Before you think about design, it helps to know what's realistic. We help homeowners across Milton Keynes and the surrounding area understand what their site can support, then turn that into a plan that works.
Permitted Development rights allow many single-storey rear extensions without a planning application, provided they stay within set limits on height, depth and proximity to boundaries. Some side extensions can also fall within Permitted Development, but the limits are tighter and rights are restricted on designated land — wrap-around, larger or two-storey side extensions will normally require planning permission. Knowing which route applies before committing to detailed drawings avoids the two most common ways extensions go wrong.
Long description. Starting from an existing house, a rear extension is proposed. If the proposal appears to comply with all relevant Permitted Development limitations and conditions, it may proceed under Permitted Development rights, and the owner may apply for a Lawful Development Certificate, known as an LDC, to obtain formal confirmation of lawfulness from the local authority. If the proposal falls outside those limits, a full planning application will normally be required instead.
Every property is different, so the first step is understanding the constraints.
Rather than starting with detailed drawings, we begin with a feasibility review — establishing what the site can support, what planning route applies, and where structural or Building Regulations issues are likely to arise. Design and technical coordination happen alongside each other, not one after the other, so nothing discovered late forces a redesign.
Once feasibility is established, here's exactly what happens next.
Understanding your objectives, the site and any known constraints before discussing the most appropriate route forward.
Typically 1–2 weeks — establishing what the site can support and which planning route applies before any detailed drawings begin.
Initial ideas are refined into a coordinated proposal that responds to the site, planning requirements and your brief.
Permitted Development, or a full planning application normally subject to an eight-week statutory determination period from validation for non-major development.
Building Regulations drawings and structural coordination, prepared so construction can proceed with confidence.
Where required, we continue supporting the project during construction, helping resolve design queries as they arise.
With the process clear, here are the questions we're asked most often.
Not always. Many single-storey rear extensions, and some side extensions, fall under Permitted Development, provided they stay within set limits on height, depth and boundary proximity. Anything larger, or on designated land, usually needs a full planning application, which local authorities normally aim to determine within eight weeks of validation for non-major development. We check which route applies to your specific project before you commit to detailed drawings.
Permitted Development is a set of national rules that let certain extensions go ahead without a planning application, provided they meet fixed size and position limits. Planning permission is a full application assessed by your local authority against its own policies — used when a project falls outside those limits, or in some conservation areas and for listed buildings.
Yes — Building Regulations apply to almost every house extension, regardless of whether planning permission was needed. They cover structural safety, insulation, fire safety, ventilation and drainage. We prepare Building Regulations drawings alongside the design work, rather than as an afterthought, so structural decisions are coordinated from the start.
Depending on the proposed work, you may need to serve notice under the Party Wall etc. Act 1996 — for example where work affects a party structure, involves building on the boundary line, or includes excavation close to a neighbouring building. We flag this early in the process so it doesn't become a late surprise; a specialist party wall surveyor can then confirm the formal requirements and next steps.
Yes. Most extensions need a structural engineer, and larger or more complex ones may need other consultants too. We coordinate this alongside the design and Building Regulations work, so decisions are made together rather than discovered as conflicts later in the process.
If a project like this looks familiar, here's what it can look like once it's built.
Site survey work is complete and we're currently assessing feasibility for a side extension, alongside the potential for a new-build replacement, before committing to a design direction.
See our current work
Project details will be published once the work reaches a suitable stage and client approval allows it.
Every one of these started with the same feasibility-first conversation.
A feasibility review is the fastest way to know what your site can support, before you commit to anything else.
Feasibility reviews are focused on understanding your site and identifying the most realistic route forward.
