Building an Extension in London


By Ema Globyte on Feb 20 2018

Are you thinking about building an extension to create more space in your property, but have no idea where to begin? Don’t fret – we’re here to help you along the way. We know that there may be about a hundred questions you are dying to know the answers to. Therefore, we have provided answers to the ones we most frequently get asked by our clients – familiarising yourself with these is a good start.


Will I need an architect?

In simple terms, if you’re not an architect yourself, the answer would be yes. You are never legally required to hire an architect, so it is entirely up to you. However, hiring an architect is likely to guarantee a better quality of work (and give you a peace of mind). You can hire an architect to only do the plans, or to help you throughout the whole process, from planning permission approval through to project management. Choosing the right architect to draw up your plans is very important, why not speak to one our in-house architect for free advice and quote. See are our architecture services for more information or contact us directly.


Will I need a planning permission for building an extension?

As previously mentioned in our post about renovation without planning permission, there are cases where you can build an extension without permission, under Permitted Development Rights. However, there are several limitations to what you can do without planning permission, so your safest bet is to consult your Local Planning Authority. For more information about what you can and can’t do when building an extension without planning permission, take a look at this technical guidance for householders.

What is a neighbour consultation scheme?

You may have heard the term being used in discussions about home extensions. Neighbour consultation scheme is a method of pre-approval from your neighbours. After you notify your local authority about your plans to build an extension, the authority will contact your adjoining neighbours to let them know about your plans. If your neighbours raise any concerns or objections, the authority will decide whether they any impact on the amenity of the neighbouring properties, and whether you can still go ahead with building an extension. Bear in mind that the scheme only applies to larger single-storey rear extensions which are permitted until May 2019.


How long will it take?

While there are several aspects that can impact the overall timeline, you can expect to complete a small extension project within approximately 3 months. A larger extension, on the other hand, may take up to 6 months – or even longer than that.

What are the stages of building an extension?

For most home extension projects, there are likely to be about 11 stages (each stage takes about a week):

  • Preparation: ensuring clear access to site; ordering building materials; arranging a digger; ensuring the site is safe to work on.
  • Groundworks: digging the foundations and getting Building Control to approve them; laying reinforcements, pipework, drainage and services; pouring and levelling concrete footing; getting it approved by Building Control.
  • Superstructure: damp-proofing course to be built up; drains installed; trenches to be dug for pipework; concrete lintels to be inserted; sand to be laid before the damp-proofing membrane is put down; insulations; concrete slab for flooring poured; another inspection by Building Control.
  • External walls: creating blockwork and brickwork; cavity wall insulation to be fitted; wall ties to be inserted to fix the new walls to existing ones; lintels for windows and doors to be fitted; door and window frames to be inserted as the walls are built.
  • Internal walls: internal walls to be built; checking that the windows, doors and roof tiles have been ordered and carpenter, and that all materials are ready.
  • Roof structure: carpenter to start building the roof structure; rooflights and dormers to be created and fitted.
  • Roof covering: roof membrane laid over the new rafters; roof battens to be cut and fitted; tiles/ slates to be laid, ridge tiles and valley tiles to be laid (with finishing details); fascias, soffits and verges to be primed, stained and painted; floor screed to be laid.
  • Windows and doors: external rendering to be completed; windows and doors to be fitted into the frames; guttering and drainpipes fitted; first-fix carpentry, plumbing and electrics completed; studwork walls to be built with floor linings fitted and pipes boxes in.
  • Breaking through: sealing off the extension from the rest of the house, steels to be put in place.
  • Plastering: walls to be boarded with insulation; plastering to be done and must be left around a week before decorating.
  • Second-fix: second-fix electrics to be carried out (sockets, switches, lights); second-fix plumbing (taps, connections); flooring to be laid; kitchen units to be installed (if applicable).

What is a ‘snagging period’?

‘Snagging period’ refers to a process during which you identify unsatisfactory or outstanding work after your building project is complete. This may include identifying issues such as leaks, electrical problems or heating issues. If there are no unsatisfactory work, during the snagging period you’ll focus on the finishing touches, such as As with any project, there are several other things to think about to ensure a project runs smoothly – which is why we are here to help you through all stages of the project. Find more information about building an extension in London on our website or get in touch with us, and we will be happy to provide advice.