Understanding Variations: How Small Changes Become Big Problems

Variations are a normal part of construction. Designs change, site conditions surprise, clients adjust their brief. The problem isn't that variations happen — it's that most projects have no disciplined process for managing them, and the cost accumulates invisibly until it's too late to do anything about it.

What a variation actually is

A variation is any change to the agreed scope of works that wasn't in the original contract. This includes:

• Additions: work added to the scope after contract execution
• Omissions: work removed from the scope (which may entitle the contractor to a margin payment even for work not done, depending on the contract)
• Substitutions: like-for-like replacements where the cost differs from the original
• Unforeseen conditions: hidden site conditions that weren't visible at tender

Each category has different commercial implications, and each requires a different response.

Why variations accumulate quietly

On an active site, the pressure is always to keep moving. A site supervisor who stops work to raise a formal variation instruction every time a small change is requested will quickly be seen as obstructive. So small changes get absorbed into the programme without paperwork, with an understanding that "we'll sort it out later."

Later never comes — or it comes at final account, when both parties have different recollections and no documentary evidence.

The cost of informality

A variation that isn't documented before the work is done has no agreed price. The contractor will submit a claim based on their actual cost plus margin. The client or head contractor will argue it should have been included in the original scope. The dispute resolution process consumes time, money, and goodwill.

On a project with tight margins, the cost of a single unresolved variation dispute can exceed the profit on an entire trade package.

A workable variation process

The process doesn't have to be bureaucratic. It needs to be consistent:

1. Site instruction issued in writing (email is sufficient, but it must be written)
2. Subcontractor or contractor submits a variation quotation within an agreed timeframe (48–72 hours)
3. Quotation reviewed and approved in writing before work proceeds
4. Variation added to the cost plan at the time of approval, not at the end of the month

Steps 1 and 4 are the ones most commonly skipped. Step 1 because it slows the site down. Step 4 because nobody updates the cost plan until something forces them to.

Red flags to watch for

• Variation claims submitted weeks after the work was done
• Claims with no breakdown — just a lump sum
• Claims referencing verbal instructions
• A variation register that's never updated
• A cost plan that still shows the original contract sum months into the project

Any of these is a signal that the variation management process has broken down. The earlier it's addressed, the lower the cost of recovery.

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Our project oversight service includes a monthly variation register review and cost plan update. Contact us to discuss what's involved.