Your guide to building a home extension 

Your guide to building a home extension Cheslyn Building Contractors

Building an extension can seem somewhat daunting and there is a lot to consider to ensure a stress free, smooth build with the required outcome. As one of the most life changing home improvement projects you could take on, requiring extra care when planning, we have put this expert guide to building a home extension together to help you through every step of the way. Getting the extra space you need could be simpler than you think with the correct advice and all bases covered….

Planning permission 

Whether or not you need planning permission for your extension depends on how big it’s going to be, and where the extension will be situated. For example, you shouldn’t need to submit an application for planning permission if you’re building a single-storey rear extension, providing it doesn’t extend beyond the rear wall of the original house by more than three metres (if your house is attached) or by four metres if you live in a detached house. No more than half the area of land around the original house can be covered by the extension either. If you live in a conservation area, you’ll need to talk to the planning department before undertaking any kind of extension and if you’re not sure whether your project will need permission or not, it’s a good idea to check with your local planning authority.

Building regulations 

Another important factor. All home extensions need to comply with the building regulations. Most obviously, this relates to structural stability – including foundations, window and door openings, lintels, beams and roof structures. Therefore, your design will normally need to incorporate a structural engineer’s calculations, submitted together with drawings as part of your building regulations application.

You need to ensure whoever carries out the work can either self-certify the work they do, or will liaise with the local Building Control Officers at your council to have their work certified and always remember that you’ll need evidence of building regulation approval for the work you’ve done when you come to sell your home in the future.

Neighbours permission 

Hopefully you will have a good relationship with your neighbours and are able to discuss your plans with them to ensure minimal disruption to all involved. If you require planning permission, the local authority will consult your neighbours as part of the process. If your neighbours object, the authority will determine the impact on them of your proposals and decide if it is acceptable or not.

Party wall act

The Party Wall act prevents building work by one neighbour that can undermine the structural integrity of shared walls or neighbouring properties. It is designed to avert and resolve potential disputes with neighbours before building work is started and the agreement grants the owner of a property the legal right to undertake certain works that might otherwise constitute trespass or nuisance. However, it also seeks to protect the interests of adjoining owners from any potentially adverse effects that such works might have by imposing a requirement that all adjoining owners be given prior notice of them.


If your insurer isn’t told about your plans, the original terms of your home insurance policy may be invalidated, so its imperative to inform them of any changes. Your premium may change when you add rooms and there is also the possibility of damage occurring when work is being done, so an up to date policy is a must. You should also check that any builder working on your property has professional indemnity insurance to cover the costs should something go wrong.

Architects role

Unless your project is very simple, it makes sense to at least talk to an architect for advice before you get going and how much or how little you commission an architect is up to you – from coming up with an initial design to seeing the project through to completion.

You will also need to create highly detailed technical drawings for your builder to follow and submit for building regulations approval and this involves mathematical calculations showing the structural integrity of your proposed extension.

Contact the professional bodies such as Royal Institution of Chartered Surveyors (RICS) or Chartered Institute of Architectural Technologists (CIAT), and always check that your architect has the relevant qualifications and professional indemnity insurance.

Choosing a builder 

You’ll need to find a good builder who can deliver the work on time and to budget. Personal recommendations are a good start, as you can also check the workmanship yourself, but always get several fixed-price quotations to compare. Check that your builder has the relevant insurances and professional certification and is happy for you to check their past work.


Ultimately, setting a budget for your home extension depends on how ambitious your plans are. The more ambitious the plans, the higher the cost. Before you accept a quote, make sure you are clear who is responsible for any additional costs. Know exactly what you are signing up for, so you can keep control of your budget. Whatever figure you come to, allow a 10-15 per cent contingency fund on top of your home extension budget for any unexpected surprises. 
For further information on a guide to building a home extension please contact us here.