Biggin Hill sits high on the North Downs, at the southern tip of London. Most homes here are rebuilt plotland bungalows, 1960s and 1970s Valley semis, or newer homes near the old RAF station. Many have a roof that could hold another bedroom.
This guide gives real 2026 figures for a Loft Conversion in Biggin Hill. It covers cost, consent, time on site and whether the work pays back. Figures come from Buildaway's Bromley pricing, the ONS, Nationwide and GOV.UK.
• Cost (2026): £28,000-£38,000 for a rooflight loft, £42,000-£58,000 for a rear dormer and £55,000-£72,000 for a hip-to-gable with dormer. A mansard runs £65,000-£90,000+.
• Timeline: 4-12 weeks on site. Allow about 3-5 months from first visit under permitted development, or 5-8 months with planning.
• Consent: most house lofts are permitted development. Flats, front dormers and the RAF Station conservation area need planning (£548 fee).
• ROI: a double bedroom and bathroom can add up to 24% to a three-bed home (Nationwide). On Bromley's £665,000 average semi (ONS), that is up to £159,600.
• Area: Biggin Hill (postcode TN16 3), in the London Borough of Bromley.
How Much Does a Loft Conversion Cost in Biggin Hill in 2026?
A loft conversion in Biggin Hill costs £28,000 to £38,000 for a rooflight conversion in 2026. A rear dormer costs £42,000 to £58,000. A hip-to-gable with a rear dormer costs £55,000 to £72,000. A bungalow dormer conversion costs £48,000 to £75,000, and a mansard £65,000 to £90,000 or more (Buildaway, 2026).
These are Buildaway's 2026 bands for the London Borough of Bromley, which includes TN16. Our Bromley loft conversion cost guide explains what each covers. Biggin Hill homes usually have parking and side access. That keeps scaffold and skip costs lower than in inner London.
| Conversion type | Best for | Guide price | Time on site |
|---|---|---|---|
| Rooflight (Velux) | Lofts with good head height | £28,000-£38,000 | 4-6 weeks |
| Rear dormer | Valley semis and detached homes | £42,000-£58,000 | 6-8 weeks |
| Hip-to-gable + rear dormer | Semis with a hipped roof | £55,000-£72,000 | 8-12 weeks |
| Bungalow dormer conversion | Plotland and chalet bungalows | £48,000-£75,000 | 8-12 weeks |
| Mansard | Where planning allows a near-full storey | £65,000-£90,000+ | 8-12+ weeks |
Prices include labour, materials, structural design, a standard staircase, building control and waste removal, to a ready-to-decorate finish. They are guides, confirmed by an itemised written quote after survey.
What Does a Luxury Loft Conversion in Biggin Hill Include?
A luxury loft conversion in Biggin Hill usually adds an en-suite, a bespoke staircase, large glazing and fitted storage under the eaves. These push a rear dormer towards the top of its £42,000 to £58,000 band, or beyond. An en-suite fit-out alone adds £5,000 to £10,000 or more.
These extras move the price most (Buildaway Bromley pricing):
- En-suite shower room: £5,000-£10,000+ for tiling, sanitaryware and waterproofing.
- Glazing: £2,000-£6,000+ for large rooflights or a Juliet balcony.
- Bespoke staircase: £1,500-£4,000+ for oak treads or a custom layout.
- Fitted joinery: wardrobes and drawers built into the eaves, priced to your design.
Our Biggin Hill bathroom renovation guide prices sanitaryware and tiles in detail. Use it to set your en-suite budget.
What Costs Sit Outside the Build Price?
Budget for fees on top of the build. A householder planning application costs £548 from April 2026, and a Lawful Development Certificate costs half that. Party wall surveyors often cost £1,000 to £2,000 or more per neighbour. VAT at 20% applies to building work on an existing home, so check every quote shows it.
Fee sources are GOV.UK planning fees and HMRC VAT Notice 708. Hold a 10% contingency for what the survey cannot see, such as rotten rafters or old wiring.
Which Biggin Hill Homes Suit a Loft Conversion?
Most Biggin Hill houses suit a loft conversion. Rebuilt plotland bungalows gain the most, as dormers can add a full upper floor. The 1960s and 1970s Valley semis suit a hip-to-gable with a rear dormer. Flats and homes in the RAF Station conservation area face the most consent steps.
Plotland and Chalet Bungalows
Biggin Hill began as a plotland. The Aperfield estate was sold in £10 plots, and owners built their own homes (Ideal Homes, University of Greenwich). Most have since been rebuilt as bungalows and chalets.
A bungalow loft is often the best-value space in TN16. Dormers on both slopes can add two bedrooms and a bathroom. Older roofs can hide asbestos, so the HSE advises a survey on any pre-2000 building first.
The 1960s and 1970s Valley Semis
Housing in Biggin Hill grew by 161% between 1961 and 1981 (Ideal Homes, post-war developments). Many of those homes sit in the Valley and off Main Road. Most are semis with hipped roofs and shallow pitches.
A hipped roof leaves little room inside. Building the hip up into a gable, then adding a rear dormer, creates a full-height bedroom and shower room. Our guide to checking if your Bromley loft can be converted shows how to measure yours.
Flats and Homes Near the Former RAF Station
Newer homes stand around the old RAF station, near the Biggin Hill Memorial Museum. Bromley lists Biggin Hill RAF Station as a conservation area. There, loft dormers need full planning. Flats have no permitted development rights, and the roof usually belongs to the freeholder.
Do You Need Planning Permission for a Loft Conversion in Biggin Hill?
Most loft conversions on Biggin Hill houses need no planning application. Permitted development allows 40 cubic metres of extra roof space on a terrace and 50 on a semi or detached home. Front dormers facing the road, flats and homes in the RAF Station conservation area need full planning permission.
The work cannot rise above the ridge, and dormers must sit about 20 cm back from the eaves. Side windows must be obscure-glazed and fixed below 1.7 metres. Balconies are not allowed. The Planning Portal and GOV.UK technical guidance set out each rule.
Past roof work counts towards the volume limit. Many plotland bungalows were altered decades ago, so measure what is left. Even under permitted development, get a Lawful Development Certificate. It proves the work is lawful when you sell. Our Bromley loft planning guide covers each route.
Does the Green Belt Affect a Loft Conversion in TN16?
Usually not, if you use permitted development. Green Belt land keeps its loft rights, unlike a conservation area. But if your scheme needs planning, Bromley tests whether it is a "disproportionate addition" to the original house. Homes towards Leaves Green, Saltbox Hill and Westerham Road should check before design starts.
The test sits in the National Planning Policy Framework. "Original" means the house as first built, or as it stood on 1 July 1948. Earlier extensions can use up most of the allowance.
Do You Need a Licence for Alterations or Covenant Consent?
Yes, if your home is leasehold or carries a covenant. A flat owner rarely owns the loft. You need the freeholder's written licence for alterations, and usually must buy the airspace. Bromley's former council homes went to a housing association in 1992, now Clarion. Newer freehold estates may restrict dormers by covenant.
Read your lease first, as GOV.UK's leasehold guidance explains. Bromley Council confirms alteration requests go to the housing association. Check for covenants on your title register from HM Land Registry.
Semis need one more consent. New steel beams often bear into the shared wall. Under the Party Wall Act, give your neighbour two months' notice before that work starts.
Which Building Regulations Apply to a Loft Conversion?
Every loft conversion needs Building Regulations approval, whatever the planning route. The main areas are structure, fire safety, stairs, insulation and electrics. Fire matters most. You need a protected escape route, fire doors and linked mains smoke alarms. Stairs need 2 metres of headroom, or 1.9 metres at the centre in a loft.
Read Approved Document B for fire and Approved Document K for stairs. Approved Document L sets roof insulation. On an exposed hilltop like Biggin Hill, good insulation pays back in winter.
How Long Does a Loft Conversion Take in Biggin Hill?
A loft conversion in Biggin Hill takes 4 to 12 weeks on site. A rooflight loft takes 4 to 6 weeks and a rear dormer 6 to 8 weeks. Design and approvals add 3 to 8 weeks first. From first visit to handover, allow about 3 to 5 months, or 5 to 8 months with planning.
| Phase | Typical time | What happens |
|---|---|---|
| Survey and design | 3-8 weeks | Measured survey, head-height check, drawings, structural calculations |
| Consent | Up to 8 weeks | LDC or planning decision; party wall notices run alongside |
| Build on site | 4-12 weeks | Scaffold, steels, floor, dormer, insulation, stairs, first fix, plaster |
| Snagging and sign-off | 1-2 weeks | Final fix, building control completion certificate |
Bars scaled to the longest upper figure. Source: Buildaway's published Bromley loft conversion timelines.
You can usually stay at home for most of the build. The loft is opened from outside, and the stair goes in near the end. Our guide to living through a loft conversion explains each noisy week.
What Can Delay a Loft Conversion in Biggin Hill?
Four local factors cause most delays. Bats may roost in roofs near North Downs woodland. Old plotland roofs can hide asbestos. A crane lifting steel near London Biggin Hill Airport may need notice first. And party wall notices on a semi need two months. Late design changes slow every job too.
All bat species are protected. If a survey finds a roost, work may need a licence, as GOV.UK's bat guidance explains. Bat surveys are seasonal, so book early. Natural England describes the wooded North Downs setting around the town.
Most loft steels go up by hand or hoist. Longer beams may need a crane. The CAA's crane notification guidance covers cranes near an aerodrome. Our Bromley loft timeline guide breaks down each week.
How to Plan a Loft Conversion in Biggin Hill
Follow these steps in order. Each one removes a common cause of delay or extra cost.
- Check the head height. Measure from the top of the ceiling joists to the ridge. About 2.2 metres is a good start.
- Check the constraints. Confirm tenure, covenants, conservation area and Green Belt status for your address.
- Book a survey. Measure the roof, test pre-2000 materials for asbestos and check for bats.
- Fix the design. Agree the dormer, stair position, en-suite and steels, then freeze it.
- Secure consent. Apply for a Lawful Development Certificate or planning permission.
- Serve notices. Give party wall notices and book building control.
- Get a fixed written quote. Ask for an itemised price, with fees and contingency shown.
- Build and sign off. Scaffold, build, then collect the completion certificate.
What Is the ROI of a Loft Conversion in Biggin Hill?
Nationwide found that adding a double bedroom and bathroom can add up to 24% to a three-bed home. On Bromley's £665,000 average semi (ONS, August 2026), that is up to £159,600. A £42,000 to £58,000 rear dormer can deliver that. Loft conversion ROI is usually the strongest of any home project.
The ONS put Bromley's average price at £520,000 in August 2026. Semi-detached homes averaged £665,000 and detached homes £1,083,000. Nationwide's research also found 10% more floor space adds about 5% to value.
Cost bars show the top of each range. Values: ONS UK House Price Index, August 2026 (provisional). Uplifts: Nationwide, October 2025.
For the wider picture, read whether a loft conversion is still a smart investment in Bromley.
Is It Cheaper to Convert the Loft or Move in TN16?
For most TN16 families, converting is far cheaper. Moving from a £665,000 semi to an £800,000 home costs £30,000 in stamp duty alone, before agent, legal and removal fees. That money buys no space. A £42,000 to £58,000 rear dormer adds a bedroom you keep, and value too.
The stamp duty figure uses GOV.UK's standard residential rates. If the roof will not work, our Biggin Hill home extension guide compares building out instead.
What Bespoke Loft Conversion Designs Suit Biggin Hill?
The best designs here use the hilltop light and long views. Popular choices are a rear dormer with an en-suite, a hip-to-gable on a Valley semi, and twin dormers on a bungalow. Good bespoke loft conversion design also plans the stair, storage and heating from the start, not as an afterthought.
- Stack the stair. Land it above the existing stair, so you do not lose a bedroom below.
- Stack the plumbing. Put the en-suite above a bathroom to keep pipe runs short.
- Match the outside. Tile-hung or slate dormer cheeks suit most TN16 roofs, and permitted development needs similar materials.
- Use the eaves. Fitted storage fills low space that furniture cannot.
- Plan a workspace. A loft office with rooflights works well, as our Bromley loft home office guide shows.
Biggin Hill Loft Conversion Terms Explained
- Permitted development (PD)
- Building work you can do without a planning application, within set limits.
- Rear dormer
- A box-shaped addition off the back roof slope that adds standing height.
- Hip-to-gable
- Building a sloping side roof up into a flat gable wall to gain space.
- Mansard
- A rebuilt roof with a steep lower slope, adding a near-full storey.
- Lawful Development Certificate (LDC)
- A council certificate proving your PD loft is lawful.
- Licence for alterations
- A freeholder's written consent, under the lease, for changes to a leasehold home.
- Party structure notice
- A formal notice to your neighbour before work to a shared wall.
- Green Belt
- Protected open land around towns. Planning schemes are judged on size against the original house.
How Do You Choose a Loft Conversion Specialist in Biggin Hill?
Choose a loft conversion specialist in Biggin Hill who surveys before pricing and sends an itemised written quote. Check trade body membership, insurance and recent Bromley lofts. Ask who handles drawings, steels, party walls and building control. A trusted loft conversion firm in TN16 will raise bats, covenants and Green Belt unprompted.
Ask every builder these five questions before you sign:
- Is the quote itemised, with fees and contingency shown?
- Who prepares the drawings and structural calculations?
- Who serves party wall notices and books building control?
- What are the payment stages?
- Can I see recent loft conversions in the Bromley borough?
Our Biggin Hill loft conversion specialists manage design, consent, build and finish as one team. Our loft conversion service sets out what is included.
Does Buildaway Give Fixed Prices and Warranties?
Yes. Buildaway prices every loft conversion with a fixed, itemised written quote after a free site visit. The price changes only if you change the brief or opening up the roof reveals hidden problems, and we agree any change first. All structural and fit-out work carries Buildaway's 18-month workmanship warranty.
Buildaway is registered with the Federation of Master Builders and holds public liability insurance.
Frequently Asked Questions
How much does a dormer loft conversion cost in Biggin Hill?
A rear dormer costs £42,000 to £58,000 in 2026. A hip-to-gable with a rear dormer costs £55,000 to £72,000. Both include structure, a staircase, insulation, electrics and building control, to a ready-to-decorate finish. An en-suite adds £5,000 to £10,000 or more. These are Buildaway's Bromley guide prices.
Do I need planning permission for a loft conversion in TN16?
Usually not, if you own a house outside a conservation area. Permitted development allows 40 cubic metres on a terrace and 50 on a semi or detached home. Front dormers, flats and the RAF Station conservation area need planning. Get a Lawful Development Certificate to prove the work is lawful.
Can you convert the loft of a bungalow in Biggin Hill?
Yes, and it is often the best-value space in TN16. Dormers on one or both slopes can add one or two bedrooms and a bathroom. Expect £48,000 to £75,000 and 8 to 12 weeks on site. Older plotland roofs should be tested for asbestos before work starts.
How long does a loft conversion take from start to finish?
Allow about 3 to 5 months from first visit under permitted development. Design takes 3 to 8 weeks, and the build 4 to 12 weeks. If you need planning, add the eight-week decision period, so 5 to 8 months in total. Bat surveys or party wall disputes can add more.
Does a loft conversion add value in Biggin Hill?
Yes, usually more than it costs. Nationwide found a double bedroom and bathroom can add up to 24% to a three-bed home. On Bromley's £665,000 average semi, that is up to £159,600. A loft that adds a small room without a bathroom adds much less.
Can I convert the loft above my leasehold flat?
Only with the freeholder's consent. The roof and loft usually belong to the freeholder, so you must buy the airspace and get a licence for alterations. Flats have no permitted development rights, so planning is needed too. For former council flats, ask the housing association, now Clarion.
The Bottom Line on a Biggin Hill Loft Conversion
Budget £42,000 to £58,000 for a typical rear dormer, or £55,000 to £72,000 for a hip-to-gable. Allow 3 to 8 months from first visit. A loft that adds a bedroom and bathroom pays back best.
Check your head height, tenure and conservation status first. Then survey, design, consent and build, in that order. When you are ready, book a free survey and fixed written quote with Buildaway.
By Cormac Hegarty, Director & Founder - Buildaway. Cormac Hegarty is the Founder of Buildaway and a residential construction specialist with a deep portfolio of projects across London.