External wall insulation

External wall insulation

= External wall insulation system=

External wall insulation system (EWIS) - a thermally insulated, protective, decorative exterior cladding system which consist of:
*foamed polystyrene
*mineral wool
*polyurethane foam
*mineral or synthetic plasterThermal insulation thickness is at least 10-15 cm, because only then can partition with heat transmission factor U=0,25-o,3 W/m2K be obtained. And only than when we will use to insulate polystyrene, mineral wool, cellulose fibre, pearlite, polyurethane foam etc. that is materials with λ≤0,05 W/mK heat transmission factor. Application of a very good thermal insulation 5 cm thick, will not achieve the increase of the wall insulating power to the valid level. It means that in layer walls with constant air void (usually 3-6 cm thick ), filling the void with insulation material will not improve partition features enough. Besides, you should remember that in many houses elements like concrete beams or lintels are huge thermal bridges with much worse insulation factors than the wall. Because of that old houses should not be insulated with less than 12 cm thick thermal insulation.

External Wall Insulation Systems

Definitely the best solutions are those where thermal insulation is laid down on the external side of the wall. It eliminates all thermal bridges resulting from construction or improper workmanship. One of the disadvantages is that windowsills have to be replaced and some flashings, also move downpipes away from the wall. But it has no influence on the effectiveness and popularity of these wall insulation systems. They are called either light-dry or light-wet methods.In houses with walls, which contain continuous and wide (6-8 cm) air void, investors decide to fill the space with loose insulation materials. The advantage is that the wall thickness does not change, therefore there is no need to replace the windowsills. The system is fast and quite clean – thus it will not damage the house surroundings. The disadvantage is the insufficient increase of walls thermal insulation and the necessity to use other insulation systems to eliminate thermal bridges.

Light-dry method

This is well known and commonly used in house renovation insulation system, consisting of two wooden (rarely metal), perpendicular slate frames fastened to the walls which have between them thick layers of mineral wool. After protecting the wool with highly vapourpermeable, wind screen insulation and timber batten nailing , to make a louvre, we assemble external cladding which becomes the new building facade. It can be boards or vinyl siding. Other facade materials like ceramic or stone moulds, laminated boards, aluminium panels etc. are rarely used. Light-dry method is one of the easiest external wall insulation systems therefore it should be preferred by people who want to do all the works themselves. Every DIY man will manage with that. Work will take longer but for sure it will be done better than by construction group. Moreover the expenses are limited to the construction materials. Also we should add that the work can be stopped at any moment and it can be done also in winter.The light-dry method is recommended for wooden houses insulation, because it is insensible for minor building movements made by seasonal timber contraction and dynamic wind influence. But than vapour insulation should also be used. It can be placed inside, under gypsum board or outside under mineral wool.

Light-wet method

This is a well known and commonly used wall insulation system, used especially in building two-layered wall houses. It can also be used in thermorenovation of houses. Theoretically this method is very easy, because we have to fasten insulating boards to the wall, reinforce them with glass fibre mesh and put on thin layered plaster.But in practice it appears that this system requires quite a lot of knowledge and skill. For example thermo insulating panels are mostly only glued to the wall, but sometimes they have to be fastened mechanically (especially on the corner and around the holes). Reinforcing mesh must be embedded in glued surfaces, it can not be put on dry surface, that is before the plaster is on the thermoinsulation layer. Work should be done in appropriate weather: temperature 5-25°C, no rainfall, strong wind etc.Preparatory works can be done by anyone, but even and aesthetic plaster application requires employment of a close and experienced team. Furthermore it is not as clean a method as the light-dry, so we should bear in mind that house surroundings can be damaged. It does not matter in building new houses, but can be important on well-preserved and tidy plots. Some of the system advantages are elimination of all thermal bridges (around lintels, battens and windows) and relatively small thickness of insulation and facade layers.In light-wet method we use mainly two thermoinsulation materials: polystyrene and mineral wool. But for old house renovation polystyrene is mainly used. Especially when walls are made of hollow tiles or bricks. Simply vapourpermeability of this materials is not as good as cellular concrete or porous ceramic. This is the reason why there is no need to use more expensive mineral wool.

Filling the air void method

This method increases thermal insulation of walls but not enough for binding regulations. You need to know everything about a particular wall when using this method because often departures from the project appear. It is necessary to level the thermal bridges. In general this external wall insulation system reduces our work to hiring properly equipped teams, who will fill the air voids with insulation material.It can be polyurethane foam, but more common are cellulose fibre, mineral wool, polystyrene and pearlite. After that we have to glue polystyrene strips (at least 5 cm thick like in light-wet method) on thermal bridges, or even better polyurethane foam as cornice or window trim. At the end usually the whole facade is refreshed, which means rendering and, or painting (3mm thick floating).


What is EWIS?
*beads and closures
*reinforcement layer
*base render coat
*finish coat Functions of EWIS
*provides a weather-proof, durable architectural facade
*conserves energy
*minimises heat loss
*controls condensation
*eliminates cold bridging
*can provide reduction in sound transmission
*satisfies new Part L Regulations
*suitable for both new build and refurbishmentCriteria for selection
*synthetic finishes may require a top coat for durability
*avoid dark and intense colours for large areas
*preferably select light pastel shades formineral renders
*thicker materials provide durable top coats
*scrape texture for natural stone appearance
*dry dash hard-wearing, good in wet/damp
*smooth finish difficult, may look poorin certain lighting conditions
*ashlar features can be incorporatedin both thin and thick systemsBenefits
*enables thermal management of buildings
*eaintains a dry, stable structure
*removes the risk of condensation
*contributes to the reduction of CO² emissions
*provides beneficial whole life costs
*creates simplicity in design
*combines aesthetics with durability
*reduces building maintenance


*National Building SpecificationSection M21Insulation with rendered finish
*Provides comprehensive framework for the specification of EWI
*Supplier’s technical documentation
*BSI British Standards and Code of Practice
*BRE Report 135: EWI, Fire performance for multi-storey buildings
*BRE Report 262: Thermal insulation avoiding the risks
*INCA Insulated render and cladding Specifiers/property owners briefing

External links

Examples of the external wall insulation systems at [http://www.polconstruct.com/external_wall_insulation Polconstruct] .

Educational link =

Textbook with CD at {http://www.externalwallinsulation.com}.

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