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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 typical terraced house 'side return' extension
or a small single storey garden extension may bear a construction
cost of around £20,000.
The cost of the subsequent fit-out will be in addition to this basic
construction figure. The fit-out cost will be more variable and
depend on the preferences of the homeowner, for example, stone flooring
is likely to have a greater cost implication than timber alternatives.
As a guideline, this additional figure may be between £10,000
and £20,000 for a small single storey extension.
A slightly 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 you an indicative estimate
for the work.
To reach this planning stage, professional fees for your architect
will begin at £750 for a small extension.
Clients should agree with any extension designer exactly what services
are required and what is included in their professional
fees. Our planning fee includes pre-application discussions with
the local authority and submitting the planning application. Any
subsequent design revisions required by the authority are also included.
Our planning package generally excludes an initial measured survey
of your property, although your architect may also undertake this
if you require.
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.
To reach this detailed design stage, your architect will develop
drawings to a detailed level as required for the building control
authority's approval. Professional fees for this stage will be similar
to those incurred up until planning approval. As an approximation,
this may be an additional £750 for a small
extension.
From this stage, many clients choose a builder independantly, and
are prepared to oversee the construction process themselves. Alternatively,
your architect will 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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