Voluntary Guidelines for Insulating Glass Unit Cavity
Width Manufacturing Tolerances
(TM-4400-XX)
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
1
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
IGMA Publication #: TM-4400-XX, Revision 01, Insert Date
Copyright 20XX Insulating Glass Manufacturers Alliance. All rights reserved.
Disclaimer
The information and recommendations contained in these guidelines have been
obtained from sources believed to be reliable. However, it should not be
assumed that all acceptable procedures are contained in these guidelines or
that additional measures may not be required under certain circumstances or
conditions. Note that the various codes and regulations referenced in this
document may be amended from time to time and it should not be assumed
that the versions referenced herein are the most current versions of such codes
and regulations. Please consult the appropriate regulatory authorities for the
most up-to-date versions. Compliance with all local governing building codes is
also required.
The Insulating Glass Manufacturers Alliance (IGMA) makes no warranty or
representation and assumes no liability or responsibility in connection with any
information contained in these guidelines.
IGMA assumes no liability or
responsibility in connection with any modifications to or adaptations of these
guidelines by any user, purchaser or other party, or in connection with the use or
misuse of any information contained in these guidelines.
While IGMA recommends the use of and reference to these guidelines by private
industry and others, these guidelines are intended to be voluntary and not
binding. Users of these guidelines are advised that these guidelines define
different visual obstructions. Users are encouraged to contact the specific
manufacturer regarding time limitations included in their warranty.
IGMA does not approve or endorse any products, services or methods
mentioned herein. These guidelines should not be referenced in any way, which
would imply such approval or endorsement.
Additional copies of this and other publications of the IGMA are available from:
Insulating Glass Manufacturers Alliance
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Telephone: (613) 233-1510 / Fax: (613) 482-9436
or
Visit the IGMA website at:
www.igmaonline.org
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating Glass
Unit Cavity Width Manufacturing Tolerances
TABLE OF CONTENTS
SECTION
NUMBER
SECTION TITLE
EFFECTIVE DATE: INSERT DATE
REVISION: 01
REVISION
EFFECTIVE
DATE
PAGE
1.0
Introduction
1
2.0
Scope
2
3.0
Terminology
3
4.0
Conformance Requirements
4
5.0
Inspection
7
6.0
Referenced Documents
8
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for
Insulating Glass Unit Cavity Width
Manufacturing Tolerances
SECTION 1.0 INTRODUCTION
EFFECTIVE DATE: INSERT DATE
REVISION: 01
1.0 Introduction
The cavity width of an insulating glass unit (IGU) after fabrication varies based on
changes in temperature, and elevation above sea level. The purpose of this guideline is
to present voluntary manufacturing tolerances for minimum IGU cavity width reduction
at the point of manufacturing. Additionally the guideline presents (2014 LBNL WINDOWS
modeling based) thermal modeling data and the resulting thermal performance at
given reduced cavity widths. The guideline is not intended to address the dynamic
aspect of cavity width variability once an IGU leaves the point of manufacture where
environmental changes occur. Nor does this guideline address naturally occurring solar
reflectance. A web based information portal has been added to the IGMA web site
(www.igmaonline.org) containing a wealth of information for consumers, designers,
specifiers and building/home owners on the topic of cavity wide variability in the
installed environment. Included in this portal readers will find; altitude effect on IGU,
temperature effect on IGU, solar reflectance, design and remediation options used to
reduce the impact of naturally occurring solar reflectance as well as a library of
information available on this topic. Cavity width compensation technology exists where
in some case (for example in cases where an IGU is manufactured at a lower elevation
and shipped to a higher elevation) the cavity width will be intentionally reduced at the
point of fabrication such that equilibrium will occur at the point of installation. In the case
where pressure-compensating adjustments are being made the recommendations
contained in this guideline don’t apply. IGMA guideline XXXX should be referenced
where cavity width compensation techniques are being utilized.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
1
TM-4400-XX, Voluntary Guidelines for
Insulating Glass Unit Cavity Width
Manufacturing Tolerances
SECTION 2.0 SCOPE
EFFECTIVE DATE: INSERT DATE
REVISION: 01
2.0 Scope
2.1 These guidelines are intended to assist in determining maximum reductions in
insulating glass cavity width at the point of manufacturing.
2.2 These guidelines are applicable for the evaluation of the manufacturing
processes of sealed insulating glass units prior to leaving the point of
manufacturing. Specifically including double (single air cavity)and triple (two air
cavities)IGU’s
2.3 These guidelines cover the fabrication tolerances of the sealed space of an
insulating glass unit. Specifically including the resulting impact on thermal
performance when the IGU air cavity is reduced to the maximum allowable
dimension.
2.4 These guidelines are not applicable for when pressure/temperaturecompensating technology is being used by the manufacturer.
2.5 These guidelines do not purport to address all of the safety concerns, if any,
associated with its use, which may occur especially in cases where
pressure/temperature compensation is being made during production. It is
therefore the responsibility of the user of these guidelines to establish
appropriate safety and health practices and determine the applicability of
regulatory limitations prior to use.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
2
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing
Tolerances
SECTION 3.0 TERMINOLOGY
EFFECTIVE DATE: Insert Date
REVISION: 01
3.0 Terminology
Refer to IGMA TR-1400-14, Language of Sealed Insulating Glass Units
IGU – An insulating glass unit consisting of one or two air cavities and two or three layers
of glass commonly referred to as double or triple insulating glass
Cavity width – The inside to outside thickness of an IGU typically measured from the
number 2 to the number 3 (double) or 5 (triple) surfaces.
Cavity width variability – The difference between the nominal cavity width thickness at
the IGU edge and the cavity width thickness measured anywhere in the IGU but
specifically near the center of glass where the greatest cavity width variability would be
expected.
Reduced cavity width – Cavity width variability where the nominal edge of glass
thickness is greater than the cavity width measured elsewhere in the IGU.
Increased cavity width – Cavity width variability where the nominal edge of glass
thickness is less than the cavity width measured elsewhere in the IGU.
Air cavity thickness – thickness of the air cavity present between glass surfaces two and
three (and four and five for dual cavity IGU).
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing
Tolerances
SECTION 4.0 COMFORMANCE
REQUIREMENTS
EFFECTIVE DATE: Insert Date
REVISION: 01
4.1 Given that increases in cavity width have less of an impact on critical
performance attributes of thermal and solar reflectance, increases in cavity width are
not restricted. Excessive increase in cavity width may result in objectionable visual
distortion and as such should be managed in accordance with the manufacturers
quality management system. See figure 4.1
Figure 4.1 Limited and Unrestricted Cavity Widths
4.2 Allowable reductions in cavity width at the point of manufacturing vary based on
cavity width and are summarized in the chart 4.2 below
Allowable IG Cavity Reduction At The Time of IG Manufacture
IG unit short side dimension
Greater than 500mm (19.7"), less than or equal to 1000mm (39.4")
IG cavity or
combined cavities
Less than or equal to 500mm (19.7")
Notes:
Greater than 1000mm (39.4")
Less than or equal to 8mm (0.315")
2mm (0.079")
2mm (0.079")
3mm (0.118")
Greater than 8mm (0.315"), less than or equal to 13mm (0.512")
2mm (0.079")
3mm (0.118")
3mm (0.118")
Greater than 13mm (0.512")
3mm (0.118")
3mm (0.118")
3mm (0.118")
1) IG Cavity reduction is to be measured at the conditions and location of manufacture
2) IG Cavity reduction is to be measured in the vertical / near vertical orientation
3) IG Cavity reduction is calculated by subtracting the center of glass gap measurement from the average measured gap at the edge of glass
4) Limits are only for reductions in center gap and do not include tempered bow considerations or IG cavity enlargements
5) Combined cavity is the total of all of the cavities within the IG unit (example: a triple with two 9mm (0.354") cavities has a combined cavity of 18mm (0.709"))
Chart
4.2, Allowable for IG Cavity Reduction at Time of Manufacture
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass Manufacturers
Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing
Tolerances
SECTION 4.0 COMFORMANCE
REQUIREMENTS
EFFECTIVE DATE: Insert Date
REVISION: 01
4.3 The impact on thermal performance of an IGU at the maximum allowable
reductions in cavity width are indicated below in chart 4.3
Allowable IG Cavity Reduction At The Time Of IG Manufacture
IG unit short side dimension
Less than or
equal
to
500mm (19.7")
Greater than
500mm
(19.7"),
less
than or equal
to
1000mm
(39.4")
Greater than
1000mm
(39.4")
2mm (0.079")
2mm (0.079")
3mm (0.118")
0.03
0.03
0.04
Double LowE, Argon Ucg increase (8 mm cavity) BTU/hr*ft2*F
0.02
0.02
0.03
Double LowE, Krypton Ucg increase (8 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.01
Greater than 8mm (0.315"), less than or equal to 13mm (0.512")
2mm (0.079")
3mm (0.118")
3mm (0.118")
Double LowE, Air Ucg increase (9 mm cavity) BTU/hr*ft2*F
0.02
0.03
0.03
Double LowE, Argon Ucg increase (9 mm cavity) BTU/hr*ft2*F
0.02
0.03
0.03
Double LowE, Krypton Ucg increase (9 mm cavity) BTU/hr*ft2*F
0.01
0.01
0.01
Double LowE, Air Ucg increase (13 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Double LowE, Argon Ucg increase (13 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Double LowE, Krypton Ucg increase (13 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Greater than 13mm (0.512")
3mm (0.118")
3mm (0.118")
3mm (0.118")
Double LowE, Air Ucg increase (14 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Double LowE, Argon Ucg increase (14 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Double LowE, Krypton Ucg increase (14 mm cavity) BTU/hr*ft2*F
0.00
0.00
0.00
Triple 2 LowE, Air Ucg increase (2 - 7mm cavities) BTU/hr*ft2*F
0.04
0.04
0.04
Triple 2 LowE, Argon Ucg increase (2 - 7mm cavities) BTU/hr*ft2*F
0.03
0.03
0.03
Triple 2 LowE, Krypton Ucg increase (2 - 7mm cavities) BTU/hr*ft2*F
0.02
0.02
0.02
IG Cavity of Combined Cavity
Less than or equal to 8mm (0.315")
Double LowE, Air Ucg increase (8 mm cavity)
BTU/hr*ft2*F
Values in red indicate increases in u factor
Calculations done with Window 7.3 with deflection model.
Chart 4.3, Impact of Cavity Width on Thermal Performance
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass Manufacturers
Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing
Tolerances
SECTION 4.0 COMFORMANCE
REQUIREMENTS
EFFECTIVE DATE: Insert Date
REVISION: 01
THIS PAGE LEFT INTENTIONALLY BLANK
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass Manufacturers
Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing
Tolerances
SECTION 5.0 INSPECTION
EFFECTIVE DATE: Insert date
REVISION: 01
5.0 Inspection
5.1 Accurate measurement of cavity width variability is critical. Two cavity width
measurements should be taken; one at the edge of the IGU, the other at the center
of the IGU. The center nominal one square foot area of the glass should be checked
and the glass dimension recorded as the narrowest dimension. Ideally measuring of
the edge thickness would be made with the IGU detached from the sash or glazing
pocket using a caliper type device capable of measuring to a tolerance of +/0.025”. Alternatively in cases where the IGU is installed into a sash or glazing pocket,
the cavity width at the edge can be measured using a nondestructive glass
thickness-measuring device. In this case the glass thickness should be measured
within 2” of the sight line edge. In all cases the devise used to measure cavity width
should be accurate to +/-0.025”. Any devise capable of nondestructively measuring
cavity width can be used providing they meet the accuracy tolerances indicated.
5.2 The difference between the edge dimension and the narrowest center of glass
dimension will be recorded as the reduced cavity width.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.
TM-4400-XX, Voluntary Guidelines for Insulating
Glass Unit Cavity Width Manufacturing Tolerances
SECTION 6.0, REFERENCED DOCUMENTS
EFFECTIVE DATE: Insert date
REVISION: 01
Referenced Documents
ASTM Standards:
C 1036-06
Standard Specification for Flat Glass
E 2190-10
Standard Specification for Insulating Glass Unit Performance
and Evaluation.
TM-4400-XX DRAFT WORKING DOCUMENT – REVISION 01, February 8, 2016
The information contained in this working document is the exclusive property of the Insulating Glass
Manufacturers Alliance. Reproduction of any part of this document is strictly prohibited.