Hampstead Renovations

Two Routes to More Space — Very Different Propositions

When a growing family needs more space, two options dominate the conversation in North London: go up into the loft, or go down into a basement conversion. Both can be transformative — but they're very different projects in terms of cost, disruption, planning risk, and the type of space created.

This guide breaks down both options honestly, so you can make the right decision for your home, budget, and lifestyle.

At a Glance: Basement vs Loft

• Basement conversion cost: £80,000–£180,000+ (new dig); £50,000–£90,000 (existing cellar)
• Loft conversion cost: £40,000–£80,000 (dormer); £55,000–£90,000 (hip-to-gable)
• Value added: Basement typically 15–25%; loft typically 15–20%
• Planning needed: Basement — often yes; loft — often Permitted Development
• Disruption level: Basement — very high; loft — moderate
• Programme: Basement — 4–6 months; loft — 8–14 weeks

The Case for a Loft Conversion

A loft conversion is usually faster, cheaper, and less disruptive than a basement. In most North London terraced and semi-detached houses, a rear dormer conversion is Permitted Development — no planning permission required. A new bedroom and en-suite can be delivered in 10–14 weeks at a cost of £45,000–£65,000.

The main limitation is that loft space is inherently limited by the existing roof structure. If your house has a hip roof, a hip-to-gable conversion can significantly increase the available floor area. Natural light through dormer windows and Velux rooflights is excellent.

The Case for a Basement Conversion

A basement conversion creates the most flexible space in the house. Away from the family's day-to-day circulation, it works brilliantly as a cinema room, gym, home office, or self-contained annexe. In larger houses, a full basement can add an entire floor of living space.

The costs are significantly higher, and the disruption during construction is considerable — with large volumes of spoil to be removed and extensive structural work. However, in prime North London locations, the value added often justifies the investment.

Our verdict: If you need bedrooms, a loft is usually the better option. If you want a flexible, private space for living, working, or entertainment, a basement is hard to beat — budget and garden permitting.

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