The appearance, quality and performance of a building envelope are totally dependent on good construction and should be installed by qualified installers trained by the company that designed the system and supplied the materials.

Building envelopes are expected to meet many performance criteria such as safety, building physics, integrity, serviceability and durability and hence must undergo stringent testing to ensure its performance in the long term. Among the most common testing standards used internationally are the CWCT (Centre for Windows and Cladding Technology), the ASTM (American Society for Testing and Materials), and AAMA (American Architectural Manufacturers Association) standards.
CWCT test standards are primarily intended for the testing of building envelopes in the UK whilst ASTM and AAMA standards are produced for use in the US and are also used in many other countries worldwide.
The CWCT standard for ‘Systemised Building Envelopes – Dec 2005’ was updated to include the stipulations of European EN Curtain Walling standards and now all test requirements are at least equal to the European standards and several even surpass those requirements. For example, for water penetration tests, EN standards require that water is sprayed at a flow rate of 2 litres/sq m per hour, whilst the CWCT standards mirror the higher rate of 3.4 litres/sq m per hour of the ASTM and AAMA standards.

Air permeability
CWCT: Here, the test pressure requirements are based on design wind loads with a minimum requirement of 300 Pa and testing is conducted in stages up to the peak test pressure – 50 Pa and then 50 Pa stages up to 300 Pa, followed by increments of 150 Pa up to peak test pressure. This standard states that 300 Pa is the minimum test pressure and that a higher test pressure may be specified when a more airtight building is required.
The maximum allowable air leakage rate is 1.5 cu m/hr per sq m at peak test pressure and there are also requirements for intermediate pressures using a formula in the standard. At the lowest maximum test pressure of 300 Pa, using the formula, there is a maximum allowable leakage rate of 0.45 cu m/hr per sq m at 50 Pa, which is well below the allowable rate of ASTM/AAMA testing.
CWCT uses classifications as per EN standards, however it does not consider that the lower classifications are suitable for use in the UK and in the case of air permeability testing, the lowest specified classification is A3 at 300 Pa with A4 at 450 Pa and A5 at 600 Pa being the higher classes.
There is no requirement for test results to be adjusted to standard conditions in either CWCT or EN standards.
There is a mandatory requirement for exfiltration testing, which should be conducted at 50 Pa and 100 Pa. While there are no performance requirements, the standard makes reference to the current building regulations requirement of 10 cu m/hr per sq m at 50 Pa and states that the specifier may wish to require lower leakage rates for the main building elements in order to allow for greater leakage in other parts of the envelope.
There is also a requirement that air leakage should not increase during the repeat test, which follows wind resistance testing, by more than 0.3 cu m/hr per sq m at the peak test pressure.
ASTM and AAMA:  In these standards, the test pressure requirements are left for the architect/project consultant to determine and the test is only conducted at that pressure. While ASTM states that the minimum test pressure should be 75 Pa, AAMA recommends that the minimum air pressure difference for walls should be 75 Pa with a maximum allowable rate of air leakage of 1.08 cu m/hr per sq m at that pressure. It then goes on to say that a maximum pressure difference of 300 Pa and a maximum allowable rate of air leakage of 1.08 cu m/hr per sq m at that pressure is recommended for buildings in which greater control of air quality and/or humidity is required. In all cases, the pressure is only held until it stabilises and then the airflow reading is recorded.
ASTM test methods also require that test results have to be adjusted to standard conditions, that is pressure at 101.3 kPa, temperature at 20.8 deg C and air density at 1.202 kg/sq m. This ensures that whatever the conditions during testing, all test sample results are based on a single set of 'standard conditions’, and are therefore comparable.
In ASTM and AAMA standards, there is no mandatory requirement for exfiltration testing (leakage from inside to the outside of the building envelope) nor for a repeat air leakage test following wind resistance testing.

Static water penetration
CWCT: Test pressure requirements are based on design wind loads with a minimum requirement of 300 Pa. Testing begins at 0 Pa for 15 minutes and then in stages of 50 Pa up to 200 Pa, then 300 Pa, followed by 150 Pa steps up to peak test pressure – each stage being held for five minutes. Therefore, a test to 600 Pa would continue for a total of 50 minutes.
Here, the lowest specified classification is R5 at 300 Pa with R6 at 450 Pa and R7 at 600 Pa being the higher classes.
A water flow rate of 3.4 litres/sq m per hour is required, although the lower rate of 2 litres/sq m per hour as per EN standards can be used. However, the spray frame must be set up so as to spray above the top of the test specimen, instead of level with the top. This ensures a greater flow of water across the sample as CWCT considers that the lower flow rate of EN standards in its unmodified method is not sufficient for UK conditions.
More importantly, CWCT performance requirements state that:
‘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.’
It also advises that:
‘To avoid difficulty in interpreting the results, it is good practice to agree which materials and zones within the building envelope may be allowed to get wet.’
ASTM and AAMA: Again, test pressure requirements are left for the architect/project consultant to determine and testing is only conducted at that pressure
The ASTM standard states that a default pressure of 137 Pa should be used, however AAMA 501-05 recommends an air pressure difference equal to 20 per cent of the positive design wind pressure with a minimum of 300 Pa, and a maximum of 720 Pa. Whichever pressure is used, the test continues for 15 minutes at that pressure. Here, the water flow rate required is 3.4 litres/sq m per hour. 
The ASTM standard defines water penetration as follows:
‘Penetration of water beyond a plane parallel to the glazing (the vertical plane) intersecting the innermost projection of the test specimen, not including interior trim and hardware, under the specified conditions of air pressure difference across the specimen. For products with non-planer glazing surfaces (domes, vaults, pyramids etc), the plane defining water penetration is the plane defined by the innermost edges of the unit frame.’
AAMA 501-05 states that there shall be no water leakage:
‘Any water leakage occurring during the period of testing shall be noted and reported, stating both the location and the quantity of leakage. Water leakage is defined as any uncontrolled water that appears on any normally exposed interior surfaces, that is not contained or drained back to the exterior, or that can cause damage to adjacent materials or finishes. Water contained within drained flashings, gutters, and sills is not considered water leakage. The collection of up to 15 ml (1/2 oz) of water in a 15-minute test period on top of an interior stop or stool integral with the system shall not be considered water leakage.’
The definition of interior stop or stool is as follows: Stop – A moulding used to hold, position or separate window parts Stool – An interior trim piece on a window which extends the sill and acts as a narrow shelf.
Table
Wind resistance
CWCT: For serviceability testing, CWCT test methods are the same as EN standards – testing is required at both positive and negative pressures. Preparation pulses are 50 per cent of design wind load or 500 Pa whichever is greater, and these pulses should be held for at least three seconds.
After the preparation pulse has been conducted, all deflection sensors are zeroed. Measurements are required to be recorded for the deflection of framing members, transoms, mullions etc. There is also a requirement for measuring the displacement of framing members at their point of support to the building structure.
Positive test pressure pulses are applied in four stages, for a minimum period of 15 seconds (+/- 5 seconds) at each stage and the pressure stages are at 25, 50, 75 and 100 per cent of design wind load, where deflection measurements are recorded at each stage.
Upon returning to 0 Pa deflection, measurements are recorded again as there are the system must return within defined limits.
The test is then repeated at negative pressure. Preparation pulses are applied, after which sensors are zeroed, However, any sensors used to measure the displacement of framing members at their point of support to the building structure should not be zeroed as there is a requirement to record the total movement that occurs between the peak positive and negative pressures.
Allowable CWCT deflection details are shown in Table 1.
After loading to peak test pressure and unloading, residual deformation to framing members shall nowhere be more than five per cent of the maximum measured deformation or 1 mm, whichever is greater, with one hour being allowed for recovery. This applies to both positive and negative tests.
The displacement of framing members at their point of support shall be less than 2 mm taken as the difference between the positions under peak positive and negative loads. The air infiltration of the sample shall not exceed that measured before the application of the design wind load by more than 0.3 cu m/hr per sq m at the peak test pressure.
Safety testing is a mandatory test in this standard.
For this test, the sample is subject to one pulse at 150 per cent of the design wind load, having first being subject to a preparation pulse at 50 per cent of design wind load or 500 Pa, whichever is greater, and these pulses should be held for at least three seconds. The sensors are then zeroed exactly as per the serviceability test. The test pressure is held for a minimum period of 15 seconds (+/- 5 seconds).
When the pressure is removed, the whole sequence is the repeated at negative pressure, performance requirements are at 1.5 times design wind load (safety).
When testing the integrity of the building envelope system at both positive and negative applications of the peak test pressure, 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.
After loading to the positive and negative peak test pressure, residual deformation of framing members shall not exceed L/500 of the span, measured between points of attachment, one hour after the loading has been removed.
Displacement of framing members at their point of support which shall be less than 3 mm taken as the difference between the positions under peak positive and negative loads.
Opening lights shall remain closed.
ASTM and AAMA: ASTM E 330-02 specifies two types of tests. Either can be used but the choice will be left to the specifier and will be decided well before any testing takes place.
Procedure A is used when there is no load-deflection curve required and after opening and closing five times etc. A pre-load of 50 per cent of the positive test load is applied and held for 10 seconds. The pressure is then released and after a period of not less than one minute or greater than five minutes. the deflection sensors are zeroed. The positive test load is then applied and sustained for not less than 10 seconds and the deflections are then recorded. The test pressure is then reduced to zero and after a period of not less than 1 minute or greater than 5 minutes, any permanent deformation shall be recorded. This procedure shall then be fully repeated at negative pressure.
The test will then be repeated exactly as described above but at a proof load, which is the test load multiplied by a factor of safety, for example by 1.5. However, the actual factor is not quoted in the standard but would be provided by the specifier well in advance of any testing.
If glass breakage occurs at any test load, carefully examine the test specimen to determine the cause of the breakage. If the breakage was caused by the deformation or failure of the supporting frame of the glass, by loosening or failure of any fasteners, or by damage to the glass caused by interaction between the glass and its supporting elements, record the findings and discontinue the test.
If the breakage was not caused by the above structural problems, replace the glass using the original fasteners and continue the test at the load where glass breakage occurred. If new structural elements or fasteners are used instead of the original ones, repeat the entire test.
There is a note in the standard which states:
‘The probability of glass breakage is directly related to the duration of the load on the glass’
This should be remembered so that any overloading or over timing of the test loads is be avoided.
Procedure B is as with Procedure A where the positive test load is applied and held for 10 seconds, unless otherwise specified. The pressure is then released and after a period of not less than one minute or greater than five minutes the deflection sensors are zeroed.
The positive test load is then applied in the number of increments specified up to the specified maximum test load. The specifier shall determine the number of increments to be used in the test, not to be less than four approximately equal increments, (25 per cent, 50 per cent, 75 per cent and 100 per cent), to the maximum test load.
At each increment, unless otherwise specified, apply and maintain the full test load for 10 seconds and record pertinent deflection readings. The test pressure is then reduced to zero and after a period of not less than one minute or greater than five minutes, any permanent deformation shall be recorded. There is no requirement for this procedure to be repeated at negative pressure.
ASTM E 330-02 does not specify any allowable deflections but AAMA 510-05 states the deflection shall not exceed L/175 of the clear span at a uniform load equal to the specified design wind pressure. It also recommends that maximum deflections normal to the plane of the wall shall be limited to L/175 for spans up to 4115 mm. For spans greater than 4115 mm but less than 12.2 m, deflections at design loads shall be limited to L/240 +1/4 inches, (6.4 mm).
AAMA also requires that a safety test is conducted following the repeat water-tightness test and shall be at 150 per cent of positive and negative design pressures. It requires that at that 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 per cent of their clear spans.
In summation, CWCT tests are generally more onerous, although the American standards include requirements for seismic tests which are not required in the UK.