Annex A: Method for calculating mass per unit area

A1 Wall mass

A1.1 Where a mass is specified it is expressed as mass per unit area in kilograms per square metre (kg/m²).

A1.2 The mass may be obtained from the manufacturer or it may be calculated by the method given in this annex. To calculate the mass per unit area of a masonry leaf use the formula below. This formula is not exact but is sufficient for this purpose.

A2 Formula for calculation of wall leaf mass per unit area

A2.1   Mass per unit area of a brick/block leaf = mass of co-ordinating area / co-ordinating area

Equation A2.1
Equation A2.1

Note: This formula provides the mass per unit area of the block/brick construction without surface finish.

Note: See Diagram A.1 for block and mortar dimensions.

A2.2 When calculating the mass per unit area for bricks and blocks use the density at the appropriate moisture content from Table 3.2, CIBSE Guide A (1999).

A2.3 For cavity walls the mass per unit area of each leaf is calculated and added together.

A2.4 Where surface finishes are used the mass per unit area of the finish is added to the mass per unit area of the wall.

A1 Block and mortar dimensions

A1 Block and mortar dimensions

A3 Simplified equations

A3.1 Two examples are given (see Table A.1 and A.2) using the equation in A2.1. For each of these examples a simplified equation is obtained for that type of construction.

Table A1 Blocks laid flat

Table A1 Blocks laid flat

Table A2 Blocks laid on edge

Table A2 Blocks laid on edge

A4 Mass per unit area of surface finishes

A4.1 The mass per unit area of surface finishes should be obtained from manufacturer’s data.

A5 Mass per unit area of floors

A5.1 The mass of a solid and homogeneous floor (without hollows, beams or ribs) can be calculated from:

Equation A5.1

Equation A5.1

A5.2 The mass of a beam and block floor can be calculated from:

Equation A5.2

Equation A5.2

Note: See Diagram A.2 for beam and block floor dimensions.

A2 Beam and block floor dimensions

A2 Beam and block floor dimensions

A5.3 For other floor types (including floors with variable thickness), seek advice from the manufacturer on mass per unit area and performance.