Loft conversion or extension: which adds the space you actually need?

If you need more space and moving is not appealing, you are usually choosing between going up into the loft or out into the garden. They are not interchangeable.

What a loft conversion does well

A loft gives you a bedroom or a home office without losing any garden. Because the roof structure and the floor below already exist, the shell of the work is often quicker than a comparable extension. It suits the interwar and 1930s housing common in Sidcup, Orpington, Eltham and Bexley, which frequently has good head height and a straightforward roof.

The constraint is head height. As a rough guide you need enough clear height under the ridge for a usable room once the new floor and insulation go in. Where a simple Velux conversion does not give enough space, a dormer or a hip to gable conversion buys it back, at more cost.

What an extension does well

An extension changes how the ground floor works. If your problem is a cramped kitchen, no dining space or no connection to the garden, a loft conversion will not fix it however many bedrooms it adds. A rear or side return extension opens the living space up, which is why it is so common on Victorian and Edwardian terraces in Beckenham and Bromley.

The comparison that matters

• Garden: a loft costs you none, an extension costs you some.
• Disruption: a loft is largely contained upstairs with scaffold outside, an extension affects the room you use most.
• Access: a loft needs a permanent staircase, which takes space from the floor below. That is the detail people forget.
• Value: both add value, but an extra bathroom or bedroom and a properly working kitchen are valued differently by different buyers.

How to decide

Write down the problem rather than the solution. If it is bedrooms, go up. If it is living space, go out. If it is both, sequence them so the disruption happens once.

We build both across South East London and Kent, so we have no reason to push you towards one. Tell us the problem and we will give you a straight view.