The more defined the design is before the works start this will allow you:

• to have greater certainty on the final cost of the works
• to make changes to the scope of the works prior to the start to align works with budget if necessary
• if you do decide to obtain tender prices from different builders, builders will provide prices on the basis of the same information which allows a much better comparison
• this gives you a fixed cost against which you can measure all subsequent cost variations
• it avoids the risk of delays (and costs associated with delays) as decisions have been made and allow a smooth progression of the works on site
• potential design issues and conflicts can be dealt with in advance of works on site and decisions can be made in good time

When dealing with existing buildings, there will always be unknown elements of works that will be discovered during construction, either necessary repair work or unexpected original design elements that need to be dealt with. However, the above process ensures that ‘unexpected surprises’ can be kept to a minimum.