Air Tight Membranes protect your building structure

It´s almost the same principle as seen around the windows & doors: Air Tight Membranes prevent draught and heatloss and protect against structural damage, caused by condensation.

Air Tight Membranes have to be installed on the shell of the building - mostly in pitch roof areas or at the highest ceiling. Timber framed houses should get air tight membranes on the entire internal building envelope.

Some facts about air tight membranes:

  • They have to be installed absolutely correct including the accurate bond to walls or other building parts
  • The right type of membrane should selected for the building by doing a moisture calculation first
  • Every overlapping or penetration need to be sealed by using airtight tape
  • Vapour variable air tight membranes should be installed after plastering
  • Most insulation products have to be fitted before the installation of air tight membranes
  • Roof areas without slabs (e.g. voids) should get counter battens to stabilise the air tight membrane
Airtight Sealing of OSB


We´ve been often asked regarding the proper sealing of OSB.

Due to the high density of those Oriented Strand Boards, in the most cases you just have to permanently seal the joints of the boards. Our Belgatape Yellow is made for this application.



In case that the OSB will not achieve the required values for air tightness, just apply our air tight paint Belgacoat Brush or Belgacoat Spray to the inner side of the board.


We highly recommend to do a Preliminary Airtightness Test (Blower Door Test) during the construction stage.

Based on our experience, the test should be done before the skimming of the slabs. Otherwise it´s almost impossible to rework in case of leakages on the membrane.

Try to check the airtightness of your new building when the windows are sealed, the air tight membranes are installed and the walls are plastered (sand&cement or hardbond).