Here's some industry terms you might be unfamiliar with.
A Provisional Sum (PS) is a term that may be included in your building contract used to describe an item when a particular aspect of work, for both materials or labour, is not fully costed.
For example, if site fees are listed as a Provisional Sum item, your builder is legally required to take reasonable steps to ensure an accurate site works cost estimate. However, if unforeseen events mean that the provisional sum is exceeded this can be added to your next progress claim.
The solution to PS items, talk to your builder about any provisional sums included in your contract and check the variances they have allowed for are reasonable to minimise any potential costs and risks. Try to get any Provisional Sum allowances changed to fixed costs by your builder, if possible, before you sign.
A Prime Cost (PC) item is a similar term for items that have been included in your contract on an agreed estimated amount but might get interchanged or selected later depending on stock availability, eg. tiles, taps, vanities, etc.
Your builder must estimate the cost of such items at or above the lowest amount these items could reasonably cost, which must not be understated. Depending upon availability, if you later select a more expensive item a variation will be required which will be charged as an adjustment to the prime cost in your next progress claim.
The solution to PC items, do your best to specify the exact brands, model numbers and colours you want for your home before you sign. Make sure your contract is as detailed and precise as possible.
Both PC and PS allowances are legitimate elements of a contract, but if you’re unsure - don't be afraid to ask, seek clarification, and get information in writing.