How to commission and build a basement extension or conversion under your Putney home, which professionals you need and the likely cost.
Converting or Extending your Cellar in Putney Because they usually involve structural work to your property such as underpinning foundations and waterproofing/tanking below ground, basement conversions and extensions are often a more expensive way to increase the space inside your home, but often the only way to do so within the constraints of a limited urban plot. This method of increasing the usable square footage is not as cheap or profitable way to increase the value of your house as a simple loft conversion, but being below ground makes for a terrifically private and sound-proofed space, often favoured for cinema rooms, gyms and music rooms. Creating the underground “man cave” is also popular with clients wanting a subterranean games room for entertaining too.
Putney Basement Costs
While a basement is not as fast to complete as a roof or rear extension, the higher cost still tends to make for a good return on investment in the expensive Putney property market. Creating a new basement storey also avoids the main issue of a typical side or rear extension, because you don’t lose any of your precious outdoor space, which is often already limited in a London house. As a rule of thumb, the overall cost of a basement conversion in this part of the capital will range from £150,000 for the more simple, to over £400,000 for larger schemes or those with a more high-end finish. A very small and simple conversion done yourself can be achieved for as little as £100,000 depending on how much of the work you feel competent enough to undertake yourself, but it’s not recommended to undertake specialist work like underpinning unless you’ve done it professionally before. At AC Architects we are often asked to price the whole project after obtaining planning permission, and we have a little black book of the most reliable local groundworks specialists, so we can help you get quotes from contractors who we have experience of doing a great job.
Putney Basement Extension Regulations
The easiest and fastest way to create a room underneath your house is to stay within the Permitted Development rules for a basement conversion, which essentially ensures the building keeps the same external appearance and does not exceed the original footprint, but it’s likely you’ll want to go a little beyond this, in order to create lightwells to get daylight into your basement. Lowering the garden at the rear of the house can often allow in light without needing to request much trickier planning to alter the house from the front/road side.
There are lots of other detailed restrictions and permitted development may also not apply to homes in a conservation area, so most property owners work through the planning process with an architect familiar with the rules and local interpretation of them.
Do I need a Certificate of Lawfulness for a Putney Basement?
While it is usually not essential to obtain a COL, you may find it hard to later sell your property without one, as this little piece of paper proves that the work on your property is lawful and in keeping with building regulations.
How Long does a Basement Extension take?
A standard basement conversion will usually take between 3 and 6 months to complete, depending on the design and finishes you choose. A simple tanking of an existing basement will be much quicker, but it’s not very common to find your old basement floor is low enough for decent standing height, so a little underpinning and excavation is almost always required, to avoid making a cheap but ultimately unusable space.
What is the minimum height for a basement conversion?
There are many opinions on this, but most specialists will consider the minimum viable height (from the finished basement floor to its ceiling) to be at least 2.2 metres. We often recommend at least 2.4m and most clients want a minimum of 2.6m but we work with you to be sure the space works for your intended use.
What does an architect cost to design a basement conversion?
While this will always depend on the scale of your project, a general rule of thumb would be to budget between £3,000 and £6,000 for an architect to design for you. Additional costs might include the planning application (if one is needed) and the creation of a builder’s plan and putting your project out to tender. Doing this process with a local architect vastly improves your chances of finding contractors that are good value, reliable and produce a high standard of work, because the local architect has much more experience of which are the good and which the not so good to work with in your area.
Can my Basement be classed as a Bedroom in Putney?
The short answer is yes, but only if the conversion is done in compliance with building regulations. A simple basement conversion has more simple rules, and your architect will advise you on the extra specifications needed, including daylight, insulation, head height and fire safety, if you want to be able to increase the official number of bedrooms listed in the estate agent’s window. If you want the property to be valued with the extra space as bedroom(s) the conversion needs to be signed off fully regulation compliant as such. The extra property value created by having more bedrooms tends to mean the extra cost of meeting the stricter regulations, but is often well worth it.