Tonbridge is a town people move to for the schools and the fast trains, and then stay in. When the family outgrows the house, a loft conversion adds the bedroom, the office or the bathroom without the cost of moving or an inch lost from the garden, designed and built in-house for a fixed written price and a ten year guarantee.
In short: a loft conversion in Tonbridge usually adds a double bedroom and an en-suite, takes six to eight weeks on site, and runs from around £50,000 to £75,000 for a dormer or hip to gable. Most are permitted development, though homes in the Tonbridge and Quarry Hill conservation areas may need a full application. With TN9 homes near a £375,000 median, the space a conversion adds is worth close to what it costs to build, which is why most families here convert rather than move.
The honest figure comes from a survey of your own roof, but the ranges below are the same indicative figures we use across Kent and show on our cost estimator. They depend on the type of conversion and the roof, not the postcode.
| Conversion type | Indicative cost (plus VAT) |
|---|---|
| Velux | £35,000 to £50,000 |
| Dormer | £50,000 to £65,000 |
| Hip to gable | £58,000 to £75,000 |
| L-shape | £65,000 to £90,000 |
| New build loft | £45,000 to £70,000 |
The sum usually favours staying put. HM Land Registry put the median TN9 sale at around £375,000 in 2026, and Nationwide has valued the uplift from adding a bedroom and a bathroom at about 20%. On a Tonbridge home that is roughly £75,000 of added value, around what the work itself costs, and you avoid the stamp duty, agent fees and upheaval of moving to a bigger house in the same town. Our guide to how much value a loft conversion adds covers it in full. The loft is the cheapest space in the house to bring into use, because the walls, the roof and the foundations are already there. Whatever the job, the price we give after the survey is fixed in writing, with staged payments, so nothing is added at the end.
In short, a Tonbridge loft conversion adds roughly its own cost back in value and keeps you in the same street, school catchment and train line, which is why most families here choose to convert rather than move.
What the roof gives you varies street by street. Near the centre and the station, the deep Victorian and Edwardian terraces with a rear outrigger are the ones that take an L-shape conversion, wrapping a bedroom and en-suite over the back. The 1930s semis that fill Cage Green, Higham Wood and Trench carry a hipped roof, and the room there comes from a hip to gable with a rear dormer added. Towards Hildenborough the newer and larger homes often already have the height for a plain dormer, or rooflights if the outside is to stay as it is; our guide to dormer versus Velux conversions weighs those two up.
| Your roof | Best conversion | Common in |
|---|---|---|
| A terrace with a rear outrigger | L-shape dormer | Victorian and Edwardian streets near the centre and station |
| A 1930s semi with a hipped roof | Hip to gable, usually with a rear dormer | Interwar and post-war semis in Cage Green, Higham Wood and Trench |
| A rear roof with decent standing height | Rear dormer | Most Tonbridge semis and detached houses |
| Head height already there, outside to stay as is | Velux or rooflight | Larger and modern homes towards Hildenborough |
Before we draw anything, we check the ridge height and where a new staircase can sensibly land, so the design matches what the roof will genuinely allow. Loft conversion, loft extension, attic conversion: the name changes, the job does not.
A loft is also the room that lets a growing family stay put in Tonbridge, keeping the school places and the commute while gaining the extra bedroom, the home office or the quiet room at the top of the house.
The good news for most of Tonbridge is that you will not need a planning application at all. A standard rear dormer or hip to gable on a house counts as permitted development, as long as the house still has its allowance and the design keeps within the size limits. The older heart of the town is where that changes. The Tonbridge and Quarry Hill conservation areas, running around the castle and the river crossing, usually strip out the roof permitted-development rights, so a dormer there goes in for a full decision by Tonbridge and Malling Borough Council. Flats, maisonettes, listed buildings and any change to the street-facing slope always need an application too. Our guide to loft conversions in conservation areas and listed buildings explains what tends to get approved.
Either way, we sort the consents. The survey tells you which route your address falls under, and if an application is needed we draw it up and submit it inside the fixed price. Building control is the separate approval that every conversion needs, permitted development or not: it signs off the structure, the staircase, the fire escape and the insulation, and that is ours to handle as well. The planning permission guide and building regulations guide have the full detail.
A handful of finished rooms from recent jobs, so you can judge the standard rather than take our word for it. On the survey we will point you to the closest match to your own roof.
Dormer loft bedroom and en-suite A rear dormer that opened up a full-height double bedroom with its own en-suite, the build we do most often on a Tonbridge semi. View project → 
Master bedroom and en-suite, Bromley A loft turned into a master bedroom with its own en-suite, the landing opened up to keep it generous. View project → 
Two-bedroom hip to gable, Beckenham A larger hip to gable planned as two rooms with roof windows, showing what a bigger roof can take. View project → There are more finished rooms in our gallery.
Every Tonbridge conversion is built by our own employed team, never subcontracted, and run by one project manager you can call from the first visit to the final certificate.
The job goes in a set order. We survey the roof for free and tell you straight what it can take. We draw it up and give you one fixed written price, yours to sit on with no obligation. Say yes and we clear the planning and building control first, around two to four weeks, then build on site for roughly six to eight weeks on a dormer or hip to gable, a little less for a Velux and more for an L-shape; our guide to how long a loft conversion takes sets out each stage. You finish with the completion certificate and a ten year written guarantee.
We build across the whole of Kent with our own team. Close to Tonbridge we also cover Tunbridge Wells, Sevenoaks and Maidstone, plus Hildenborough and the surrounding villages. See every town on our loft conversions across Kent page, or the full patch on our areas we cover page.
For most Tonbridge houses, no. A rear dormer or hip to gable normally counts as permitted development. You only need a full application to Tonbridge and Malling Borough Council if the home is in the Tonbridge or Quarry Hill conservation area around the old centre, is listed, is a flat or maisonette, or the work changes the street-facing roof slope. We settle which on the survey and handle any application within the price.
As a guide, a Velux conversion runs from around £35,000, a dormer from £50,000 to £65,000, and a hip to gable from £58,000 to £75,000, which is a common build on the town’s interwar semis. These are the same ranges on our costs estimator, and your own price is fixed in writing after a free survey.
For most homeowners, yes. With TN9 homes selling at a median of around £375,000 (HM Land Registry, 2026) and Nationwide valuing a new bedroom and bathroom at about a 20% uplift, that is roughly £75,000 of added value, around what the work costs, while you keep the garden and stay in the same town, schools and station.
On site, a typical dormer or hip to gable takes six to eight weeks, a Velux three to five, and a bigger L-shape up to twelve. Before any building, count two to four weeks for the drawings and the approvals. The full timeline comes with your written quote.
Most interwar and post-war semis in areas like Cage Green, Higham Wood and Trench have a hipped roof, so the space usually comes from a hip to gable, often with a rear dormer. Squaring off the sloping side of the roof is what gives full head height across the new room.
For a standard dormer or hip to gable, no. The design, drawings and structural calculations are done by our own team, so there is no separate architect to appoint. If the job needs a full planning application, drawing it up and submitting it is part of what we do.
Yes. We work across Tonbridge town and out to Hildenborough and the villages around it, plus nearby towns such as Tunbridge Wells and Sevenoaks, always with our own team.
Yes, and nothing is subcontracted. Our own team both surveys and builds every Tonbridge conversion, which is what lets us stand a ten year written guarantee behind the finished work.
Thinking about the loft on a Tonbridge home? Book a free design survey. We measure the roof, tell you honestly what it will take, and hand you one fixed written price with no obligation.
We cover Tonbridge and the surrounding area with our own team. Call 0800 028 0099 or use our contact page.
Book a free, no-obligation design visit. We will tell you what your roof allows, show you what it could look like, and give you a fixed price. No pressure, no jargon.
A short conversation about the house and what you are hoping to do. No sales pitch.
We measure up and tell you honestly what your roof allows, what it would look like, and what it involves.
Itemised, with no hidden extras, and a ten-year written guarantee on the finished work.
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