Builder Quotes Explained

If you've recently requested quotations for a house extension, loft conversion or renovation project, you may have been surprised by the results.

One builder quotes £85,000. Another quotes £110,000. A third comes back at £135,000.

At first glance, it can seem impossible that three experienced builders could arrive at such different figures for what appears to be the same project.

The reality is that builder quotations often vary significantly, and there is usually a reason why.

Understanding those reasons can help you make a more informed decision, avoid costly surprises and ensure you're comparing like for like. If you are still working out the likely budget, start with our guide to house extension costs in Kent.

In this guide, we'll explain why builder quotes differ, what homeowners should look out for, and how to compare quotations properly before committing to a contractor.

Why Do Builder Quotes Vary So Much?

Many homeowners assume that all builders are pricing exactly the same thing.

In practice, that's rarely the case.

Even when builders receive the same drawings, they may make different assumptions about the work involved, the specification required and the risks associated with the project.

This can result in quotations differing by tens of thousands of pounds.

Different Builders Interpret Drawings Differently

Architectural drawings provide an essential starting point, but they don't always tell the whole story.

Some builders will include every item they believe may be required. Others may only price what is explicitly shown on the drawings.

For example, one builder may allow for:

• Additional drainage work
• Steelwork contingencies
• Upgraded insulation
• External landscaping

While another builder may exclude those items entirely.

The result is two very different quotations for what appears to be the same project. This is also why specialist input, such as structural calculations, can make a quote easier to compare. Our structural engineer guide explains when that detail may be needed.

Some Quotes Include More Detail Than Others

A detailed quote often requires significant time and effort to prepare.

Builders who invest that time will usually provide a breakdown showing:

• Groundworks
• Structural work
• Roofing
• Windows and doors
• Electrical work
• Plumbing
• Finishes

Other quotations may simply provide a single figure with very little explanation.

While a shorter quote can look attractive, it can sometimes hide costs that appear later as extras. Our builder questions checklist covers the questions to ask before signing.

Labour Costs Can Vary Significantly

Not all building companies operate in the same way.

Some builders employ large teams of skilled tradespeople. Others rely heavily on subcontractors.

Some companies have offices, project managers and administrative staff, while others operate with minimal overheads. These differences affect pricing.

Higher labour costs do not necessarily mean a builder is overpriced. They may simply reflect a different business structure or level of service.

Experience Comes at a Cost

Builders with extensive experience in extensions and renovations often charge more than those who are newer to the market.

This can be frustrating for homeowners working within a budget.

However, experienced builders often bring:

• Better project planning
• Stronger trade relationships
• Improved quality control
• Faster problem solving
• More accurate pricing

Paying slightly more upfront can sometimes reduce the risk of costly mistakes later.

Risk Is Priced Differently

Every construction project carries some uncertainty.

Builders must assess risks such as:

• Ground conditions
• Drainage issues
• Structural challenges
• Access restrictions
• Material price fluctuations

Some contractors include substantial contingencies within their quote. Others price more aggressively and deal with issues as they arise.

Neither approach is automatically right or wrong, but it can have a major impact on the figures you receive.

One Builder May Have Missed Something

It happens more often than homeowners realise.

A particularly low quotation can sometimes indicate that a builder has misunderstood part of the project or accidentally omitted key elements.

This doesn't necessarily mean they're being dishonest. It may simply be an error.

Unfortunately, if those omissions become apparent during construction, additional costs often follow.

This is one reason why the cheapest quote is not always the cheapest project.

Specification Makes a Huge Difference

The quality of materials included within a quotation can vary enormously.

Windows and Doors

One builder may allow for standard uPVC products. Another may have priced premium aluminium systems. The difference could easily run into thousands of pounds.

Kitchens

One quotation may include a basic kitchen allowance. Another may assume a higher-end specification.

Flooring and Finishes

Tiles, flooring, decorating and joinery can all vary dramatically in cost depending on the products selected.

Unless these assumptions are clearly stated, comparisons become difficult.

What Should Be Included in a Builder's Quote?

A good quotation should clearly explain:

• Scope of work
• What's included
• What's excluded
• Payment schedule
• Estimated programme
• Key assumptions
• VAT position
• Provisional sums and allowances

The more transparent a quotation is, the easier it becomes to compare against competing bids. For more general selection advice, see our guide on how to choose a builder.

Understanding Provisional Sums

One of the most common causes of confusion is the use of provisional sums.

A provisional sum is an allowance for work that cannot be accurately priced at the time the quotation is prepared.

Examples might include:

• Drainage alterations
• Landscaping
• Kitchen supply
• Bathroom fixtures

Large provisional sums can make a quote appear cheaper than it ultimately becomes.

Always ask builders to explain any provisional allowances in detail.

The Danger of Choosing the Cheapest Quote

Every homeowner wants value for money.

However, selecting a builder based purely on price can be risky.

A significantly lower quote may indicate:

• Missing items
• Unrealistic allowances
• Poor understanding of the project
• Future reliance on variations
• Financial pressure within the business

If one quotation is dramatically lower than the others, it's worth investigating why.

Very often, the middle quote represents the most realistic assessment of the project.

How to Compare Builder Quotes Properly

When reviewing quotations, focus on more than just the final figure.

Ask yourself:

• Are the builders pricing the same specification?
• Have all builders received the same information?
• Are exclusions clearly identified?
• How detailed is each quotation?
• Are provisional sums reasonable?
• What experience does the builder have?
• What do references and reviews say?
• How confident do you feel in their communication?

The answers to these questions are often more important than the headline price. If you want a clearer process, see how My Build My Way helps homeowners compare builders.

A Simple Example

Imagine you receive three quotes for a rear extension.

Builder	Quoted Price
Builder A	£85,000
Builder B	£108,000
Builder C	£132,000

At first glance, Builder A appears to offer a saving of £47,000.

However, after reviewing the quotations, you discover:

• Builder A excludes drainage works.
• Builder A excludes decorating.
• Builder A includes minimal kitchen allowances.
• Builder A includes large provisional sums.

Suddenly the gap becomes much smaller.

Once all costs are accounted for, the difference may only be a few thousand pounds rather than tens of thousands.

Final Thoughts

It's perfectly normal for builder quotations to vary, sometimes by £20,000, £30,000 or even £50,000 or more.

The important thing is understanding why.

The cheapest quote is not always the best value, and the most expensive quote is not always overpriced.

By looking beyond the headline figure and comparing quotations properly, homeowners can make more confident decisions and reduce the risk of unexpected costs during construction.

If you are ready to compare suitable builders for your own project, start your project enquiry here.