Why Extension Quotes Vary So Much

Why the Cheapest Quote Often Ends Up Costing More



If you’ve asked a few builders to quote for a single-storey extension, you’ve probably seen prices all over the place.


One looks cheap.
One feels reasonable.
One feels expensive.


Same drawings. Same house. Different numbers.


For homeowners across Leeds and West Yorkshire, extension quotes can look very different — even for very similar projects.


For most family homes, a typical single-storey rear or side extension is usually in the region of 20–30 square metres. On paper, it looks straightforward. In reality, the way builders price that space can vary significantly.


Here’s why extension quotes differ so much — and how to compare them properly.


You’re Not Comparing the Same Work


Three builders can all quote for a “25m² extension” and still be pricing completely different things.


One builder might be pricing a basic structure with minimal finishing.
Another might include a finished extension, but only to a basic specification.
Another might include everything required to hand it over ready to use, with proper allowances and protections in place.


They all describe the same job. It isn’t.


Why Cheap Quotes Don’t Stay Cheap


Low quotes usually stay low by leaving things out.


Common omissions include:


  • Building control fees and inspections
  • Making good to the existing house after the build
  • Proper plastering and internal finishing
  • Adequate electrical and plumbing allowance
  • Flooring beyond bare screed
  • Decoration
  • Waste removal
  • Any realistic pricing for issues uncovered once work starts


Those costs don’t disappear. They tend to appear later as “extras”, once the job is underway and options are limited.


That’s when budgets drift, and disputes start.


What a Proper Quote Should Include


A proper quote isn’t just a higher number. It’s a clearer one.


A properly prepared quote should include:


  • A clearly defined scope of works
  • Materials and finishes described properly, not vaguely
  • Known fees included from the outset
  • Labour priced realistically
  • Appropriate insurance for the works
  • A written contract and payment schedule
  • A realistic programme, not optimistic promises


A proper quote includes everything within the agreed scope of works, with all inclusions and exclusions clearly stated in writing. That clarity protects both parties and avoids misunderstandings later.


Pricing Risk vs Relying on Variations


Experienced builders don’t keep prices low by relying on variations later. They price known construction risks realistically at the quoting stage.


Older houses and groundworks can present issues that aren’t always visible before work starts. A properly prepared quote reflects typical risks based on experience, rather than being artificially reduced and then increased later through extras.


Any genuine changes to the agreed scope of work should be discussed, priced, and agreed in writing before proceeding.


Estimates vs Fixed Quotes


This catches people out more than anything else.


An estimate is an approximate figure based on limited information and may change as work progresses.
A fixed-price quote is a defined price for a clearly specified scope of work and should only change if the scope itself changes.


Always ask which one you’re being given. Many problems start when homeowners think they have a quote, but legally they only have an estimate.


Vague Specifications Cause Problems


Terms like “good standard” or “quality finish” don’t mean anything unless they’re backed up by detail.


How many sockets?
Which doors and windows?
What insulation?
What flooring?
What’s excluded?


If it isn’t written down, it’s open to interpretation — and that’s where extra costs and disagreements come from.


Clear specifications protect both the homeowner and the builder by ensuring expectations are aligned before work starts.


Labour Quality Matters


Labour is one of the biggest differences between quotes.


Cheaper labour often means:


  • Rushed work
  • Corners cut
  • Failed inspections
  • Long snagging lists


Skilled tradespeople cost more because they know what they’re doing and take pride in the finish. That usually results in a smoother build and fewer issues during and after completion.


Insurance Isn’t Optional


Reputable builders carry appropriate insurance for the work they undertake.


Homeowners should always ask what insurance is in place and request confirmation before work begins. Insurance arrangements should be appropriate to the scope of works and remain in place for the duration of the project.


If something goes wrong and insurance isn’t in place, the risk can land back on the homeowner.


VAT and Why Quotes Can Look Misleading


In the UK, builders are required to register for VAT once taxable turnover exceeds the statutory threshold (£90,000 at the time of writing).


Some builders quote excluding VAT, some include it, and some are not VAT registered at all. A cheaper quote isn’t always cheaper once VAT is compared properly.


Always check whether VAT is included so you’re comparing like for like.


Timelines and Reality


Any construction programme is an estimate based on the information available at the time of quoting. Timelines can be affected by weather, inspections, material availability, access, and client-requested changes.


Realistic planning and clear communication are key to keeping disruption under control.


The Real Cost of Getting It Wrong


The biggest cost isn’t choosing the wrong number. It’s choosing the wrong approach.

We’re often asked to quote for work where:


  • A previous builder walked off site
  • Building control wouldn’t sign it off
  • Finishes weren’t acceptable
  • Corners were cut to keep costs down


By that stage, fixing the problem usually costs more than doing it properly from the start.


How to Compare Extension Quotes Properly


Don’t just look at the total.


Ask every builder:


  • Is this a fixed price or an estimate?
  • What exactly is included and excluded?
  • What quality of materials are being used?
  • What insurance covers the job?
  • How are changes handled?
  • What’s the payment schedule?
  • What’s the realistic timeline?


The builder who answers clearly — and backs it up in writing — is usually the safer choice.


Final Word


We don’t aim to be the cheapest option. We aim to provide clear, realistic pricing for defined work, carried out properly and documented correctly from the outset.


Our approach is designed to minimise surprises, disputes, and unnecessary cost increases during construction.


If you’re comparing extension quotes, compare what’s included, how clearly it’s specified, and how changes are handled — not just the final figure.

If you’re planning a build, ourhouse extensionspage explains how we approach pricing and project management in more detail.





Written by 4G Building Projects — experienced extension builders working across West and North Yorkshire.