In 2024, two near-identical Victorian terraced houses on streets parallel to each other in Belsize Park came to market. Both were four bedrooms, 2,200 square feet, with south-facing gardens. One—unmodernised, with a tired kitchen, original single-glazed sash windows, and a boiler from 1998—sold for £2.65 million (£1,205 per sq ft). The other—comprehensively renovated with a basement extension, new kitchen, underfloor heating throughout, and smart home integration—sold for £4.1 million (£1,864 per sq ft).

The second house commanded a £1.45 million premium. Yet the renovation had cost approximately £650,000. The "done-up" premium—the additional value created by high-quality renovation above and beyond the direct cost of work—was £800,000.

This is not an isolated case. Across Hampstead, Belsize Park, and the wider NW3 postcode, comprehensively renovated properties consistently achieve a 35-50% price premium over unmodernised equivalents. Understanding this dynamic is essential for homeowners deciding whether to renovate before selling, and for investors assessing whether to buy, renovate, and sell.

The Data: Price Per Square Foot in NW3

Land Registry data from 2024, combined with our analysis of 150+ sales in Hampstead and Belsize Park, reveals clear patterns:

Unmodernised Properties

• £1,150-£1,350 per sq ft for Victorian/Edwardian terraces
• £1,000-£1,200 per sq ft for 1930s houses
• £950-£1,100 per sq ft for post-war properties

"Unmodernised" means: original kitchen and bathrooms (or dated replacements from the 1990s), no basement or loft extension, single-glazed windows, outdated heating systems, no insulation or energy efficiency measures.

"Touched" Properties

• £1,400-£1,550 per sq ft for Victorian/Edwardian terraces
• £1,250-£1,400 per sq ft for 1930s houses
• £1,150-£1,300 per sq ft for post-war properties

"Touched" means: kitchen and bathroom updates, double-glazed windows, new boiler, some decorative refresh. The property is livable but not exceptional. Most buyers would undertake further work within 3-5 years.

Fully Renovated (Turnkey)

• £1,800-£2,100 per sq ft for Victorian/Edwardian terraces
• £1,600-£1,850 per sq ft for 1930s houses
• £1,400-£1,650 per sq ft for post-war properties

"Fully renovated" means: basement or loft extension, complete re-wiring and re-plumbing, underfloor heating, premium finishes (engineered oak, natural stone), bespoke joinery, landscaped garden, smart home systems. Nothing requires attention for 10+ years.

The Value Gap

The difference between unmodernised and fully renovated is consistently £600-£750 per sq ft. For a 2,500 sq ft house, that equates to £1.5-£1.875 million in added value.

Yet the cost of achieving that renovation is typically £250,000-£500,000 depending on scope. The gap—the "done-up premium"—represents genuine value creation, not merely cost recovery.

Breaking Down ROI by Intervention Type

Not all renovation work generates the same return. Here's what our analysis shows:

Basement Conversions: 70-90% ROI

A basement excavation adding 500-700 sq ft costs £200,000-£350,000 (£400-£500 per sq ft of new space). The market values this space at £1,200-£1,500 per sq ft (discounted from ground-floor space because it is below ground).

Example: A 600 sq ft basement costing £280,000 adds £720,000-£900,000 in property value.

Why the premium? Basements are permanent additions that cannot be easily replicated. In Hampstead, where planning restrictions and tree protection make above-ground extensions difficult, basements are the only viable expansion option. Buyers pay a premium for space that is legally and practically difficult to add themselves.

When ROI is lower: Poorly executed basements (low ceiling height, inadequate natural light, damp issues) are valued at only £700-£900 per sq ft—barely covering cost. Quality matters.

Loft Conversions: 50-70% ROI

A loft conversion adding 400-500 sq ft costs £60,000-£120,000 (£150-£240 per sq ft). The market values this space at £1,000-£1,300 per sq ft (again, discounted from ground-floor space).

Example: A 450 sq ft loft costing £90,000 adds £450,000-£585,000 in value.

Why lower than basements? Loft conversions are easier to execute (no excavation, fewer structural complexities) so buyers discount them slightly. Additionally, lofts often sacrifice storage space (the void is valuable for water tanks, luggage, seasonal items).

When ROI is higher: Lofts with en-suite bathrooms, good headroom (2.3m+ ceiling height), and quality finishes command the top end of the range. Lofts accessed by a pull-down ladder or with poor natural light barely break even.

Kitchen Extensions: 40-60% ROI

A side-return or rear extension adding 200-300 sq ft costs £80,000-£150,000 (£400-£500 per sq ft). The market values this space at £1,400-£1,700 per sq ft (close to ground-floor rates because it is on grade and naturally lit).

Example: A 250 sq ft side-return extension costing £115,000 adds £350,000-£425,000 in value.

Why decent ROI? Extensions create open-plan living—the most desirable layout for families. A Victorian terrace with a cramped galley kitchen becomes a modern family home with a 30ft open-plan kitchen-diner.

When ROI is lower: Over-extensions that sacrifice all garden space are penalized. Buyers in Hampstead value outdoor space; if your extension leaves only a 15ft paved yard, the value uplift is muted.

Complete Refurbishment (No Extension): 30-50% ROI

Full refurbishment of an existing footprint—new kitchen, bathrooms, flooring, heating, decorating—costs £100,000-£200,000 (£50-£80 per sq ft). The value uplift is harder to quantify because you are not adding space, but preventing obsolescence.

Example: A £150,000 refurbishment might add £200,000-£300,000 in value.

Why lower ROI? You are competing with buyers who are willing to do the work themselves (and many buyers in Hampstead want to customize). A house that is "livable but dated" attracts buyers who see an opportunity; a fully renovated house attracts buyers who want move-in readiness—a smaller pool.

When ROI is higher: Premium finishes (marble bathrooms, bespoke joinery, integrated appliances) justify a higher price because they signal quality and save the buyer years of decision-making and site management.

Location-Specific Variations

Not all NW3 streets are equal. The done-up premium varies by micro-location:

Prime Hampstead (Redington Road, Frognal, Downshire Hill)

• Unmodernised: £1,300-£1,500 per sq ft
• Fully Renovated: £2,000-£2,300 per sq ft
• Premium: £700-£800 per sq ft

Buyers in these streets expect perfection. An unmodernised house is a project; a renovated house is a home. The premium is highest because the buyer pool is affluent and time-poor—they will pay to avoid construction.

Belsize Park (Eton Road, Buckland Crescent, Elsworthy Road)

• Unmodernised: £1,200-£1,400 per sq ft
• Fully Renovated: £1,800-£2,000 per sq ft
• Premium: £600-£650 per sq ft

Still highly desirable, but slightly less premium than core Hampstead. The renovation uplift is strong but not as extreme.

West Hampstead (Mill Lane, Broadhurst Gardens)

• Unmodernised: £1,000-£1,200 per sq ft
• Fully Renovated: £1,500-£1,750 per sq ft
• Premium: £500-£550 per sq ft

Further from the Heath and Hampstead Village, but still NW3. The done-up premium is lower because the absolute price ceiling is lower—buyers at this price point (£1.5-£2.5m) are more willing to undertake their own renovation.

The "Pre-Sale Refresh" Strategy

Not every seller needs a full renovation. If you are planning to sell within 12-24 months, a targeted "Pre-Sale Refresh" can add disproportionate value:

High-Impact, Low-Cost Interventions

External Redecoration (£8,000-£15,000): Repainting the front façade, cleaning brickwork, replacing tired window boxes, and refreshing the front door creates instant kerb appeal. First impressions set the tone for viewings.

Kitchen Repainting/Refacing (£5,000-£12,000): If the kitchen layout is sound but the cabinets are dated, repainting or replacing cabinet fronts and adding new worktops (quartz or Silestone) refreshes the space without the cost of a full replacement.

Bathroom Retiling (£3,000-£8,000 per bathroom): Ripping out old tiles, re-tiling with contemporary large-format tiles, and replacing taps and showerheads transforms a bathroom for £8,000—far less than a full renovation (£15,000-£25,000).

Flooring Continuity (£10,000-£25,000): If the house has a patchwork of carpets, laminates, and old tiles, installing engineered oak throughout creates visual continuity and signals quality. Cost is £30-£50 per sqm installed.

Landscaping (£5,000-£15,000): Overgrown gardens and cracked paving reduce value. A simple reset—new turf, gravel paths, border planting—costs £10,000 and adds £30,000-£50,000 in perceived value.

Expected ROI: 200-400%

These interventions cost £30,000-£70,000 in total. The value uplift from improved presentation and buyer perception is typically £100,000-£250,000. This is not because you have added £250,000 of work, but because you have removed buyer objections and positioned the property as "ready to enjoy" rather than "needs work."

The Timing Question: Renovate Before or After Sale?

The decision to renovate before selling depends on your timeline, cash availability, and risk tolerance.

Renovate Before Selling If:

You Have Time (12-18 Months): Renovation takes time—design, planning, construction, snagging. If you need to sell within 6 months, renovation is impractical.

You Have Cash: Renovation is cash-intensive. Bridging loans and overdrafts erode profit margins. If you must finance the renovation, the interest costs reduce your net gain.

You Want Maximum Value: A turnkey property attracts more buyers and higher offers. If your goal is to maximize sale price, renovating first is the correct strategy.

The Property is Undesirable in Its Current State: If the house is so dated or compromised (single glazing, no central heating, asbestos) that it will only attract investors or developers, renovating allows you to access the owner-occupier market—where prices are 20-30% higher.

Sell Unmodernised If:

You Need to Sell Quickly: Unmodernised properties sell to cash buyers and developers who move fast. Renovated properties attract owner-occupiers who need mortgages, surveys, and longer chains.

You Lack Design Confidence: If you renovate to your taste and the market disagrees, you have wasted money. Unmodernised properties allow buyers to impose their vision.

The Market is Hot: In a rising market, buyers tolerate imperfection because they are competing for scarce properties. In a falling or stagnant market, renovation is essential to stand out.

Case Studies: Real Examples from 2024

Case 1: Basement + Full Refurbishment

Property: 4-bed Victorian terrace, Elsworthy Road, Belsize Park, 2,400 sq ft (before renovation)

Original Condition: Unmodernised, single glazing, dated kitchen, no extension

Renovation: Basement excavation (+650 sq ft), full refurbishment, new kitchen, bathrooms, flooring

Cost: £480,000 (£200/sq ft including basement)

Sale Price (Post-Renovation): £4.5 million (£1,475/sq ft on new total area of 3,050 sq ft)

Comparable Unmodernised Sale (Same Street, 6 Months Earlier): £2.8 million (£1,167/sq ft on 2,400 sq ft)

Value Added: £1.7 million (renovation cost £480k → net gain £1.22 million)

Case 2: Pre-Sale Refresh

Property: 3-bed Edwardian house, West Hampstead, 1,800 sq ft

Original Condition: Tired but functional, no structural issues

Intervention: External repaint, kitchen reface, bathroom retile, new flooring, garden landscaping

Cost: £52,000

Sale Price (Post-Refresh): £1.95 million (£1,083/sq ft)

Comparable "As-Was" Sale (Same Street, Similar Condition): £1.72 million (£956/sq ft)

Value Added: £230,000 (refresh cost £52k → net gain £178k)

Case 3: Loft Conversion Only

Property: 3-bed Victorian terrace, South Hampstead, 1,600 sq ft (before loft)

Original Condition: Modernised ground floor, but no loft conversion

Renovation: Loft conversion adding 450 sq ft with en-suite

Cost: £95,000

Sale Price (Post-Loft): £2.7 million (£1,317/sq ft on new total of 2,050 sq ft)

Comparable Without Loft (Same Street): £1.95 million (£1,219/sq ft on 1,600 sq ft)

Value Added: £750,000 (loft cost £95k → net gain £655k)

Note: This is the highest ROI example because the street had very few loft-converted properties, so the addition was rare and valuable.

The Investor's Calculation

For investors buying to renovate and sell (the "flip" model), the numbers are tighter:

Purchase Price (Unmodernised): £2.5 million

Renovation Cost: £400,000

Holding Costs (Finance, Council Tax, Insurance, 18 months): £120,000

Agent Fees (1.5%) and Legal Costs: £50,000

Total Investment: £3.07 million

Sale Price (Renovated): £3.8 million

Gross Profit: £730,000

ROI: 24% over 18 months (~16% annualized)

This is attractive—but dependent on accurate cost estimation, efficient project management, and a stable or rising market. If costs overrun (common in basement projects) or the market softens, profit margins compress rapidly.

Conclusion: Value vs. Cost

The done-up premium is real, substantial, and predictable. Across Hampstead and Belsize Park, comprehensive renovation adds £600-£800 per square foot in value—consistently exceeding the direct cost of work by 40-80%.

But this premium is not automatic. It depends on:

• Quality of Execution: Poor workmanship, cheap materials, or inappropriate design destroy value.
• Market Positioning: Renovating for your taste rather than market expectations reduces ROI.
• Location: The premium is highest in prime streets where buyers expect perfection.
• Timing: In a rising market, renovation is amplified; in a falling market, it is insurance against price drops.

For homeowners planning to live in the property for 10+ years, the calculation is different—you are buying quality of life, not ROI. But for those renovating with an eye on eventual sale, the data is clear: thoughtfully executed renovation is one of the most reliable ways to create substantial value in North West London property.

For homeowners looking to maximize sale value, our partners offer a "Pre-Sale Refresh" package designed to boost kerb appeal and market readiness instantly, ensuring your property achieves its full potential in the current market.