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With New Zealand’s history of leaky buildings, it is considered critical that a house facade is weather tight.
The best method to test weather-tightness is the E2/VM1 test method.
E2/VM1 is a test method for proving the weather-tightness of wall claddings on low-rise buildings within the scope of NZS 3604:2011Timber-framed buildings. The test was derived from AS/NZS 4284:2008 Testing of building facades, which, in turn, was derived from work by CSIRO in Australia in the 1970s.
In AS/NZS 4284:2008, the water penetration tests consist of spraying the specimen with a known amount of water and subjecting it to a steady pressure and then cyclic pressure tests. Failure generally occurs when uncontrolled water is visible on the inside surface of the façade.
Water penetration tests differ
The water penetration criterion used in AS/NZS 4284:2008 is similar to other tests around the world and assumes the use of structural materials that do not absorb water. However, this is not necessarily suitable for typical low-rise residential construction, which will often include materials that do absorb water.
Residential systems could have a damaging leak, but this may not manifest as water visible on the inside surfaces. For this reason, E2/VM1 has a slightly different set of water penetration tests and a slightly different failure criterion.
As well as water penetration tests equivalent to those in AS/NZS 4284:2008, E2/VM1 requires that holes be drilled in the cladding and the tests repeated. After that, the wet wall test is performed, where pressure is applied across the cladding itself rather than the whole wall. Failure is when the cavity is breached or, in the case of the wet wall test, when water penetrates the cladding.
E2/VM1 checks for cavity drainage
E2/VM1 checks that the cavity works. In terms of the “4Ds of weather-tightness” (deflection, drainage, drying and durability), the test is primarily concerned with drainage. Water that penetrates the cladding must not reach the underlay.
Drilling holes in the outer layer of the cladding attempts to test the effect of workmanship errors, for example: will the cavity (nominally 20 mm wide in E2/VM1) still drain water away even if some defect allows water in?
Wet wall test checks deflection of water
The wet wall test is unique among international water penetration standards and is arguably the toughest part of the test because it stresses the cladding itself.
In most test situations, a cladding on a cavity will only have a very small pressure difference across it, regardless of the actual test pressure. This replicates the real situation where façades are typically designed to separate the roles of water shedding (cladding) and holding air pressure (air barrier or lining).
The cavity is usually vented to the inside of the test chamber so the pressure inside the cavity is the same as that in the main chamber. This will structurally load the underlay and linings but means there is no pressure difference driving water through the cladding. Therefore, attempts to make the test harder simply by increasing the test pressure will not have a big effect, because the pressure across the cladding will still be close to zero.
The wet wall test ensures the cladding itself offers a degree of protection. In terms of the 4Ds, the wet wall test is checking deflection of water.
The devil is in the detail
It is important to get the surrounding details of cladding installation correct, as these are often a source of system failure. Weak points can occur particularly at termination points in the cladding- such as eternal/internal corners, around windows or other penetrations e.g. meter boxes. Therefore extra care needs to be taken to ensure that these areas are designed and installed correctly.
E2/VM1 very stringent
In summary, compared to other water penetration tests around the world, E2/VM1 is among the more stringent:
Image source: TV3.co.nz