Tender quantity verification is the exercise of testing quantities produced by somebody with an interest in the answer. On design and build, and on any tender where contractors measure their own work, it is the only independent check the client gets.
The objection is usually that the client cannot afford to remeasure the whole scheme. That is true and it is not the exercise. Sampling the items that carry the value gives most of the benefit for a fraction of the effort.
Where the value sits
On a typical residential scheme a small number of elements carry most of the cost: substructure, frame, envelope, internal division, and the repeated unit fit out. Checking those covers the majority of the money.
Within each, a small number of items dominate. Checking every item in a bill is disproportionate; checking the ten items that carry half the value is a day's work with a real chance of finding something.
The sampling should be visible to the contractor, because a bidder who knows the significant items will be checked prices them more carefully.
What errors look like
Under measurement, which shows up as a rate that looks reasonable against a quantity that does not. It becomes a variation or a claim later, and the client pays at negotiated rates rather than tendered ones.
Over measurement, which inflates the price and, on a remeasurable contract, corrects itself downward later. On a lump sum contract it does not.
Omission, which is the hardest to find because there is nothing to look at. The check for this is structural: does the breakdown contain a line for every element the drawings show.
Double counting, particularly where quantities have come from a model and geometry overlaps. That risk is covered in BIM quantity take-off, what the model does not contain.
The structural check comes first
Before any arithmetic, compare the breakdown against a list of what the scheme contains. Every element on the drawings should appear somewhere in the price.
Elements that reliably go missing include builder's work in connection, temporary works, external works components, fire stopping, testing and commissioning, and the making good around everything.
This check takes an hour and finds more money than a day of remeasurement, because an omitted element is a whole line rather than a percentage error on one.
Rate sanity, not rate negotiation
Comparing rates against other bids, against previous projects and against first principles identifies items that are out of pattern. Out of pattern is not the same as wrong.
A rate far below the others may indicate a quantity error elsewhere in the bid, a different assumption about method, or a genuine advantage. A rate far above may indicate a risk the bidder has seen and the others have not.
Either way the useful response is a question rather than an adjustment. Bidders answering those questions frequently correct their own errors during the process.
Who carries the error
On a traditional contract with client provided quantities, an error in the bill is the client's risk and gets corrected. By contrast, on design and build with contractor measured quantities, it is generally the contractor's risk.
That difference tempts clients to skip the check on design and build. It should not, for two reasons. A contractor who has under measured will look for recovery elsewhere, usually through change. And a contractor who has made a serious error may not be able to absorb it, which becomes the client's problem in a different form.
The contractual position is covered in NRM2 explained for developers.
Timing
The check has to happen before appointment, during the tender period or immediately after bids return. After appointment the leverage is gone and any correction is a negotiation.
That means the programme has to allow for it, which is a fortnight rather than a month on most schemes, and it is time that repays itself on the majority of projects.
Where it is not done, the errors surface during construction as the pattern described in quantity assumption risk.
What this means for you
Do not attempt to remeasure the scheme. Sample the elements that carry the value, and check structurally for what is missing before checking arithmetically for what is wrong.
Then put the questions to the bidders during the tender period. Most of the value in this exercise comes from the answers rather than from the analysis. Our approach sits under quantities and take-off.
Have a contractor's quantities and no way to test them?
Send the breakdown and the drawings. We will sample the significant items and tell you what the numbers support.