Variation and Payment Dispute for Added Fire Dampers and Late Shop-Drawing Approval
A hospital mechanical contract is measured under a national mechanical price list. The contract drawings show fire dampers at main duct penetrations, but the approved revised layout adds 85 dampers at branch ducts that were not shown. The contractor claims the 85 dampers as a variation and also claims a 30-day extension because the consultant took 28 days to return ductwork shop drawings. The contractor has submitted a progress payment including the dampers at a negotiated rate higher than the price-list rate. The supervisor's site diary shows that the contractor continued work in other areas during the shop-drawing review, but the affected ductwork was on the critical path for a plant room. The contractor threatens to stop work if the payment is not certified in full.
1. Assess whether the 85 fire dampers are a variation and how the quantity should be measured and valued.
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The first question is whether the dampers were required by the contract or by a later instruction. The original drawings showed dampers at main penetrations; the revised layout adds dampers at branch ducts. If the branch dampers are a genuine design change, a code requirement not reasonably included in the original scope, or an instructed addition, they are likely a variation. If they were already required by the applicable fire code and should have been foreseen, the contractor may not be entitled to an addition, depending on the contract.
The quantity should be measured from approved shop drawings and site records, not from the contractor's unaudited total. The supervisor or quantity surveyor should verify the 85 locations, duct sizes, access provisions, and whether any are duplicates of dampers already included.
Valuation should follow the contract: price-list rates where applicable, and a negotiated new rate only where the item is genuinely new. A rate higher than the price list requires justification, such as different size, access difficulty, or fire-rated construction. The supervisor should not certify the full claimed amount until measurement and rate basis are agreed.
2. Evaluate the 30-day extension claim for late return of shop drawings. What facts and records matter?
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The extension claim depends on cause, notice, and critical-path effect. The consultant's 28-day review is a fact, but the contractor must show that the review period exceeded the contractual review period and that the delay actually affected completion.
The site diary indicating work continued in other areas is relevant but not decisive. If the affected ductwork was on the critical path for the plant room, a delay to that work can support an extension even if other work continued. The supervisor should check the contractor's programme, the date the shop drawings were submitted, the contractual review period, the date of return, and the date the plant room work actually became critical.
The contractor also has a duty to mitigate. If the contractor could have advanced other work or revised the sequence, the full 30 days may not be justified. The supervisor should require a time-impact analysis and contemporaneous records. The extension should be granted only for the demonstrated critical delay, not automatically for the full review period.
3. The contractor threatens to stop work unless the full payment is certified. How should the supervisor and quantity surveyor respond professionally?
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The supervisor should not certify an unverified amount because of a threat to stop work. Certification must reflect measured work and the contract valuation rules. If part of the damper claim is undisputed, that portion can be certified while the disputed rate or quantity is referred for resolution. The supervisor should record the threat and notify the owner.
The quantity surveyor should prepare a measured comparison: contract quantities, revised quantities, approved variations, and any omitted work. The contractor should be invited to a measurement review with access to records. If the contractor stops work without justification, the contract's remedies apply; the supervisor should not create a false payment record to avoid that outcome.
Ethically, the supervisor's signature is a professional certification, not a negotiating tool. The correct response is a clear written position: what is certified, what is withheld, why, and what information is needed. The owner should be advised of the schedule risk separately from the payment decision.