A variation is any change to the scope, specification or quantity of work after the contract is signed. They are normal: the client decides on stone cladding after seeing the elevations, the architect updates a slab thickness, soil conditions on excavation are worse than expected. The question is not whether you will have variations — you will — but how they are priced and approved.

The correct sequence

  1. Variation is identified (client request, design change, or site condition).
  2. Contractor submits a variation order in writing, with quantities and rates derived from the original BOQ where possible.
  3. Clerk-of-works or client's engineer reviews and either approves, queries or rejects.
  4. Once approved, the variation is incorporated into the next interim payment certificate.
  5. Only then is the work executed.

The most common failure mode

Steps 2 and 3 get skipped. The contractor builds the variation first, then bills for it at handover. The price they bill is whatever number lands. The client has no leverage — the work is done, the wall is plastered, the only choice is pay or fight. Almost every project that overruns badly in Uganda overruns this way.

How variation rates should be derived

  • If the variation uses a line already in the BOQ, the existing rate applies. New quantity × old rate.
  • If the variation is similar to an existing line but different (e.g. C25 concrete instead of C20), the rate is derived from the original — usually a small percentage adjustment, documented.
  • If the variation is entirely new, the contractor submits a new rate with cost breakdown (materials, labour, plant, overheads, profit). The client's engineer reviews.
  • A 5–10% contingency in the original BOQ covers small variations without re-pricing. Beyond that, every variation needs a written order.

Why mid-project surprises are a red flag

If, three months into a build, your contractor is presenting you with variations totalling 15% of contract value that you never approved in writing, one of two things is true: either the original BOQ was deliberately under-quoted to win the contract, or the contractor is using variations as a profit stream rather than a fair adjustment mechanism. Both are warning signs that the project is being managed against you, not with you.

For clients managing variations themselves

Three rules. First: no variation is built until you sign the order. Second: rates come from the BOQ where they exist; new rates require a cost build-up you can see. Third: keep a running total. If variations exceed 10% of the contract sum, stop and review scope before approving more.