House extension   UK
 Home extension guide - how to build a house extension and refurbish your home


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Contract Obligations between the Home Extension Builder and Yourself.

What to expect from your builder during the house extension works

1 - Pre-arranged access.

2 - Timely requests for instructions and decisions for items or works yet to be agreed.

3 - Advanced warning of interruption of house services (gas, water, telephone and electrics).

4 - Pro-active & timely management.

5 - Use of properly trained and skilled trades.

6 - Ensuring a safe and secure site during the works.

7 - Clearing up mess and keep the site tidy during each and every day.

8 - Ensuring quality control at all levels and stages of the works.

9 - Maintaining adequate insurance during the works.

10 - Sticking to the specifications. Any deviations or alternative materials are to be pre-agreed before ordering or installation.

11 - Making good all damaged structures or surfaces.

12 - Paying his trades and any other fees when required.

13 - Working during agreed hours of the day and times of the week. Any work outside normal hours is to be pre-agreed with the home owner.

14 - Maintaining Health and safety of the site, occupants and employees.

15 - Advising the home owner of any delays or slippage of the programme.

16 - Ensuring that the works are being inspected by the Building Inspector and at the relevant stages.

17 - Keeping dust and mess down to a minimum.  Sealing of the working areas from the remaining living areas of the house.

18 - Has the house extension builder complied with the Party Wall Act conditions.

What the home owner should be doing during the home extension works on site

1 - Allow builder access - you could be held liable for delays if you do not.

2 - Monitoring the works - are you getting what you expected.

3 - Arrange funding and access to monies for payments to the builder within 7 days of invoice or costing schedule being submitted.

4 - Keeping records of men on site per day and any inclement weather causing delays.

5 - Checking any interim payment requests for fairness & works completed to date.

6 - Contact your Building Designer / Agent if you have any worries or concerns.

7 - Check that the works are being inspected and approved by the Site Visiting Building Inspector.

8 - Providing information to your home extension builder when required and without delay (selection of kitchen units, bathroom equipment etc.)

9 - Try to only liaise with the main contractor or the dedicated site agent.  Do not instruct trades directly without the main contractor knowing.

10 - Do not be afraid to ask any questions.  Do not be afraid to obtain a second opinion from your Building Designer.

11 - Do not pay any upfront monies for normal works.  Some high priced materials may require a deposit for the order to be accepted - ensure that the deposit reaches the required person by paying direct if required.

12 - Obtain receipts for all payments made.

13 - Always try to resolve any disputes pragmatically.  Sometimes builders have very real practical issues to deal with that you may not understand or appreciate.

14 - Ensure that you have complied with the Party Wall Act and obtained the required neighbour approvals or awards before starting on site.

What is a reasonable contract period for the house extension works?

As a guide, 12 weeks would be reasonable period for a medium two storey extension with minimal internal alterations. However, it will still take 4 weeks later for the builders to finally leave. Whatever the builder states, allow at least 4 weeks longer.

How to value interim payment requests form your home extension builder that they are fair and reasonable

It is not always easy for the homeowner to establish the true cost of works completed to date for a home extension scheme by the builder. In the real world every builder would love to use your money to build the extension rather than committing their own funds first so it is not unusual for the builders to load the value of the first few draws for money on the job. If you have pre-agreed stage payments with your builder then this is irrelevant as that is now part of the contract terms.

Twice weekly draws based on estimated works & materials on site to date can be a little harder to evaluate. One good method is for the builder to prepare a breakdown of the works into the various work elements (at least 40 items) & place a financial figure alongside before the works start on site. This should then make it easy to identify the areas completed ready for payment on a simply tally sheet.

What is practical completion

This is when the majority of the works have been completed that allows the client to use or move in to. There may still be some minor works outstanding but it would be unfair to delay formal acceptance of this practical completion date due to minor issues. Practical completion sets the time period for the releasing of the final 2.5% retention monies & any subsequent warranty periods.

Is my home extension project a ‘notifiable’ project under the Health and Safety CDM regulations?

Most domestic house extensions are outside of the formal CDM health and safety regulations where you would have to employ a dedicated Health & Safety person to manage & maintain the sites Health and safety file during the works.

However, there are some catches. The regulations where originally introduced in 1994, under the ‘Health and Safety at Work act’. The current version revised in 2007. The requirements will also apply if you are developing a residential property, not for you own use, but for instance, to sell on, or rent out.

The CDM regulations will require you to appoint a consultant, whose duty it is to coordinate Health and Safety issues. The duty holder is referred to as the ‘CDM coordinator’, formally known as the ‘Planning supervisor’. However, the full force of the regulations, only apply if the development is above a certain size, defined as being, work that lasts for more than 30 days, or involves more than 500 person days of construction work.

The CDM regulations introduced a major change in responsibilities, in that it placed responsibilities on the client for Health and Safety issues, hitherto the preserve of the contractor, in addition to the appointment, and hence cost, of an additional duty holder, the CDM co-ordinator. The principle duties placed on the client are:

•     To check competence and resources of all appointees.

•     To ensure there are suitable management arrangements for the project welfare facilities.

•     To allow sufficient time and resources for all stages.

•     To provide pre-construction information to designers and contractors.

•     To appoint a CDM co-ordinator.

•     To appoint a principal contractor. Typically this would be the main contractor. In any event, the contractor who is responsible for Health and Safety on site.

•     To provide any information he is aware of, that relates to Health and Safety, to the CDM coordinator .

•     To retain the Health and Safety file in his possession, and allow access to it by those concerned.

Where the project is below the size defined above, there is no requirement to notify the ‘Health and Safely Executive’ and the appointment of a CDM coordinator is not required, however, the first three duties in the above list, should still be complied with. Further information regarding the ‘CDM regulations’ can be found on the web site of the ‘Health and Safety Executive.’

What is a Prime Cost sum (PC sum)

"PC Sums" are initially given value estimates by the client (or whoever is drawing up the tender documents) and their values are usually included within the tender pricing.  This would normally be to cover items to be supplied/fitted by a Nominated Sub-contractor - i.e. a supplier that the client insists on using and whose goods or services must be used by the main contractor. The logic being that whoever wins the tender process will have to use the same supplier at the same cost so it can't be a differentiation factor in the bids.

The values used are usually estimated and should be near the actual cost of the item or service required. The actual cost values are simply slotted in when they are known as the build progresses with any adjustments made to the final contract price.

An additional percentage figure is usually added by the main contractor to cover the administration. This should be the subject of a clause in the contract. Whether the PC Sum covers fitting or only supply should be stated in the tender documents drawn up by the client or his appointed Building Design Agent. 

What is a provisional sum (also called contingency sum).

A sum of money included in the contract and so designated for the implementation of extra works or the supply of extra goods, materials, plant or services, or for contingencies, which sum may be used in whole or in part, or not at all, as instructed by the client or their Supervisor.  This sum for home extension work usually allows for unforeseen items (deeper foundations, an extra steel beam etc.)































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