Measurement conventions

A technique used by 'takers off' when measuring items in the substructure and the external walls is the calculation of a centre line or mean girth. In Scotland a different approach in sometimes used, known as 'over and between'.

Figure 2 Calculation of a centre line or mean girth.

Detail A

Figure 3 is a plan of a simple building where the mean girth approach would be applicable. Depending on circumstances the mean girth can be calculated from the internal or external face; in the following example the internal dimensions will be used.

Figure 3 Building where the mean girth approach is applicable.

Note: using the internal dimensions as a basis; for each internal corner twice times, half times the thickness of the wall is added to the internal girth.  The resulting dimension (shown below); 42.00 represents the average or mean girth and this can be used in the measurement of many items such as; trench excavation, masonry, concrete in foundations, etc.

Insets

Figure 4 Mean girth length.

In this example again the mean girth length will be calculated. As far as calculating the mean girth is concerned the internal and external angles in the inset cancel each other out, therefore to calculate the mean girth 4/2/ the thickness of the wall needs to be either added to the internal girth or deducted from the external girth.