7 Perimeter fastening of the roof sealing

Perimeter fastening, which is also called perimeter fixing, is a mechanical fastening of the roof sealing along its perimeters and in the field area, regardless of the type of wind-uplift protection of the roof waterproofing (application method). It is designed to transmit the horizontal forces that may occur in the roof sealing into the supporting substructure. Perimeter fastenings can be carried out as line fastening or linear fastening.

7.1 Requirements

According to e. g. the Regulations for waterproofed roofs 30, perimeter fastening is necessary for

  • loose laid single ply coverings
  • profiled steel decks and
  • roof build-ups with light surface protection and rigid foam thermal insulation, bonded with cold-bonding adhesives with after-tacking effect.

Perimeter fastening is generally recommended, especially in cases of drainage to bracket-mounted gutters on outer walls.

Perimeter fastenings must be installed

  • at roof perimeters,
  • at flashings of upstands with an edge length over 25 cm,
  • at structural expansion joints,
  • at roof penetrations for single and arcade rooflights as well as
  • at valleys if the sum of the roof slopes is higher than 5 %.

30 Regulations for Flat Roofs, section 2.6.1 (national regulations).

7.2 Line fastening

7.2.1 Line fastening with EVALON® coated metal sheets

Line fastening of backed and unbacked EVALON® waterproofing membranes is primarily carried out with EVALON® coated metal sheets. To do this, the edge of the membrane must be welded constantly to a mechanically fixed coated metal angle (“steel edge” of the roof sealing)31 to ensure a non-positive connection.

For backed waterproofing membranes (EVALON® V/VG/VSK/VGSK) the non-positive connection is achieved by using an unbacked EVALON® tape which is welded to both the waterproofing membrane and at least the horizontal flange of the coated metal angle up to the valley line.

Kapitel 7.2.1

At parapet valleys and valleys along upstands, coated metal angles sheet (5 x 5 cm) are fixed to the parapet or the upstands. The bottom fastening of the coated metal angles can be done directly into the substrate, or in case of thermal insulation layers, into battens which are sufficiently secured in the substrate. Coated metals sheets are to be fastened with non-corrosive screws or other suitable fastening elements32.

SubstrateSurface conditionalwitra primer SK / SK-L
Bituminous feltPE foil / fleeceyes1
Bituminous feltfine sand coating / talcum coatingyes
Bituminous feltgrit or fine slate coatingyes
Existing bitumenweathered, dirtyyes
Synthetic membranesweatheredno2
Concreteslightly moist to dry, smoothed
and well-cleaned, free from gravel
clusters, burrs and sharp edges
Steel / zinc sheetsdegreasedyes2
1 shortly torch with propane until the surface shows through in dark may be

2 necessary depending on the type of material, to be tested in individual cases;
generally, consultations with the alwitra Technical Department are obligatory.

A coated metal drip edge should be fastened with two rows of fasteners (generally screws) and secured at the gutter bracket with the bracket clamp. Fasteners may show through the welded on tape.

kapitel 7.2.1 bild 2

The joints of the coated metal sheets must be made in such a way that thermal expansion or contraction stresses arising from thermally induced changes are absorbed without causing damage.

In order to prevent welding in the joint area, all joints prior to the welding-on of the tape, which must have a width of at least 16 cm, will be covered with adhesive tape with a width of at least 2 cm (e. g. crepe tape).

Kapitel 7.2.1 bild 3

7.2.2 Line fastening with clamping bars (Peel-Stops)

If line fastening with rigid clamping bars, the bars must be waterproofed using an unbacked tape.

Fasten the clamping bars with at least 5 suitable fastening elements per metre onto the substrate or an auxiliary supporting substructure.

Kapitel 7.2.2

At roof perimeters with alwitra edge trim profiles (T plus/TW 125 plus/TA/TA-4F/TAG/ art-line 1), the protection of the roof sealing against wind uplift is achieved by line fastening using the mechanically fastened supporting flange or the fillet plate of the roof edge trim.

Kapitel 7.2.2 Bild 2

31 Coated metal sheets are not clamping profiles!

32 Wire and clout nails, as well as so called gas concrete nails, are not suitable.

7.3 Linear fastening

7.3.1 Linear perimeter fastening using single fixings

The perimeter fastening can also be carried out by using single fixings in a row (linear fastening).

Kapitel 7.3

The perimeter fastening of EVALON® waterproofing membranes can be done with approved membrane fasteners (min. 3 fasteners/m) set in a row.

Kapitel 7.3 Bild 2

Generally, between the individual fasteners the flashing sheet must also be completely welded in the valley.

7.3.2 Linear perimeter fastening with alwitra kerbs

If, during installation, kerbs of alwitra daylight and smoke and heat vents are directly fastened on the roof waterproofing at waterproofing level and to the edge planks around the opening or to an adequately suitable construction, perimeter fastening of the roof sealing is ensured.

Linear perimeter fastening with alwitra kerbs