How much does a loft conversion cost in London? In 2026, a simple rooflight conversion starts from around £35,000, a rear dormer from £45,000, a hip-to-gable from £55,000 and a mansard from £65,000. Adding an en-suite, needing full planning permission or major structural work all push the price up, and there are fees on top of the build to budget for too.
In this guide we break down how much a loft conversion costs by type, the extra costs people often forget, what affects the price, how much value it adds, and how to keep the cost down. For our current prices and a fixed quote, see our loft conversion cost page.
How much does a loft conversion cost by type?
So, how much does a loft conversion cost for your house? It depends mainly on the type:
| Type | What you get | Typical time on site | Price from |
|---|---|---|---|
| Rooflight (Velux) | New floor, roof windows, insulation and stairs; the roof shape stays the same | 4–6 weeks | £35,000 |
| Rear dormer | A box-shaped extension at the back, giving full head height for a double bedroom and en-suite | 6–8 weeks | £45,000 |
| Hip-to-gable | The sloping side roof is built up into a vertical gable; suits semis and end-of-terraces | 7–9 weeks | £55,000 |
| Mansard | The rear roof slope is rebuilt almost vertical, giving the most space; usually needs planning permission | 8–10 weeks | £65,000 |
These are starting prices for typical London houses. Larger lofts, combined dormers (such as an L-shaped dormer) and high-spec finishes cost more. Our guide to the different types of loft conversion explains each one in detail.
Costs to budget for on top of the build
When you ask how much a loft conversion costs, the build price isn’t the whole answer. These are the other costs to budget for. Some builders include them; others don’t, so always check what a quote covers.
| Cost | Typical amount |
|---|---|
| Architectural drawings and design | Varies with the project; often included by specialist loft companies |
| Structural engineer’s calculations | Varies with the project |
| Planning application (if needed) | £548 in England |
| Lawful Development Certificate (if Permitted Development) | £274 in England |
| Building control fees | Around £500–£1,500, depending on the council |
| Party wall surveyor(s) | Around £800–£2,000 per neighbour, if they appoint their own |
| Scaffolding | Depends on the house and access |
| Bathroom fittings, flooring and decorating | Depends on what you choose |
| VAT | 20%; check whether prices include it |
You can read more about when you need planning permission in our loft conversion planning permission guide, and about party walls in our party wall guide. It’s also wise to keep a contingency of around 10% for anything unexpected; see contingency in construction.
Our own quotes are itemised and fixed before work starts, so you can see exactly what’s included.
What affects the price of a loft conversion?
Two lofts of the same type can cost very different amounts. The main factors:
- Size and shape of the roof. A bigger loft or a wide dormer needs more materials and labour.
- An en-suite or bathroom. Plumbing, drainage and fittings add cost, but a bedroom with its own bathroom also adds the most value.
- Structural work. Steel beams, new floor joists and any repairs to the existing roof or walls.
- Head height. If the loft is too low, lowering the ceilings below or raising the roof adds significantly to the cost.
- Planning permission. Lofts built under Permitted Development avoid a full planning application; mansards, flats and conservation areas usually need one.
- The staircase. A new stair above the existing one is usually simplest; awkward layouts cost more.
- Moving services. Water tanks, a gravity-fed heating system or wiring in the loft may need to move or be replaced.
- Fire safety work. Fire doors and alarms are always needed; an open-plan ground floor may need extra work. See our guide to loft conversion building regulations.
- Finish and fittings. Flooring, bathroom suites, built-in storage and windows can vary by thousands of pounds.
Is a loft conversion worth the cost?
For most London homes, yes. A loft conversion usually costs far less than the value it adds, and much less than moving.
- Added value: Nationwide’s research found that adding a bedroom and bathroom to a three-bed, one-bathroom house can increase its value by up to 24%. On a £700,000 London house, that’s up to £168,000.
- Compared with moving: Which? puts the average cost of moving home in London at over £32,000 in stamp duty and fees alone, before you pay more for a bigger house.
- Compared with an extension: a single-storey rear extension in London often costs £80,000–£150,000 and usually adds living space rather than a bedroom.
Our guides does a loft conversion add value? and loft conversion vs extension go into the numbers in more detail.
How to keep your loft conversion cost down
- Choose the right type. A rooflight conversion costs least if your loft already has the head height; a rear dormer gives the most space for the money on most London houses.
- Build under Permitted Development where possible. It avoids a full planning application.
- Keep the bathroom simple. Standard-sized fittings and a sensible layout save money.
- Plan the stairs above the existing staircase. It’s usually the simplest position.
- Decide before you start. Changes during the build are the most common reason costs rise.
- Get a fixed, itemised quote. Our guide to estimate vs quote explains why it matters.
- Don’t choose on price alone. The cheapest quote often leaves things out; see how to choose a builder.
AQs
How much does a loft conversion cost in London in 2026?
As a guide, a rooflight conversion starts from around £35,000, a rear dormer from £45,000, a hip-to-gable from £55,000 and a mansard from £65,000, before extra fees.
How much does a loft conversion cost with an en-suite?
An en-suite adds the cost of plumbing, drainage and fittings to the price. Most rear dormer conversions with an en-suite in London fall between £45,000 and £75,000, depending on size and finish.
What is the cheapest type of loft conversion?
A rooflight (Velux) conversion, because the roof shape stays the same. It only works if your loft already has enough head height: at least 2.2m from the top of the ceiling joists to the ridge.
Does the cost include VAT?
Always check. Some quotes show prices before VAT at 20%, which makes a big difference to the total.
How long does a loft conversion take?
Usually four to ten weeks on site, depending on the type, plus time beforehand for design, approvals and party wall notices.
Do I need to pay for planning permission?
Only if your loft needs it. Many lofts are built under Permitted Development, in which case a Lawful Development Certificate (£274 in England) is recommended as proof. A full planning application costs £548.
How do I get an accurate price?
Book a free survey. We’ll measure your loft, discuss what you want and give you an itemised, fixed price.
Get a fixed price for your loft
Now you know how much a loft conversion costs in general, find out what yours would cost. See our loft conversion cost page for current prices, or book a free survey for an itemised, fixed quote.
