Is a lump-sum quotation fixed no matter what?
No. A lump sum fixes the price for the scope described, not for whatever the owner ends up wanting. It is adjusted for variations, provisional sums, and any other adjustments the contract allows. How fixed it really is depends on how completely the scope was described, how many items are provisional or excluded, and how the contract allocates the risk of site conditions.
From the RRD Field Guide, checked against the sources cited in Variation Orders and Provisional Sums: How to Stop Surprise VOs on Singapore Building Works. General information, not advice for your project.
The fuller picture
Surprise variation orders usually come from scope that was never fully defined, items excluded from the quote, provisional sums used as placeholders, and concealed site conditions. Owners reduce them by defining scope in drawings and an itemised schedule, pricing exclusions when comparing quotes, requiring written instructions and quotations before varied work starts, and agreeing valuation rules in the contract.
More questions on this topic
- What is a variation order?
- What is the difference between a provisional sum and a prime cost sum?
- Can a contractor claim for variations done on verbal instructions?
- How are variations valued?
- What are dayworks?
- How should I compare quotations with different exclusions?
- Who bears the cost of concealed conditions found during A&A works?