Weather Performance tests
Difference between AAMA and CWCT
Presented by: Sudeshkumar
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The abbreviation AAMA stands for American Architectural Manufacturers Association. This association is based in USA. It
publishes technical documents and standards related to Facade industry. AAMA provides guidelines with minimum
performance requirements and test procedures for weathertightness testing of Curtain walls in reference to the ASTM
(American Society for Testing and Materials) standards.
The abbreviation CWCT stands for Centre for Window and Cladding Technology. This research and education organization is
based at the University of bath, UK. It publishes technical documents and standard related Facade industry. CWCT provides
guidelines with minimum performance requirements and test procedures for weathertightness testing of Curtain walls in
reference to the BS EN (UK version in English of a European harmonized standard) standards classification.
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A brief comparison between AAMA and CWCT for standard weather performance tests of Curtain walls with performance criteria is
listed below in the tabular format.
AAMA
CWCT
Air Permeability
The test for air leakage shall be conducted as per the procedure
specified in ASTM E 283 standard.
The Specification must establish air pressure difference and
allowable rate of air leakage. AAMA recommends a minimum
air pressure difference for walls of 75 Pa (1.57 psf) and a
maximum allowable rate of air leakage of 0.3 L/s•m2 (0.06
cfm/ft2 or 1.08 m3/hr.m2), which is adequate for many
buildings. A maximum pressure difference of 300 Pa (6.24 psf)
and a maximum allowable rate of air leakage of 0.3 L/s•m2
(0.06 cfm/ft2 or 1.08 m3/hr.m2) is recommended for buildings
in which greater control of air quality and/or humidity is
required.
The test to determine the air infiltration and, if required,
exfiltration shall be conducted on the sealed specimen
subjecting it to increasing positive differential pressure in steps
lasting 10 seconds up to the peak test pressure. The pressure
levels should be 50, 100, 150, 200, 300 and then in increments
of 150 Pa upto the peak test pressure. At each pressure level,
the differential pressure and airflow should be recorded. For
exfiltration, at test pressures up to 100 Pa the permissible air
exfiltration rate through the building envelope system shall not
exceed the values stated by the Specifier. The sealing tapes on
the sealed specimen shall be removed in stages starting from
fixed joints and then finally removing sealing from any opening
lights. At each step the whole incremental pressure sequence
as specified above shall be repeated.
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AAMA
CWCT
Air Permeability
Allowable air infiltration rate at peak test pressure is as belowmentioned:
Through building envelope system excluding any leakage
through opening joints – 1.5 m3/h.m2.
Through opening joints – 2.0 m3/h.m2.
Test pressure:
The peak test pressure shall be determined by the Specifier
using one of the classes in BS EN 12152 as follows:
Class
Peak Pressure
A2
300 Pa
A3
450 Pa
A4
600 Pa
AEXXXX
>600 Pa
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AAMA
CWCT
Resistance to water leakage
Static water penetration
The test for static water penetration shall be conducted as per
the procedure specified in ASTM E 331 standard.
The Specification must establish a minimum air pressure
difference at which no water leakage will occur. AAMA
recommends an air pressure difference equal to 20% of the
positive design wind pressure with a minimum of 300 Pa (6.24
psf) and a maximum of 720 Pa (15 psf).
This test generates a static air pressure difference across the
building envelope whilst spraying water over the exterior face
of the test specimen at a fixed volumetric flow rate (2.0 or 3.4
litres/minute/m2). While water is being sprayed continuously,
the positive pressure differential is applied in steps, with each
step lasting five minutes. The pressure levels should be 50, 100,
150, 200, 300 and then in increments of 150 Pa upto the
required peak test pressure. The pressure is then returned to
zero in one step and the spraying stopped.
Performance Criteria:
There shall be no leakage onto the internal face of the building
envelope system at any time during the test. At the completion
of the test there shall be no standing water in locations
intended to remain dry. The emergence of any water on the
inside face shall be recorded together with the pressure level at
which the leakage occurred.
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AAMA
CWCT
Static water penetration
Test pressure:
The peak test pressure shall be determined by the Specifier
using one of the classes in BS EN 12154 as follows:
Class
Peak Pressure
R5
300 Pa
R6
450 Pa
R7
600 Pa
RE.xxxx
>600 Pa
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AAMA
CWCT
The test for water penetration under dynamic air pressure shall
be conducted as per the procedure specified in AAMA 501.1
standard.
The dynamic water penetration test subjects the test mock-up
to the effects of pulsating wind gusts and wind- driven rain. This
test can be particularly useful in checking the performance of
pressure-equalized wall systems. The Project Specification must
establish the minimum air pressure difference at which no
water leakage will occur. AAMA recommends an air pressure
difference equal to 20% of the positive design wind pressure
with a minimum of 300 Pa (6.24 psf) and a maximum of 720 Pa
(15 psf).
The dynamic testing may be employed, using either:
Dynamic aero engine, or
Dynamic fan.
Both methods are suitable for use on curtain walling if the only
openings in the face of the wall are protected drainage
openings. The dynamic fan method is not suitable for use on
rainscreens and other envelopes with open joints or ventilation
openings. This test method is not recommended for sloped
glazing with a low slope.
Dynamic water penetration
The wind generator shall be run at the speed recorded during
the calibration test to provide an airflow onto the specimen.
Suction may be applied to the inside of the test specimen to
achieve the required test deflections, but it should be limited to
25% of the peak static test pressure. Maintaining the wind flow,
water shall be sprayed on the external face of the specimen at
the rate of 2.0 o 3.4 litres per minute per square metre of wall
frontal area, in such a way as to completely and continuously
cover the face. These conditions should be maintained for a
period of 15 minutes.
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AAMA
CWCT
Dynamic water penetration
Performance Criteria:
There shall be no leakage onto the internal face of the building
envelope system at any time during the test and it should be
examined for further evidence of water penetration
immediately following the test. At the completion of the test
there shall be no standing water in locations intended to
remain dry. The emergence of any water on the inside face
shall be recorded together with the pressure level at which the
leakage occurred.
The specimen should also be examined for any damage or
displacement of additional items such as brise soleil. Any
damage shall be recorded.
Test pressure:
The peak test pressure shall be determined by the Specifier
using one of the classes in BS EN 12154 as follows:
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AAMA
CWCT
Wind resistance
Wind resistance - Serviceability
The test for structural performance at the specified positive
and negative design wind pressures shall be conducted as per
the procedure specified in ASTM E 330.
This test shall be conducted by subjecting the specimen to
positive and negative serviceability test pressure (100%)
without loss of serviceability, and with recoverable and residual
deformations within prescribed limits.
Deflection shall not exceed 1/175 of the clear span at a uniform
load equal to the specified design wind pressure. AAMA
recommends that the positive and negative design wind
pressures be determined in accordance with SEI/ASCE 7-02 or
by boundary layer wind tunnel testing. Deflection of exterior
wall framing members is tested at design wind pressures.
AAMA recommends that maximum deflections normal to the
plane of the wall shall be limited to L/175 for spans up to 4115
mm (162 in) For spans greater than 4115 mm (162 in) but less
than 12.2 m (40 ft) deflections at design loads shall be limited
to L/240 + 1/4 in. (For more information on deflection of
framing systems refer to AAMA TIR-A11-04.)
One pulse between zero and the peak test pressure should be
applied. The test pressure should be raised in four equal
increments and held for 15 +/- 5s at each step including the
serviceability pressure. The displacements of framing shall be
measured at each increment. After this sequence, any damage
or functional defects should be noted. Residual deformations
should be measured on returning to zero load. If residual
deformations exceed deformations exceed those allowable, a
period of one hour should be permitted for recovery. Operable
components should be opened and closed five times, and any
changes in ease of operation noted.
Repeat the test for static water resistance (ASTM E331) after
this test.
After completing the first load test, the preparation and test
procedure shall be carried out with reversed loads.
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AAMA
CWCT
Wind resistance - Serviceability
Repeat Air infiltration:
The air infiltration of the building envelope system after
application of the peak design pressures shall meet the
permissible air leakage criteria and shall not exceed the air
leakage measured before application of the serviceability wind
load by more than 0.3 m3/h.m2 at the peak air infiltration test
pressure.
Repeat watertightness test with same criteria as mentioned
above.
Performance Criteria:
Allowable deflection criteria:
a)Framing members generally
Length
Allowable Deflection
H≤3000
∆ ≤ H/200
3000<H<7500
∆ ≤ 5 + H/300
7500≤H
∆ ≤ H/250
All dimensions are given in mm.
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AAMA
CWCT
Wind resistance - Serviceability
b) Framing members with single glazing:
For four edge support:
• 1/125 of their length measured along the pane edge.
For two edge support:
• 1000/180 of the square of their span between supports.
c) Framing members with double glazing units:
For four edge support:
• 1/175 of their length measured along the unit edge, or
15mm, or more restrictive limits if set by the unit
manufacturer, whichever is lesser.
For two edge support:
• 1000/540 of the square of their span between supports or
20mm, or more restrictive limits if set by the unit
manufacturer, whichever is lesser.
d) Framing members supporting sealed multiple glazing units
incorporating three or more panes of glass:
• The deflection limits agreed with the unit manufacturer.
e) Surface and framing members to which brittle materials such
as plasterboard or natural stone units are to be fixed:
• The deflection limits agreed with the material supplier.
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AAMA
CWCT
Wind resistance - Serviceability
Recommended values in case of absence of specified
information:
Brittle materials such as plasterboard:
• 1/360 of the extent of the board, or 10mm whichever is the
lesser.
Natural stone units:
• 1/360 of their length measured along the stone edge, or
3mm, whichever is lesser.
f) Spandrel systems spanning horizontally between loadresisting attachments to the main building frame:
• The Specifier shall state the maximum allowable
deflections.
g) Rainscreen panels:
• 1/90 of the span measured between the points of
attachment of the panel for aluminium, glass and steel, or
• 1/360 of the span measured between the points of
attachment, or 3mm whichever is the lesser, for stone and
similar brittle materials, or
• More restrictive limits set by the panel manufacturer.
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AAMA
CWCT
Wind resistance - Serviceability
Allowable residual deformation criteria:
• Residual formation to framing members shall nowhere be
more than 5% of the maximum measured deformation or
1.0mm, whichever is greater, with one hour being allowed
for recovery. Residual deformation due to plastic
deformation of components is never acceptable.
• Displacement of framing members at points of support shall
be minimized and shall be less than 2mm taken as the
difference between the position under peak positive and
peak negative load.
There shall be no damage and functional defect.
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AAMA
CWCT
Wind resistance - Safety
The test for structural performance at 150% of positive and
negative design wind pressures shall be conducted as per the
procedure specified in ASTM E 330.
This test shall be conducted by subjecting the specimen to
positive and negative safety test pressure (150%) without
damage and residual deformations within prescribed limits.
For curtain walls, storefronts and sloped glazing AAMA requires
that structural test pressures shall be 1.5 times the design wind
pressures to provide a factor of safety. At this load no glass
breakage or permanent damage to panels, fasteners, or
anchors, shall occur, and permanent deformation to wall
framing members shall not exceed 0.2% of their clear spans.
A single pulse equivalent to peak test pressure should be
applied. The load transition time should be less than one
second and the pressure should be maintained at the peak
value for 15 +/- 5s. After this sequence, any damage or
functional defects should be noted. Displacements of framing
members should be measured on returning to zero pressure. If
residual deformations exceed deformations exceed those
allowable, a period of one hour should be permitted for
recovery.
After completing the first load test, the preparation and test
procedure shall be carried out with reversed loads.
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AAMA
CWCT
Wind resistance - Safety
Performance Criteria:
Integrity of building envelope system:
There shall be no permanent damage to framing members,
panels or anchors. Framing members shall not be buckled.
Panels, glazing beads and decorative capping pieces shall
remain securely held, and gaskets shall not be displaced.
Allowable residual deformation criteria:
It shall not exceed 1/500 of the span, measured between points
of attachment to the building, one hour after the loading has
been removed.
Displacement of supports:
Displacement of framing members at supports shall not exceed
3mm taken as the difference between the position under the
peak positive load and peak negative load.
Opening lights:
Opening lights shall remain closed.
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