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Ventilation grids tested in the driven rain

We won’t leave you out in the rain!

The water repellent ventilation grids from MLL-HAMBURG are designed to restrict the ingress of water during rain, yet to allow the circulation of air into or out of an air ventilation unit or a part of a building. They are used in many applications in which differences of wind direction and speed, local turbulence, droplet speed and size, rain distribution and draining surface water from surrounding parts of a building may occur.

As it is impossible to develop a standardised test procedure that can simulate the entire range of possible scenarios, MLL-Hamburg developed its weather protection/ventilation grids at the “ift”, Rosenheim

in accordance with the EN 13030:2001 standard in terms of their weather resistance in driven rain and the associated efficiency under wind stress.

Tested systems:

  • MLL - weather protection grid Type 622
    • Slat shape: Z-slat with mechanism against sliding water
    • Free ventilation cross section: 50%
    • Slat distance: 50 mm
  • MLL - Weather protection grid Type 622V IP23D
    • Slat shape: V-slats, penetration safe
    • Free ventilation cross section: 47%
    • Slat distance: 33 mm
    • Protection class: IP 23 D
  • MLL - weather protection grid Type 742.4
    • Slat shape: Z-slat with mechanism against sliding water
    • Free ventilation cross section: 53%
    • Slat distance: 66 mm
  • MLL - weather protection grid Type 782
    • Slat shape: V-slats, penetration safe
    • Free ventilation cross section: 54%
    • Slat distance: 50 mm

The systems were tested in the version with and without a fly screen.

Test conditions:

  • Wind speed: 5.0m/s, 10.0m/s and 13.0m/s
  • Water volume: 2l/m² min
  • Jet arrays: 2
  • Jets per jet array: 3
  • Test duration: 15 per wind speed

Objectives of the tests performed:

  • Certification of weather resistance of MLL weather protection grids and slat facades
  • Determination of the efficiency under stress caused by wind pressure
  • Effect of the flow velocity and the pressure loss (loss coefficients) on weather resistance.
  • Increase in weather resistance through the use of the fly screen.
  • Classification of weather protection systems according to water penetration

Quality grades


Water penetration

Excellent water protectionA0.0 - 1.0%
Good water protectionB1.1 - 5.0%
Normal/medium water protectionC5.1 - 20.0%
Low water protectionD> 20.0%

MLL System Type

Resistance %

Penetration %

Quality grade

622 with fly screen93.766.24C
622 without fly screen90.836.57C
742.4 with fly screen96.63 3.37B
742.4 without fly screen 95.564.44B
782 with fly screen99.720.28A
782 without fly screen99.360.64A

Due to the testing of various weather protection grids with different slat shapes, a basis was created here, whereby the results  of “water repellency” can be transferred to other weather protection systems of the same slats or similar design of MLL weather protection products. 

Areas of application:

Protection against ingress of rain water and waterlogging.

Fields of use:

  • As a substitute for glass panes in for windows.
  • Installation in brickwork openings
  • Doors
  • Inlet and outlet channels for ventilation systems