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Engaging Your Local House Extension Builder - Advice Guide

When you have found your local builder there will be a lot more detail yet to resolve before you can formally engage their services.  Here are a few areas that you should be discussing.


There are various forms of contracts available to the building owner including forms from JCT and the Federation of Master Builders. The latter offer a very simple and straightforward contract that would be suitable for most extension works.

Some building owners rely on an exchange of letters agreeing to start and completion dates, payment terms, liquidated damages etc. based upon the information shown on the drawings and specifications supplied by your Professional Agent. This is also a suitable method of contract provided your Agents Plans are concise in most areas and you are reasonably satisfied with your selected builder.


These are normally agreed within the contract used and by mutual agreement. However a few golden rules to observe are:- Never pay in advance of the works, always pay for work done and try and withhold a small retention (say 5%) as a sum on trust to ensure that any defects will be put right by the builder within 6 months of completion. For works longer than say 2 weeks it is customary and fair to agree to stage payments either agreed in advance or costed on site as work proceeds.


Always telephone the builders first to check their availability and to see that they are interested in tendering for the described works. Many builders in very busy times tend to ‘cherry pick’ the work but will not want to formally refuse the project for fear of not being offered other work in the future so they tend to ‘forget to price’ leaving you waiting in limbo for several weeks. Always make sure that they personally visit site and discuss things through prior to submitting a price. Give them a defined tender return date of say 3 weeks. and be prepared to chase them 5 weeks later.

Most builders are very good at what they do but their administration procedures are sometimes lacking especially those working from home. Please remember that it takes a lot of work and effort for a builder to price a job correctly especially if he is obtaining prices from subcontractors such as plumbers and electricians etc. who often let the main contractor down.

Therefore, please respond to ALL BUILDERS quotations and DO NOT ignore the unsuccessful prices. The biggest complaint from builders is that they spend a lot of effort completing prices and some may have even paid for a quantity surveyor to hear nothing further from the building owner. It is customary and helpful to all unsuccessful tenders to advise them of the successful price so that they can see if their margins or profits are wide of the mark for any future work and this can only benefit building owners in the long run. You do not have to advise them of the successful builder.


This is usually a very big grey area that needs to be clarified before the builder starts on site. All builders should have Third Party Liability insurance of say 5 million pound and you are advised to check that they have a current policy. This insurance only covers third party claims eg if a scaffold tube falls into your next door neighbours green house or worse. Most good builders have additional insurances that cover the cost of the contract in hand.

There are also ‘ALL RISKS’ policies to cover the entire site value and not just the contract but these are often very expensive and need to be made out in joint names between the building owner and the builder. You should try and establish that he has adequate cover, if required, and that he only employs bonafide sub-contractors having their own insurance or, extensions to the builders insurance that allow for his sub-contractors.

You also have duties to advise your own buildings insurer that you are having building works completed and get them to confirm that you are still covered. Additional premiums may be required to gain insurance extensions for the works. Failure to inform them could lead to loss of a claim as building works are usually perceived to carry additional risks to a building that require notification to insurers - DO NOT fall into the ‘technical trap’ so often used these days by insurers as reasons not to pay a claim.



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