separation layer

Separation layers arranged directly under the roof covering can fulfil a variety of tasks. Whether a separation layer is used or which separation layer is to be used should thus be already taken into account in the planning phase.

Separating layers can:

protect the wooden formwork or wood-based sheets from moisture during the construction phase.
improve sound insulation,
compensate for minor unevenness in the substrate,
provide protection for the metal roofing against nails pushing out of the formwork,
improve sliding properties during thermally induced length changes,
protect the metal on the underside against damaging alkaline influences and possible harmful chemicals in the substrate
support the roof covering and the sub-roof with regard to the rainproof function.

Separating layers must not absorb or store water, must not allow driving rain to pass through and must withstand temperatures directly beneath the metal roof. Depending on the function that a separating layer is to assume, a suitable product must be agreed with the manufacturer of the separation layers.

If, for example, the separation layer’s function is to provide additional sound insulation, the use of stronger, heavier bituminous separation layers is recommended by PREFA.

Note

PREFA recommends the use of suitable separation layers under PREFA roof coverings. PREFA advises against using structured separation layers in combination with PREFA roof products.

In addition to the framework conditions specified above, the manufacturer’s information on the arrangement of separation layers is defined by PREFA as follows:

With snow loads greater than 3.25 kN/m² or in terrain categories 0, I or II, installation with a separation layer is required.
With a roof pitch up to 25°, a separation layer is required for R.16 roof tiles, DS.19 shingles and FX.12 roof panels.
For roof structures with an unheated (ventilated) roof space, a sub-roof must comply with the requirements of national regulations (sub-roof standards), and at least a separation layer is required.

Terrain category 0 - lakes and coastal areas exposed to the open sea.

Terrain category I - lakes and areas with low vegetation and without obstacles.

Terrain category II - areas with low vegetation such as grass and individual obstacles (trees, buildings) with a distance of at least 20 times obstacle height.

Terrain category III - areas with uniform vegetation and buildings or with individual objects with distances of less than 20 times obstacle height (e.g. villages, suburban developments, forest areas).

Terrain category IV - areas where at least 15% of the surface is covered with buildings with an average height of 15 metres.

Terrain categories according to EN 1991-1-4