UK Construction Glossary: 20 Terms Every Homeowner Should Know
Plain-English definitions of provisional sum, prime cost, practical completion, retention, snagging, and 15 more construction terms homeowners need to understand.
Your builder's quote lands in your inbox. It's peppered with terms like "provisional sums," "prelims," and "retention." You nod along, sign, and hope for the best.
In short: Construction has its own language. Misunderstanding even one term can cost you thousands or leave you without legal protection. This glossary covers the 20 terms you're most likely to encounter in a builder's quote, a contract, or on site - explained in plain English.
You don't need a construction degree. You just need to know what these words actually mean before you sign anything.
Provisional Sum
A provisional sum is an estimated allowance for work that can't be priced accurately yet. You'll see these in quotes for drainage, groundworks, or anything where the full picture only emerges once the builder starts digging.
The important thing: provisional sums are adjusted to actual cost once the work is done. If the allowance was £3,000 and the real cost is £4,500, you pay the difference. If it comes in at £2,200, you save money. Always ask your builder which items are provisional and why - it tells you where the financial uncertainty lies.
See our guide on what a builder's quote should include for how provisional sums should be presented.
Prime Cost Sum
A prime cost (PC) sum is an allowance for materials or fittings that you haven't chosen yet. Your builder might include a PC sum of £2,000 for bathroom tiles, meaning that's the budget assumed in the quote.
You're free to spend more or less. If you pick tiles that cost £3,200, the quote goes up by £1,200. If you find something you love for £1,400, you save £600. Knowing which items carry a PC sum helps you understand where you have flexibility - and where you might accidentally blow the budget.
Practical Completion
Practical completion is the point at which building work is substantially finished and fit for its intended use. A few minor items might remain - a scuff on a doorframe, a missing cover plate - but the building is safe and usable.
This is a significant milestone. It usually triggers the release of half the retention money and starts the clock on the defects liability period. If your builder claims practical completion but you're still waiting for a functioning kitchen, push back.
Retention
Retention is money you hold back from the builder - typically 2.5% to 5% of the contract value - as insurance against defects. Half is usually released at practical completion, and the other half at the end of the defects liability period.
It gives the builder a financial incentive to come back and fix problems. Without retention, you lose your main lever. On a £60,000 project, 5% retention means you're holding £3,000 - enough to motivate most builders to sort out any issues. Read more about managing costs and hidden charges.
Defects Liability Period
The defects liability period (DLP) is a set window - usually 6 to 12 months after practical completion - during which the builder must return to fix any defects at their own cost. Cracks appearing, doors sticking as the house settles, a leak at a junction - these are the builder's responsibility during the DLP.
Make sure your contract specifies the length of this period. Without it, getting a builder back to fix problems becomes a negotiation rather than an obligation.
Snagging
Snagging is the process of walking through a finished project and recording every minor defect, incomplete item, or cosmetic issue. The result is a snagging list - a punch list of items the builder must rectify.
Common snags include paint runs, uneven grouting, scratched glass, gaps in sealant, and doors that don't close properly. A thorough snagging inspection before you release the final payment protects you. Some homeowners hire an independent snagging company for objectivity.
Variation
A variation is any change to the agreed scope of work after the contract is signed. You decide you want bifold doors instead of French doors. That's a variation.
Variations should always be documented in writing, with the cost impact agreed before the work proceeds. Verbal agreements on variations are the single biggest source of disputes in residential construction. If your builder suggests a change, get a written variation order before they proceed.
Day Work
Day work (or day rate) means the builder charges by the day rather than quoting a fixed price. Rates vary by trade and region but typically range from £150 to £350 per day for a tradesperson.
Day work suits small, unpredictable jobs - exploratory work, repairs, or tasks where the scope is genuinely unknown. For anything substantial, a fixed price quote gives you far more cost certainty.
Preliminaries
Preliminaries (prelims) are the overhead costs of running a building site. Think scaffolding, skip hire, temporary electrics, site toilets, insurance, and project management time. On larger projects, prelims can account for 10-15% of the total build cost.
Some builders break prelims out as a separate line item. Others absorb them into the overall price. Either way, understanding that these costs exist helps you compare quotes fairly. A quote that looks cheap but doesn't include prelims isn't actually cheaper - the costs are just hidden. See how to read a builder's quote for more on spotting this.
Making Good
Making good means repairing and finishing all the surfaces, junctions, and areas disturbed by building work. After a new doorway is knocked through, the surrounding plaster needs patching and painting. After pipes are run through a floor, the boards need reinstating.
Watch for quotes that mention making good without specifying what it covers. "Making good to existing surfaces" could mean a quick skim coat or a full replaster, repaint, and retile. Clarify the detail before you sign.
Contingency
A contingency is a budget buffer - typically 10-15% of the total project cost - set aside for the unexpected. Hidden rot behind plasterboard. Asbestos in an artex ceiling. A drain run that needs rerouting.
Every renovation project should have a contingency. If your builder hasn't included one, add it yourself. Spending it is optional; not having it when you need it is painful. Our guide on hidden costs in home renovations covers the most common surprises.
JCT Contract
JCT (Joint Contracts Tribunal) contracts are the UK construction industry's standard-form contracts. For residential projects, the JCT Minor Works Building Contract (MW) is the most commonly used. It covers payment terms, variations, completion, defects, and dispute resolution in a balanced way.
Using a JCT contract rather than a builder's own terms gives you much stronger legal protection. The Federation of Master Builders recommends JCT contracts for all domestic building work.
Building Warrant
If you're building in Scotland, you need a building warrant rather than a building regulations approval. It serves the same purpose - ensuring your project meets structural, fire, and energy standards - but the application process and fees differ.
You must obtain a building warrant before work begins, and a completion certificate before you can occupy the building. The process is managed by your local authority's building standards team. For projects in England and Wales, see our planning permission guide.
Fixed Price Quote
A fixed price quote is a legally binding commitment to complete a defined scope of work for a stated price. Once you accept it, the builder cannot increase the price unless you change the scope.
This is the gold standard for homeowners. It transfers the risk of cost overruns to the builder, who has the experience and knowledge to price accurately. If a builder refuses to provide a fixed price quote, that's a red flag - read our piece on builders who won't give written quotes.
Estimate
An estimate is an educated guess at what work will cost. It's useful for early budgeting, but it's not binding. The final price can be higher or lower.
The critical distinction: a quote is legally binding; an estimate is not. Many builders use the terms interchangeably, which causes confusion. If your document says "estimate" at the top, you don't have a fixed price. Ask for a proper quote before committing.
Tender
A tender is a formal submission of a price, usually in response to detailed architectural drawings and specifications. Tendering is more structured than quoting - builders receive identical information and submit sealed prices, allowing a fair comparison.
Tendering is common on larger projects (typically £100,000+) and is usually managed by an architect or quantity surveyor. For smaller residential work, getting three to five comparable quotes serves the same purpose.
Schedule of Works
A schedule of works is a detailed list of every work item, material, and finish included in the quote. It's the reference document for what you've agreed to pay for - and what you haven't.
A good schedule of works makes disputes almost impossible. If the builder says underfloor heating was never included, you can point to the schedule. If you think a particular finish was agreed, the schedule settles it. Always ask for one, and review it carefully before signing.
Bill of Quantities
A bill of quantities (BoQ) is a document prepared by a quantity surveyor that breaks down every material, labour hour, and cost by measured quantity. It allows precise, like-for-like comparison between builders because everyone is pricing the same items.
For projects over £50,000, commissioning a BoQ can save you far more than it costs. Without one, you're comparing quotes that may include different scopes, materials, and allowances. Our guide on comparing builder quotes explains how to do this effectively.
Certificate of Completion
A completion certificate (or building regulations completion certificate) is issued by building control after they've inspected your finished work and confirmed it complies with the Building Regulations. Without it, you may face problems when selling your property or remortgaging.
Always check that your builder has arranged for building control sign-off. Some builders submit the initial building notice but forget (or avoid) booking the final inspection. Chase this yourself if needed - it's your property and your problem if the certificate is missing. See our guide on quotes missing building regulations for more.
Party Wall Agreement
A party wall agreement is required under the Party Wall etc. Act 1996 whenever building work affects a shared wall, boundary, or involves excavation near a neighbouring property. You must serve notice on your neighbours before work starts.
If your neighbour agrees, you can proceed with a simple written acknowledgement. If they dissent (or don't respond within 14 days), you'll both need to appoint party wall surveyors, which typically costs £700-£1,500 per neighbour. Factor this into your project budget from the start.
How MyBuildAlly helps
Understanding these terms is the first step. The second is knowing whether your builder's quote uses them correctly and fairly.
MyBuildAlly's AI quote checker analyses your quotes against current UK pricing data and flags missing items, vague allowances, and terms that could leave you exposed. Upload a quote and get a detailed breakdown in minutes - no jargon, no guesswork.