UK Homeowner’s Guide
Unsure what’s possible in your roof space?
Send us your loft photos and a quick sketch — we’ll tell you if it’s viable, PD or needs planning, and what it could cost.
Loft conversions — the UK essentials in one place
A loft conversion can add a new bedroom, home office or bathroom while avoiding a full footprint extension. Most houses can convert the roof space under Permitted Development (PD) if volume limits and design rules are met; others need a planning application (for example, flats/maisonettes, conservation areas with Article 4, or big rear dormers on street frontages).
- Typical costs: £18,000–£30,000 (roof-light/Velux), £35,000–£65,000 (rear dormer), £55,000–£95,000+ (hip-to-gable / L-shaped dormer), London often higher.
- Timeline: Design & approvals 4–10 weeks; build 5–12 weeks depending on type/complexity.
- Value uplift: Commonly 10–20%+ for an extra bedroom with ensuite, strongest in high-demand areas.
- Key checks: head height (2.2m+ desirable), roof structure, stair position, fire protection, and Party Wall where semi/terrace.
This guide focuses on England & Wales. Always confirm local rules with your council and the Planning Portal.
What counts as a loft conversion?
Any work that turns unused roof space into habitable rooms — usually a bedroom, office or bathroom — is a loft conversion. It may be as simple as adding roof-light windows, or as involved as constructing a rear dormer or hip-to-gable extension to gain headroom and floor area.
If you live in a flat or maisonette, PD rights usually do not apply — you’ll almost always need planning permission. Houses usually have PD rights unless they’ve been removed.
For broader planning context, see our pillar guides: Planning Permission, Do I Need Planning Permission?, Planning Permission Cost, and Planning Permission Drawings.
Loft conversions: Permitted Development or planning application?
Many house loft conversions are possible under Permitted Development (PD) — no planning application — provided you meet the General Permitted Development Order (GPDO) conditions. Key PD tests include:
- Volume added: up to 40m³ (terraced) or 50m³ (semi-detached/detached), including any past roof additions.
- No extension beyond plane of the existing roof slope fronting the highway (i.e., no front dormer on most streets).
- Materials similar in appearance to the existing house.
- No verandas/balconies; side-facing windows obscure-glazed & 1.7m above floor level.
- Dormer set back at least 20cm from the eaves (measured along the roof slope), with the dormer not higher than the existing ridge.
Even for PD projects, councils can ask for an informal lawful development check or a formal Lawful Development Certificate (LDC). We usually recommend an LDC for re-sale certainty and mortgage/valuation comfort.
External references: Planning Portal — guidance | GOV.UK — planning permission in England & Wales
Main types of loft conversion
1) Roof-light (Velux) conversion
The simplest — add roof-lights, insulate, and fit out the space. Best where head height already exists (tall ridge). Lowest cost and disruption.
2) Rear dormer
A box dormer to the rear roof slope to gain headroom and usable floor area. Common on terraces and semis; often PD if volume & set-backs are respected.
3) Hip-to-gable
For hipped roofs (common on semis), you extend the side roof up to a gable end and usually add a rear dormer. Big gain in volume; usually needs careful PD volume math.
4) L-shaped dormer (typical on rear outrigger)
Popular on Victorian terraces with a rear outrigger, creating excellent headroom over the main and rear roof. Normally needs precise PD checks; sometimes a planning application.
Loft conversion costs (UK ranges)
Budget bands vary by region, access, finishes, and structural complexity. London and the South East trend higher.
| Type | Typical Build Cost | With Ensuite | Notes |
|---|---|---|---|
| Roof-light (Velux) | £18,000–£30,000 | +£4,000–£8,000 | Head height needed; minimal structure changes. |
| Rear dormer | £35,000–£65,000 | +£5,000–£10,000 | Most common; check PD volume and eaves set-back. |
| Hip-to-gable + rear dormer | £55,000–£95,000+ | +£5,000–£12,000 | Major structural work; big area gain on semis/detached. |
| L-shaped dormer | £60,000–£100,000+ | +£6,000–£12,000 | Great for two rooms/ensuite layouts on terraces. |
Need clearer numbers? See also: Planning Permission Cost and Making Plans for design/approval budgeting.
Not sure if your idea fits Permitted Development?
We’ll check your project against PD rules and let you know if you need a full planning application.
Process & timeline
- Feasibility & survey (Week 1–2): Head height checks, stair position, structure, drainage, dormer options.
- Design & drawings (Week 2–4): Plans/sections/elevations, stair compliance, fire strategy. See Planning Permission Drawings.
- PD/LDC or planning application (Week 4–10): PD confirmation or a householder application if required. Target 8 weeks for decision.
- Building Regulations (parallel): Either Full Plans or Building Notice route; structural calcs, fire, stairs, thermal.
- Party Wall (where relevant): Serve notices to neighbours on semis/terraces. Allow 1–8 weeks depending on responses.
- Build (5–12 weeks): Strip-out, steels, dormer framing, stair install, first fix, insulation/board, second fix, decorate.
Building Regulations essentials
- Structure: Steel beams/timbers sized by an engineer to support new loads and maintain bearing onto walls/party walls.
- Fire protection: 30-minute protected escape route (doors/linings), smoke alarms to each storey, and in 3-storey homes a fire door strategy or sprinklers/alternative.
- Stairs: Max rise 220mm, min going 220mm, pitch ≤42°, 2.0m headroom (some relaxations near sloping roof with central 2.0m clearance).
- Thermal: Roof, walls and dormer cheeks insulated to current U-values; continuous vapour control & ventilation.
- Ventilation: Background vents + mechanical extract for bathrooms (min 15 l/s typically) with ducting to external air.
- Sound: Floor upgrades for impact/airborne sound; consider resilient bars and acoustic quilt.
For broader compliance topics, see our Building Regulations guide.
Party Wall & neighbours
On semis/terraces, steel or dormer work often affects the party wall. You’ll usually need to serve Party Wall etc. Act 1996 notices. Good drawings and early chat with neighbours reduce delays.
Will a loft conversion add value?
In many markets a well-designed loft can add 10–20%+, particularly where it creates a primary bedroom with ensuite and maintains good first-floor bedrooms. Valuers prefer documented approvals (LDC/planning) and Building Control sign-off. Good daylight and stair positioning are critical.
Local council quirks (patterns we see)
- Milton Keynes & Buckinghamshire: Careful on rear dormer bulk and materials; set-backs and ridge height consistency are watched. LDCs are common for re-sale peace of mind. See Buckinghamshire Planning.
- Guildford & Surrey districts: Conservation pockets and Article 4 streets around town centres can remove PD — planning app likely. See Planning Permission Guildford.
- London boroughs: More design scrutiny on dormer massing and materials; mansard expectations in some terraces; costs trend higher.
If your property has previous extensions, we’ll audit PD volume to avoid breaching cubic limits. Where PD is tight, a modest redesign can often bring it back into compliance.
Common pitfalls & quick fixes
- Insufficient head height: Consider a dormer, a lower ceiling to first floor (selectively), or re-planning stair location.
- Over-dominant dormer: Reduce width/height, increase eaves set-back, or switch to twin dormers with a central valley.
- Poor ventilation/overheating: Cross-ventilation, solar control glass, roof-light blinds, and proper duct runs to outside.
- Stair squeeze: Winders/quarter landings can help — but maintain clear widths and headroom for Building Regs.
- Budget creep: Fix specs early (sanitaryware, tiling, roof finishes). Keep a 10–15% contingency.
Loft conversions — FAQs
What are loft conversions?
A loft conversion turns roof space into habitable rooms (bedroom, office, bathroom) through insulation, structure, windows and access (stairs). Types include roof-light, rear dormer, hip-to-gable and L-shaped dormers.
Do loft conversions need planning permission?
Many house lofts are Permitted Development if they meet GPDO limits (volume, set-backs, materials, no front dormer, etc.). Flats/maisonettes, conservation areas with Article 4, or removed PD rights usually require a planning application.
Is a loft conversion permitted development?
Often yes for houses within volume limits: up to 40m³ (terraced) or 50m³ (semi/detached). Front dormers facing the highway aren’t PD. Always verify and consider an LDC for proof.
How much does a loft conversion cost (UK)?
Roof-light £18k–£30k; rear dormer £35k–£65k; hip-to-gable/L-shaped £55k–£100k+. Ensuite typically adds £4k–£12k. London is higher. Design, approvals and structural calcs are additional.
How much does a loft conversion cost in London?
London pricing can be 10–25% above UK averages due to access, labour and scaffolding. Many dormers with ensuite land in the £55k–£85k band; larger L-shapes frequently exceed £90k.
How much will a loft conversion add to value?
Commonly 10–20%+ if it creates an extra bedroom (ideally with ensuite) and keeps good bedroom balance below. LDC/planning approval and Building Control sign-off support valuations.
How long do loft conversions take?
Design & approvals 4–10 weeks depending on PD/planning; construction 5–12 weeks depending on complexity and bathroom scope.
Can any loft be converted?
Most can, but minimum head height (2.2m desirable), stair position, and structure are critical. Low ridges may need a dormer, partial ceiling drop, or may be uneconomic.
Different types of loft conversions
Roof-light (Velux), rear dormer, hip-to-gable, and L-shaped dormer. Choice depends on roof form, head height and budget.
How to do a DIY loft conversion?
Because of structure, fire safety and warranty implications, full DIY is risky. Many homeowners DIY finishes only. Structural design, steel installation, stairs and compliance should be led by professionals.
Do you need planning to convert a loft?
Houses often proceed under PD; flats/maisonettes and some conservation streets require planning. When unsure, obtain a Lawful Development Certificate.
Why are loft conversions so expensive?
Hidden structure (steels), complex access/scaffolding, stair creation, and bathroom ventilation/tiling raise costs. Roofs also need robust insulation and airtightness detailing.
How are loft conversions done?
Typical sequence: scaffold and external works, steels and floor, dormer formation, roof-lights, stairs, first fix, insulation/board, second fix, decoration. Building Control inspects key stages.
Can a loft conversion be classed as a bedroom?
Yes if it meets Building Regulations (structure, stairs, fire protection, ventilation, insulation) and has suitable escape/egress and headroom. Valuers prefer approvals/sign-off.
Are loft conversions always hot or cold?
A well-insulated, well-ventilated loft shouldn’t be uncomfortable. Use proper U-values, airtightness, cross-ventilation, and consider solar-control glazing and blinds.
How much is a loft conversion for a 3-bed semi?
Rear dormers typically fall in the £40k–£70k band regionally (higher in London), plus finishes and ensuite if needed. Hip-to-gable options trend higher.
How much does an attic conversion cost?
Same ranges as above: roof-light £18k–£30k; dormer £35k–£65k; hip-to-gable/L-shape £55k–£100k+.
How long loft conversion take? (quick)
Build phase is commonly 5–12 weeks; allow extra for design/approvals.
Loft conversion calculators — are they accurate?
Online calculators give rough bands only. Site access, structural spans, stair design and bathroom spec can swing the figure significantly. Use them as a starting point.
Are barn conversions a good investment? How much do they cost?
Different category: barn conversions are not lofts, involve full dwelling conversions and fall under separate planning policies (often Class Q or full planning). Costs and risks are much higher; talk to us if you’re exploring one.
How much loft conversion London?
Expect 10–25% uplift on UK averages; access, traffic management and scaffolding add cost in many boroughs.
For broader planning topics and next steps, see our pillars and stones: Planning Permission · Do I Need Planning Permission? · Planning Permission Drawings · Building Regulations
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