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Side Extension Advice



Side extension advice is often hard to come by, if you’re about to embark on this adventure then read our handy tips to help guide you through the process…the good and the bad.


Currently in this uncertain market people are seemingly turning to extending their home rather than selling up and buying bigger. With this in mind it makes us think about the most cost effective way of maximizing our homes potential. For many, this is a side extension as a great number of homes have a traditional floor plan that looks like this.

What is a side extension?

If your home has this typical floor plan usually found within a period terrace or semi-detached house/apartment then often enough the kitchen plus a random bathroom or utility room are found in the rear outrigger/projection of the house creating a narrow kitchen and A-another room with a side alley that serves as your access to the rear garden. This side alley is often dark and thus a little damp and is not used for anything other than a walkway. This create a an L-Shape and is thus often known as the side extension or Side return if the extension projects out further than the existing rear wall.


Because the side alley is not used frequently we can utlise this area and build on the land to increase the internal floor area to the rear rooms increasing the living space to the full width of the existing house. The garden remains intact and you have the opportunity to transform the layout into a 21st century living style.


Handy tip – Take the value of your home (say £550,000), divide it by the existing floor are (say 120m2), (=£4,583 per m2), multiply it by the extension area (area of the side alley) (say 6m x 2m = 12m2) £55,000 would be the value you gain on your property without making changes to your kitchen or bathroom. This should serve as your budget for that element of the work without considering the inflation of property prices in that area.


What are the drawbacks and how can you offset them?

The simple side extension has a huge number of benefits but before you embark on that journey it is important to think about the potential negatives of doing this work along with how to cope with them. Firstly by completing a side extension you fill in the space between the middle room of the house (often the dining room/office room/random room that nobody knows what to do with) and the outside world (garden) so the ventilation and light is reduced. However all is not lost here, if you have enough glazing to the new extension and you change the existing window to a door then the light is still able to pour through into that middle room BUT it is still reduced compared to before!

The same principle applies if you use Velux windows, a flat roof and lantern/glazed roof light or other similar products. Additionally and we will touch on these later in the article, you can use your door/window choice at the new rear of the house to maximize the incoming light such as bifold doors, sliding doors, crittall doors and panels etc.. creating as much glazing as possible rather than a pair of patio doors and a window.


What planning permission do I need?

Many people don’t know that a side extension in this circumstance does not need planning permission on the most part, unless it is a flat or apartment or In a conservation area then Permitted Development rights apply and you can build it without going through the planning process. HOWEVER this does not mean that you don’t have to use an architect or not create drawings for the build. In our opinion it is worth every penny to commission an architect to carry out the drawing part of the extension process because they will guide the builder at every stage of the build and will provide you with a reference of what the works should look like once complete.


To qualify for PD the extension cannot extend past the rear of the house by three meters so a large Wraparound extension would not be included in this right, assuming it is an attached house. It is four meters for a detached house. (Please check with your local authority for up to date guidelines).


Side extensions and their permissions also have a limit on the height which is four meters unless they are within two meters of a boundary wall (a neighbour) then three meters is the max and they must not exceed more than half of the area of the land around the original house. Additionally the width cannot exceed half of the existing width of the house (so if the full width of the house is 6 meters then your max extension width would be 3m without planning permission).

Its important to note that other permissions are required even if you qualify for PD rights, for example you will need to notify your local authority of your intention to build as well as your neighbours, who need to accept your proposals. It is always worth consulting your architect before you proceed.


What other permissions do I need?

You will need and it is advised that you gain Building regulation approval which covers things like fire risk, drainage, electrics, external walls and roofs and how the extension is built by an external advisor who inspects the work throughout the process (they are independent of the builder so its wise to join the visit to see what he is instructing the building to do), to do this you can use the local authority or an approved private inspection service (often quicker but perhaps a little more expensive).


Many of the build process issues relating to building regulations will be dealt with during the application process when the inspector makes comments on the drawings completed by the designer or architect. This way you wont be delayed once you start the project however it is common for the building regulation inspector to ask for slight changes to the way the work is being done on site if they feel it is not up to standard. You will need to apply for a full plans application for building regulation before any of the works start, in your application you will need to include a full set of planning drawings or notification drawings if you are using PD rights, plus a set of construction drawings (in summary planning drawings are an outline version of what you are building with a few key labels highlighting what some materials are and construction drawings are much more detailed which show the floor level build up or wall sections etc..) the approver will then check your plans and provide a decision within five weeks.


The alternative to full plans for smaller building projects (a side extension is often included in this) is a Building Notice which is quicker and less detailed. Work can usually start within five days of the application but with this method comes the risk of ensuring the work is built in accordance with the regulations, if its not then you could be liable to make and pay for alterations later down then line. Notwithstanding that it could also be dangerous for anyone who lives in the property if certain regulations are not met by the builder.


If you have a main sewer (not a private drain) running through your garden then you will need a build over agreement from your local water provider e.g. Thames Water


What happens during the build?

Here is a brief list of how the works will progress throughout the build process along with an estimated duration;

How does the Party Wall Act affect my build?

The party wall agreement is a tricky one to navigate, you could end up spending a lot of money trying to gain permission to build your extension as the rules are a little unfair (commercially) to the person wanting to carry out the build.


Under the Party Wall Act, you must provide notice to your neighbour if you want to carry out any building work near or on the shared boundary (wall or land, The Party Wall). This must be communicated within two must to a year before the build actually starts. Your neighbour will then confirm, reject or question further the extent of the works and how they will affect their property.


Hopefully you can draw up a Party Structure notice (link here) and have your neighbours approve this and move forward with your build but if not here is where it can get expensive. Your neighbour is entitled to ask for a surveyor to be involved which you have to pay for and if they don’t feel comfortable with a joint surveyor they can ask for their own and again you have to pay for it.


Many of the problems arising out of party wall agreements are light pollution, noise (you didn’t used to hang out in your alley way but now you have a trendy kitchen it could get loud with a party wall) and structure (cracks in the walls on your neighbours side and who fixes them). In our many years of experience we have found that a good old fashioned amicable chat works the best, remember you have to live with your neighbours once you have finished the build!


Who’s involved in the work?


Inception– You are the start of the show here!


Design– Often a Designer or Architect, and more frequently now builders are becoming their own designers with a Design and Build banner attached to their name. From these you will need your planning drawings and your construction drawings (for the builder and for the Building regulation team).


Building Regulations– Your local authority or a private approved company.


Party wall notice– Again you can do this if your negotiation skills are up to the challenge or you can use a party wall surveyor (or two). (For apartments or multi level dwellings you will need an agreement for each party wall not just left or right, this includes up or down and diagonal).


Builder – We think tendering with six builders is appropriate and carry three forward to a final round of negotiating. Note – Make sure you go and see a project example (and hopefully speak to the client).


Interior Designer– Not always necessary but they do think differently to a builder and an architect and they can often provide that lacking finesse your project needs to be the dreamy build you anticipated.


Structural Engineer– Unless the builder provides their own (in the price) it is wise to get a SE round to see the proposed extension and to provide the necessary details for the builder to purchase the right type of steel, including how they are connected.


The star of the show?

For us the star of this show is the potential to fit a new kitchen to this amazing space, by opening up the full rear of the house you can add in a kitchen island and even a dining space (making that middle room even more difficult to furnish), our fave is a banquette seating area on the party wall, dining table, kitchen island with space for a bottle of plonk and a long run of kitchen units on the other side (no wall units but perhaps a shelf).




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