Cost & Value · 4 September 2026

Provisional Sums and PC Sums in a Landed Build Quotation: What They Cover and Where Owners Get Caught

Two builders quote for the same house, off the same drawings. One total is noticeably lower than the other. The owner picks the lower one, and eighteen months later has paid more than the higher quotation asked for in the first place.

This happens often, and it is usually not dishonesty. It is allowances. Somewhere in both documents are lines that are not prices at all — they are placeholders for things nobody has decided yet — and the two builders set them at different levels. Everything downstream follows from that, and almost nobody compares them before signing.

This is how those lines work, what to ask about each one, and how to compare two quotations that contain them.

Two different things, often used interchangeably

A prime cost sum, usually written PC sum, is an allowance for a supply item you have not chosen yet. Floor and wall tiles, sanitary ware, taps and mixers, ironmongery, light fittings, sometimes kitchen appliances. The builder has to put a number in the quotation to make it add up, but you will choose the actual product later, and the difference between the allowance and what you choose is adjusted at the end.

A provisional sum is an allowance for work that cannot be measured yet. Not because nobody has chosen it, but because nobody yet knows what is there. Piling before a soil investigation. Works to an existing structure that has not been opened up. Drainage connections whose position is not confirmed. Repairs to something that is currently hidden behind a finish.

The distinction matters because they behave differently. A PC sum resolves the day you walk into a showroom and choose. A provisional sum resolves only when the ground is opened or the wall comes down, which is later, and by then you are committed.

Neither is padding, and a quotation with none of them is not automatically better. The alternative to an allowance is a builder guessing, then pricing the guess with enough margin to survive being wrong. That is worse for you, not better, because you cannot see it.

Why the same house produces very different totals

Set two quotations side by side and the allowances are usually where the gap lives.

Builder A sets a tile allowance at a level that buys a competent, widely available tile. Builder B sets one that buys the cheapest thing in the trade catalogue. Both are legitimate numbers to put in a document. But Builder B's total is lower, and it will stay lower right up until the day you stand in a showroom, realise what the allowance actually buys, and pay the difference on every square metre in the house.

Multiply that across tiles, sanitary ware, ironmongery and lights, and the "cheaper" quotation is not cheaper. It is a different document making a different assumption about you.

The same logic applies to provisional sums, with a sharper edge. A generous piling provisional sum looks like an expensive builder. A thin one looks like a keen one. Neither of them knows what is under the house, and only one of them is being honest about that. We have written separately about why builders quote different prices from the same drawings, and allowance levels are the single largest contributor.

The four questions to ask about every allowance line

These take one email and they change what you are looking at.

1. What quantity is this allowance based on? A tile allowance is a rate multiplied by an area. If the area assumed is smaller than the house actually has, the line will be exceeded even if you choose exactly the tile the allowance was set for. Ask for the rate and the quantity separately, not the product.

2. Is it supply only, or supply and install? This is the most common misunderstanding in the whole subject. A tile PC sum is normally supply only. Adhesive, laying, cutting, skirtings, edge trims and wastage sit in the builder's own rates, not in the allowance. Which means a decision that looks like a supply upgrade can also be a labour upgrade — large-format tiles are slower to lay and need a flatter substrate, natural stone needs different handling and sealing, and a diagonal or herringbone pattern is a different labour rate from a straight lay. If you choose something the laying rate did not assume, expect that to appear too. Ask which is which, per line.

3. How is the difference adjusted, and does it carry margin? When you spend above the allowance, is the extra passed through at cost, or does the builder's overhead and profit apply to the difference? Both are normal practice. Only one of them is what you assumed. Get the answer in writing before signing, not when the adjustment appears.

4. When does the selection have to be made? Every allowance has a date behind it, because the trade that installs it is booked and the item may be made to order. A selection made late does not delay the job by the number of days you were late; it delays it until the material arrives and then until that trade is next free.

Wastage, and why the arithmetic never quite works

Owners frequently calculate the shortfall themselves, then find the adjustment is larger than they expected. Two reasons, both legitimate, both worth knowing in advance.

Tiles and stone are not bought to the exact area. There is cutting waste at every edge and around every fitting, more with a large format because offcuts are less reusable, and more again with a diagonal or patterned lay. Sensible practice also buys a small surplus from the same production batch and keeps it, because a replacement tile bought two years later will not match — shade lots differ, and a repair with a near-match is visible forever.

Second, showroom prices are frequently quoted before delivery, and sometimes before the trims, spacers and adhesive appropriate to that product. The number you were shown in the showroom is not always the number that lands in the adjustment.

None of this is a reason to distrust the adjustment. It is a reason to ask, at selection time, what the delivered and laid figure is rather than the showroom figure.

Provisional sums and the ground

The ground is where provisional sums do the most damage, and it is also where they are easiest to remove.

Until somebody has actually investigated the soil, nothing below ground can be priced properly — pile type, pile length, how many, what happens to groundwater, and what the excavation needs in the way of support. Every builder quoting your job without that information is putting a number in a box, and the honest ones will tell you the number is a placeholder. We have written about how Singapore's soil conditions actually vary, and the variation is not small.

The useful move is to get the soil investigation done early, before the quotations rather than after. It converts the largest provisional sum in the document into a measured one, and it does so while you still have the ability to choose between builders on a like-for-like basis. Owners routinely leave it until after the contract is signed, which is precisely when the information has the least value to them.

The same applies to A&A works on an existing house. Anything sitting behind a finish is provisional until the finish comes off. Where opening up early is possible, it is worth doing.

The thing that is not an allowance at all

This is the one that catches people hardest, and it is worth reading twice.

A provisional sum is money set aside for something everyone agrees is in the job. An exclusion is something that is not in the job at all, and it has no line, no allowance and no number. It appears later as a variation, priced as a variation, at a point when you have no ability to shop around.

So the question to ask is not only "what are the allowances?" It is "what is excluded?" — in writing, as a list. Typical candidates on a landed project include external works and landscaping, driveway and gate, the swimming pool and its plant, air-conditioning, solar, authority submission fees, the professional fees of the architect and QP, temporary accommodation, and utilities during construction. Some of these belong outside a builder's scope perfectly reasonably. The problem is never that they are excluded. The problem is discovering it in month seven. The hidden costs first-time landed builders meet covers this ground, and whether the architect and QP are inside the builder's quotation is the single most misunderstood exclusion of all.

How to actually compare two quotations

Do not compare the totals. Normalise first.

List every allowance line in both documents next to each other. Where they differ, pick one figure — yours, not either builder's — and substitute it into both. Then re-add. What you get is a comparison of the two builders' actual work, which is the thing you are trying to choose between, rather than a comparison of their assumptions about your taste.

Then look at what each has excluded, and add the excluded items into whichever document is missing them, at whatever figure you can establish. It will not be exact. It does not need to be exact; it needs to stop you comparing a complete document with an incomplete one.

Finally, look at the proportion. If a large share of a quotation sits in allowances, that document is not a price. It is a range wearing a suit, and the honest conversation to have is about how to reduce that share — usually by making decisions earlier and investigating the ground sooner — rather than about the total at the bottom.

What we do about it

We do not publish a price list, for reasons set out in why there is no price list for landed building works — every house is different and a list would be a fiction. But an allowance is a different thing from a price, and an owner is entitled to know exactly what each one assumes, in quantity and in specification, before signing anything.

If a builder cannot tell you what quantity an allowance is based on, whether it includes installation, and how the difference is adjusted, that is worth knowing early. It is a five-minute answer for anyone who built the number honestly.

Wong Lye Pte Ltd is a licensed builder holding a BCA General Builder Class 2 (GB2) licence. What we take on is set out on the A&A works page.

Comparing quotations and not sure what you are looking at? WhatsApp us on 9107 2601 — tell us the house type, how many quotations you have, and roughly what share of each sits in allowances, and we will tell you which lines are worth pressing on first.

"Rewiring" is one of the lines most often quoted as a single allowance when it is really four decisions — see rewiring a landed house for what to ask a builder to break out.

Common questions

What is the difference between a PC sum and a provisional sum?

A PC or prime cost sum is an allowance for a supply item you have not chosen yet, such as tiles, sanitary ware, ironmongery or light fittings. A provisional sum is an allowance for work that cannot be measured yet because nobody knows what is there, such as piling before a soil investigation or repairs behind a finish that has not been opened up. A PC sum resolves the day you choose; a provisional sum resolves only when the ground is opened or the wall comes down, which is much later and after you are committed.

Does a tile PC sum include laying the tiles?

Normally not. A tile PC sum is usually supply only, with adhesive, laying, cutting, skirtings, edge trims and wastage sitting in the builder's own rates. That is why a selection which looks like a supply upgrade can also be a labour upgrade: large-format tiles are slower to lay and need a flatter substrate, natural stone needs different handling and sealing, and a diagonal or herringbone lay is a different labour rate from a straight one. Ask, line by line, which allowances are supply only and which include installation.

Why is the adjustment bigger than the difference I calculated?

Two usual reasons, both legitimate. Tiles and stone are not bought to the exact area: there is cutting waste at every edge and around fittings, more with large formats and patterned lays, and sensible practice buys a surplus from the same production batch because a replacement bought later will not match on shade. And showroom prices are often quoted before delivery, and sometimes before the trims and adhesive suited to that product. At selection time, ask for the delivered and laid figure rather than the showroom figure.

Why does a soil investigation belong before the quotations?

Because until the soil has been investigated, nothing below ground can be priced properly - pile type, length and number, groundwater, and what the excavation needs in the way of support. Every builder quoting without that information is putting a placeholder in a box, and that placeholder is usually the largest provisional sum in the document. Investigating early converts it into a measured item while you still have the ability to compare builders like for like. Left until after the contract is signed, the same information has far less value to you.

How should I compare two landed build quotations that contain allowances?

Do not compare the totals. List every allowance line in both documents side by side, and where they differ, substitute one figure of your own choosing into both before re-adding, so you are comparing the builders' actual work rather than their assumptions about your taste. Then list what each document excludes and add the missing items into whichever is short of them. Finally look at what proportion of each quotation sits in allowances - if the share is large, the document is a range rather than a price, and the conversation worth having is about reducing that share by deciding earlier and investigating the ground sooner.