Look Carefully at Exclusions

Exclusions are just as important as inclusions.
 

Some quotations contain a clear list of excluded work. Others are vague and leave the homeowner to discover the gaps later.
 

Common exclusions include:
 

• Planning and professional fees

• Building Control fees

• Structural engineering fees

• Party Wall surveyor fees

• Kitchen units and appliances

• Bathroom fittings

• Worktops

• Specialist glazing

• Rooflights

• Floor finishes

• Decorating

• Landscaping

• External paving

• Drainage diversions

• Utility-company charges

• Asbestos removal

• Making good outside the immediate work area

• VAT
   

Ask each builder to identify exclusions clearly.
 

Do not assume that an item is included merely because it seems obvious.

 

Understand Provisional Sums

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

For example, a builder may not know the exact depth of the foundations until excavation begins. The condition and route of existing drains may also be unclear before the ground is opened.
 

A quotation may therefore include provisional sums for:
 

• Foundation depth

• Drainage alterations

• Structural steelwork awaiting final calculations

• Electrical work

• Plumbing alterations

• Kitchen installation

• Sanitary fittings

• Floor finishes

• Landscaping

• Making good hidden areas
   

Provisional sums are not necessarily a warning sign. Some uncertainty is unavoidable, particularly when extending an older house.
 

However, they should be realistic and clearly identified.
 

A low provisional allowance may make a quotation appear attractive initially, only for the final cost to rise significantly later.

 

Check Whether VAT Is Included

Always establish whether VAT has been included in the total.
 

A quotation of £80,000 plus VAT is not an £80,000 project.
 

Where VAT applies at the standard rate, the difference is substantial.
 

Some builders show VAT separately. Others include it in the final figure. A small contractor may not be VAT registered.
 

Before comparing quotations, make sure you are comparing like with like.

 

Ask About Structural Steelwork

Structural steelwork can represent a significant cost in an extension project.
 

The quotation should explain whether the builder has included:
 

• The supply of steel beams

• Fabrication

• Delivery

• Lifting and installation

• Padstones

• Connections and plates

• Temporary supports

• Making good

• Any specialist equipment required on site
   

If the structural engineer’s calculations are not yet available, the builder may only be able to include an allowance.
 

This should be reviewed when the final structural information is issued.

 

Ask About Foundations and Ground Conditions

Standard quotations often assume a particular foundation depth.
 

However, the required depth may change because of:
 

• Trees

• Clay soil

• Previous structures

• Made ground

• Nearby drains

• Local ground conditions

• Building Control requirements

• Unexpected obstructions
   

Ask what foundation depth the builder has allowed for and what rate will apply if deeper excavation is required.
 

This is particularly important where there are mature trees near the proposed extension.

 

Check the Drainage Allowance

Drainage is a common source of additional cost.
 

Ask whether the quotation includes:
 

• Moving existing inspection chambers

• Diverting drains

• New underground pipework

• Rainwater drainage

• New gullies

• Connections for kitchens, utility rooms and WCs

• Building over or close to existing drains

• Making good patios and external surfaces
   

Where the drainage arrangement is uncertain, the builder should state the assumptions used when preparing the quotation.

 

Be Clear About Kitchens, Bathrooms and Finishes

A new kitchen-diner extension may look complete on the drawings, but the quotation may not include the kitchen itself.
 

Similarly, a new downstairs WC or shower room may appear on plan while the sanitary fittings, tiles and finishes remain excluded.
 

Clarify whether the quotation includes:
 

• Kitchen units

• Kitchen installation

• Appliances

• Worktops

• Splashbacks

• Sanitary fittings

• Tiling

• Flooring

• Light fittings

• Decoration

• Bespoke joinery

• Underfloor heating

• Radiators
   

Where products have not yet been chosen, ask for realistic allowances.

 

Check Windows, Doors and Rooflights

Large glazed doors, rooflights and roof lanterns can make a major difference to the cost of an extension.
 

Establish whether the price includes:
 

• Supply and installation

• The frame material

• Double or triple glazing

• Opening configurations

• Threshold details

• Internal and external finishes

• Trickle vents where required

• Safety glazing

• Rooflight flashings

• Any electrical controls

• Manufacturer warranties
   

A basic allowance for standard doors will not cover a premium sliding-door or bifold-door system.

 

Compare Payment Terms

The quotation should explain when payments are expected.
 

Avoid arrangements where a large proportion of the total cost is requested before meaningful work has begun.
 

For an extension project, payments are commonly linked to progress stages, such as:
 

• Initial deposit

• Completion of groundworks

• Walls raised to roof level

• Roof completed and watertight

• First-fix plumbing and electrics

• Plastering completed

• Second-fix work

• Practical completion

• Final snagging
   

The precise arrangement will depend on the project and the builder.
 

The main principle is that payments should reflect progress on site and be agreed clearly before construction begins.

 

Ask How Variations Will Be Handled

Even with good drawings, changes may arise during the work.
 

You may decide to upgrade the glazing, alter the kitchen layout or add extra electrical points. Unexpected site conditions may also require additional work.
 

Ask the builder how variations will be managed.
 

Ideally:
 

• Additional work should be described clearly

• The cost should be agreed before the work proceeds where possible

• Any impact on the programme should be recorded

• Changes should be confirmed in writing
   

This helps prevent informal decisions on site from becoming expensive surprises later.

 

Look Beyond the Price

A builder is not automatically the right choice simply because the quotation is the lowest.
 

Consider:
 

• Relevant experience with similar extensions

• The quality and detail of the quotation

• References from previous clients

• Examples of completed projects

• Insurance

• Communication

• Availability

• The proposed programme

• The people who will be working on site

• Whether subcontractors will be used

• How problems and changes will be managed

• Whether the builder appears organised and realistic
   

A detailed quotation can be a useful indication of how the builder approaches the project.
 

If the paperwork is vague, rushed or difficult to understand before construction begins, communication may not improve once the work is underway.

 

Be Cautious With an Exceptionally Low Price

There may be a genuine reason why one builder is cheaper than the others.
 

A smaller firm may have lower overheads. A builder may have a gap in the programme. The quotation may reflect an efficient approach to the work.
 

However, a price that is dramatically lower than the others should be checked carefully.
 

Ask whether anything has been omitted.
 

A very low price may result from:
 

• Missing items

• Unrealistic allowances

• A misunderstanding of the drawings

• VAT being excluded

• A shell-only quotation

• An intention to charge extras later

• Insufficient consideration of structural work

• Limited experience with similar projects
   

The aim is not to choose the most expensive builder.
 

It is to understand why the prices differ.

 

Put the Agreement in Writing

Once you have selected a builder, make sure the agreed scope, price and payment terms are confirmed in writing.
 

For a substantial extension, a written building contract is strongly advisable.
 

The contract should address:
 

• The agreed drawings and specification

• The contract price

• Start and completion dates

• Payment stages

• Variations

• Provisional sums

• Responsibilities for materials and approvals

• Insurance

• Delays

• Defects and snagging

• Dispute resolution

• Termination arrangements
   

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

 

Compare Value, Not Just Price

The best builder quotation is not necessarily the cheapest and it is not automatically the most expensive.
 

The strongest quotation is usually the one that prices the project clearly, identifies the uncertainties honestly and gives you confidence that the builder understands the work.
 

Before making a decision, compare the drawings, specification, inclusions, exclusions, provisional sums, VAT position and payment terms carefully.
 

A little extra time spent reviewing quotations at the beginning can help prevent substantial costs and disputes later.

 

Find Suitable Extension Professionals

Planning an extension involves more than choosing a builder.
 

Depending on the project, you may also need architectural design support, Building Regulations drawings, structural calculations, Building Control input, Party Wall advice and specialist suppliers.
 

Tell us a little about your extension and the stage you have reached. We can help connect you with suitable professionals for the next steps.