How Much Does a House Extension or Loft Conversion Cost in the UK? [2025 Guide]

Let's start with the classic rear extension — the go-to move for homeowners craving more kitchen-dining space without the hassle of moving.

• Basic spec: from £2,000/m²
• Standard spec: £2,000–£2,800/m² (most common)
• High spec: £3,000+

💡 Example: A 20m² rear extension including a dining area, WC, and utility room may cost:
£86,000 – £95,000+ (based on £2,890/m², pitched roof, brick/block build)
Of course, aim for the higher end if you want crittall doors, polished concrete floors, and underfloor heating that warms your soul and your feet.

We often hear this: "It's just a narrow bit down the side—it must be cheaper, right?"
Not quite. Side-return extensions, especially in London, can be deceptively complex. Many Victorian and Edwardian houses hide structural quirks behind charming facades. Planning constraints, party wall agreements, and squeezing steelwork into tight spaces often increase the effort and the cost.
Throw in a kitchen or bathroom (hello, plumbing and waterproofing), and you have a project that matches or exceeds a rear extension.
So yes, side-return extensions can be smaller — but not always simpler or cheaper.

Converting your dusty old attic into a liveable loft is one of the best ways to add value and space, but what should you budget for?

• Velux (rooflight) loft: from £35,000–£45,000
• Dormer loft: £55,000–£75,000+
• Mansard / L-shaped lofts: £75,000–£100,000+

These figures vary depending on whether you're adding a bathroom, how much structural work is needed, and whether your street has tricky planning policies.
Need a mansard loft with dormers, a proper staircase, and bespoke walnut cabinetry? You're heading into six-figure territory. But it's worth it when done right.

Now we're talking top-to-bottom transformation. Costs range dramatically depending on what you're renovating and to what standard:

• Cosmetic updates (paint, flooring, lighting): £400–£800/m²
• Mid-range renovation (bathrooms, kitchens, layout tweaks): £1,200–£1,800/m²
• Full refurb with extensions and loft: £2,000–£2,800/m²

🏠 Real-life 2025 example from Masters:

• 14m² rear extension
• Ground floor reconfiguration (52m²)
• First floor layout change + 2 bathrooms (52m²)
• New mansard loft with two dormers and three roof lights (28m²)
• GRP flat roof, parapet walls, mid-to-high spec finishes

Total construction cost: £355,000 + VAT
Cost per m²: ~£2,450 + VAT (excluding design, planning, windows & wardrobes)
The price may seem costly, but the result is often a completely transformed home that functions better, looks more stylish, and suits contemporary living.

Are you dreaming of somewhere to stash your car, bikes, tools, or questionable exercise equipment? Here are 2025 garage costs:

• Single garage (flat roof): £21,000 – £33,000
• Single garage (pitched roof): £25,000 – £40,000
• Double garage: £36,000 – £58,000

These figures don't include EV chargers, smart storage systems, or converting half into a home gym (yes, that's trending now).

In a word? Yes.
London is the most expensive region in the UK to build anything. Even within London, there's variation:

Zone 1 prices often come with Zone 1 headaches—limited access, parking permits, storage challenges, and sometimes neighbours who don't love the sound of angle grinders at 8 a.m.

Quite a lot, actually. Here's what really drives (or derails) a project budget:

• Specification level – You can tile a bathroom in metro tiles or marble—big difference.
• Structural complexity – Hidden beams, load-bearing surprises, or awkward layouts = £££
• Design clarity – Vague drawings cost you more than you think
• Professional fees – Architect, structural engineer, party wall surveyor: ~15–16%
• Statutory fees – Planning, building control, and possible CIL contributions
• VAT – Usually 20%, unless the work qualifies for a reduced rate
• Unexpected conditions—like discovering your walls are hollow, the floor isn't level, or you have rising damp—we've seen it all.

Here's what makes pricing accurate and fair — for everyone involved:

• A detailed design – The clearer the brief, the better the price
• A defined scope – Avoid "scope creep" (also known as budget's worst enemy)
• A Bill of Quantities (BoQ) – Breaks down labour, materials, and quantities line by line.
• A Schedule of Works & Finishes – Tells exactly what's going where and to what standard.
• With these documents in place, you can invite quotes from serious contractors and compare like-for-like. No guesswork. No surprises. Just professional clarity.

Renovating in London in 2025 isn't cheap — but if done well, it's worth every penny. A well-planned extension or conversion adds space, value, and a whole lot of day-to-day joy.
At Masters, we build projects the right way—with detailed estimates, respectful communication, high-quality delivery, and a commitment to leaving every home better than we found it.
So, are you ready to make your space work harder, look smarter, and feel better?