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House extension cost: a price guide for London
Although there is no precise formula for obtaining an accurate cost
for your extension (prior to obtaining a fixed quote for the project
from a builder), the following figures give indicative levels for
work in London: A creatively designed terraced house extension,
featuring large areas of glazing may bear a construction cost of
around £40,000.
The subsequent fit-out will be in addition to this construction
sum. This figure will be more variable and depend on the preferences
of the homeowner, for example, stone flooring will have a greater
cost implication than timber alternatives. As a guideline, the fit-out
cost may be between £10,000 and £20,000
for a small single storey extension.
A more accurate cost indication for your extension may be obtained
at the planning stage of your project. At this time, the outline
design is complete, and floor plans are ready to be submitted with
a planning application to the local authority. A builder will then
be able to give an indicative estimate for the
work.

It is important to note that any builder's estimates for the complete
build cost that you obtain at this stage can only be an indicative.
Builder's estimates can be revised until you have agreed a written
quote for the work.
An estimate may develop into a fixed quote for your extension when
detailed, post-planning architectural drawings have been produced
and a builder has visited the property to discuss your requirements
and survey the site conditions. This quote will form part of a contract
between the client and the builder that will be signed by both parties
before work begins on your extension.
From this stage, many clients choose a builder independantly, and
are prepared to oversee the construction process themselves. Alternatively,
your architect may produce a formal tender package to invite a number
of experienced builders to submit quotes for the project. Your architect
will also be able to provide a full site supervision service until
the project's completion if desired.
Once work has begun on site, payments are normally made to the builder
at monthly intervals.
It is wise to ensure that there is a contingency sum included in
any quote obtained with a builder. This sum will only be used to
pay for unforseen additional costs should they occur. On average,
around 5% of the quote is sufficient for a typical
extension. If the contingency was not required, it will be deducted
from the final bill once works are complete.
Please visit 'Our ideas'
to see Architecture for London's previous house extension plans,
or contact us to book an initial design
and planning consultation at your home today.
HOUSE / KITCHEN EXTENSIONS
BUILDING REGULATIONS
PLANNING 
INTERIOR DESIGN
LOFT / BASEMENT CONVERSIONS
ARCHITECT

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