How to Price Velux and Skylight Installation: Labour, Materials and Margin Guide
Quick Answer: A standard pitched-roof rooflight installation prices at £900-£2,200 supply and fit for a single window into an existing tiled or slated roof, rising to £1,800-£4,500 for a flat-roof rooflight (which needs an upstand/kerb and waterproofing) and £3,000-£8,000+ for a large structural opening or roof lantern. Labour is typically 1-2 days for a roofer/carpenter for a pitched-roof unit. Where the opening enlarges the structure or alters the roof, Building Regulations apply (Part A structure, Part L thermal, Part B fire/escape, Part K guarding), and rooflights are usually permitted development subject to projection and obscure-glazing rules.
Summary
Rooflight installation ("Velux" is a brand name now used generically) spans a huge price range because "fitting a skylight" can mean anything from dropping a single window between existing rafters in an afternoon to forming a large structural opening with steel trimming and internal plastering over several days. The pricing mistakes nearly all come from quoting the easy version and discovering the hard one: the rafters need trimming, the room below needs a plastered reveal/liner, scaffolding or a tower is needed for access, and the flat-roof version needs a built-up kerb and waterproofing the pitched version doesn't.
The biggest single cost driver is pitched roof vs flat roof. A pitched-roof rooflight that fits between existing rafters (most domestic Velux sizes are designed to) is a relatively quick, well-rehearsed job. A flat-roof rooflight needs a timber upstand/kerb built, the flat-roof membrane dressed up and over it, and a frost-and-condensation-managed detail — substantially more labour and risk of leaks. The second driver is whether the opening is between rafters (no structural work) or wider than a rafter bay (rafters cut and trimmed with new trimmers, a structural job).
This guide breaks down the pricing by scenario — single pitched-roof window, multiple windows, flat-roof rooflight, structural opening, and roof lantern — with worked examples, day rates, and the regulations that determine whether the job is notifiable. For loft conversions where rooflights are part of a bigger job, see loft conversion pricing guide; for the installation detail see roof window installation.
Key Facts
- Standard pitched-roof rooflight (e.g. 780×980mm to 940×1600mm) — £180-£600 supplied (centre-pivot, manual)
- Top-hung / escape rooflight — £350-£900 supplied (larger opening, egress-compliant)
- Electric / solar-powered opening rooflight — £550-£1,400 supplied (motor, rain sensor, controls)
- Flat-roof rooflight (fixed, double/triple glazed) — £400-£1,600 supplied
- Flat-roof opening/walk-on rooflight — £900-£3,500 supplied
- Roof lantern (uPVC/aluminium, e.g. 1.5×1m to 3×2m) — £700-£3,500+ supplied
- Flashing kit (tile / slate specific) — £60-£180 supplied
- Upstand/kerb (flat roof, builder-made or proprietary) — £150-£500 supplied/built
- Roofer/carpenter day rate — £200-£350 regional, £300-£450 London
- Pitched-roof single unit labour — 0.5-1.5 days
- Flat-roof unit labour — 1-2 days (kerb + waterproofing)
- Structural opening (rafters trimmed) — +1-2 days, plus structural sign-off
- Plastered reveal/liner — £150-£400 plus plasterer time
- Scaffolding/tower — £150-£600 (tower) to £600-£1,500 (scaffold) depending on height/duration
- VAT — 20% standard; rooflights as part of qualifying works (e.g. some new-build/conversion) may differ
- Min pitch / max pitch — most pitched rooflights suit ~15-90°; flat-roof units need a min fall (kerb)
Quick Reference Table
Spending too long on quotes? squote turns a 2-minute voice recording into a professional quote.
Try squote free →| Scenario | Labour Days | Material Cost | Total (Regional) | Total (London) |
|---|---|---|---|---|
| Single pitched-roof rooflight (between rafters) | 0.5-1.5 | £250-£700 | £900-£1,800 | £1,200-£2,200 |
| Electric/solar opening rooflight | 1-1.5 | £600-£1,500 | £1,400-£2,800 | £1,800-£3,400 |
| Two/three pitched-roof rooflights | 1.5-3 | £600-£1,800 | £1,800-£4,200 | £2,400-£5,200 |
| Flat-roof rooflight (with kerb + waterproofing) | 1-2 | £500-£2,000 | £1,800-£4,500 | £2,400-£5,500 |
| Structural opening (rafters trimmed) | 2-4 | £700-£2,500 | £3,000-£7,000 | £4,000-£8,500 |
| Roof lantern (with kerb + plastering) | 2-4 | £1,000-£4,000 | £3,500-£8,000 | £4,500-£9,500 |
Detailed Guidance
Single Pitched-Roof Rooflight — The Bread-and-Butter Job
Domestic rooflights are dimensioned to fit standard rafter spacings (typically 600mm centres), so a single unit can usually be installed between existing rafters with no structural work. The sequence:
- Set out and mark the opening internally and externally
- Strip tiles/slates around the opening
- Cut and remove the roofing membrane and battens within the opening
- Fit the timber frame/box around the opening
- Install the window and fix to the frame
- Fit the flashing kit (tile- or slate-specific, matched to the covering profile)
- Re-lay tiles/slates around the unit, dressing the flashing
- Internally: form and plaster the reveal/liner (often splayed for light)
Pricing example (regional, single manual centre-pivot into tiled roof):
| Item | Cost |
|---|---|
| Rooflight (e.g. 780×980mm, double-glazed) | £320 |
| Tile flashing kit | £95 |
| Timber, battens, membrane, fixings | £60 |
| Roofer/carpenter 1 day | £280 |
| Reveal plastering (0.5 day plasterer) | £140 |
| Access (tower hire) | £120 |
| Waste/sundries | £40 |
| Margin 22% | £254 |
| Total | £1,409 |
Flat-Roof Rooflight — The Kerb Is the Job
A flat-roof rooflight cannot sit flush — water would pond against it. It needs a timber upstand (kerb), typically 150mm+ high, built around the opening, with the flat-roof waterproofing (EPDM, GRP, felt, or liquid) dressed up and over the kerb to form a continuous watertight detail before the rooflight is bedded on top. This is where the cost and the leak risk live.
Additional considerations:
- Insulated kerb to manage cold bridging and condensation (a cold kerb sweats)
- Fall — the surrounding flat roof must fall away from the kerb so water drains, not pools
- Glazing — flat-roof units are usually triple-glazed or have a thermal upgrade because they face the sky and lose heat
- Walk-on / flush glass units cost considerably more
The waterproofing detail must integrate with the existing flat-roof system — see flat roofing and epdm flat roof. Get the kerb-to-membrane lap wrong and it leaks.
Structural Openings — When Rafters Get Cut
If the rooflight (or a row of them) is wider than a single rafter bay, one or more rafters must be cut and the load carried by trimmers (horizontal members) fixed to the adjacent intact rafters. This is structural work under Building Regulations Part A and usually needs:
- A structural assessment / engineer's detail for larger openings
- Trimming timbers sized to carry the redistributed load
- Building Control notification and inspection
- More labour (1-2 extra days) and sign-off
Don't quote a wide opening as a "between rafters" job — the structural work and Building Control add materially to both time and cost. See pitched roof structure.
Roof Lanterns
A roof lantern is a raised, multi-pane glazed structure (uPVC or aluminium framed) sitting on a flat-roof kerb, common over kitchen extensions. Pricing combines the lantern cost (size- and frame-dependent), the kerb construction, the flat-roof waterproofing around it, and internal plastering of the opening below. Large aluminium lanterns over 2×3m, structural openings, and bespoke shapes push toward the top of the range. See roof lantern.
Access, Reveals and the Hidden Costs
Three costs are routinely under-quoted:
- Access — a single ground-floor extension rooflight might need only a tower (£100-£300/week), but a two-storey roof needs scaffolding (£600-£1,500), which can equal the cost of the window itself.
- Internal reveal/liner — the plastered, often splayed, reveal below the window is real plasterer time and is what the customer sees daily. Quote it.
- Making good — re-laying tiles/slates to match (especially on older or non-standard coverings), and matching internal finishes.
Regulations
- Part A (Structure) — any opening wider than a rafter bay; trimming and load
- Part L (Conservation of fuel and power) — rooflight U-value requirements; new rooflights must meet minimum thermal standards
- Part B (Fire safety) — in a loft conversion or habitable roof room, an egress (escape) rooflight of minimum openable size and sill height may be required as a means of escape
- Part K (Protection from falling) — guarding and the cleanability/safety of glazing in some locations
- Part F (Ventilation) — rooflights can provide purge ventilation
- Permitted development — most rooflights are PD provided they don't project more than 150mm above the existing roof plane, aren't above the highest part of the roof, and (on side elevations facing a boundary) use obscure glazing and restricted opening. Listed buildings and conservation areas have tighter rules. See permitted development householder.
Frequently Asked Questions
How much does it cost to fit a Velux window?
A single standard pitched-roof rooflight that fits between existing rafters typically costs £900-£1,800 supply and fit regionally (£1,200-£2,200 in London), including the flashing kit, internal reveal plastering, and access. Electric/solar opening units cost more (£1,400-£2,800), and flat-roof rooflights cost more again (£1,800-£4,500) because they need a built-up kerb and waterproofing.
Do I need planning permission for a roof window?
Usually not — rooflights are generally permitted development provided they don't project more than 150mm above the existing roof slope, don't sit above the highest part of the roof, and (on side-facing elevations near a boundary) are obscure-glazed with restricted opening. Listed buildings and conservation areas have tighter rules and may require consent. The structural and thermal work may still be notifiable under Building Regulations even when planning isn't needed.
Why is a flat-roof skylight so much more expensive than a pitched one?
Because it needs a timber upstand (kerb) built around the opening, with the flat-roof waterproofing dressed up and over it to form a watertight, condensation-managed detail — work a pitched-roof unit (which sits between rafters with a simple flashing kit) doesn't require. The kerb construction, the waterproofing integration, and the higher-spec (triple) glazing for the sky-facing position all add cost and labour.
Does fitting a skylight need Building Regulations approval?
A like-for-like or between-rafters rooflight is generally not notifiable for structure, but it must still meet Part L thermal (U-value) requirements. An opening wider than a rafter bay involves cutting rafters and is structural work under Part A, requiring Building Control. In a habitable loft room, Part B may require an egress (escape) rooflight of a minimum size. When in doubt, check with Building Control.
How long does it take to fit a roof window?
A single pitched-roof rooflight between rafters is typically 0.5-1.5 days including the internal reveal. A flat-roof rooflight with a kerb and waterproofing is 1-2 days. A structural opening with rafters trimmed adds 1-2 days plus Building Control sign-off, and a roof lantern is 2-4 days including kerb, waterproofing, and plastering.
Regulations & Standards
Building Regulations Part A — Structure (trimming openings, load)
Building Regulations Part L — Conservation of fuel and power (rooflight U-values)
Building Regulations Part B — Fire safety (egress/escape rooflights in habitable roof rooms)
Building Regulations Part K — Protection from falling, collision and impact (guarding, glazing)
Building Regulations Part F — Ventilation (purge ventilation)
BS 5534:2014+A2:2018 — Slating and tiling (re-laying covering around the rooflight)
BS 6229:2018 — Flat roofs (kerb and waterproofing detail)
Town and Country Planning (GPDO) 2015 — permitted development for rooflights
GOV.UK — Approved Document L — rooflight thermal requirements
Planning Portal — Roof windows and rooflights — permitted development
GOV.UK — Approved Document B — escape provision
NFRC — Roofing technical guidance — rooflight installation and flashing
GOV.UK — Approved Document A — structural openings
roof window installation — installation method and flashing detail
rooflights skylights — rooflight types and selection
loft conversion pricing guide — rooflights as part of a loft conversion
roof lantern — roof lantern construction and glazing
permitted development householder — permitted development rules