EPS Application:Sandwich constructions light outer walls

Sandwich constructions light outer walls
The need for rationalized building methods and employment of materials has encouraged the use of light prefabricated components. Lightweight walls are now largely assembled from such components, which are commonly sandwich constructions and may have provision for ventilated sidings.
In order to control the environment within buildings, high thermal inertia is often essential. In cool climates with heated buildings this is always the case; in warm climates much depends on the relative importance of daytime and nighttime use, the diurnal temperature range, whether or not the building is air-conditioned, and to what extent the building is exposed to direct sunlight. In general, all air-conditioned buildings need high thermal inertia.
The thermal inertia of a building can be indicated in several ways, but a simple measure is the quantity C/AU, where C is the total thermal capacity of the buildings and its contents, A is the area of the enclosing elements through which heat is lost or gained by transmittance, and U is the average thermal transmittance of the enclosing elements. The quantity C/AU has the dimensions of time; it is large, fluctuations in inside temperature will lag behind fluctuations in outside temperature, fluctuations in inside temperature , and will be very much smaller.
The thermal capacity of outside walls decreases with their superficial mass. However, to keep C/AU constant, it is not necessary to reduce the maximum value of U in direct proportion to the superficial mass; floors, partitions, etc. make a considerable contribution to the total thermal capacity, C, and in any case many light materials have higher specific thermal capacities than masonry ( e.g. wood, ca 2 j/g. k, compared with ca 0.8j/g. k for brickwork or concrete). Guidance on the maximum thermal transmittances of lightweight walls is often included in national standards, which can take into account typical layouts and materials, both of which affect the thermal capacities of buildings. For instance, in West Germany it has been recommended that the maximum value of U for most areas should be 0.9 W/m2 .k for walls with superficial masses of 200kg/ m2 or more, falling linearly to 0.6w/m2 .k at 50kg/m2 .
Thermal bridging often requires considerable attention in lightweight walls; particular care should be taken with the insulation of joints and metal frames.
Where a wall has two leaves separated by an unventilated airspace, condensation problems may arises if the leaf exposed to the higher water- vapour pressure does not have the higher vapour resistance. In cool climates the inner leaf is generally exposed to the higher vapour pressure, but the situation may be reversed in air-conditioned buildings in warm climates. When vapour barriers are used, it is essential that their joints are properly lapped and sealed. Sidings giving protection against driving rain should be backed by a fully ventilated space; it is then best to neglect any contributions they make to thermal insulation.
When expanded Styropor is used together with wood, only water-based preservative solutions should be applied to the wood. Organic solvents and their vapours damage expanded Styropor.
Expanded Styropor can be used for the insulation of both lightweight loadbearing walls and non-loadbearing walls such as curtain or panel walls. It can be used in stud walls constructed by carpenters on site, in factory –made compound unites- often already made up into complete wall elements-, and in sandwich panels (e.g. between asbestos sheet ) for cladding or infilling framed buildings.