Masonry facades

With a few exceptions, most construction materials expand in response to an increase in temperature. Exposed surfaces are subject to the effects of solar radiation, which tends to increase surface temperatures above ambient air temperatures.

Temperature ranges can be diverse. For Europe a range of -25 to +80°C could be reflective of typical in-service surface temperatures. UK temperature variations are less severe - a range of 85 degrees is more appropriate for dark, heavyweight claddings.

BRE Digest 228 Part 2 (1979) deals with the estimation of thermal and moisture movements and stresses, in which BRE advocate the use of a simple formula to determine linear changes of size (note: this does not simply apply to brickwork):

R = α´Lt

Where,

R = change of size

α´ = coefficient of linear thermal expansion

L = length

t = temperature difference

The coefficient of linear thermal expansion of brick-work is typically in the range 5-8 x 10-6per °C80. Thus, assuming that the brickwork was laid at a temperature of 10°C in a panel 6,000mm in length, theoretical expansion of 3.36mm (70 x 6000 x (5 x 10-6)) would be possible along with a potential contraction of 1.68mm. Factors such as the texture and colour of the brick would affect the degree of movement. In practice, some measure of restraint can be expected and it is probable that movements would also be accompanied with dimensional changes brought about by changes in moisture content.

Expansion in brickwork tends to occur uniformly in each axis (unlike some building stones which can display anisotropic tendencies).

Calcium silicate bricks exhibit thermal movement of about 1.5 times that of clay brickwork, the co-efficient of linear thermal expansion being about 8-14 x 10-6per °C. In restrained conditions, this movement may be less.