Guide · Loft Conversions
Dormer vs Velux Loft Conversion: Which Is Right for You?
Velux is cheaper, faster and usually doesn't need planning. Dormer adds significantly more usable head height and floor area. Here's how to choose between the two on real budgets and real roofs.
Last updated: May 2026 · By Jamie Pocock
Quick Answer
Choose Velux if you have 2.2m+ existing apex height, want to spend £30,000–£45,000, and need the conversion finished in 6 weeks. Choose dormer (£45,000–£65,000, 8–10 weeks) if you want a usable double bedroom rather than a single, need a bathroom upstairs, or have under 2.2m apex height. Dormer adds 30–50% more usable floor area — almost always worth the extra cost if the budget supports it.
What each type physically does to the roof
Velux conversion
The roof line stays untouched. Velux skylight windows are cut into the existing slope to bring light in. Floor is laid, walls and ceilings insulated and lined, stairs installed, electrics and heating run. The internal space is the existing loft volume — sloping ceilings on both sides, full standing height only at the apex.
Dormer conversion
A box-shaped extension is built outward from the rear (or side) slope of the roof, creating a vertical wall, vertical sides, and a flat or pitched roof. Inside the dormer, you have full standing height across the entire dormer floor area — typically doubling the usable space compared to a Velux on the same roof.
Space gained — the real difference
On a typical 7m × 4m loft footprint with a 35° pitch:
- Velux: usable floor area (1.5m+ head height) ~12–15m². Bedroom that fits a double bed but wardrobes have to sit under the slopes.
- Dormer (rear, full-width): usable floor area ~22–28m². Room for double bed, full-height wardrobes, en-suite, sometimes a desk area.
The dormer roughly doubles the usable space. For most families, that's the difference between a single guest room and a master bedroom suite.
Cost difference and break-even
Typical 2026 figures: Velux £30,000–£45,000, dormer £45,000–£65,000. The dormer costs roughly £15,000–£20,000 more for roughly twice the usable space. Cost per usable m² actually drops significantly with the dormer.
Property value uplift varies too. In Hertfordshire and Essex, a Velux conversion typically adds 8–12% to value; a dormer conversion typically adds 15–20%. The dormer pays back its incremental cost faster at sale than the Velux.
Full pricing detail in our loft conversion cost guide.
Planning permission
Both can often be done under Permitted Development on most semi-detached and detached houses, subject to volume limits (40m³ for terraced, 50m³ for semi/detached). Larger dormers, side dormers and any conversion in conservation areas, on listed buildings, or in Article 4 zones need full planning permission.
Velux conversions almost always fall within PD. Dormers sometimes exceed PD volume limits — design carefully to stay within them where possible, or accept the planning timeline (typically 8–12 weeks) and £258 application fee.
Direct comparison
| Factor | Velux | Dormer |
|---|---|---|
| Cost (2026) | £30,000–£45,000 | £45,000–£65,000 |
| Build time | 5–7 weeks | 8–10 weeks |
| Usable floor area | 12–18 m² | 22–32 m² |
| Standing height (full) | Apex only | Full dormer area |
| Bathroom feasible? | Tight, sometimes no | Yes, comfortably |
| Planning | Usually PD | Often PD, sometimes planning |
| External roof appearance | Unchanged | Visible from rear/side |
| Property value uplift | 8–12% | 15–20% |
Other things that influence the choice
Existing apex height. Below 2.2m at the apex, Velux conversions are tight. Below 1.9m, they don't really work as habitable rooms. A dormer effectively raises the ceiling across the dormer footprint and rescues low-pitched lofts that wouldn't be liveable as Velux conversions.
Front of house vs rear. Front-facing dormers usually need full planning permission and conservation officers often resist them on visual grounds. Rear-facing dormers are nearly always achievable and rarely controversial. Side dormers depend on the street context and party-wall position.
Property type. Mid-terrace houses are limited to 40m³ under PD (versus 50m³ for semis and detached). That often constrains the dormer size. Bungalow loft conversions are nearly always dormer or hip-to-gable because the apex height is rarely sufficient for Velux.
Resale market signal. Estate agents in Hertfordshire and Essex consistently price dormer conversions higher per m² than Velux conversions, even controlling for total floor area. Buyers value the full standing height and en-suite feasibility.
Future extension plans. If you're also planning a rear extension later, the dormer should be designed in coordination — roof line, rainwater goods and finishes need to flow together. Plan once, not twice.
About the Author
Jamie Pocock — Owner & Lead Contractor
Jamie has 25 years' hands-on experience in roofing and building across Hertfordshire and Essex. He runs every J&Co Contractors project personally — from quote to completion — and writes these guides from real on-the-tools knowledge of what works, what doesn't, and what costs what in 2026.
- 25 years' hands-on roofing and building experience
- CRC Certified Roofer — self-certifies under Building Regs
- SafeContractor approved
- Insurance-backed workmanship guarantee on every job
FAQs
Frequently asked questions
Not sure whether dormer or Velux is right for your loft?
We'll survey your roof, talk through what's achievable under PD, and quote both options where they're both viable. No hard sell — the right answer is whatever genuinely suits your roof and budget.
Page last updated: May 2026 · J&Co Builders Ltd · 1 Ugley Hall Cottages, Bishop's Stortford CM22 6JB