Building an Extension in 12 Steps.

April 4, 2017

Building an extension is the best way (and more often than not, the most cost-effective way) to create extra living space. Unlike moving you do not pay stamp duty, nor do you have to fork out for selling fees. Also, your lifestyle (schooling, commuting times etc.) won’t be affected as you get to remain living in an area you are happy with.

That said, knocking walls, ordering materials, managing tradesmen, hiring skips, hiring tools, electrics, tiling, plumbing, carpentry, planning permission, permits, parking concerns… can seem like an endless and overwhelming task. However with careful planning and know-how, it is very doable and the end reward of self-satisfaction is enormous. Just ask anyone who’s ever built an extension!

Recently we got together with a local residential builder, a planning officer and quantity surveyor, and put together the following list to give you an idea of the process involved:

Note: for the purpose of giving you an idea of the scale and timeframe required, we have given a single story extension as an example. For a two-story extension, add three to five weeks. If living on-site, allow more time again!

Before you begin…

  • Ensure your skip hire company offers an ‘exchange and return’ service. This will allow you to arrange collection of your skip as required and receive a new one in exchange.
  • Ensure tradesmen will have access to water and electrics.
  • Schedule regular communication (be it in meetings or phone calls) with the builder/tradesmen to ensure you are up-to-date or in control of the management of the project.

Stage 1: foundation stage (weeks 1-2)

The digging of the foundation will commence. If you are project managing this yourself you will need to arrange for a digger to be on-site.

Stage 2: drainage, damp proofing, and pouring of concrete (weeks 3-4)

A drainage system and a damp proof course will be put in place.

Once drainage, and damp proofing is in place, sand and concrete will be poured.

You may need to order the materials for this stage yourself. Ask your builder what he requires for this and arrange for these to be available for day 1 of this stage.

Stage 3: external Walls (week 5)

External walls are built.

Stage 4: internal walls and order materials (week 6)

Internal walls are built.

Any materials required further down the line should be ordered by now, as these often require a three-five week lead time.


Stage 5: roof structure (week 6-7)

A carpenter or roofing specialist will put the roof structure together including any skylight window frame requirements.

Stage 6: roof completion (week 7)

The roof membrane is laid over the rafters, and roof battens are then cut accordingly and fitted over.

Stage 7: windows and doors (week 8)

The windows and doors are fitted.

Stage 8: first phase electrics and plumbing (week 9)

Electricians and plumbers often work together at this stage for maximum efficiency.

Stage 9: break through from existing house (week 10)

It is wise at this stage to pack away and close off as much as possible in the existing house, as things are about to get messy, and dust is a given!

Stage 10: plastering (week 11)

Ensure your plasterer has access to a water source.

Allow at least one week for the plaster to dry out before decorating.

Stage 11: second fit electrics and plumbing, and installation of flooring and carpentry (for e.g. kitchen units) (week 12)

This is the stage where delays are most likely to occur. It is best to have all tradesmen are working together at the same time, to avoid this happening.

Stage 12: snagging

Do a thorough inspection to identify any issues to be raised with the tradesmen for e.g. leaks or electrical problems.