Single vs Double Storey Extensions

Both add space, but they solve different problems. A single-storey extension grows your ground floor. A double-storey extension grows two floors at once and gives you more space for your money per square metre. Here is how the two compare for an Aberdeen home, side by side.

It is one of the first decisions any homeowner faces when planning a home extension. Do you build out across one level, or stack two storeys and gain bedrooms upstairs at the same time? The honest answer is that neither is "better" in the abstract. The right choice depends on what you actually need, what your plot allows, and how much disruption you are willing to live through. This guide sets out the real differences so you can walk into your survey with a clear view.

The side-by-side comparison

The table below is the quickest way to weigh the two options against the factors that tend to decide it: cost, disruption, how likely you are to need planning permission, what each does to your footprint and garden, and who each one tends to suit.

Single-storey extensions in detail

A single-storey extension adds floor space across one level, usually at the rear or to the side of the house. It is the route most people picture when they think of an extension: a bigger kitchen, a dining area, a family room or a utility, opening out onto the garden. Because the work stays largely at ground level and outside the existing house, it is the simpler and tidier of the two builds.

Pros of a single-storey extension

• Lower total cost, starting from around £45,000, so it is easier to budget for.
• Less disruptive, with most of the work outside and your upstairs untouched.
• More likely to fall within permitted development, which can keep the planning side simpler.
• Ideal for creating bright, open-plan living space and a strong connection to the garden.

Cons of a single-storey extension

• You only gain one floor of space for the footprint you give up.
• It takes more of your garden to add the same number of rooms as a two-storey build.
• It does not add bedrooms or upstairs bathrooms unless you reconfigure the existing house.

If your goal is a larger kitchen or a knocked-through living and dining space, a single-storey extension is usually the most direct way there. It also pairs neatly with internal changes such as a new kitchen fitted into the new footprint.

Double-storey extensions in detail

A double-storey, or two-storey, extension builds upwards as well as outwards, adding matched space on both the ground and first floors within a single footprint. The classic use is a larger kitchen or living room below with a new bedroom, often with an en suite, directly above. Because the foundations, the roof and the scaffolding are shared across two floors rather than one, you tend to get noticeably more space for each extra pound spent.

Pros of a double-storey extension

• More space per pound, because the costly roof and foundations serve two floors.
• Adds bedrooms and bathrooms upstairs, not just living space downstairs.
• Uses the same ground footprint to add two rooms, so it protects more of your garden.
• Can transform a smaller family home into one that genuinely suits a growing household.

Cons of a double-storey extension

• A higher total cost, starting from around £75,000.
• More disruption, as the scaffolding stays up longer and first-floor rooms are affected during the build.
• More likely to need a full planning application because of its height and visual impact.
• Design needs more care so the upper floor sits comfortably against the existing roofline.

Who each one suits

Strip away the detail and the choice usually comes down to whether your need is on one floor or two.

1. Choose single-storey if you mainly want more living, kitchen or dining space, you have garden to spare, you want to keep cost and disruption down, and you would rather stay within permitted development where possible.
2. Choose double-storey if you need extra bedrooms or bathrooms as well as ground floor space, your plot is tight and you want to protect the garden, and you want the most space for your overall budget.

Many Aberdeen homes sit somewhere in between, and the deciding factor is often the plot itself, the orientation of the garden, and how the new upper floor would meet the existing roof. That is exactly the kind of thing a site survey settles quickly. Before then, it helps to understand the rules, so our guide to extension planning permission in Aberdeen is a useful next read.

Planning permission and building warrants in Scotland

Whichever you choose, the two approvals to keep separate are planning permission and the building warrant. Planning is about whether you are allowed to build what you propose, given its size, height and impact. A single-storey rear extension often falls within permitted development, while a double-storey extension is more likely to need a formal planning application from Aberdeen City Council or Aberdeenshire Council.

The building warrant is a separate approval that covers how the work is built: structure, fire safety, insulation and energy standards. In Scotland an extension that creates habitable space needs a building warrant regardless of which type you pick, and you cannot legally start the relevant work without it. We handle both the planning side and the warrant for you. For the full picture, see our pillar guides on permitted development versus planning permission and building warrants in Scotland.

How to make the decision

Start from the rooms you need rather than the build you fancy. List what is missing from your home today: more kitchen space, a fourth bedroom, an extra bathroom, a home office. If that list is all on one floor, a single-storey extension is likely the simplest answer. If it spans two floors, a double-storey almost always gives better value than building two separate single-storey projects later. Then weigh that against your plot, your budget and how much disruption suits your household.

You do not have to settle this on paper. The clearest way forward is a free survey, where we measure the space, talk through both options honestly, and give you a written quote for each so you can compare like for like. If you are also weighing an extension against using the roof, our comparison of routes alongside a loft conversion and our guide to loft conversion types are worth a look first.