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Loft conversion vs extension: which adds more, and when

Needing more space usually comes down to a choice between going up into the roof or out into the garden. Neither is automatically the right answer, it depends on the house, the garden and what the extra space is for.

What a loft conversion typically adds

A loft conversion usually adds one or two bedrooms and often a bathroom, without touching the garden or the building's footprint. It tends to suit a family that has run out of bedrooms but is happy with the ground-floor layout and garden as they are.

What an extension typically adds

A ground-floor extension usually adds to a kitchen, dining or living space, sometimes with a bedroom above if built as a two-storey extension. It suits a household that wants a larger, more open ground floor more than it wants an extra bedroom.

Cost comparison

A rooflight loft conversion (£20,000 to £40,000) is often the more affordable route to an extra room compared with a single-storey extension (£36,000 to £68,000), though a dormer loft conversion (£50,000 to £75,000) can cost more than a modest extension depending on scale. The numbers overlap enough that the decision should be driven by what you actually need the space for, not cost alone.

Disruption and timeline

A loft conversion generally disrupts daily life less than an extension, since the existing ground floor stays fully usable throughout, though access for a staircase does affect one part of the house. An extension usually means living around an open side of the house for the build period, longer for a larger single-storey extension.

The honest answer

Both are worth pricing before deciding, since the right answer depends on your specific roof structure, garden size and what the extra space needs to do. A site visit lets us give a genuine comparison for your actual property rather than generic guidance.