builder | Miller Architect

What is the best way to have a fitted kitchen designed, supplied and installed as part of a house extension or refurbishment project? I am often asked this as there are various approaches.

Island kitchen, Dormans Park, nr East Grinstead Underwood Kitchens

One approach is to have the fitted kitchen fully designed and specified by the architect and installed by the builder as part of the contract works. This involves the architect specifying all of the components including the base and wall units, countertops, splashbacks, sinks, taps and equipment. Both the architect and the builder are paid for their services with regard to the kitchen.

Another approach is for the client to purchase the kitchen components outside the contract (either designed and specified by the architect or by a specialist) and provide them ‘free issue’ to the contractor who installs the kitchen as part of the contract works.

L-shaped kitchen, Forest Row Homebase KitchensHomebase Kitchens

Yet another approach is to have the fitted kitchen designed, supplied and installed by a specialist outside the contract after the extension or refurbishment work is finished. This avoids paying either the architect or the builder for any services with regard to the kitchen but has the disadvantage of pushing back the date when the kitchen is operational.

I have evolved an intermediate approach whereby the standard form of building contract is amended with a clause added requiring the builder to permit access during the final weeks of the contract (it is his site so he can otherwise deny it) by a specialist directly engaged by the employer under a separate contract. Subject to negotiation this approach can allow the client to procure a specialist kitchen design, supply and install ‘package’. The builder provides a ‘serviced shell’ for the kitchen (to suit the specialist’s design) comprising the finished floor, walls and ceiling plus capped-off services in the shape of hot and cold water supplies, waste, extract ventilation, gas, power and lighting. The specialist then installs the kitchen into this ‘serviced shell’. Finally the builder makes the final connections for the services and all fitted kitchen appliances and includes the kitchen in the project GasSafe and electrical certification.

Kitchen design is a personal thing for all clients in terms of the style and layout of the kitchen, the type and amount of equipment and the expense which can vary by up to a factor of ten. I think it is best for the architect to simply set the design parameters in terms of the location and general layout (such as an L-shape, galley, island, peninsula etc) and then allow the client to develop and finalise the design, supply and installation with a specialist.

How much does a house extension cost in London and the south east?

My analysis of actual costs for competitively tendered projects by reputable local building contractors in the south east within commuting distance of London suggests a current ‘ball park’ figure of £3,000/m2 for a single storey extension and a further £2,000/m2 where there is a second storey. These figures are based on a full fit-out to a reasonable standard of specification including bathrooms. They will go up if the project is located closer to central London and down if the project is further out. Tender prices have been rising steadily over the last few years. The tender price inflation forecast in this month’s Building Magazine is for a 5% increase over the coming year however builders that I have spoken to are suggesting that it will be more than this. House extensions attract VAT at 20% and a client contingency of say 10% is advisable.

Single storey extension at ‘Charwin’ under construction

Whilst m2 area costs are a good guide, design complexity and the level of specification can make a big difference. There are also project specific costs such as the cost of demolitions where required and the cost of other work within the existing house. The cost of the foundations can increase beyond the cost of the standard depth of one metre if the ground conditions are poor. External drainage costs can increase if extensive reconfiguration is required. If the design requires a structural steel frame rather than individual steel members this would be an extra as would the cost of a ground source heat pump installation with its associated ground loops and / or bore holes. The biggest single cost that is not included above is the cost of a new kitchen which can vary enormously. Several years ago I had two concurrent projects where the cost of the similarly sized kitchens differed by a factor of ten.

Two storey extension at ‘Fir Tree Cottage’ under construction

Architects provide ‘ball park’ estimates based on m2 rates but if cost ‘is of the essence’ a quantity surveyor or construction cost consultant / estimator can produce a more detailed estimate on an ‘elemental’ basis where every element of the project is costed. Typically for a project of this size clients opt to rely upon the architect’s estimate until the tenders are returned. At the end of the day it is the tender price at which a building contractor is willing to carry out the work that matters.

I am usually the starting point for a house extension project. The full architectural service is typically in three roughly equal parts which are concept design and developed design to Planning Application / technical design up to Building Regulations and tender / contract administration and construction to handover and close out. Partial services are available (eg just the first part or just the first two parts). I normally provide the ‘principal designer’ role as part of the architectural service. During the technical design stage the core team typically comprises a structural engineer to provide calculations for Building Regulations purposes, an underground drainage engineer to carry out the design for the underground drainage and an energy assessor to demonstrate energy efficiency in compliance with the Building Regulations. Consultant fees for this core team will typically be around 13% of the building cost. There will also be local authority fees for Planning (where required) and Building Regulations.

A house extension can be a viable alternative to moving house as it avoids the disruption and the cost of moving, stamp duty, legal and estate agents fees etc. On top of the desire for extra living space and bedrooms, information technology is driving a move towards living and working from home with the demand for additional space for a home office. As well as this the process, if handled properly, can be very rewarding.