4 Waterproofing concept for the roof area

4.1 Application principles

Roof waterproofing design 4 » non-used roof areas

According to DIN 18531 – waterproofing for non-used roofs – the minimum nominal thicknesses of synthetic waterproofing membranes are to be designed according to requirements and application category.

Application category K1 (standard configuration)

Roof waterproofing to meet standard requirements fall into application category K1. As a precondition, the minimum slope of the surface to be waterproofed must not be less than 2 %.

The following applies for EPDM membranes (EVALASTIC®):
Minimum nominal thickness 1.2 mm (Thickness without backing and self-adhesive layer)

e. g. EVALASTIC® V with polyester fleece backing
Marking according to DIN 18531-2

DE= roof waterproofing single ply
E1= property class 1
EPDM= description of synthetic material
BV= bitumen-compatible
K= backing
PV= polyester fleece
1.2= membrane thickness in mm without backing

For roofs and/or roof areas with a slope < 2 %, as regards material selection for the roof waterproofing the design rules for application category K2 apply.

Application category K2 (enhanced configuration)

Roof waterproofing to meet higher demands of designers/investors (e. g. due to high-grade building usage, multi-storey buildings, difficult-to-access buildings) fall into category K2. A slope of at least 2 % at waterproofing level and at least 1 % in the valley areas must be observed.

The following applies for EPDM membranes (EVALASTIC®):
Minimum nominal thickness 1.5 mm
(Thickness without backing and self-adhesive layer)

» Used roof areas

For used roofs (DIN 18195) with high loads, e.g. terraces, intensive roof gardens, the minimum nominal thickness is 1.5 mm (Thickness without backing and self-adhesive layer)

e. g. EVALASTIC® V with polyester fleece backing
Marking according to DIN 18195-2

BA= waterproofing for foundations
EPDM= description of synthetic material
BV= bitumen-compatible
K= backing
PV= polyester fleece
1.5= membrane thickness in mm without backing

» Seam overlap

EVALASTIC® waterproofing membranes are marked with several dashed lines along one longitudinal edge. These markings can be used as guiding lines for the corresponding lap width and are

  • approx. 5 cm for bonding and loose laying under ballast (min. overlap 4 cm)
  • approx. 11 cm for load distribution plates 40 x 82 mm
  • approx. 12 cm for load distribution plates Ø 50 mm

Skizze zum Text

For application on unbacked, rigid polystyrene foam (e. g. EVALASTIC® V, loose laid under ballast), the lap width should be at least 6 cm. If necessary, the insulation boards have to be protected from hot air ingress or spilt solvent agent in the membrane lap area to avoid damage to the insulation material.

» Laying order

Regardless of the type and the laying method of the membranes, the seam laps can be arranged both with or against the “water flow”, due to the homogeneous seam welding.
When installing with the “water flow”, water may ingress under already laid membranes if it rains while waterproofing works are still in progress.

laying order

» “Separation” of the roof waterproofing

The field sheet is always “separated” from the waterproofing membrane of parapet and kerb flashings. However, membranes of the field area are principally raised approx. 5 cm on parapets and kerbs. Timber or insulation fillets are not required.


» Laying direction

Generally, the EVALASTIC® waterproofing membranes can be laid parallel or perpendicular to the roof slope. If using mechanical seam fastening of the waterproofing membranes on corrugated steel or timber decks, the membranes have to be laid perpendicularly to the span direction of the steel sheets or the boarding.

laying direction

» Position of butt joints

At the end of the membrane, i. e. normally after 25 m, the backed EVALASTIC® V / VGSK waterproofing membranes can be butt-jointed or hot air welded at an overlap of approx. 2 – 3 cm and covered with an unbacked tape of at least 16 cm width.

Unbacked membranes, however, are laid, correspondant to the longitudinal edge, with an overlap of at least 4 cm at the end of the membrane.

Double T-Joints

Double T-joints should be avoided!

Double T-joints are avoided by a staggered arrangement of the membrane ends.

If membrane ends are arranged withoutstagger, the end joints are to be covered with an unbacked tape of at least 16 cm width.


In case of low ambient temperatures, small ripples may show on the waterproofing membrane after laying (especially when warm weather returns).

» Tips for installation

Fix the membranes at one end mechanically, then heat the membranes slightly during installation and pull it tight.

» Formation of expansion joints

Waterproofing of type I joints (DIN 18531):
Over the joint the roof waterproofing can be laid flat in a single ply. For roof waterproofing with EVALASTIC® waterproofing membranes over joints, they

  • can be laid flat in bonded build-ups with expansions up to 5 mm
  • in case of loose laid EVALASTIC® membranes, can be laid over joints up to 10 mm, provided the membranes are supported at the joint area.

Type I

Waterproofing of type II joints (DIN 18531): Depending on the extent and the frequency of expansion joints, the type of sealing is to be decided upon individually, e.g.

  • by installing loops of EVALASTIC® tapes including suitable support profile (e.g. round PE foam cord) for expansions up to 25 mm (joint width up to 30 mm)

Type II

Type II joint sealing may be raised over the waterproofing level, e. g. by placing wedgeshaped insulation elements or cants (fillets). Parts of the field area separated by elevations have to have independent drainage.

4 The corresponding national regulations apply.

4.2 Selection of membrane / tape widths

The manufacturing of different membrane and tape widths allows for a quick and almost faultless laying, regardless of the roof geometry and the laying method (see chapter 6).

  • For loose laid waterproofing membranes (EVALASTIC® V) with ballast, membrane widths up to 1.55 m can be used.
  • For loose laid and mechanically seam fastened waterproofing membranes, usually EVALASTIC® V membranes are used according to the fastening plan. Depending on the required amount of fasteners, 1.05 m / 1.55 m wide membranes and 0.54 m / 0.79 m wide tapes are available.
  • For bonded waterproofing membranes (EVALASTIC® V) depending on the application method (rolling / folding), membrane widths of 1.55 m or 1.05 m or EVALASTIC® VGSK with a self adhesive coating and a width of 1.05 m on a suitable substrate can be used.