Questions to Ask Before Hiring a Builder for an Extension

Updated 5 October 2026

Hiring a builder for an extension is not just a price comparison. You are choosing who will manage a complex piece of work involving structure, sequencing, materials, building control and often several trades. The questions you ask before appointment can expose gaps that a headline quote hides.

Ask for a written quote, not just a verbal figure

Citizens Advice recommends getting written quotes from at least three different traders before deciding who to use. It also distinguishes a quote from an estimate: a quote is a fixed price for the agreed work, while an estimate is only an indication.

Ask the builder to show the scope, materials, exclusions, VAT treatment, payment terms and the circumstances in which the price can change.

Ask exactly what is included

For an extension, clarify whether the quote includes demolition, excavation, foundations, drainage, structural steel, roofing, windows and doors, insulation, plastering, electrics, plumbing, heating alterations, decorating, waste removal and making good.

If some of those items are excluded or provisional, identify who will arrange and pay for them.

Ask who is responsible for building regulations

Do not assume planning permission and building regulations are the same thing. In England, building regulations approval commonly applies to extension work even where planning permission is not required.

Ask whether the builder expects the homeowner, designer or contractor to deal with the building control body, inspections and completion paperwork. If registered installers are used for certain types of work, ask what self-certification documents will be provided.

Ask about previous extension work

Request examples of comparable projects rather than generic photos. Similarity matters: a simple rear extension is not the same as a project involving large structural openings, complex drainage or work to an older property.

Where practical, ask previous clients about communication, variation handling and how problems were resolved, not only whether the finished work looked good.

Check insurance

Citizens Advice recommends checking that the trader has appropriate insurance before work starts. Ask for evidence of relevant cover and make sure it matches the nature and scale of the project.

If the builder employs staff, employers' liability requirements may also apply to the business. The important point is to verify current cover rather than relying on a logo or old certificate.

Ask how changes are handled

Extensions often change when hidden conditions are uncovered or the homeowner alters a specification. Ask how variations are described, priced and approved before extra work proceeds.

A good process records the change, cost impact and programme impact so both parties know what has been agreed.

Ask for the payment schedule

Payments should be tied to an agreed structure rather than improvised as the job progresses. Understand what is due, when it is due and what work or materials the payment relates to.

Be cautious about paying for large amounts of work that have not yet been delivered without understanding how the payment is protected.

Ask who will actually be on site

Find out whether the person quoting will manage the work, which trades will be subcontracted and who your day-to-day contact will be. This matters when decisions or problems arise during construction.

Ask what completion documents you will receive

Depending on the work, these may include building control completion documentation, electrical certificates, gas-related certificates, product warranties, commissioning records or other evidence of compliance.

Questions worth taking to the meeting

Is this a fixed quote or an estimate?
What is included and excluded?
Is VAT included where applicable?
Who deals with building control and inspections?
Which trades will be subcontracted?
What insurance do you currently hold?
How are variations approved?
What is the payment schedule?
What is the expected programme?
What completion certificates and warranties will I receive?

Sources and verification

Citizens Advice — Before you get work done on your home: written quotes, comparing at least three traders, quote-versus-estimate distinction, insurance and contract checks.
GOV.UK — Use a competent person scheme: self-certification, certificates and checking registered installers.
GOV.UK — Building work, replacements and repairs to your home: routes for building-regulations compliance and checking competent-person registration.

Jurisdiction note: building-control references here relate mainly to England. Rules differ elsewhere in the UK.

Legacy article body backup — 2026-10-04

This field preserves the pre-enrichment draft before evidence and visible-source backfill.

When hiring a builder for an extension, it's essential to obtain accurate quotes that reflect the scope and complexity of your project. A single quote can be misleading if you don't ask the right questions.

Getting the Right Quote

Before comparing quotes from different builders, ensure each has provided a comprehensive breakdown of their costs. Ask about any additional fees or charges that may not be included in the initial quote, such as VAT or delivery costs. You should also inquire about the payment terms and whether there are any penalties for late payments. Additionally, it's crucial to ask about the builder's experience with similar projects and what materials they plan to use.

Understanding the Contract

When examining your builder contract, it is essential to scrutinise the scope of work and how it will be executed. Ensure that the agreed-upon specifications and materials are clearly outlined, as this can significantly impact the final product's quality and cost. You should also review the payment schedule, including any deposits or advance payments required, to avoid financial difficulties later on. Additionally, familiarising yourself with the builder's terms of termination will help you understand your options if any issues arise during construction. This section of the contract may appear lengthy, but it is crucial to understanding your contractual obligations and protecting your interests.

Checking References and Reviews

When researching potential builders for your extension project, it's essential to check references and reviews from previous clients. You can start by asking friends, family members, or acquaintances who have had similar extensions built if they've worked with a reliable builder in the past. Look for online reviews on websites such as Rated People or TrustATrader to see what other homeowners have said about their experiences with local builders. Pay particular attention to comments about communication skills, work quality, and reliability, as these are key factors to consider when hiring a builder. A good reference check can provide valuable insights into the builder's strengths and weaknesses.

Inspecting the Builder's Worksite

Arrive at the building site during normal working hours and observe the builders' work from a distance to get a general impression of their organisation and efficiency.
Check that all necessary safety equipment is available and being used by the builders, including hard hats, harnesses, and protective gloves.
Look for any evidence of damage to existing buildings or structures, such as cracks in walls or broken windows, which may indicate sloppy workmanship.
Take note of the condition of tools and equipment, looking for signs of wear and tear, and whether they are being properly stored when not in use.
Observe how the builders interact with each other and their clients, paying attention to communication skills, teamwork, and customer service standards.

Ensuring Compliance with Building Regulations

A homeowner is planning to extend their semi-detached house and hires a builder. Before the project begins, they ask their potential builders about compliance with building regulations, specifically regarding the required roof pitch for the extension. The builder explains that they will ensure the new roof complies with the Building Regulations 2010, which dictate a minimum roof pitch of 35 degrees to prevent water from pooling on the roof. The homeowner asks what checks will be made to confirm this and the builder responds that they will conduct a site survey and obtain a certificate from a Local Authority Building Control officer before commencing work.

Before instructing the builder on the scope of your project, it's essential to discuss the timeline and milestones that will be met. You should ask when they plan to start work, what is their typical completion date, and what stage of the project you can expect to see progress at. Additionally, consider asking about their method for managing site waste and ensuring that all materials are sourced from reputable suppliers. It's also crucial to discuss payment terms; will you need to pay in installments or all upfront? Furthermore, inquire about their experience with projects similar to yours, as well as any relevant certifications or insurance coverage they possess.

When inquiring about the builder's experience with extensions, it is also prudent to ask about their method for managing the project timeline and budget. A clear understanding of how they will allocate resources and priorities can help avoid costly delays or overruns. It would be beneficial to request examples of past projects that share similar characteristics to your extension, such as size or materials, to gauge the builder's adaptability. Furthermore, it is wise to inquire about their approach to communication, including how often you can expect updates on progress and any issues that may arise. Asking about their system for managing and documenting changes to the original design can also provide insight into their level of flexibility and responsiveness.

Many service businesses are now using tools such as Servadra to handle routine enquiries, freeing staff to focus on complex client matters.

Frequently Asked Questions

What is the difference between a traditional builder and a specialist contractor?

A traditional builder typically has more general experience and skills, whereas a specialist contractor specializes in a specific area of construction, such as timber frame or steel frame buildings.

How do I know if my builder has the necessary insurance coverage?

To verify your builder's insurance coverage, check their public liability and employers' liability policies, which should be clearly outlined on their website or upon request.

Can I see examples of previous work?

You can ask to see examples of previous work by requesting portfolios or photo albums from completed projects, allowing you to assess the quality of their craftsmanship.