What is External Wall Insulation?

K.C. Bruning
K.C. Bruning
A roll of mineral wool insulation.
A roll of mineral wool insulation.

External wall insulation (EWIS) is the combination of multiple layers of materials applied to the outside of a building in order to protect the interior from exterior elements. It usually consists of an insulating layer, the finish, and potentially another decorative layer. The layers can be made of items such as plaster, mineral wool, foamed polystyrene, or polyurethane foam. When combined, these materials provide thermal insulation, while also forming the exterior layer of the building.

The basic construction of an external wall insulation system is an insulating layer, covered by a weatherproof finish. Insulating layers are made of boards or slabs of material, while finishes are often different types of mesh, rockwool, acrylic, or silicone. Other materials, such as tiles and brick slips, can be added on top of or incorporated into the finish to increase the protection factor and add a decorative element.

External wall insulation boards and slabs can be made of a wide array of materials. Boards are typically constructed of extruded or expanded polystyrene. Slabs can be made of phenolic, polyurethane, or polyisocynurate foam. They can also be made of mineral fiber or rigid slabs of glass or rock.

Typical finishes for external wall insulation are different kinds of mesh made of materials such as steel, mineral fiber,or polypropylene. Decorative elements, such as tiles, brick slips, painted boards and clay can be used with or in place of mesh. Glass, cement, polyvinyl chloride (PVC) and plaster are other possible finishes. The combination of materials used typically depends on the desired thickness of the insulation, which is often dictated by the characteristics of the local climate.

There may also be a strip of insulation placed around openings such as windows and doors. This helps to avoid thermal bridging, which is a localized weakness in the level of insulation. Thermal bridges can cause a gap in protection that compromises the overall effectiveness of external wall insulation.

Often external wall insulation is used as an element of green construction, as it is believed to help to reduce the emission of CO2 into the atmosphere. It can also lower the cost of maintaining a consistent temperature in the building, whether through cooling or heating. Builders and end users also find external insulation appealing because it can be made both durable and attractive. Another strong benefit of external wall insulation is its ability to ward off condensation and keep the building dry, thus reducing the overall need for maintenance.

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    • A roll of mineral wool insulation.
      By: brozova
      A roll of mineral wool insulation.