Extension vs Loft Conversion: Which Adds More Value?
Both add space. Both add value. But they serve different needs and have different cost profiles. This guide helps you decide which is right for your home and budget.
The details
Cost comparison
A typical rear extension (24m²) costs £65,000–£95,000 all-in. A typical loft conversion (dormer with en-suite) costs £48,000–£72,000 all-in. The loft conversion is cheaper, but the extension adds more ground-floor living space — which is what most families need.
Value comparison
A loft conversion adding a 4th bedroom typically adds 10–20% to property value. A rear extension creating a kitchen-diner adds 5–10%. Per pound spent, a loft conversion usually delivers a better ROI — but the extension transforms daily living more dramatically.
Disruption comparison
Loft conversions are less disruptive — most work happens above you, accessed from scaffolding. You can usually stay in the house throughout. Extensions disrupt the ground floor (especially the kitchen) for 10–16 weeks. Many families move out or set up a temporary kitchen.
| Factor | Rear Extension (24m²) | Loft Conversion (dormer) |
|---|---|---|
| Typical all-in cost | £65,000–£95,000 | £48,000–£72,000 |
| Value added | 5–10% | 10–20% |
| Build time | 10–16 weeks | 8–12 weeks |
| Planning needed? | Usually PD | Usually PD (rear dormer) |
| Disruption level | High (kitchen out of action) | Moderate (above you) |
| Best for | Kitchen-diner, open-plan living | Extra bedroom + bathroom |
| Garden impact | Reduces garden | No garden impact |
Our verdict
Choose a loft conversion if you need an extra bedroom or bathroom and want the best ROI. Choose an extension if you want a bigger kitchen-diner or open-plan living space. Many homeowners do both over time — the loft conversion first (cheaper, less disruptive), then the extension.
Common questions
Frequently asked questions
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