The Bill of Quantities — What It Is, Why It Matters, and What Happens Without One

So folks, I want to talk about a document that most homeowners in Ireland have never heard of — and that most homeowners on larger residential projects really should have.

The Bill of Quantities.

Or the BoQ, as it is known in the industry.

Now. I know what you are thinking. Another bit of paperwork. Another cost. Another thing the professionals want you to pay for before a single brick is laid.

Bear with me. Because the BoQ is not paperwork. The BoQ is protection. And the difference between a project that has one and a project that does not is, in my experience, the difference between a project that finishes close to the agreed price and one that finishes with a final account that nobody recognises.

What is a Bill of Quantities?

A Bill of Quantities is a document that describes every element of a construction project in measured quantities, with a space beside each item for the builder to insert his price.

It is prepared by a quantity surveyor — usually me — from the architect's drawings and the engineer's details, once the design is sufficiently developed. It lists every trade. Demolition and groundworks. Concrete. Masonry. Carpentry and joinery. Roofing. Plastering. Floor and wall finishes. Plumbing and heating. Electrical. External works.

Each trade is broken down into individual items. Not 'plumbing — allow a sum.' But 'supply and fix 22mm copper pipework — 14 linear metres.' Not 'roofing — as per drawings.' But 'supply and fix 300 x 300mm natural slate roofing tiles — 85 square metres, including felt, battens, and lead flashings.'

Every item is measured. Every item is described. And the builder prices every item individually.

The result is a tender document that is, as far as it is possible to achieve, a like-for-like comparison. Three builders pricing the same BoQ are pricing the same job. The same quantities. The same descriptions. The same scope.

What happens without a BoQ

Most residential projects in Ireland — particularly extensions and renovations under a certain size — go to tender without a full Bill of Quantities. The builder prices from the drawings and the spec. He makes his own assumptions about quantities, his own allowances for items that are not fully specified, his own assessment of risk.

As I said in the piece on tenders, three builders pricing the same drawings without a BoQ are not pricing the same job. And the differences between those three prices are often not a reflection of the builders' efficiency or their rates — they are a reflection of their assumptions.

But the more significant problem happens during the build, not at tender stage.

Without a BoQ, there is no agreed baseline for what was included in the contract sum. When a variation arises — and variations always arise — there is no document that both sides can point to and say: this is what was agreed, and this is what has changed. The scope is defined only by the drawings and the spec, and drawings and specs always contain ambiguities.

Those ambiguities are where disputes grow. Quietly, at first. Then loudly, at the end, when the final account is being settled and the numbers are significantly different from where they started.

I'll be honest with you. The projects I see that end in disputes in Ireland are almost always the ones that had no BoQ. Not because the builder was dishonest. But because without a measured document that both sides signed up to, there is no agreed answer to the question: what did we actually contract to build?

The four numbers in a BoQ that matter most

If you have a BoQ on your project — or if you are considering commissioning one — here are the four things I look at most carefully.

First — the preliminaries. This is the section that covers the builder's time on site. His supervision costs, his site establishment, his plant and equipment. On a well-prepared BoQ, the preliminaries will be broken down in detail. A builder who has priced realistic preliminaries is a builder who has thought seriously about how long the job will take.

Second — the provisional sums. As I discussed in the tender piece, provisional sums are allowances for items not yet fully designed. A BoQ with a large number of provisional sums is a BoQ that is based on an incomplete design. It is not wrong — design is always incomplete at some stage — but it is worth understanding what is provisional and what is firm.

Third — the contingency. A well-prepared BoQ will carry a contingency allowance — typically 8 to 12 per cent — to cover items that could not be foreseen at the time of tendering. Ground conditions. Hidden defects in existing structure. Items that only become visible when the building is opened up.

Fourth — the PC sums. Prime cost sums are the material selections not yet finalised — kitchen, tiles, sanitaryware. These are where the homeowner's decision-making has the biggest impact on the final account. Understanding what each PC sum allows, and whether that allowance is realistic for the standard you want, is critical before the contract is signed.

When a BoQ is worth doing — and when it is not

A full Bill of Quantities is not the right tool for every residential project. For a small extension — say, under €100,000 — the cost of preparing a full BoQ may not be proportionate to the benefit. A well-prepared specification and a detailed cost plan will often be sufficient.

But for larger projects — full house renovations, substantial extensions, new builds — a BoQ earns its cost many times over. I prepare Bills of Quantities for residential projects up to €1 million in Ireland. In my experience, on projects of that scale, the BoQ is the single most effective tool available for controlling cost and preventing disputes.

The spec is what you are building. The BoQ is the spec with prices attached. Together, they form the foundation of a contract that both sides understand and both sides can be held to.

Spec without prices is just hope. The BoQ turns hope into a contract.

Anyway, that is the BoQ in plain English. If your architect has not mentioned it on your project, it is worth asking the question. And if you want me to look at whether a BoQ is appropriate for your job, here is how that works.

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If your architect hasn't priced a BoQ, you're walking in half-blind. I prepare one for jobs under €1m. → [link to BoQ service]

If I can help in any way, let me know.