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

Air permeability refers the volume of air that would pass through a window or door in its closed position and at a certain pressure. It is the measure of a window or door’s performance to combat airflow in and out of a building.

Relevant standards for air permability: 

  • BS EN 1026:2016 Windows and doors - air permeability - test method
  • BS EN 12207:2016 Windows and doors - air permeability - classification

For air tightness classification, the windows and doors are tested in accordance with BS EN 1026:2016. In this 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.

The classes range from class 0 to class 4:

  • Class 0 (the lowest value, achieves the least air tightness)
  • Class 1
  • Class 2
  • Class 3
  • Class 4 (the highest value, achieves the highest air tightness)

The energy efficiency of overall building is highly dependent upon air permeability as overall air leakage may have negative impacts on its performance as cool air will need to be heated.

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.