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House extension planning permission advice for homeowners

© 2026 APN Extensions | apnextensions.co.uk

Find Extension Builders

Finding the right builder is one of the most important decisions in any extension project. Tell us about your plans and the stage you have reached, and we can help connect you with suitable extension professionals.

A well-designed extension can transform a home.

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It may create a larger kitchen and dining room, improve the connection with the garden, provide space for a growing family or allow the property to work more effectively for many years to come.

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However, even the best design will depend on the quality of the construction work.

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Finding the right extension builder is therefore one of the most important decisions you will make during the project.

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The aim is not simply to find the cheapest quotation.

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You need a builder who understands the drawings, has relevant experience, communicates clearly and can deliver the required standard of work within a realistic budget and programme.

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Looking for an Extension Builder?

 

Extension projects vary considerably.

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A straightforward single-storey rear extension is different from a wraparound extension involving extensive structural alterations, drainage diversions, steel beams and a complete kitchen refurbishment.

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A double-storey extension, bungalow extension or combined extension and loft-conversion project may require an even broader range of experience.

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Before approaching builders, it is helpful to explain:

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  • The type of property

  • The location

  • The type of extension

  • The approximate size

  • The stage the project has reached

  • Whether planning permission has been obtained

  • Whether Building Regulations drawings are available

  • Whether structural calculations have been prepared

  • The proposed budget

  • The intended timescale

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The clearer the information, the easier it is to identify suitable builders for the project.

What Types of Extension Builders Can You Find?

 

Depending on your property and the work involved, you may be looking for help with:

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  • Rear extensions

  • Side-return extensions

  • Wraparound extensions

  • Full-width extensions

  • Double-storey extensions

  • Kitchen and dining-room extensions

  • Bungalow extensions

  • Conservatories and orangery-style extensions

  • Garage conversions

  • Internal remodelling

  • Structural alterations

  • Extensions combined with loft conversions

  • Larger home-renovation projects

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Some builders focus primarily on smaller domestic extensions.

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Others are better suited to complex projects involving extensive refurbishment, multiple trades and a longer programme of work.

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The right match will depend on the scale and nature of your project.

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Start With a Clear Brief

 

Before requesting quotations, decide what you want the builder to price.

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This may sound obvious, but many homeowners approach builders too early.

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A brief description and a few photographs may be enough for an initial conversation or rough budget estimate.

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However, they will rarely be enough for a detailed and reliable quotation.

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For a meaningful price comparison, builders should ideally receive the same package of information.

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This may include:

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  • Design drawings

  • Planning drawings

  • Building Regulations drawings

  • Structural calculations

  • Drainage information

  • A written specification

  • Details of windows, doors and rooflights

  • Information about kitchen or bathroom work

  • Expected finishes

  • Any relevant planning conditions

  • Access arrangements

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Without a consistent package, each builder may make different assumptions.

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One builder may include structural steelwork, plastering and electrical work. Another may leave these out and add them later as extras.

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The lowest initial price is not always the lowest final cost.

Do You Need Planning Permission Before Contacting Builders?

 

You can speak to builders before planning permission has been granted.

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This can be useful during the early stages if you want to understand the likely build cost or discuss practical construction issues.

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However, it is important to distinguish between an early estimate and a detailed quotation.

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Some extensions may fall within permitted development rights.

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Others will require a householder planning application.

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Larger rear extensions may use the prior-approval route in appropriate circumstances.

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The correct planning position should be checked before construction begins.

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For a more accurate quotation, it is generally better to provide builders with an agreed design and sufficient technical information.

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Why Building Regulations Drawings Matter

 

Planning drawings normally show the size, shape and appearance of the extension.

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Building Regulations drawings go further.

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They help explain how the extension should be built.

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Depending on the project, the technical drawings may include:

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  • Foundation details

  • Wall construction

  • Floor build-ups

  • Roof details

  • Insulation

  • Drainage layouts

  • Ventilation

  • Fire-safety notes

  • Structural references

  • Window and door details

  • Rooflight or roof-lantern details

  • Materials and construction notes

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This information gives builders a clearer basis for pricing the work.

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It can also reduce uncertainty once construction begins.

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Structural Design and Steelwork

 

Many extension projects involve structural alterations.

 

A common example is the removal of the original rear wall to create a large open-plan kitchen, dining and family room.

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The work may require:

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  • Steel beams

  • Columns

  • Padstones

  • Connections

  • Temporary supports

  • Foundation design

  • Roof alterations

  • Structural calculations

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If the structural design has not been prepared, builders may need to include provisional allowances or make assumptions.

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This can lead to differences between quotations and additional costs later.

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For more complex projects, structural calculations should ideally be available before the final quotations are requested.

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Main Contractor or Separate Trades?

 

Some homeowners appoint one main contractor to manage the entire project.

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This is often the simplest route.

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The contractor may coordinate:

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  • Groundworkers

  • Bricklayers

  • Roofers

  • Carpenters

  • Plumbers

  • Electricians

  • Plasterers

  • Decorators

  • Kitchen installers

  • Glazing suppliers

  • Waste removal

  • Scaffolding

  • Other specialist trades

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This can reduce the amount of day-to-day organisation required from the homeowner.

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However, the contractor may include a margin for managing subcontractors and materials.

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Another option is to appoint a builder for the main structural work while arranging selected items separately.

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For example, the homeowner might obtain separate quotations for:

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  • Windows and glazed doors

  • Rooflights or roof lanterns

  • Kitchens

  • Worktops

  • Flooring

  • Decorating

  • Landscaping

  • Underfloor heating

  • Bespoke joinery

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This approach can provide greater control over the specification and may reduce costs.

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However, it also requires more organisation.

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The best route depends on your experience, available time and appetite for managing the project.

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Questions to Ask an Extension Builder

 

Before appointing a builder, ask practical questions.

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These may include:

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  • Have you completed similar extension projects?

  • Can you provide references?

  • Can I see examples of completed work?

  • Who will manage the site?

  • Will you use subcontractors?

  • What insurance do you hold?

  • When can you start?

  • How long do you expect the work to take?

  • What is included in the quotation?

  • What is excluded?

  • Which items are provisional sums?

  • Is VAT included?

  • How will payments be structured?

  • How will changes and additional work be agreed?

  • Who will coordinate Building Control inspections?

  • How will waste removal and site access be managed?

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The answers should give you a clearer sense of how the builder operates.

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Good communication matters.

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If a builder is difficult to contact, vague about the price or unwilling to explain the scope of work before appointment, the situation may not improve once construction begins.

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Compare Several Quotations

 

Where possible, obtain quotations from more than one builder.

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Each builder should receive the same drawings and specification.

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Compare the quotations carefully rather than looking only at the final figure.

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Check whether each quotation includes:

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  • Site setup

  • Demolition

  • Groundworks

  • Foundations

  • Drainage alterations

  • Brickwork and blockwork

  • Structural steelwork

  • Roof construction

  • Scaffolding

  • Windows and doors

  • Rooflights

  • Plumbing

  • Heating

  • Electrical work

  • Plastering

  • Carpentry

  • Kitchen installation

  • Bathroom installation

  • Flooring

  • Decoration

  • External making good

  • Waste removal

  • VAT

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The quotations should also identify exclusions and provisional sums.

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A simple comparison table can help reveal significant gaps.

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What Are Provisional Sums?

 

A provisional sum is an allowance for an item that cannot be priced precisely at the time of the quotation.

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Some uncertainty is unavoidable.

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For example, the builder may not know the exact foundation depth until excavation begins.

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The route and condition of existing drains may also be unclear.

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A quotation may therefore include provisional sums for:

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  • Foundation depth

  • Drainage alterations

  • Structural steelwork

  • Electrical work

  • Plumbing

  • Kitchen installation

  • Sanitary fittings

  • Flooring

  • External paving

  • Landscaping

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Provisional sums are not automatically a problem.

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However, they should be realistic and clearly stated.

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An unrealistically low allowance can make a quotation appear attractive initially, only for the final price to increase later.

Be Clear About the Level of Finish


One builder may quote for a completed extension.
 

Another may quote for a shell.
 

There is no universal definition of a shell-only package.
 

It may include the foundations, walls, roof, windows and basic plaster finish.
 

However, some builders may exclude electrical work, plumbing, decoration, flooring or kitchen installation.
 

Clarify whether the quotation includes:
 

  • Kitchen units

  • Kitchen fitting

  • Worktops

  • Appliances

  • Bathroom fittings

  • Tiling

  • Flooring

  • Decoration

  • Light fittings

  • Underfloor heating

  • Radiators

  • External paving

  • Landscaping

  • Glazed doors

  • Rooflights

  • Roof lanterns
     

Do not assume that an item is included simply because it appears on a drawing.

 

Payment Terms


Agree the payment structure before work begins.
 

For an extension project, payments are often linked to progress stages.
 

These may include:
 

  • An initial deposit

  • Completion of foundations

  • Walls raised to roof level

  • Roof completed and watertight

  • First-fix plumbing and electrics

  • Plastering

  • Second-fix work

  • Practical completion

  • Final snagging
     

The precise structure will depend on the project.
 

The important point is that payments should reflect progress on site and be set out clearly in writing.
 

Avoid paying an excessive proportion of the total cost before meaningful work has been completed.

 

Put the Agreement in Writing


A written contract is strongly advisable for a substantial extension project.
 

It should record:
 

  • The agreed drawings

  • The specification

  • The contract price

  • The payment schedule

  • The start date

  • The expected programme

  • Provisional sums

  • Exclusions

  • The process for variations

  • Responsibilities for materials

  • Insurance

  • Delays

  • Snagging

  • Defects

  • Completion arrangements

  • Dispute resolution
     

A clear written agreement protects both the homeowner and the builder.

 

Watch for Warning Signs


There is no single test that guarantees a successful project.
 

However, some warning signs should encourage caution.
 

These may include:
 

  • A quotation that is dramatically lower than the others

  • A reluctance to provide references

  • No written quotation

  • Requests for large upfront payments

  • Vague explanations of what is included

  • Pressure to begin immediately

  • A lack of relevant extension experience

  • Poor communication

  • Unclear insurance arrangements

  • Cash-only demands without proper paperwork

  • An unwillingness to work from drawings

  • No clear process for changes or extras
     

A lower price may be genuine.
 

A smaller builder may have fewer overheads or a gap in the programme.
 

However, an unusually low quotation should be checked carefully.

 

Builder Availability


Good builders may already have projects booked several months ahead.
 

This can be frustrating when you are keen to begin, but availability should not be the only deciding factor.
 

A builder who can start tomorrow is not automatically the best choice.
 

Consider:
 

  • Relevant experience

  • The quality of the quotation

  • References

  • Communication

  • Organisation

  • Insurance

  • The proposed programme

  • The level of finish

  • The builder’s understanding of the drawings
     

It may be worth waiting for the right contractor rather than rushing into an appointment.
 

What Other Professionals May Be Needed?


An extension builder is only one part of the project.
 

Depending on the work, you may also need:
 

  • Architectural design support

  • Planning advice

  • Building Regulations drawings

  • Structural calculations

  • Building Control input

  • Party Wall advice

  • Drainage investigations

  • Asbestos surveys

  • Glazing suppliers

  • Kitchen specialists

  • Project management

  • Other trades and specialist services
     

A coordinated approach can help prevent gaps between the design, approvals and construction work.

 

Find Suitable Extension Builders


Finding the right builder starts with a clear understanding of the project.
 

The more developed the drawings and specification, the easier it becomes to obtain realistic quotations and compare them properly.
 

Tell us a little about your property, the extension you are considering and the stage you have reached.
 

Whether you are planning a rear extension, side-return extension, wraparound extension or larger home-renovation project, we can help connect you with suitable extension professionals.

 

Tell Us About Your Extension


Use our enquiry form to tell us:
 

  • Where the property is located

  • What type of extension you are considering

  • Whether you already have drawings

  • Whether planning permission has been obtained

  • Whether you need design or technical support

  • When you hope to begin the work
     

The more information you provide, the easier it is to identify the right support for your project.

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