# 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

**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*

**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 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*

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

*Equation A5.2*

**Note: **See Diagram A.2 for 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.