Builders’ quotes can differ by thousands—or tens of thousands—of pounds even when each builder has received the same drawings. That does not automatically mean the highest quote is excessive or the lowest is a bargain.
The usual reason is that the builders have not priced exactly the same package of work. Each quotation reflects its own scope, specifications, assumptions, allowances, construction method, approach to risk and business costs. The headline totals cannot be compared reliably until those differences have been identified.
In brief: A large price gap is a reason to investigate, not a reason to choose. Compare what each builder has included, excluded, assumed and left uncertain before deciding which quotation offers the best value and the most dependable basis for a contract.
Why can builders price the same project so differently?
A set of drawings describes the proposed building, but it rarely answers every question needed to calculate the cost of constructing it. Unless the tender information also includes a detailed specification, structural information, schedules and clear responsibility for every part of the work, each builder must fill in the gaps.
One may allow for extensive groundworks, a full electrical installation and complete decoration. Another may assume standard foundations, a limited number of electrical points and no decoration. Both can say they have priced the drawings, but they have priced different interpretations of them.
The most common causes are summarised below.
| Cause of the difference | How it changes the price | What the homeowner should check |
|---|---|---|
| Scope and exclusions | Necessary work may be included in one quote and absent from another | Compare every work section, not only the total |
| Design information | Missing details force builders to make different assumptions | Confirm the documents and revision numbers used |
| Material specification | Products that look similar on a drawing may differ greatly in cost | Ask for named products, performance standards or clear allowances |
| Provisional sums and allowances | A low allowance reduces the tender total without fixing the eventual cost | Compare the amount and basis of every allowance |
| Site conditions and access | Restricted access, occupied homes and difficult ground increase labour and plant costs | Check the site assumptions written into each quote |
| Labour and management | Team structure, supervision and subcontractor rates vary | Establish who will manage and carry out the work |
| Preliminaries and overheads | Scaffolding, skips, welfare, insurance and management may be priced differently | Check whether all site-running costs are included |
| Risk and contingency | Builders make different judgments about uncertain work | Identify which risks are fixed, provisional or excluded |
| Programme and workload | Duration, availability and market demand affect pricing | Compare proposed start dates, durations and resources |
| VAT | One price may include VAT while another excludes it | Restate every quote on the same VAT basis |
| Pricing errors or tactics | An item may be missed, duplicated, underpriced or deliberately marked up | Ask for clarification before relying on an unusual figure |
1. The scope is not genuinely the same
Scope is the work the builder has agreed to provide. Drawings may show the finished result without stating who will undertake all the work required to achieve it.
Differences commonly arise around:
- demolition and temporary support;
- excavation, spoil removal and imported stone;
- drainage alterations;
- scaffolding and access equipment;
- structural steelwork and fire protection;
- insulation and airtightness work;
- electrical points, consumer-unit work and certification;
- plumbing, heating alterations and commissioning;
- kitchen, bathroom and flooring installation;
- decorating, external finishes and making good;
- skips, cleaning and final waste removal; and
- Building Control attendance, testing and completion information.
A low quotation may therefore be the price of a smaller scope rather than a lower price for the same work. This is why the inclusions and exclusions described in What Should Be Included in a Builder’s Quote? matter as much as the total.
2. The builders have priced different information
Reliable comparison depends on every builder receiving the same tender information at the same time. This may include:
- architectural drawings and their revision numbers;
- structural drawings and calculations;
- a schedule of works or room-by-room specification;
- window, door, ironmongery and finish schedules;
- mechanical and electrical requirements;
- planning and Building Regulations conditions relevant to the work;
- site surveys, drainage information and asbestos reports where applicable; and
- an identical list of questions and tender instructions.
RICS guidance describes competitive tendering as contractors bidding on identical tender documentation. The principle is just as important on a domestic project: if one builder has later drawings or more complete information, the returned prices do not share the same basis.
Even where the documents issued were identical, quotations should state which documents were used. A builder pricing an earlier drawing revision may have omitted a rooflight, a larger opening or a change in external materials without anyone noticing.
3. Drawings leave room for different specifications
“Supply and fit bathroom”, “new flooring” and “allow for lighting” are not costed specifications. The prices depend on what is supplied, its quality, how it is installed and what associated work is included.
For example, two quotes may both include windows, but one may allow for standard white uPVC units while the other includes aluminium frames, specialist glazing and more complex installation details. The difference is real, but it is not a difference in price for an equivalent product.
Specifications should be defined wherever possible. Where a final selection has not been made, each builder should use the same realistic allowance so that the choice does not distort the comparison.
4. Provisional sums and prime cost items are different
A quotation can contain a substantial amount that is not fixed.
A provisional sum is generally an allowance for work that cannot yet be fully defined or accurately priced. Groundworks are a common example where the design or site conditions remain uncertain.
A prime cost item is an allowance associated with a product or item that has not yet been selected, subject to the wording of the quotation or contract. Sanitaryware, tiles and ironmongery are common examples.
Two quotations can show very different totals simply because one builder has used £5,000 of optimistic allowances and another has used £15,000 of realistic allowances. The £10,000 gap is not necessarily a saving. It may be cost that has been deferred until the actual work or products are known.
For every allowance, establish:
- what it covers;
- whether it includes supply, delivery, installation, waste and VAT;
- what quantity and quality have been assumed;
- how the final amount will be adjusted;
- whether overhead and profit will be added; and
- whether the work affects the construction programme.
BYB expert tip: Compare the fixed-price content separately from provisional sums and product allowances. A quotation with the lowest total but the greatest unresolved cost may carry the highest final-cost risk.
5. Site conditions change the cost of doing the work
The same extension design can cost more to build on one property than another. Price is affected by how the work must be carried out, not only by what is shown in the finished design.
Relevant factors include:
- narrow or shared access;
- no space for a skip, storage or mechanical plant;
- manual removal of excavated material through the house;
- parking restrictions or permits;
- work above or beside neighbouring property;
- an occupied home requiring extra protection, cleaning and phasing;
- uncertain ground, drainage or existing structure;
- listed-building or conservation requirements;
- restricted working hours; and
- the need to keep services, kitchens or bathrooms operational.
Builders may inspect the same site and reach different conclusions about labour, plant, protection and programme. Those assumptions should be made explicit rather than left inside the price.
6. Construction methods and material choices vary
There is often more than one compliant way to complete a detail. Builders may prefer different structural systems, suppliers, waterproofing products, roof coverings or sequencing methods. Their quotations may also allow for different standards of finish.
A higher material price does not prove better quality, and a lower price does not prove corner-cutting. The important question is whether the proposed product and method satisfy the design, Building Regulations, manufacturer’s requirements and the homeowner’s expected finish.
Where the quotations differ, ask each builder to identify substitutions or alternatives to the tender specification. Do not accept “or similar” without knowing what standard the alternative must meet.
7. Labour, supervision and subcontracting are priced differently
Contractors have different team structures. One may employ trades directly, another may rely on subcontractors, and another may use a small core team with specialist trades brought in as required.
Rates vary with skill, location, availability and the complexity of the work. The amount of management also varies. A quotation may include a dedicated site manager, regular coordination and detailed programming; another may assume the business owner will visit periodically while trades organise parts of the work themselves.
Neither model is automatically right or wrong. It should, however, be suitable for the project. Complex structural work, occupied refurbishments and projects involving many interfaces usually require more coordination than straightforward work.
8. Preliminaries, overheads and profit are not consistent
Preliminaries are project-specific costs needed to set up, manage and complete the site. They can include scaffolding, welfare, temporary protection, skips, plant, insurances, supervision, cleaning, health and safety measures and temporary services.
Overheads are the contractor’s wider business costs, such as vehicles, premises, administration, estimating, software and insurance. Profit is the return the business adds for undertaking the work and accepting its commercial risk.
A sole trader and a larger building company will not have the same cost structure. That does not mean one necessarily offers better value. The concern arises when unavoidable costs appear nowhere in the quotation and there is no clear explanation of how they are covered.
9. Builders price uncertainty and risk differently
Fixed prices transfer defined pricing risk to the builder. Where information is incomplete, the contractor may:
- include a contingency within the price;
- use a provisional sum;
- exclude the uncertain work;
- qualify the price with an assumption; or
- increase the price to reflect the risk being accepted.
These approaches produce different totals and different risk for the homeowner. A higher fixed price may provide greater cost certainty. A lower price with broad exclusions may leave more risk with the client.
The objective is not to eliminate every uncertainty—often that is impossible—but to identify who carries it, how it will be valued and what evidence will be required if the cost changes.
10. Programme, availability and workload affect the price
A builder with a suitable gap in the programme may price differently from one who would need to reorganise existing commitments, engage additional labour or work to a compressed deadline. Seasonal demand, local workload and material lead times can also affect the quotation.
An unusually high price can sometimes mean the contractor is willing to take on the project only at a premium. It can also reflect a faster programme or more site resources. Ask about the proposed start date, duration and staffing before interpreting the price difference.
11. VAT can create an apparent difference
Check whether every total includes VAT. GOV.UK states that most work on houses and flats by builders and similar trades is charged at the standard rate of 20%, although exceptions apply. A quotation of £80,000 plus VAT is £96,000 at the standard rate; it is not cheaper than a VAT-inclusive quotation of £92,000.
A contractor may legitimately be below the VAT registration threshold or voluntarily registered. VAT status alone is not a measure of competence or reliability. It is simply essential to compare the amount you will actually pay and to verify any claimed reduced or zero rate against current HMRC rules.
BYB expert tip: Create one VAT-inclusive comparison column even if the quotations present tax differently. Keep professional fees and other client costs separate so they are not accidentally counted in one tender but not another.
12. A quote may contain an error—or may be priced strategically
Quotations are prepared by people and mistakes occur. A quantity may be wrong, a subcontractor’s figure may be missing, VAT may be applied inconsistently or a work section may be duplicated.
Prices can also be strategic. A builder may price keenly because the project suits the team and programme. Another may include a premium because the work is difficult, distant or inconvenient. In less acceptable cases, a low initial figure may depend on vague scope and chargeable extras later.
Do not assume intent from the total alone. Ask for written clarification. A competent contractor should be able to explain the basis of the price and correct a genuine error before a contract is signed.
How different should builders’ quotes be?
There is no universal percentage that makes a difference “normal”. The acceptable spread depends on how complete the design is, how consistently the work has been specified and how much uncertainty remains.
On a small job, fixed costs can create a large percentage difference even when the cash difference is modest. On an extension or refurbishment, hidden conditions and incomplete specifications can produce a much wider range. As the design and tender information become more detailed, unexplained price differences should reduce.
Use the spread as a diagnostic signal:
- A narrow spread may indicate that the scope is understood consistently, but it does not prove that nothing has been omitted.
- A wide spread usually indicates differences in scope, specification, allowances, risk or pricing accuracy that must be reconciled.
- One outlier—high or low—requires clarification; it should not automatically be rejected or selected.
- A wide spread that remains after normalisation may reflect genuine differences in delivery model, programme, overheads, profit or appetite for the project.
If you are trying to decide whether a particular price is fair, read our guide: Is My Builder’s Quote Reasonable?
Worked example: three very different totals can describe a similar cost
The figures below are illustrative. They show why the initial total should not be treated as the comparable price.
Builder A initially appears £23,000 cheaper than Builder C. Once missing work, inadequate allowances and an enhanced specification are treated consistently, the apparent difference disappears.
Normalisation does not guarantee the final cost. It creates a common basis for comparing the quotations and exposes the decisions or uncertainties that still need to be resolved.
What we commonly find when reviewing builders’ quotations
During independent quotation reviews, the largest differences are often not in the obvious structural work. They sit in shorter descriptions and boundary areas where responsibility is unclear.
Recurring examples include:
- one builder pricing complete electrical and plumbing work while another includes only alterations;
- decoration, floor finishes or making good included in one quote and excluded from another;
- very different provisional sums for foundations, drainage or steelwork;
- supply allowances that do not include fitting, delivery, waste or the builder’s margin;
- structural or architectural revisions not reflected in every price;
- scaffolding, access, skips and welfare absorbed into one total but absent from another;
- client-supplied items with no clear allocation of unloading, storage, installation or defects responsibility; and
- ambiguous wording such as “as necessary”, “standard specification” or “by client” without further definition.
These are not minor administrative points. They affect who pays, what will be delivered and how easily a later disagreement can be resolved.
How to compare different builders’ quotes fairly
Use the following process before ranking the prices.
1. Confirm the basis of each quotation
List the drawings, revisions, specifications, surveys and instructions issued. Ask each builder to confirm in writing that the quotation is based on the same set.
2. Build a scope comparison
Create rows for each work package—preliminaries, demolition, groundworks, structure, roof, windows, services, finishes and external work. Record whether each item is included, excluded, provisional or unclear.
The full process is set out in How to Compare Builders’ Quotes.
3. Put VAT on the same basis
Compare either all VAT-exclusive totals or, preferably for a homeowner, the total amount payable including VAT. Do not mix the two.
4. Separate fixed prices from allowances
List provisional sums, prime cost items and other allowances separately. Test whether the figures are sufficient for the expected work and products.
5. Add the cost of exclusions needed to complete the project
An exclusion does not make the work unnecessary. Add a reasonable figure for essential excluded work to the relevant quote, or obtain a firm price, before comparing totals.
6. Resolve assumptions and qualifications
Ask the same written questions of each builder and circulate any clarification that changes the tender basis. This prevents one contractor from pricing new information while the others remain unaware of it.
7. Compare commercial terms
Review price validity, programme, payment stages, variation procedure, delay provisions, insurance, defects obligations and the proposed contract. A quotation is not a substitute for a suitable written building contract.
Citizens Advice explains that accepting a quotation can create a binding agreement and recommends obtaining the price and work details in writing. It also distinguishes a fixed-price quotation from an estimate. Check whether each document is actually a quote or an estimate before relying on its total.
8. Assess the builder as well as the number
Once the prices are comparable, consider relevant experience, references, current projects, insurance, communication, availability, management arrangements and financial demands. Value is the relationship between price, scope, quality, certainty and delivery—not simply the lowest figure.
For a focused decision on low bids, see Should I Choose the Cheapest Builder’s Quote?.
BYB expert tip: Do not begin by asking a builder to reduce the price. First establish why the figures differ. Removing genuine scope to match a lower quote can create a saving; forcing down a correctly calculated price without changing the work can create pressure elsewhere in quality, programme or variations.
Questions to ask when quotations do not match
Send the questions in writing and retain the answers with the quotation:
- Is this a fixed quotation or an estimate?
- Which drawings, specifications and revision numbers have you priced?
- Is VAT included, excluded or not applicable, and what rate has been used?
- Please confirm all exclusions and all work expected to be provided by the client or others.
- Are scaffolding, access equipment, skips, welfare, protection, cleaning and making good included?
- What does each provisional sum or allowance cover, and how will it be adjusted?
- Do product allowances include delivery, installation, waste, overhead and profit?
- What assumptions have been made about foundations, drainage and the existing structure?
- What electrical, plumbing, heating, ventilation and certification work is included?
- Are decoration, floor finishes, external works and final completion items included?
- Who will supervise the project, and which work will be subcontracted?
- What start date, duration and working arrangements have been assumed?
- How long is the price valid?
- How will variations be described, priced and approved before the work proceeds?
- What payment schedule and form of contract are proposed?
Answers such as “everything is included” are not sufficiently precise for a substantial project. Ask for the relevant work and responsibility to be identified.
What should you do with a quote that is much cheaper?
Do not accept or reject it on price alone.
First, check that it is a quotation rather than an estimate. Then identify omissions, exclusions, low allowances, VAT treatment and the exact documents priced. Ask the builder to confirm that any apparently missing work is included and to amend the wording where necessary.
If the lower figure remains credible after the scope has been normalised, it may reflect a leaner business, favourable supplier rates, an efficient construction method or a project that fits the builder’s programme particularly well. Complete the usual checks on experience, references, insurance, contract terms and payment demands before making a decision.
If the builder will not clarify material ambiguities, the price cannot be treated as dependable however attractive it appears.
What should you do with a quote that is much higher?
Ask the builder to explain the main cost differences by work section. The quotation may contain more complete scope, higher specifications, more realistic allowances, stronger project management or a larger transfer of risk to the contractor.
It may also contain an error, unnecessary work, a premium for limited availability or a cautious interpretation of incomplete information. A high total is not evidence of quality by itself. Compare it on the same normalised basis and decide whether any additional specification, service or certainty is valuable to you.
Frequently asked questions
Why can two builders’ quotes for the same extension be £20,000 apart?
Because the drawings do not necessarily define the complete priced scope. The builders may have included different work, materials, allowances, preliminaries, VAT and risk. Break down the £20,000 difference by work package before deciding that one builder is cheaper or more expensive.
Is the cheapest builder’s quote likely to increase?
Not necessarily. A lower fixed quotation can be genuine. The risk is greater where the document is vague, contains significant exclusions or low provisional sums, or is actually an estimate. Confirm how changes and allowances will be valued under the proposed contract.
Should every builder receive exactly the same information?
Yes. Issue the same drawings, revisions, specifications, surveys and tender questions to each builder. If one builder raises a point that changes the scope, provide the clarification to all tendering builders so their prices remain comparable.
Can I ask a builder for a more detailed breakdown?
Yes. The breakdown should be proportionate to the size and complexity of the work, but you need enough detail to identify scope, allowances, exclusions and payment stages. A builder may protect detailed internal rates, but should still be able to explain what the quotation includes and how major sections differ.
Should a builder’s quote include VAT?
It should state clearly whether VAT is included and the rate applied. Most work on existing houses and flats is standard-rated, but exceptions exist. Compare the total payable and check unusual VAT treatment against current HMRC guidance.
What percentage difference between builders’ quotes is acceptable?
There is no reliable universal percentage. A large difference is more concerning when the design and specification are complete and the quotations remain far apart after normalisation. Investigate the cause rather than using an arbitrary percentage to reject a price.
Should I choose the middle quotation?
Not automatically. The middle price can contain the same omissions or weak allowances as the lowest. Choose only after comparing scope, specification, uncertainty, commercial terms and the builder’s suitability.
How many builders’ quotes should I get?
For many domestic projects, three written quotations provide a useful comparison without creating an excessive tender list. The quality and consistency of the information issued matter more than collecting a large number of incomparable prices. Read How Many Builders’ Quotes Should I Get? for the full approach.
Can a builder charge more than a written quotation?
A quotation is generally an agreed price for the defined work, but the amount can change where the scope changes, additional work is agreed, allowances are adjusted or the contract provides another valid basis. Record variations and their price in writing before the work proceeds. For advice on a specific dispute, obtain appropriate consumer or legal advice.
Before you appoint a builder
The right question is not simply, “Which builder is cheapest?” It is, “What will each builder provide, what remains uncertain, and what am I likely to pay for a properly completed project?”
Before You Build independently reviews builders’ quotations for homeowners. We identify differences in scope, exclusions, allowances, assumptions and likely cost risks before a builder is appointed. We do not appoint contractors or accept referral fees.
Have your quotation reviewed before you commit: View BYB quote review services.