowledge of how and under what circumstances the impedance scanning system can be used, as well as its
limitations;
7.1.4 Have a thorough understanding of the construction and components used in the roofing or waterproofing system assembly
under test, such as types of membranes, roofing insulations, decking, and attachment;
7.1.5 Confirm the composition of the roofing or waterproofing assembly and endeavor to obtain historical data regarding the
construction, age, and performance of the roofing or waterproofing assembly; and
7.1.6 Have a thorough understanding and knowledge of roofing and waterproofing technology including types of roofing or
waterproofing membranes and materials, decks, insulation materials, system assemblies and construction procedures, equilibrium
moisture content, moisture migration in buildings, as well as health and safety requirements when carrying out roofing or
waterproofing moisture surveying.
7.2 Data Interpreter—Individuals interpreting the field data shall have knowledge of: impedance scanner principles of operation,
moisture migration transport mechanisms, environmental effects, oven dry and equilibrium moisture contents (EMC), thermal
resistance ratios (TRR), verification methods, and roofing and waterproofing construction as it applies to moisture analysis and
gravimetric analysis to diagnose and interpret the readings from the roofing or waterproofing system surveyed.
NOTE 4—See A1.4 for additional information on technique and anomalies.
8. Impedance Scanning Techniques
8.1 Two techniques, (A) and (B), for conducting moisture surveys using impedance scanners are:
8.2 Technique A—Continuous Systematic Scanning and Recording—This practice involves moving (rolling) the impedance
scanner in a systematic and continuous row-by-row manner when traversing the roof surface.
8.2.1 As the scanner is rolled along each run or row in a systematic fashion, continuous impedance readings shall be displayed
on the scanner’s meter. These readings shall be visually observed by the operator.
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8.2.2 All areas where elevated moisture content levels are indicated by increased impedance readings displayed on the scanner’s
meter shall be referenced, recorded, and marked on the roof surface or the appropriate position on the roof drawing or both by the
operator.
8.2.3 This technique is applicable to the mobile-wheeled unit as it gives a continuous reading while traversing the roof surface
(see 6.2.2).
8.3 Technique B—Grid Format Scanning and Recording—This practice involves the scanning the roof using a grid format where
the scanner is moved within the grid pattern.
8.3.1 Scanning is done with a grid pattern layout system in which the scanner is moved in a uniform fashion within the grid
pattern. Readings are taken and recorded at each grid intersection point or at regular similar spaced intervals on or between grid
lines; additional readings are taken and recorded in areas where elevated moisture levels are indicated by increased impedance
readings.
8.3.2 See 9.3 for information on grid system layout.
8.3.3 This technique is considered applicable to both handheld and the mobile-wheeled impedance scanners as referenced in 6.2.1
and 6.2.2.
8.4 When impedance or comparative moisture level readings or other markings are recorded on the roof surface, obtain permission
from the building owners or their agent before marking the roof surface with paint or similar marking material. Ensure that
materials used for marking are compatible with the roofing or waterproofing systems so damage does not occur.
9. Preparation
9.1 Preparation as Applying to Both TechniqueTechniques A and B—Before commencement of nondestructive impedance testing,
the operator shall:
9.1.1 Confirm the composition of the roofing or waterproofing assembly and obtain any available historical data regarding the
construction, age, and performance of the roofing or waterproofing assembly;
9.1.2 Obtain a roofing and waterproofing plan drawing, if available; and
9.1.3 Prepare drawings (if not available) and survey report sheets for each roofing or waterproofing section being surveyed on to
which scanner readings and other relevant data shall be recorded.
9.2 Calibration as Applying to Both TechniqueTechniques A and B:
9.2.1 Before carrying out a roofing or waterproofing moisture survey with either a handheld or mobile-wheeled impedance
scanner, it is necessary to calibrate the equipment on an area of roofing or waterproofing where the surface and subsurface
insulation and components are dry.
9.2.2 Core samples taken for calibration purposes shall consist of specimens of the roofing or waterproofing system at least 2 in.
[50 mm] in diameter to include roofing or waterproofing membrane and all materials from the top surface down to the deck.
9.2.3 Core samples shall be taken by cutting through the system down to the deck and shall be evaluated by appropriate methods
to determine composition, condition, and moisture content. If decking material is capable of moisture absorption, its moisture
condition shall be also be evaluated by appropriate means (see Note 5). Typically, core samples taken from dry reference locations
shall be retained for gravimetric analysis in accordance with Test Method C1616 at the
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