Line of balance

The line of balance is a production technique used for the planning of work involving repetitive tasks and the production of multiple units. In the construction industry this applies to the planning and coordination of projects such as multiple housing units, the fitting out of multiple hotel rooms or apartments, multiple foundations or plant bases and the like.

The fundamental principle of the line of balance technique is to establish the balance of resources such that the rate of progress of the individual trade activities do not delay or impact on each other. For example, in the fit out of a new apartment block, the first activities in each of the apartment units may comprise of the following:

• metal stud partitions and plasterboard one side;
• first fix services;
• plasterboard partitions second side and ceilings; and
• plaster and skim.

If there are 50 apartments then obviously each of the above activities will occur 50 times. The trades concerned could be indicated as a single ongoing activity however this would prove difficult to track and monitor. The key to this project would be to ensure that the works in each apartment are being fully completed in a timely and sequential manner.

Figure 13 shows the first 2 trades of metal stud partitions and first fix services in a linked bar chart type format. The left hand column shows the apartment numbers rather than the activity descriptions, with the stud partition works starting at apartment 1 progressing sequentially to apartment 10 (shaded activities). The start of the partition work to each apartment is determined by the completion of the preceding apartment, implying that the works are undertaken by one gang working progressively through the apartments. It can be seen that following the completion of the stud partitions in apartment 1 the first fix service installations are shown as commencing with these services activities following this same progressive sequence through the apartments.

Figure 13: Line of balance - Stud partitions and Services 1st Fix

In figure 14 the first 4 fit-out activities for apartments are shown in a 'line of balance' format. 

Figure 14: Line of balance - fit-out activities

The actual duration of each activity for each apartment and thus the steepness of the sloping lines are determined by the trade labour allocated for each activity. It is ideal, although not usually practical, to 'balance' the labour and thus the production of each of the trades so that all of these lines run in parallel. It can be seen above that the services first fix is taking longer to complete than the other trades and this could effectively be rectified by employing additional gangs to progress the latter apartments a little earlier.

It is usual to make an allowance, or insert a 'buffer' time, between the completion of one trade in each apartment and the start of the next trade. This represents an element of contingency but it also reflects reality, as it is unlikely that the first fix services installations will commence at the very moment that the stud partitions are completed.