Kerabit Dual is a membrane which is overlapped halfway across the width, the result being a secure dual-layer roofing conveniently with one product, involving no hot work. Kerabit Dual is grey in colour. One roll will provide 4m2 of finished roofing.

Kerabit Dual has been designed for a do-it-yourself builder for waterproofing of balconies 1:80 or steeper and maximum depth of 7.5 m.  

Adhesive very sticky

In order for the roofing to be secure and remain waterproof for years, the adhesive surfaces must effectively adhere to one another. Take the high adhesiveness into account when installing Dual.  Once the adhesive surfaces have been laid against one another and have adhered to one another, the installation can no longer be amended without new lengths. 

The outside temperature should be at least +10oC when Kerabit Dual is installed. Note. Dual is only for cold balcony structures.


  • A substrate of Kerabit OSB roof plates, of other building board suited for the purpose, or of tongue-and-groove roof boards
  • Kerabit Eave Flashing for lower eaves and Kerabit Bargeboard for gable eaves; colour options are black and dark grey
  • Kerabit Sealing Adhesive
  • Triangular batten for gable eaves and around the chimney
  • Roofing nails for securing Dual to the understructure
  • Nails for securing the eaves flashings and triangular battens to the understructure
  • Cut Kerabit Valley Underlay for chimney upturns and for a possible valley
Manufacturer / Manufactured for Kerabit Oy, Lohja plant
Country of origin Finland
Conformity marking CE
Reaction to fire Manifacturer´s declaration of the fire test
Fire Classification


Manufacturer’s declaration of conformity Kerabit modified bitumen roofing
Quality control Quality control carried out at the Plant quality control and a quality control agreement between the Plant and Eurofins Expert Services Oy
Nominal thickness 3,9 mm
Nominal weight 4700 g/m²
Supportive layer polyester
Rolls size 1,1 x 8 m
Colours grey
Need for materials 1 roll = 4 m² of finished roofing
Packages / pallet 24 rolls
Weight / package 34,3 kg
Weight / pallet 849 kg

Balcony waterproofing with Dual

A balcony is similar to a low-slope roof in structure. The inclination must be at least 1:80 so that water can be led off. Kerabit Dual may be applied onto a wood or concrete understructure. A concrete surface is treated with an adhesive solution Kerabit BIL 20/85 prior to laying the membrane.

Balcony structure
1. Decking or Kerabit OSB Roof Board
2. Eave flashing
3. Kerabit Dual Bitumen Membrane, coating with a wooden rack or slab

A drip edge flashing is installed to the edge of the balcony. A triangular batten is fixed next to the wall and Kerabit Dual is turned up onto the wall for at least 300 mm.