A double storey extension is the most effective way to add serious living space to your home. By building over two floors, you gain bedrooms or bathrooms upstairs and a larger kitchen, dining area, or living room downstairs — all within a single build project and on the same footprint as a single storey extension.

At Crownhill Building Services, we have been designing and building two storey extensions across Milton Keynes for over 20 years. From compact two storey rear extensions that add a bedroom above a new kitchen, to large side-and-rear designs that effectively double the size of a home, we have the experience to handle every scale of project.

Double storey extensions are a popular choice for growing families who need extra bedrooms and bathrooms without the upheaval and cost of moving house. The cost per square metre is typically lower than a single storey extension because you share foundations, roof structure, and scaffolding across two floors — giving you significantly more space for your investment.

Structural and Planning Considerations

Building upwards introduces structural requirements that a single storey extension does not. Steel beams and lintels are almost always needed to transfer loads from the upper floor and roof through to the foundations. We work closely with structural engineers to design steelwork that is efficient, cost-effective, and properly specified for your property.

Unlike most single storey extensions, a two storey extension will usually require full planning permission from Milton Keynes Council. Permitted development rights do allow some two storey rear extensions, but the conditions are strict — the extension must not extend more than three metres from the original rear wall and must be at least seven metres from the rear boundary. We will assess your property and advise you on the best route before any work begins.

Building Control approval is required for every two storey extension. We handle the registration, manage all inspections throughout the build, and ensure you receive your completion certificate at the end of the project.

What Can You Achieve with Two Floors?

The advantage of two storeys is flexibility. Common configurations our clients choose include:

Bedrooms and en-suites upstairs — adding a master suite with walk-in wardrobe, a children's bedroom, or a guest room with its own bathroom
Open-plan living downstairs — removing the back wall to create a spacious kitchen-diner or family room with views and access to the garden
Home office above, utility below — making use of both floors for practical, everyday spaces that free up your existing rooms
Side extensions — building alongside the house over two floors to add width as well as depth, often incorporating a new hallway and staircase

Timeline and Process

A typical double storey extension takes 12 to 16 weeks to build, depending on size and complexity. We manage every stage in-house — foundations, blockwork, steelwork, first floor joists, roofing, windows, first and second fix electrics and plumbing, plastering, and decoration. You deal with one team from start to finish, and we provide a detailed fixed-price quote with no hidden costs.

We start with a free site visit to discuss your ideas, measure up, and give you an honest assessment of what is achievable. From there, we produce plans, handle all approvals, and agree a build schedule that works for your family.

Our Work