Thermal resistance - Walls.

Monday, January 3, 2011

For reasonable indoor comfort a wall should provide resistance to excessive transfer of heat both from inside to outside and from outside to inside during periods of cold or hot, seasonal, outside temperatures.

The materials that are most effective in resisting heat transfer are of a fibrous or cellular nature in which very many small pockets of air are trapped to act as insulation against the transfer of heat.

Because of their lightweight nature these materials do not have sufficient strength to serve as part of the structure of a wall by themselves. Lightweight insulating materials are either sandwiched between materials that have strength or behind those that resist penetration of wind and rain, or serve as internal wall finishes.
The majority of walls for traditional small buildings, such as houses, are constructed with solid blocks such as brick or are framed from small sections of timber. Which one of the two types of wall is used will generally depend on the availability of materials, such as clay for making bricks, stone for making blocks or timber for frames.

Walls may be classified as solid or framed. A solid wall (sometimes called a masonry wall) is constructed of either brick, or blocks of stone, or concrete laid in mortar with the blocks laid to overlap in some form of what is called bonding or as a monolith, that is, one solid uninterrupted material such as concrete which is poured wet and hardens into a solid monolith (one piece of stone), A solid wall of bricks or blocks may be termed a block (or masonry) wall, and a continuous solid wall of concrete, a monolithic wall.

A frame wall is constructed from a frame of small sections of timber, concrete or metal joined together to provide strength and rigidity, over both faces of which, or between the members of the frame, are fixed thin panels of some material to fulfil the functional requirements of the particular wall. Figure 42 is a diagram of the two types of wall.

Each of the two types of wall may serve as internal or external wall and as a loadbearing or non-loadbearing wall. Each of the two types of wall has different characteristics in fulfilling the functional requirements of a wall so that one type may have good resistance to fire but be a poor insulator against transfer of heat. There is no one material or type of wall that will fulfil all the functional requirements of a wall with maximum efficiency.

Traditional small buildings, such as houses, are commonly built as a square or rectangular box of enclosing walls as the most economical means of enclosing space. The walls of a single detached building are exposed on all sides to wind, rain and the variations of outside temperature.


Two buildings constructed on each side of a common separating wall, usually described as semi-detached, enjoy the advantage of a shared internal dividing wall and only three external walls exposed to wind and rain, as illustrated in Fig. 43. A disadvantage of the shared dividing wall is that it may not serve as an effective sound barrier.

A continuous terrace of houses enjoys the benefit of shared, common dividing walls, reduction in exposure to wind and rain and the likely disadvantage of the poor sound insulation through two common dividing walls

 
Fig. 43 Type of house.

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