How to: Do a side addition

How to: Do a side addition

A side addition can add useful space to the ground floor of a building. They are a staple of contemporary Victorian house refurbishments, where the unusable side passage is built over to add space to a kitchen. In this sort of development, the trend is to use glass or numerous windows to the roof above the side addition to allow natural light into the space.


A side addition is one of the most expensive ways to add space to your home. This is because the side passage to most Victorian terraced homes are typically only a meter wide so when building over these areas, there is a high proportion of wall relative to the floor area. The introduction of expensive glazed elements can also add to the cost.

In terms of budgeting for your side addition, as a general rule you should allow £4,500 per square meter of space, plus the cost of fittings.  

The aesthetics of a fully glazed side addition do usually justify its cost and most modern Victorian home developments benefit from this attractive design addition.


Though most houses benefit from permitted development rights, the typical side extension to a Victorian home will fall outside of these rights. Full planning permission is therefore usually required. 

In applying for planning you will need to appoint an Surveyor, Architect or Architectural Designer to draw up the existing plans of your entire home, as well as the proposed plans for the side addition. You should allow £1,000 to £2,000 for this service.


Side additions usually require extensive structural works and disturbance to the original dwelling. This all takes time, so allow 4 months for the building phase. Also, as your development is likely to require planning you should allow 3 months for this stage. In all, allow between 9 months to a year for the complete planning, procurement and build process.


The works will usually be taking place in your kitchen so unless you are able to set up a temporary facility in another part of the house, you will likely have to consider temporary accommodation. Also, if you are part of a terrace then bear in mind that the contractor will be moving all the materials for the build as well as spoil from the excavations through your front door. 


As you are likely to want your side addition to form part of the living space of your home you will need to form a large opening through your existing wall. This opening will be supported by a large 'goal post' structure with steel posts at the sides supporting a large steel beam overhead. A structural engineer will be required to design this element and you will have to appoint them in addition to your surveyor/designer. Their fees will typically fall within the £700 to £1250 bracket.


You may have noticed a metal cover in your side passage, or perhaps a large metal pipe running down the back of your property which then disappears into the ground at the start of your side alley. Both indicate the presence of a sewer running beneath your side passage. Your structural engineer will need to design the foundations of the side addition to span over this pipework and if this system is shared then you will need to apply for a 'build over' agreement to your local water authority. There is a charge for this and your designer will have to produce a drawing in support of the application. Allow £300 to £500 for this application.

The Party Wall etc. Act

As you will be building right up to the boundary, you are required to give notice to your neighbour under the Party Wall etc. Act. This will require the appointment of a surveyor and you may have to pay for an additional surveyor to act for your neighbour if they dissent. Try to keep your neighbour informed of the works you want to carry out and allay their fears at the start of the process. This should reduce the chance of them dissenting to your notice which could double the cost of the award. Allow £500 - £2000 for this process.


Rear additions are typically 30% cheaper than a side addition and more likely to fall under the permitted development rights to a house. They can typically be much deeper than a side addition, which is restricted by the width of the existing side passage. However, if the rear of your property is narrow, whilst increasing length, a rear addition may create a long 'passage-like' space which may not be as usable as a wider, smaller space. 


A side addition really does add something special to a Victorian refurbishment. Though only a meter in space may be added, this can be an extra 30% of the width of the existing space. The natural light that can also be gained from the roof lights of the side addition will brighten any Victorian kitchen and also add a further feeling of space to the enlarged room. 

You can also consider combining a side addition and a rear addition to form an L shaped conversion but that is a subject for another post...