You have asked three builders to quote for the same extension. The prices come back thousands of pounds apart. One might be offering the complete job. Another is pricing for a shell with almost nothing finished. A third has forgotten to include VAT.

You are not comparing three quotes for the same thing. You are comparing three entirely different services that happen to involve the same house.

This guide explains why extension quotes vary, what builders often leave out, and what you should be looking for before you decide.

Key topics covered:

• Why the same extension produces wildly different prices
• What cheap quotes typically exclude
• The difference between an estimate and a fixed-price quote
• Insurance and warranties: what you are paying for (or not)
• How to compare quotes properly
• Why getting this right from the start matters

You Are Not Comparing Like for Like

The single biggest reason extension quotes vary is that builders are not pricing the same scope of work.

Most builder quotes cover the shell only. That means the structure, roof, windows and doors. What it does not mean is building regulations fees, skip hire, plastering, electrical finishing, floor finishes, or any making good to the existing house after the works are complete.

A full project budget should include professional fees covering the architect, structural engineer and surveyors, which typically add 8 to 15 per cent to construction cost. It should also account for planning fees, party wall costs if neighbours share a boundary, fittings and finishes, and a contingency of at least 10 to 15 per cent for unexpected costs.

When you strip all of that out, a quote that looks competitive on paper can end up costing significantly more by the time the project is finished.

What Cheap Quotes Leave Out

A low quote tends to stay low in only one way: it does not include everything needed. The shortfall shows up as extras once work is underway.

Common items missing from low quotes include:

Building regulations fees, skip hire and waste disposal, making good the existing structure after work, plastering and internal finishes, full electrical and plumbing installation, decoration, and any contingency for unforeseen ground conditions or structural issues.

Homeowners should plan for hidden costs that can impact their budget, such as variation orders from changes during construction, site access issues, and unforeseen structural work. It is recommended to set aside 10 to 15 per cent of the total budget as a contingency to cover unexpected expenses.

Add up those omissions and a quote that appeared several thousand pounds cheaper than the competition can easily end up costing the same or more by completion.

Estimate vs Fixed-Price Quote

This distinction matters more than most homeowners realise, and most do not spot it until the final bill arrives.

An estimate is a rough approximation. It is not legally binding and can vary considerably from the final cost. Some builders use estimates to secure work at an attractive number and add charges as the project progresses.

A fixed-price quote specifies exactly what work will be done and at what cost. Costs only change if the scope of work changes, and any variation should be agreed in writing before proceeding.

Always insist on a fixed-price quote with a detailed written specification.

VAT: The Cost That Catches Homeowners Out

Most builder quotes are stated excluding VAT. A £50,000 quote becomes £60,000 after VAT. This catches many first-time extenders off guard. Always confirm whether VAT is included or excluded before comparing figures.

Builders are required to register for VAT once their annual turnover exceeds the current threshold. Established, busy builders are almost always VAT registered. Always check, and always compare quotes on the same basis.

Insurance and Warranties

Cheap builders often carry minimal insurance because most homeowners do not check until something goes wrong.

A properly insured builder carries public liability insurance, employers liability insurance and contract works cover. Reputable builders should also be able to offer a structural warranty on completed work.

If a builder cannot demonstrate adequate insurance, that is a reason to walk away. The cost difference between a properly insured builder and one with minimal cover is small relative to the project value.

How to Compare Quotes Properly

Once you have multiple quotes, the way to compare them is not to look at the bottom line first. Go through each one and ask:

Is this a fixed-price quote or an estimate? What exactly is included and what is excluded? Are materials specified by product and quality, or described vaguely? Does the price include building regulations fees? What insurance does the builder carry and can they provide documentation? What warranty applies to the structural work? Is VAT included or excluded? What is the payment schedule? What is the realistic timeline?

A quote that answers all of those questions clearly and in writing is worth more than one that comes in cheaper but leaves everything vague.

Why Getting This Right Matters

The consequences of choosing the wrong builder are not just financial. A project that fails building regulations requires expensive remedial work before a completion certificate can be issued. Extensions with poor workmanship affect property valuations and can complicate future sales.

Cowboy builders provide unrealistically cheap quotes. Not only could the work quality be poor and lack guarantees and warranties, but costs often increase as the job progresses.

It is always cheaper to do the work properly once than to pay a second time to fix it

Your Next Steps

Use Your Space works with homeowners across Solihull, Warwick, Knowle, Dorridge, Bentley Heath, Shirley, Balsall Common, Leamington Spa and Kenilworth to deliver extensions properly from the outset.

We provide detailed fixed-price quotes that specify every element of the work. No vague descriptions, no hidden extras, no surprises. If you are planning an extension and want a quote you can actually rely on, contact Use Your Space today.

 

How Do I Finance a Loft Conversion or Extension?

The information contained on this blog is for educational and informational purposes only and is not intended to address your particular personal needs. It is not, and should not be considered, financial advice or a recommendation. You should consult with a professional to determine what may be best for your individual needs.

A loft conversion or extension is one of the smartest investments you can make in your home. It adds space, adds value, and costs far less than moving house. The part that stops most homeowners in their tracks is not the build itself. It is working out how to fund it.

Here is a plain-English breakdown of every realistic option available to you in 2026.

What This Guide Covers:

• What these projects actually cost
• Using your savings
• Personal loans
• Remortgaging
• Further advances
• Secured loans
• Credit cards
• Which option suits which situation

What Does the Work Actually Cost?

You need a real number before you can choose a finance route.

According to the Federation of Master Builders, a single-storey extension costs between £1,800 and £3,000 per square metre in 2026. A 20m² extension typically runs between £36,000 and £60,000 depending on specification, excluding professional fees and contingency.

Loft conversions range from around £55,000 to £120,000 depending on conversion type. Velux conversions sit at the lower end. Full dormer or hip-to-gable conversions sit at the higher end.

Get a fixed-price quote before you decide how much to borrow. An estimate is not good enough at this stage.

Using Your Own Savings

No interest. No debt. No approval process. If your savings cover the full cost, this is almost always the right choice.

The drawback is timing. Building costs can rise while you save, and a project that costs £45,000 today may cost more in two years. If you have most of the funds but not all, combining savings with a smaller loan is worth considering rather than borrowing the full amount.

Personal Loans and Home Improvement Loans

A personal loan is the most straightforward borrowing route for projects up to around £25,000 to £35,000. You borrow a fixed amount and repay it in fixed monthly instalments over an agreed term, typically two to seven years.

The Bank of England base rate currently stands at 3.75% following a cut in December 2025. Representative APRs on personal loans vary depending on the lender and your credit profile. Most mainstream lenders cap unsecured personal loans at £25,000, though some go higher.

Personal loans are unsecured, meaning your home is not at risk if you miss payments. Your credit rating is, however, and missed payments affect future borrowing.

This option suits smaller projects or situations where savings cover most of the cost and you need to bridge a gap.

Remortgaging

Remortgaging means taking out a new mortgage larger than your current one. The difference is released to you as a lump sum to fund the work.

Mortgage rates are generally lower than personal loan rates, making this one of the more cost-effective routes for larger projects. It suits homeowners who have built up meaningful equity, are at or near the end of their current fixed term, and need to borrow a sum that exceeds what a personal loan can provide.

Check early repayment charges on your existing deal before proceeding. Also consider whether extending your mortgage term increases your total repayment cost, even if the monthly payment looks lower.

Further Advance

A further advance lets you borrow additional money from your existing mortgage lender without switching providers. The process is simpler than a full remortgage and often involves lower fees.

The rate applied to the additional borrowing may differ from your current mortgage rate, so check the cost carefully. This suits homeowners who want to avoid switching lenders and have enough equity to support the additional borrowing.

Secured Loans

A secured loan sits alongside your existing mortgage rather than replacing it. Because your home is used as collateral, secured loans typically carry lower interest rates than unsecured personal loans and allow you to borrow larger sums.

The trade-off is that your property is at risk if you miss repayments. The application process also takes longer because the lender needs to assess your property.

This is worth considering where remortgaging is not practical due to high early repayment charges and you need to borrow more than a personal loan permits.

Credit Cards

Credit cards are not a realistic way to fund an extension or loft conversion in full. They are useful for covering smaller costs during the build, such as fixtures, fittings or decoration, particularly on a 0% purchase deal.

The discipline required is clearing the balance before the 0% period ends. Revert rates on credit cards are typically far higher than any other borrowing option.

Which Option is Right for You?

The right route depends on how much equity you hold, your current mortgage terms, your credit profile, and the total project cost.

As a general guide: use savings first if available. Use a personal loan for smaller gaps up to around £25,000. Remortgage or take a further advance for larger projects where you have equity and are not tied into costly early repayment charges. Consider a secured loan where remortgaging is not practical but you need to borrow a larger sum.

Whatever route you take, get your fixed-price quote first. Knowing the exact figure makes every conversation with a lender far more straightforward.

Your Next Steps

Use Your Space works with homeowners across Solihull, Warwick, Knowle, Dorridge, Bentley Heath, Shirley, Balsall Common, Leamington Spa and Kenilworth to deliver extensions and loft conversions properly, on budget and on time.

Contact Use Your Space today for a detailed fixed-price quote you can take straight to your lender.