How to Check a Construction Variation Quote

The checklist

1. Tie it to the change. Every line should relate to the instruction, drawing revision or site condition that triggered the variation. Lines that don’t are questions.
2. Check the arithmetic. Quantity × rate for each line, then the sum of lines against the stated total, then GST.
3. Check quantities. Measure the change from the drawings or instruction yourself, even roughly. Compare it against the claimed quantity.
4. Check rates. Where the original quote or contract has a rate for the same work, compare it. A changed rate is not automatically wrong, but it should be identified and explained.
5. Look for what didn’t change. If a wall grows by a third but excavation stays the same, ask why.
6. Look for new exclusions or qualifications that weren’t in the original quote.
7. Isolate the unexplained balance and ask for it to be broken down.

Worked example: a retaining wall extended by 8 m²

The original accepted quote and the variation price for extending the wall (all figures ex GST):

Original quote
  Block wall         24 m² × $185 = $4,440
  Excavation         lump sum     = $1,600
  Ag drain           24 m  × $42  = $1,008
  Total                           = $7,048

Variation (revised price)
  Block wall         32 m² × $185 = $5,920
  Excavation         lump sum     = $1,600
  Ag drain           32 m  × $45  = $1,440
  Extra footing      new item     =   $650
  Sum of lines                    = $9,610
  Stated total                    = $9,860

Now split the claimed change into proven and unexplained parts:

Claimed increase      $9,860 − $7,048            = $2,812

Proven by lines
  Wall quantity       +8 m² × $185               = $1,480
  Drain quantity      +8 m × $42                 =   $336
  Drain rate change   32 m × ($45 − $42)         =    $96
  New footing                                    =   $650
  Total proven                                   = $2,562

Unexplained balance   $2,812 − $2,562            =   $250
  (= stated total $9,860 − sum of lines $9,610)

From this you have four specific issues to raise:

• The $250 difference between the stated total and the sum of the lines.
• The drain rate rising from $42 to $45 per metre ($96). Is there a reason, and does the contract allow it?
• Excavation unchanged at $1,600 despite a longer wall. Is it genuinely sufficient, or will it be claimed later?
• Whether the extra footing is a consequence of the instructed change.

Items like the rate change are issues for professional review: whether they are payable depends on your contract and the circumstances, which software can’t decide.

Watch provisional sums

Many variations arise when a provisional sum is adjusted to actual cost. Rock excavation is the classic case. A provisional sum is an estimate, so when comparing tenders or checking a variation, track it separately from firm prices. The engine example below shows a tender comparison where one excavation price includes a $5,000 provisional sum. The flag reminds you that this figure can move.