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Home extension building contracts 

All home extension works should have a written contract to protect both parties.  A contract is no more than a written agreement of what one party will be providing for an agreed remuneration or other compensation  agreement.  Fortunately, if your home extension designer or architect has done his job correctly, most of this written agreement will already be in place within the drawings and the specification manual.

Therefore do you need any extra contract documents?  Usually yes but only for the agreement of start and finish dates, method of interim payments, retention agreements, defects liability period, how variations are to be handled, how extra costs are to be calculated, reference to the tender documents priced on forming the basis of the contract, etc. plus signatures.

There are some pre formed contracts available to the general public from institutions such as The JCT.  The FMB also do a very good plain English contract.  Alternatively you can simply state all the missing items referred to above within a simple letter that is signed by both parties.

Each party should be issued with a dual signed set of ALL the contract documents being the basis of any resolution or dispute. Never allow the main signed contract documents to be used on site as they will get damaged and lost.  Supply your builder with at least 3 sets of all the drawings and specifications for his own use on site and back at the office.

The Agreement for Minor Building Works (MW98) is the most widely used form of building contract for home extensions.

It is generally suitable for home extension building work up to a value of £100,000.

The contract should only be used between a building contractor and a client who has engaged a home extension designer or architect to provide contract administration duties during the build.

The contract is around 28 pages and includes the articles of agreement, conditions, supplemental conditions and guidance note. Although it is a relatively small document, all the main terms of the contract are included.

This form of contract can be used when the client, through his adviser, has prepared either

  • Drawings
  • Drawings and specification
  • Drawings and schedules
  • Drawings specifications and schedules

One of these and the contract form the contract documents.

The main conditions of this contact covers

Commencement and completion

  • Commencement and completion
  • Extension of time
  • Damages for non-completion
  • Practical completion
  • Defect liability

Control of the Works

  • Assignment
  • Sub-contracting
  • Contractor's representative
  • Exclusion from the works
  • Architect's/Contract Administrator's instructions
  • Variations
  • Provisional sums


  • Progress payments and retention
  • Penultimate certificate
  • Notices and amounts to be paid and deductions
  • Final certificate
  • Contribution, levy and tax charges
  • Fixed price
  • Right of suspension by contractor

Injury, damage and insurance

  • Injury to or death of persons
  • Injury or damage to property
  • Insurance of the works by Contractor - Fire etc
  • Insurance of the works and any existing structures by Employer


  • Notices
  • Determination by Employer
  • Determination by Contractor

These are some of the conditions within the contract. You need to know of their existence but not necessarily how they operate, all are administrated by the contract administrator, he/she will also be able to advise and explain your obligations under the contract and discuss what if scenarios'.

Your main obligations under this contract are

  • Give procession of the site to the contractor
  • Not to interfere with the contractors access to the works
  • Pay the contractor for the work done
  • Take out or increase your Insurance if the works are to an existing building.

In 1999 the Joint Contract Tribunal (JCT) issued a new form of contact the Building Contract for a Home Owner considering domestic building works. This building contact is one of the simplest forms of contact available and is intended to be used when no home extension design agent or professional advisers are employed to supervise the works on site.

The contract basically asks a series of questions by leaving blank spaces to be filled out.

  • The names and addresses of the customer and the contractor
  • The description of the work to be done
  • What statutory approvals the customer will obtain
  • What facilities the contractor is permitted to use on site free of charge
  • The price
  • Stage payments
  • How long the work will last
  • Contractors insurances
  • What hours the contractor can carry out work
  • Whether the premises will be occupied during the contract period
  • How disputes our handled.

This simplest form of building contract sets out the minimum requirements. By answering the above questions it covers all the main areas where disputes between homeowners and contractors arise. It also forms the basis of any dispute between the home owner and contractor and often avoids the need for costly lawsuits.

Anybody considering undertaking minor improvement works to their properties is well advised to have some form of written contract with the contractor. This form of contract sets out clearly all the important information required in plain English.


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