Medir un bill of quantities según NZS 4202

Take off quantities the way the standard measures them: net as the work is fixed in place, in the unit the rule for that trade names, with the deductions the rule requires and no others. Keep each dimension attached to the drawing and revision it came from so the take-off can be re-read rather than re-done.

Por que: Net measurement is what makes two bills comparable, and it is also what makes a bill re-measurable when the design moves. A quantity that already has an allowance baked into it cannot be checked against a drawing by anybody except the person who made it, and that person is usually the one not available when the tender query arrives.

Assemble each measured item as the composite the standard describes: the labour, the material, the plant and the incidental work the rule says the rate covers. Where a rule deems something included, put it inside the assembly rather than leaving it as a separate line somebody will price twice.

Por que: Nearly every dispute about a bill is a coverage dispute, not a quantity one: two people agreeing on the square metres and disagreeing about whether the rate included the edge trim. Building the coverage into the item makes it visible to the estimator pricing it and to the contractor reading it, which is the only place it can be settled cheaply.

Put the measured work into the trade sections the standard uses, and keep preliminary and general as its own section rather than spreading site costs through the trades. Carry provisional and prime cost sums as their own items with what they cover written against them.

Por que: A bill is priced by subcontractors who each read one section and ignore the rest, so the structure decides who sees what. Time-related site cost buried in the trades is cost nobody prices as time-related, and it is the first thing to be argued about when the job runs long.

Set the waste allowance per material as a factor the rate carries, and let the purchase quantity be derived from it rather than typed into the bill. The measured quantity stays the net one the drawing supports; the quantity ordered from the merchant is a different number for a different purpose.

Por que: Waste added to the measured quantity breaks the one property that makes a bill useful, which is that anybody can check it against the drawing. It also double counts the moment a rate that already allows for waste is applied to a quantity that also does, and nobody notices because both numbers look reasonable on their own.

Run the bill through the checks before it goes out: items with a unit that does not match the rule for their trade, items with no quantity, sections the drawings imply and the bill does not carry, and rates that fall outside a sane band for their unit. Fix what is wrong and record what is deliberate.

Por que: A bill goes to several tenderers on the same day, so an error in it is not one error, it is one error multiplied by the number of people pricing it, and every one of them prices around it differently. Half an hour of checking before issue is the cheapest half hour in the whole tender period.

Record the basis of the bill in one place: that it is measured to NZS 4202, the drawings and revisions it was measured from, the specification it reads with, every departure from the standard and every exclusion and assumption the quantities rest on. Issue it with the bill rather than keeping it in the file.

Por que: The standard only does its job when the departures are stated, because a tenderer is entitled to assume the rules were followed everywhere it is silent. A bill issued without its basis puts the risk of every unstated assumption onto whoever priced it, which is the party least able to see it, and that is exactly the claim that comes back nine months later.