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During of the application of flat roof insulation boards, one must take into account the following:

The installation process must prevent the enclosure of moisture, both during and after the application of the insulation layer.

Process the boards in a dry condition and store them in a dry place!

Loose dirt must be removed before installation. The installation surface must be clean, dry and flat.

The insulation boards must be handled with care. Damaged boards may not be installed.

The insulation boards must be installed firmly against eachother and must placed in a staggered composition.

The boards must fit tightly at the at protruding edges.

For PIR L insulation boards, the board side marked “Upper Side” must be installed upwards.

Infill pieces which are smaller than 300 mm may only be used in the middle area of the roof surface.

It must be ensured that the roofing system cannot be perforated by sharp items and/or concentrated loads.

If the insulation boards are installed on a non-load bearing subsurface, such as steeldeck structures, then the ratio of the thickness of the

insulation plate and the upper width must be a minimum of 1:3.

Boards with a minimum thickness of 50 mm do not have to terminate on a load-bearing surface, if the overhang of the board is smaller or

equal to 110 mm.

Differences in height between connecting board edges may not amount to more than 3 mm.


The necessity for a vapour-resistant layer must be determined on the basis of a building physics calculation.

The result is dependent on the climate class of the building, the type of substructure and the insulation.

Vapour barrier quality:

Class (µd)



≥2 to < 5 m

PE foil (thickness 0.2 mm) with overlaps of at least 100 mm


≥5 to < 25 m

PE foil (thickness > 0.2 mm) and aluminium laminates with sealed seams

Bituminous glass fleece V50/16

Bituminous polyester fleece P 150/16


≥25 to < 200 m

Reinforced bitumen V3, V4, P3 or P4

Polymer bitumen APP or SBS (minimum thickness = 3 mm), glass fleece or

reinforced PES



Reinforced bitumen with metal foils (ALU3)

Multiple-layer vapour barriers made of polymer bitumen (> 8 mm)

The choice of a vapour barrier is dependent on the subsurface and the climate class.

In case of renovations of vapour-resistant roofing, the insulation board can be installed directly on the old roofing, after which new roofing can be

immediately applied. The installation of an additional vapour barrier is not always required here. This has to be verified by means of a calculation.

In such cases, it is very important to thoroughly check the quality of the old roofing, checking it for possible deficiencies. If deficiencies are

detected, then the old roofing cannot be taken into account and an additional vapour barrier always has to be installed.