External wall insulation

An external wall insulation system (or EWIS) is a thermally insulated, protective, decorative exterior cladding procedure involving the use of expanded polystyrene, mineral wool, polyurethane foam or phenolic foam, topped off with a reinforced cement based, mineral or synthetic finish and plaster.

The thickness of thermal insulation is dependent on whatever type is required in order to create a partition with a heat transmission factor of U=0.25-0.3 W/m2K. When calculating the actual insulation requirements, consideration must be given to current Building Regulation standards. Consideration must also be given to exposure and durability, and whether the structure might be subjected to vandalism etc. In many older properties, special attention is required for concrete beams or lintels which act as thermal bridges providing poor insulation.

External wall insulation systems generally comprise firstly an insulation layer (an element which helps to achieve the requisite thermal performance); and secondly,a protected weatherproof finish (usually a render, although brick slips, tiles, and decorative boards can also be used). Insulating render can also be an advantage in certain locations. Choice of types and sizes will depend on the substrate and design exposure requirements.

Dry finishes are usually fixed to the substrate by means of timber battens independently fixed to the substrate.

Any system selected and installed, should be certified by a notified body.

A selection of traditional finishes is currently utilised within the external wall insulation industry. Dry-dash render is a traditional render application commonly used. By this method, dry dashing aggregate is thrown onto the wet render to create a natural aggregate finish. Available in a wide variety of colours, sizes and textures, the practice is relatively cheap. Manufactured aggregates such as ceramics and glass can be used for more specialised projects, but the costs will be greater than for projects using natural aggregates.

Scratch plaster render is a coloured cementitious render scratched while the surface is still workable, but after the initial setting has taken place. The surface of the render is removed by the action of the scratching tool, and approximately 2 to 3 millimetres (0.079 to 0.118 in) of render are removed exposing the open matrix of the aggregate mix. The true colour of the render is exposed with a light even texture.

...
Wikipedia