What Should Be in Your Extension Building Contract? A Scottish Homeowner's Guide

Most disputes on house extensions do not start with bad workmanship. They start with a misunderstanding. The homeowner thought the price included the kitchen flooring; the builder thought it did not. The homeowner expected to pay at the end; the builder expected payments every fortnight. Nobody wrote down what happened if the job ran late.

A clear written contract is how you avoid that. It protects you, and it protects the builder. This guide sets out what a good extension contract in Scotland should cover. It is not legal advice; for that, speak to a solicitor.

Why a proper contract matters

A quote on its own is not a contract. Nor is a message thread. For a job the size of an extension, you want a written agreement that both sides sign before work starts.

In Scotland, the Scottish Building Contract Committee (SBCC) publishes standard forms of building contract, including forms intended for homeowners and occupiers. Many architects use these, or similar, on domestic projects. Standard forms are useful because they are balanced, tested, and cover the things people forget. Whatever form you use, the key contents are similar.

1. Who is who

The homeowner, often called the employer or client.
The builder, the contractor.
The architect or contract administrator, if there is one.
The site address.

2. What is being built: the scope

This is the most important part. The contract should refer to:

The drawings, with revision numbers.
The specification.
The builder's quote or tender, and any schedule of works.
Any exclusions, clearly listed.

Common grey areas to be clear about:

Kitchen, flooring and decoration: in or out?
Electrics and plumbing: to what extent?
Landscaping and making good outside.
Skips, scaffolding and welfare.
Building warrant fees, structural engineer fees and other professional costs.
Provisional sums, which are allowances for things not yet fully designed.

3. The price and how it is built up

Is it a fixed price for the defined scope, or are parts provisional, to be adjusted once the cost is known? Provisional sums and allowances are common for things like kitchens, sanitaryware or unknown ground conditions. The contract should make clear how those will be adjusted.

The price should state whether VAT is included.

4. How and when you pay

On extensions, payment is usually made in stages, often based on interim valuations of work completed, or on agreed milestones such as foundations, wallhead, roof on and first fix. The contract should set out:

How payments are calculated.
When they are due.
How long you have to pay.
What happens if a payment is disputed.
Any deposit, and what it covers.

Be wary of large upfront payments not linked to work or materials on site.

5. Variations

Changes happen on almost every project. The contract should explain:

Who can instruct a change.
That changes should be agreed in writing.
How the price of the change will be worked out.
How changes affect the programme.

6. Programme

Start date.
Expected completion date, or duration.
How delays are handled, including weather, late information and changes.
Whether there are any agreed consequences if the builder finishes late without good reason.

7. Retention

Some contracts allow the client to hold back a small percentage of each payment until completion and the end of the defects period. It is more common on larger projects, but some domestic contracts include it. If it is included, the contract should say how much and when it is released.

8. Defects and snagging

What happens at completion: a snagging inspection.
A defects period after completion, during which the builder returns to fix defects that appear.
How defects are reported and how quickly they are dealt with.

The end of a warrant job in Scotland also involves the completion certificate.

9. Insurance

The builder should hold appropriate insurance, including public liability and employer's liability. Works insurance, covering the extension and the existing house during the build, is important too. Check with your home insurer early: many policies need to be told about major building works.

10. Permissions and compliance

The contract should be clear about who is responsible for planning permission, the building warrant and the completion certificate process. In Scotland, a completion certificate submitted to building standards at the end of a warrant job is an important document, so make sure it is someone's job.

11. Health and safety

Under the Construction (Design and Management) Regulations, domestic clients have duties that usually pass to the contractor or designer. The contract can clarify who is taking on those duties.

12. Disputes

How disagreements will be resolved: discussion first, then adjudication, mediation, or another agreed route.

13. Ending the contract

What happens if either party needs to end the contract: insolvency, serious breach, or the job being suspended.

How we approach contracts

We put every job on a written contract before work starts, with the scope, price basis, payment stages and programme set out clearly. If your architect has a preferred standard form, we are comfortable working with it.

Before you sign for a house extension, line the quotes up on the same scope. How to compare extension quotes sets out what to check.

FAQ

Do I need a formal contract for a house extension? For a job of this size, a written, signed contract is strongly recommended. It sets expectations and protects both sides.

What is an SBCC contract? The Scottish Building Contract Committee publishes standard building contracts used in Scotland, including versions designed for homeowners. Your architect or solicitor can advise which suits.

Should I pay a deposit to my builder? Some builders ask for a deposit, often to secure materials or a slot in the programme. Make sure it is reasonable, recorded in the contract and linked to something specific.

Who is responsible for the building warrant? It varies. Often the architect applies for it, and the builder works to it. The contract should say who handles the completion certificate.

Can I change things once the contract is signed? Yes, through variations. Agree each change, its cost and effect on the programme in writing.