PC Sums in a New Build: What They Are and Whether Yours Are Realistic
Somewhere in most New Zealand build contracts is a short list of PC sums: an allowance for flooring, one for the kitchen, one for tiles, one for carpet. They look like decisions. They are placeholders. And because they are set before anyone has chosen anything, they are the most common reason a build ends up over budget without anybody having done anything wrong.
What a PC sum is
PC stands for prime cost. A PC sum is the builder's allowance for an item the client has not yet chosen, usually the finishes: flooring, kitchen cabinetry and benchtops, tiles, carpet, tapware, lighting. The builder puts a figure in the contract so the total can be priced. When you make the real selection, the difference between the allowance and the actual cost is charged, or credited, as a variation. A provisional sum is similar but covers work whose scope is uncertain, such as earthworks or drainage, rather than a product you will pick.
Why PC sums are so often too low
Three reasons, and none of them is bad faith. A builder pricing competitively is under pressure to keep the headline number down, and PC sums are the easiest place to do it. A builder who does not know your taste will allow for a standard product, not the one you will actually fall in love with in a showroom. And some PC sums are supply only, so the installation is priced elsewhere or not at all. The result is a contract that looks affordable and a selections round that quietly adds tens of thousands.
How to check a PC sum before you sign
Ask three questions of every allowance. Is it supply only, or supply and install? Is it including or excluding GST? And what product, specifically, does the figure assume? A flooring PC sum of $60 a square metre, supply only, ex GST, is a laminate. If you are picturing a wide-board European oak, that allowance is a third of where it needs to be, and better to know now than at the selections meeting.
Then put your own numbers beside the builder's. Our interior finishes budget calculator gives an indicative range for flooring, wall boards, kitchen cabinetry, benchtops, tiles, carpet, cladding and window dressings, by the level of finish you actually want, in about two minutes. It is a guide rather than a quote, but it tells you quickly which allowances are realistic and which need a conversation before the contract is signed.
What realistic looks like for flooring
Marchand engineered European oak is $190 a square metre supply, ex GST, with installation typically $55 to $80 a square metre on top depending on the substrate and the pattern. A herringbone floor sits at the upper end of that installation range. For a 110 square metre living, kitchen and hall area that is a floor in the low to mid twenty thousands, installed, ex GST. If the flooring PC sum in front of you is under $10,000 for that area, it is not allowing for an oak floor; it is allowing for the conversation to happen later, at your cost.
Setting PC sums instead of accepting them
The better approach is to give the builder the allowances rather than take theirs. Decide the floor first, because it is the largest surface and sets the tone for the kitchen and everything after it, and because the oak is the one line in the scheme that holds its price at every level of finish. Then work through the kitchen, the stone, the carpet and the cladding in that order, each chosen against the one before. Our colour scheme guide walks the sequence, and a concept box puts the whole set of samples in your hand for $10, collated by our interior designers after a short call. Walk into the contract meeting with the samples and the numbers, and the PC sums become yours.
Frequently asked questions
What is the difference between a PC sum and a provisional sum?
A PC (prime cost) sum is an allowance for a product you have not yet chosen, such as flooring or a kitchen. A provisional sum is an allowance for work whose extent is not yet known, such as foundations on a sloping site. Both are adjusted by variation once the real cost is known.
Do PC sums include installation?
Sometimes. Always ask. A supply-only flooring PC sum can leave the installation, underlay, moisture testing and preparation to be priced separately.
Are PC sums GST inclusive?
Either, and contracts differ. Confirm which, and compare like with like when you check them against supplier prices.
What is a realistic flooring PC sum for engineered oak in NZ?
For Marchand oak, $190 a square metre supply plus $55 to $80 installation, ex GST. Multiply by the floor area and add wastage of around ten per cent for plank and more for herringbone.
Can I change a PC sum before signing?
Yes. Before the contract is signed the allowances are negotiable, and a builder would usually rather price a realistic figure than manage a variation later. Bring your selections and your numbers to the meeting.
Last reviewed September 2026.