Single vs. Double Storey Extensions: Pros and Cons

When you need more space, the primary decision is whether to expand the footprint of your home or build upward. In the South West, where property styles range from compact Torbay terraces to detached homes in Exeter, the right choice depends on your specific goals, plot size, and budget.

At V3 Build, we have delivered both types of projects across Devon. This guide breaks down the advantages and disadvantages of single versus double storey extensions to help you make an informed choice.

Single Storey Extensions

This is the most popular choice for Devon homeowners looking to create open-plan kitchen-diners or additional ground-floor living space.

The Pros

Single storey extensions allow for vaulted ceilings and overhead glazing, such as roof lanterns or skylights. These features flood the ground floor with vertical light that a standard window cannot provide. These projects are typically faster to complete, with a construction phase usually lasting between three to four months. Furthermore, you can often stay in your home while work is carried out, as the construction can be sealed off from the rest of the house. Many single storey rear extensions also fall under Permitted Development, potentially removing the need for a full planning application.

The Cons

Because you are spreading the footprint, you will lose a larger portion of your outdoor area. Additionally, while it improves the saleability of a home through modern layouts, it typically adds less raw market value than an extra bedroom. From a cost perspective, you still incur the major expenses of foundations and a roof, but you only gain one floor of living space, often resulting in a higher cost per square metre.

Double Storey Extensions

A double storey build is the ideal solution for growing families who need extra bedrooms and bathrooms without the expense of moving house.

The Pros

While the total price is higher, the cost per square metre is often lower because the expensive foundational and roofing elements are shared across two floors. Adding a fourth or fifth bedroom with an ensuite can increase your property’s value by 10% to 20%, offering a strong return on investment. Crucially, you double your internal living area while using the same ground-floor footprint as a single storey build, preserving your garden.

The Cons

These projects are more complex. Existing foundations may need reinforcing to take the extra weight, and internal layout changes—such as adding a staircase—can be costly. In Devon, local councils are often stricter on double storey builds due to potential overshadowing or privacy concerns for neighbors. The process also takes longer, usually five to seven months, and the scale of the work may require you to move out temporarily.

Comparison at a Glance

For a single storey extension, the typical duration is 12 to 16 weeks with costs ranging from £1,800 to £3,000 per square metre. It is best for kitchen-diners and maximizing natural light.

For a double storey extension, the typical duration is 20 to 28 weeks. While the total cost is higher, the efficiency of the build often makes it more cost-effective per square metre of space gained. It is the superior choice for adding bedrooms and increasing long-term resale value.

Which is right for you?

If your primary goal is to create a bright, social hub for the family, a single storey extension is usually the winner. However, if you are looking to maximize your investment and need more sleeping space, a double storey extension offers significantly more utility for the footprint used.