Questions And Answers

George,
I am an architect with experience in private property alterations and extensions of both historic listed country manor houses to urban semi-detached properties. For the sake of argument, i will assume that the property is not listed or of historic significance which will complicate matters for you.
Options to consider ..... assuming a typical semi-detached Chiswick 2/3 storey edwardian property :-
(A) A typical side or rear ground floor extension will generally require planning permission, attract rights to light issues and be about £2,300/sqm (good quality fittings & finish).
( Loft extension of a typical interwar victorian or edwardian property should be relatively easy given that loft space heights can achieve 2.5m clear height for more than 50% of the intended floor area and typically cost upwards of £20k depending on size and complexity (dormer windows, planning issues etc.). Staircase to be extended to an additional floor level, loft floor to be strengthened, plumbing and drainage for an ensuite and usually a dormer window to the rear requiring planning permission.
(C) Basement extension / excavations have proved popular in London where property owners have been opting to stay put and having previously extended outward and upward, are now faced with digging down to create more space. If the property is terraced or semi-detached, it will involve a party wall agreement with neighbours (allow up to £5k) as excavations will likely involve underpinning of party & other walls foundations and possibly retaining walls to part of the rear garden if you wish to bring in natural light and rear garden access. Basement is the most expensive option and often fraught with unforseen issues such as complex services diversion, waterproofing/tanking etc.
My advice, subject to your requirements and in ascending order of costs, is to start with option (A) Ground Floor Rear Extension to provide additional living / garden room space, then (B)Loft conversion to gain an aditional bedroom(s) and en-suite. If you wish to create a formal entertaining/ drawing room space and extricate the kitchen from ground floor and to create an additional family room ... option (C)should be considered.

Greg Bell RIBA (gbell@frankennis.com)

regarding adding-value I suggest you seek the services an estate agent with local knowledge.

What is your budget? as this will determine which extension(s) will give the best return.

Richard Ellis www.ellisaa.eu

I'm thinking of around £150k, but not sure if this is enough. I guess it depends on the scale of the basement work?

George,
If you think it beneficial, I can take a look at the property at no expense or obligation to yourself. Generally speaking, a loft conversion and rear extension will create added value to your property greater than the sums spent. Basement improvements due to their added complications (noted above) will add value but the full benefits of daylit useable space are limited and the added value benefits are somewhat diluted as a result. I advise that you discuss the potential increase in value with a local estate agent familiar with the local area and the particular market demands. Without knowing the precise area of Chiswick, I cannot say precisely. I would say that in my experience, larger houses created in areas where mainly smaller properties exist are limited by a perceived glass ceiling in values in the area. There will be more benefit in added value created if larger properties exist in the location already. Basically if the market is there for larger, proportionally & carefully designed extended properties of a similar size, then you should not have too much to worry about. I suggest that you discuss with local Estate Agents such as Oliver Finn, Foxtons, Bernard Marcus, or Andrew Nunn.