Rear and side extension to a ground floor flat by architecture practice ao-ft. Photo by Tim Crocker.
A well-planned extension can transform your home, but extending a flat is a little more complex than extending a house.
Flats don’t have permitted development rights, and you'll need to secure multiple approvals, including planning permission, freeholder consent, and other legal consents.
Without these approvals in place, selling your flat in the future could become problematic. Conveyancing solicitors will request documentation during the sale process, so it’s essential to get everything in order early.
In our guide below we cover the key steps and consents required to ensure a successful extension project.
Unlike houses, flats and maisonettes do not benefit from permitted development (PD) rights. This means that any extension will require full planning permission from your local planning authority (LPA).
In most cases, local planning policies are more restrictive than PD rules for houses, so expect your extension to be smaller than the maximum permitted under PD rules for other properties.
To increase your chances of approval, it’s important to familiarise yourself with your local policy. Your LPA may have specific guidance on residential alterations and extensions, outlining rules on the scale, materials and the design of extensions. Following this guidance will help streamline the process.
Garden flat extension interior by Hayhurst & Co. Photo by Kilian O' Sullivan.
If your flat is leasehold, you’ll need to gain formal consent from your freeholder before any work can begin. This usually comes in the form of a "Licence to Alter," which is a legal document detailing the scope of the proposed works and the conditions under which they can take place. The process can take several months, so it’s wise to allow extra time for negotiations and approval.
If your flat is part of a share of freehold, the process can sometimes be smoother as you’ll have more influence over the decision-making process. However, even in a share of freehold arrangement, you will still need to formalise consent through a Licence to Alter (or another formal agreement depending on your specific lease terms).
If your extension affects shared walls, ceilings, or floors, you’ll likely need to serve a Party Wall Notice at least two months before work starts. You may need to notify both the freeholder and leaseholders above your flat, as well as neighbouring property owners who could be affected.
Flats are particularly prone to remedial damage due to the shared structure of the building, especially when working on ceilings and walls between properties. To avoid disputes, it’s a good idea to conduct a condition survey of the neighbouring flats before starting work. That way, any new damage caused by the extension can be properly documented and repaired.
It's advisable to factor in a contingency budget for potential repairs as part of your overall project costs.
Ground floor flat extension by architecture practice Sonn.
You must comply with building regulations to ensure your flat extension meets safety and construction standards. This will require you to notify your local building control department or hire a certified private inspector.
While some home extensions can be built under a Building Notice, extending a flat typically requires Full Plans Approval. This involves submitting detailed drawings and specifications for review by building control before work begins. Full Plans Approval is often a condition for gaining consent from your freeholder as well, so it’s a necessary step.
You’ll need to appoint an architect and a structural engineer to prepare plans and structural calculations for both planning permission and building regulations approval. Their expertise will ensure that the design meets all safety requirements.
In addition to planning permission and building regulations approval, you may need other consents depending on your flat’s location and its specific characteristics.
Managing disruption is key when extending a flat. Depending on the scope of your project, you may need to alter or upgrade existing electrics and plumbing. Power or water may need to be temporarily switched off during certain stages of construction, so it’s important to inform your neighbours well in advance.
Additionally, flats tend to be more affected by noise and dust due to shared spaces and proximity to other residents. Keep communication open with your neighbours and try to minimise disruption as much as possible.
Garden flat rear extension and garden room by Nic Howett Architect. Photo by Henry Woide.
Appointing an architect for your ground floor flat extension can greatly simplify the process. Architects manage the complex planning, design, and approval stages, helping you navigate planning permission, freeholder consent, and building regulations while ensuring a practical and appealing design.
They'll also maximise your space, improving the layout and flow of your home. By liaising with all parties, they help prevent delays and complications.
A structural engineer will provide the necessary drawings and calculations to secure building regulations approval, offering reassurance to your freeholder and neighbours. For party wall matters, a party wall surveyor can manage agreements and handle disputes if any neighbours object to your plans.
By securing the right approvals and managing the process carefully, you can successfully extend your ground floor flat and enjoy the benefits of extra space and improved functionality.
The information provided in this article is intended for general guidance and educational purposes only. For specific expert advice on your project, consult a skilled residential architect featured on Designs in Detail.
About the Author
Aron Coates is an architect with over two decades of experience, working on projects ranging from historic building restoration to contemporary home design.
