May 2, 2025
Extending your home is one of the most effective ways to enhance space, increase property value, and avoid the cost and disruption of moving house. Whether you’re adding a new kitchen, creating a larger living area, or accommodating a growing family, deciding between a single-storey and a double-storey extension is a crucial step in the planning process.
Both options offer distinct advantages and limitations, and the right choice depends on your budget, goals, property type, and planning constraints. This in-depth guide will walk you through the key differences, benefits, and challenges of single-storey and double-storey extensions to help you make a well-informed decision for your home renovation journey.
Single-storey extensions are generally less expensive to build compared to double-storey extensions, as they require less structural reinforcement, reduced scaffolding, and fewer internal changes. For example, adding a kitchen or open-plan living space to the rear of a home can often be done under permitted development rights, keeping costs and paperwork to a minimum.
However, double-storey extensions offer better cost-per-square-metre value. Although the initial investment is higher, you gain significantly more floor space without doubling the overall cost. This can be more economical in the long run, particularly if you're planning to stay in your property for many years or intend to rent it out later.
In the UK, many single-storey extensions fall under permitted development if they meet specific size and design criteria. This streamlines the process and saves time and costs on formal planning applications. However, if your property is listed or in a conservation area, stricter rules apply.
Double-storey extensions typically require full planning permission due to their impact on neighbouring properties, light, and privacy. You’ll need to consider height restrictions, overlooking concerns, and overall design integration with the existing structure.
It’s essential to work with an architect or extension specialist who understands local authority guidelines. A pre-application consultation with your council can also identify potential obstacles early.
A single-storey extension is ideal for creating large, open-plan spaces such as a kitchen-diner, lounge, or utility area. It can open up the ground floor, enhance the connection to the garden, and improve day-to-day functionality.
A double-storey extension offers greater flexibility. In addition to ground-floor space, it can add one or more bedrooms, a home office, or even a bathroom upstairs. This makes it suitable for growing families or those looking to futureproof their home.
If your goal is to add substantial living space on both floors without compromising your garden or outdoor area, a double-storey extension might be the better choice.
One drawback of any extension is its effect on your outdoor area. A single-storey build typically takes up more of the garden footprint, especially if extending to the rear or side. This can reduce lawn size, patio areas, or external access.
Double-storey extensions can preserve more of the garden since they build upward rather than outward. This is especially useful for properties in urban areas with limited plots or terrace housing where outdoor space is already constrained.
Think about how much time you spend in the garden and whether preserving it is a priority. A design that balances indoor and outdoor flow, perhaps with bi-fold doors or roof lanterns, can help retain the sense of openness even with a single-storey build.
All extensions cause some disruption, but the scale and duration vary. Single-storey projects are typically quicker to complete and less intrusive, with many homeowners able to remain in the house throughout the process.
Double-storey extensions take longer to build due to the complexity of structural work, plumbing, and additional staircases. In many cases, scaffolding, steelwork, and access to upper floors are required, which may make staying in the house impractical.
Noise, dust, and temporary loss of access to parts of the home are common in both cases, but should be factored into your timeline and temporary living arrangements.
Home extensions are a significant investment, but they often yield strong returns—especially when executed with high-quality finishes and practical layouts.
A well-designed single-storey extension can boost your home’s value by up to 10–15%, particularly if it enhances kitchen and living areas, which are key selling points.
A double-storey extension can add even more value, typically between 15–25%, due to the addition of extra bedrooms or bathrooms. However, location, design coherence, and market demand play a big role in ROI.
Before committing, it’s worth consulting local estate agents or property professionals to determine whether your plans align with what buyers in your area are seeking.
Modern single-storey extensions allow for striking design features such as full-width sliding doors, skylights, and seamless garden integration. This is ideal for creating sociable family spaces or entertaining areas filled with natural light.
Double-storey extensions must blend more carefully with the existing structure to avoid looking bulky or out of proportion. Achieving symmetry and continuity with rooflines, brickwork, and windows becomes more important.
That said, a two-storey build can transform a property’s exterior and offer a dramatic reimagining of its layout and kerb appeal when thoughtfully designed.
New extensions must comply with Building Regulations Part L, which sets standards for insulation and energy performance. A single-storey space may lose more heat due to a larger roof and glazed surfaces but can also be easier to insulate and heat.
Double-storey extensions, with increased vertical space, may require more comprehensive integration into your central heating system or even an upgrade to your boiler. Zoning your heating and using smart thermostats can improve efficiency.
Energy-efficient materials, triple-glazing, underfloor heating, and renewable technologies such as air-source heat pumps are worth considering in both types of build.
Not always. Many single-storey extensions fall under permitted development rights, provided they meet specific size and height limits. However, rules vary depending on location, property type, and previous modifications. Always check with your local authority or planning consultant.
For single-storey extensions, staying in the house is often feasible. For double-storey projects, especially those affecting stairs or bedrooms, it may be more practical to move out temporarily to avoid significant disruption and delays.
Yes, in most cases. A double-storey extension adds both ground and upper floor space, making it attractive to buyers. The added bedrooms or bathrooms often result in a higher return on investment than single-storey builds.
A single-storey extension typically takes 3–4 months, while a double-storey one can take 4–6 months or longer, depending on site access, weather, planning delays, and custom features.
That depends on your goals. Building out (single-storey) is often simpler and faster, ideal for open-plan living. Building up (double-storey) provides more overall space and better value but involves more structural work and planning challenges.
Choosing between a single-storey and a double-storey extension involves balancing cost, space, functionality, planning regulations, and long-term value. A single-storey extension may suit those seeking quick, accessible open-plan improvements without extensive disruption. Meanwhile, a double-storey extension can deliver more substantial space and investment return, especially for families thinking ahead.
Before deciding, it’s wise to consult architects, planners, and builders to assess what’s feasible on your property. By understanding your goals and exploring both options in detail, you’ll be better equipped to create a home that meets your present and future needs.
If you’re planning a renovation, extension, or full home transformation, visit our website Milkov & Son Construction to explore our expert services and recent projects. Take the first step toward creating your dream space by contacting us online or calling +44 7951 625853.
