Weathertightness requirements for windows and doors

24.03.2021

One of the fundamental purposes of most buildings is to provide protection from extreme weather conditions such as wind, rain and snow for people live in. Weathertightness refers air permeability, water tightness and resistance to wind loads. Since being exposure to wind and rain, weatherthightness is more important for external windows and doors in this buildings. 

Performance Testing

Weathertightness is the endurance of your building components against natural elements like wind and rain. Weather performance testing includes a series of investigations that measure this resistance that doors, windows, roof assemblies, walls and other components of a building exhibit. Based on their performance in this test, building elements like windows and doors are given a ’class’ that indicates the efficacy of that element in withstanding natural weather elements. Air permeability, water tightness and resistance to wind loads are three tests done to check for weather tightness.

Air Permeability

The air permeability test is the measure of a window or door’s performance to combat airflow in
and out of a building. In the UK, as a requirement for building regulations, the components of a
building are tested for air permeability by EN 12207 by the third party accredited testing
facilities. In the air permeability test, the air is forced at the window from one side and sucked in
from another. The results of this test assign doors or windows to a class, ranging from class
0(no test) to class 4(tested with air pressures of 600Pa). The energy efficiency of a building is
highly dependent upon air permeability as overall air leakage may have negative impacts on its
performance.

Water Tightness

Application of a consistent water spray test and constantly increasing air pressure on the doors
or windows are used to determine the water-tightness of the elements. A water tightness test is
conducted following BS EN 1027 and a building component is recognised as failed when the
water seeps through the sample and leakage is observed. Leakage is any onset of uncontrolled
water on the inner side of any part of the sample, except for condensation and water retention
within the product. For the sake of classification, the time and maximum pressure achieved
before completion of the test is recorded as per BS EN 12208.

Resistance To Wind Load

A series of tests including deflection test, repeated pressure test, operational test, air
permeability test and a safety test is incorporated to measure the resistance to wind load of a
sample door or window. A unit of pressure P1 is applied to calculate the deflections in the parts
of the sample while another pulsating pressure P2 is applied for 50 cycles to evaluate
resistance against wind. A third pressure P3 is applied to assess the safety of the sample in
extreme provisions. To estimate the damages that occurred during this test, the air permeability
test is performed yet again.

Benefits Of Weather Performance Testing

Weather performance testing, along with being the requirement for building regulations in the
UK, is highly significant for the building owners as well as the users. These tests assure them of
weather tightness and prevent unfortunate incidents under extreme weather conditions. Energy
efficiency is another benefit of getting weather performance testing done for the doors and
windows of your building. Any building component that performs well in the weather tightness testing is likely to be durable in the long term due to its high endurance against natural elements.

What Are The Relevant Standards For Weather Tightness?

EN12207 provides standards for air permeability tests and EN12208 does that for water
tightness. However, water tightness testing is executed under BS EN 1027. The performance
levels, as per CWCT Standard for building envelopes, requires successful testing for water
tightness under an air pressure that is equivalent to 1/4th of the design wind load. As per
experience, this will provide acceptable performance, considering that the installation is carried
out with expertise.

How To Decide The Required Performance Level?

The location of the building determines the required performance level of the components used
in it. The architect or designer of the building should specify the performance levels for any new
developments. If the manufacturer is supplying the windows and doors to private dwellings then
the exposure category and wind loading suitable for the location should be taken into
consideration.

Exposure is dependent on the following factors

  • Basic wind speed at sea level.
  • Site terrain category
  • The design height of the window.
  • The height of the building is above sea level.
  • Topographical (orographical factor) position
  • Dormer factor. In the case of a dormer window, wind turbulence may cause an increase in wind speed, which consequently increases the wind loads in this vicinity.

Things To Consider Before Testing

There will be buildings where windows are not installed as a single unit, rather as an assembly. In such cases, to ensure the satisfactory performance of the entire assembly, the components joining the windows must be evaluated as well. Failure to do so may result in air leakage, rain penetration and decreased efficiency. 

Only the evaluated and approved joining details should be used. 

Available guidance for the test procedures of windows is designed for single units and guidance for assessing the joining components is under development. Large assemblies of windows that extend above one floor should be tested according to the standards for testing curtain walls.