Getting Daylight Back Into a Solid Roof
A solid or tiled roof makes a conservatory warmer and darker. A roof window or a lantern buys some of the light back. Here is what each costs as two different jobs, what Building Regulations and planning ask of the opening, and the one lantern price nobody publishes. The roof itself is priced at what a solid roof adds and saves and at replacing a conservatory roof with tiles.
Roof window · fitted as part of a new solid or tiled roof · each · VAT not stated
£450 to £750 £750 to £1,200 if added later
Thin evidence1 publisher, both bands on one page · published 1 May 2026 · checked 14 September 2026
How much do conservatory roof windows cost?
A standard-size roof window costs £450 to £750 fitted as part of a new solid or tiled conservatory roof, and £750 to £1,200 added to a roof that is already on. Both are per window, from one UK quote-comparison publisher's cost guide published 1 May 2026, and neither says whether VAT is included. We grade both Thin evidence. Checked 14 September 2026.
Those are two jobs, not two ends of one range: a window built into the new roof as it goes on, or an opening cut into a finished roof, which the same publisher itemises as the window plus flashing, scaffolding, labour and finishing. Lanterns are priced separately below, and only ever on flat roofs. To price the roof and the window together, see what a new roof would cost you, then add each window as its own line.
Roof window, rooflight or lantern: which one is on your quote?
Installers use the three words loosely. Approved Document L, the energy guidance under the Building Regulations in England, does not, and the difference changes the U-value the unit must reach.
| Term | What Approved Document L says | Limiting U-value | Calculated as if |
|---|---|---|---|
| Roof window | “A window installed in the same orientation as, and in plane with, the surrounding roof.” | 1.4 W/m²K, or Window Energy Rating Band B | Vertical |
| Rooflight | “A glazed unit installed out of plane with the surface of the roof on a kerb or upstand. Also sometimes referred to as a skylight.” | 2.2 W/m²K, over its outer surface area | Horizontal |
| Lantern | Treated as a rooflight: a glazed unit on an upstand, out of plane with the roof | 2.2 W/m²K | Horizontal |
Approved Document L, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments: Appendix A, Table 4.2 and paragraph 4.5. Checked 14 September 2026.
A roof window is calculated as if upright and a rooflight as if flat, so the two limits are not comparable numbers. Ultraframe's own explainer treats skylights and rooflights as different products; the regulations treat them as one. And the lantern limit of 1.6 W/m²K quoted by one price guide is the document's figure for windows in new homes, not for rooflights.
What each option costs, fitted and supply only
Per unit, as published. Roof window figures are for conservatory roofs. Lantern figures are for flat roofs, the only roof anyone prices them on.
| Option | Published price | VAT at source | Evidence | Source |
|---|---|---|---|---|
| Roof window fitted with a new solid or tiled roof, each | £450 to £750 | Not stated | Thin1 source | Publisher A, 1 May 2026 |
| Roof window added to an existing tiled roof, each | £750 to £1,200 | Not stated | Thin1 source | The same guide |
| One roof window line in an itemised 4m × 4m solid roof quote | £1,200 before VAT, £1,440 with VAT | Before VAT | Thin1 source, above its own band | Publisher A, tiled roof cost guide, prices verified July 2026 |
| Roof window, supply only, entry centre-pivot model | £305 before VAT, £366 with VAT | Before VAT on one, not stated on one | Reasonably2 sources, 1.11× | VELUX, costs of adding a roof window, undated; Publisher B, 11 June 2026 |
| Conservatory rooflight, supply only, one shop's range | £168.64 to £1,357.16 | Included | Thin1 source | One shop's conservatory rooflight range |
| Small uPVC lantern, 850mm × 850mm, fitted, flat roof | £1,100 to £1,500 | Not stated | Thin1 source | Publisher B, 28 July 2026 |
| Medium aluminium lantern, about 1.5m × 2m to 3m × 2m, fitted, flat roof | £1,800 to £3,500 | Not stated | Reasonably3 sources, 1.94× | Publisher B, 28 July 2026; Publisher A, 1 May 2026; Publisher C, 18 October 2022 |
| Entry lantern, supply only | £499.80 to £704.70 before VAT | Before VAT on two, not stated on one | Reasonably3 sources, 1.41× | A supplier's Korniche lantern list; a trade reseller's price list; Publisher C, about £550 |
| Lantern set into a pitched solid conservatory roof, fitted | We do not have a figure | n/a | No figure | No publisher itemises one |
Where a price is before VAT we say so and add VAT at 20 per cent. Where a publisher states no VAT position we do not guess one. Checked 14 September 2026.
The medium lantern band includes an older publisher that prices the lantern and its fitting separately, added together here. The last row is blank on purpose: nobody publishes a lantern price for a pitched solid conservatory roof, and a flat-roof figure would be a guess. A national trades directory's lantern table is left out because its labour figure alone is higher than its own cheapest installed price.
Why the same roof window is quoted at £450 and at £1,440
Three things move the price of one window. A quote should say which apply.
- When it goes in. Fitted with a new roof, £450 to £750. Cut into a finished roof, £750 to £1,200.
- Whether VAT is in the figure. In the one itemised 4m by 4m solid roof quote published, the roof, scaffolding, lighting and window lines add up to £10,650, and the £12,780 total is that plus VAT at 20 per cent. The £1,200 window is £1,440 with VAT.
- Access and sealing. Scaffolding for a new roof is already on the roof quote; a window cut in later needs access again. Flashing is an average of £100 on the manufacturer's figure, possibly including fitting, and £100 to £180 on the publisher's.
That itemised quote is a new-roof job, so £1,200 before VAT is still 1.6 times the same publisher's £750 new-roof ceiling. Nothing published explains the gap, so we show both figures and average neither. Ask for your window price with and without VAT, and whether it goes in with the roof or after it.
Can you put a lantern on a conservatory roof?
Sometimes, and nobody publishes what it costs when the roof is a pitched solid one.
The two sources that answer this directly disagree, and neither shows its evidence. A national trades directory says a lantern can replace a polycarbonate or glass panel in an existing conservatory roof. A quote-comparison publisher says lanterns go on flat-roofed sections, not standard pitched conservatory roofs. Whether your roof structure can take the opening is a survey question.
Every published lantern price assumes a flat roof, where opening up an existing roof for one adds £500 to £2,000 on one publisher's figures, Thin evidence, 28 July 2026. None of it transfers to a pitched solid conservatory roof.
A lantern roof is a different product
Some companies sell a lantern roof: a whole replacement conservatory roof in a raised lantern shape, not a unit set into a solid roof. A whole conservatory built with one is a third thing again. Ask which a quote means before comparing it with this page.
How much light do roof windows give back?
No published figure we have found is backed by a test, so we do not give you one.
Manufacturers and price guides publish multipliers for how much light a roof window or lantern adds, or a solid roof takes away. They disagree, and none says how the number was measured. Three area rules also circulate, and they measure three different things.
| Rule | Figure | What it is |
|---|---|---|
| VELUX guidance | Glazed area of all windows no less than 20% of the floor area | A manufacturer's daylight minimum, undated |
| Trades directory lantern guide | Lantern footprint no more than 20 to 25% of the room's floor area | A design rule of thumb, July 2026 |
| Approved Document L, extensions | Windows, roof windows, rooflights and doors together no more than 25% of the floor area, plus openings lost | An energy cap, reaching a conservatory only once it counts as an extension |
Checked 14 September 2026.
A glass roof instead
If daylight matters more than warmth, the real comparison is a solid roof against a new glass conservatory roof.
Light against heat
Roof glazing lets in heat as well as light, the problem a solid roof was bought to solve. For the summer side, see how to keep a conservatory cool in summer.
What Building Regulations ask of a roof window in a solid roof
In England it turns first on whether your conservatory is exempt, and a solid roof conversion is building control work in its own right. Who signs that off, and the fee, are at who signs off a conservatory roof replacement.
| What Approved Document L says | Where |
|---|---|
| A conservatory is exempt from the energy efficiency requirements if it is at ground level, no more than 30 m², glazed to Part K, still separated from the house by a wall, door or window, and not heated by the home's system | Paragraph 0.14 |
| A roof window must reach 1.4 W/m²K or Window Energy Rating Band B, as if vertical. A rooflight must reach 2.2 W/m²K, as if horizontal, over an outer surface often larger than the opening | Table 4.2, paragraph 4.5 |
| The roof's own 0.15 W/m²K is an area-weighted figure that leaves out roof windows and rooflights, which meet their own limits | Table 4.2, note 1 |
| The whole unit, frame included, is the controlled fitting. New glass in an existing frame is not | Paragraph 10.6 |
| Not exempt but still separated from the house: new roof windows and rooflights meet the limits above, and the 25% glazing cap does not apply | Paragraph 10.13 |
| Separation removed or heating extended: treated as an extension, with windows, roof windows, rooflights and doors capped at 25% of the floor area plus openings lost | Paragraphs 10.12 and 10.7 |
Approved Document L, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments. Checked 14 September 2026.
For scale on the last row: 25% of a 4m by 4m conservatory is 4.0 m², shared with the glazed walls and doors, and one standard 78cm by 118cm roof window takes 0.92 m² of it. Which row you are in is a question for your building control body, best asked in writing before the roof is designed. A new edition of Approved Document L takes effect on 24 March 2027 for most work, renumbering these paragraphs with the same limits.
Do you need planning permission for a roof window or lantern?
Usually not for a roof window in England. Possibly for a raised lantern.
Roof alterations to a house can be permitted development under Class C, and the government's guidance names roof lights and roof windows among them. The alteration must not stick out more than 150 millimetres beyond the slope of the original roof, or rise above the highest part of the original roof. Original means the house as it was built, or as it stood on 1 July 1948 if it is older, so ask your council how that applies to a conservatory added later. A window on a side-facing roof slope must be obscure-glazed and fixed shut, unless the part that opens is more than 1.7 metres above the floor. Flats, houses created or built under permitted development rules, and homes whose rights have been removed do not have these rights.
A roof window sits in plane with the roof, so its frame and flashing usually stay within the 150 mm limit. For a lantern, one publisher gives a profile of 300 to 500 mm above the roof, well past it. If the lantern on your quote stands more than 150 mm proud, it is outside that limit, so ask your council first. Changing the roof itself is covered at planning permission to change a conservatory roof.
The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class C, the government householder technical guidance on permitted development, September 2019, and Planning Portal guidance on roof alterations. Checked 14 September 2026.
Opening roof windows: ventilation as well as light
Whether an opening roof window counts as purge ventilation depends on how far it opens and how big the opening is.
Approved Document F, 2021 edition, exempts conservatories up to 30 m² from its ventilation requirements. Where they apply, a hinged or pivot window opening under 15 degrees does not count as purge ventilation, the kind that clears a room quickly. From 15 to 30 degrees the openings must total at least a tenth of the room's floor area; at 30 degrees or more, a twentieth. Ask for the opening angle on the data sheet rather than assuming a centre-pivot qualifies.
An electric or solar window costs £200 to £400 more than a manual one on one publisher's figures, £200 to £500 on a second and £300 to £800 on a third: four times apart, so Thin evidence. A conservatory roof vent is a different product, a spare part for a polycarbonate or glass roof. In a solid roof, the opening is the roof window.
Approved Document F, Volume 1: Dwellings, 2021 edition. Opener prices: Publisher A, 1 May 2026; Publisher D, 21 August 2026; Publisher E, September 2026. Checked 14 September 2026.
Fit them with the roof, not after
The cheapest roof window is the one on the original roof quote.
Adding a window later costs £300 to £450 more per window on the one publisher that prices both jobs. Some solid roof systems plan for it: Guardian Warm Roof offers VELUX roof windows or a Solstice rooflight, VELUX calls itself that roof's exclusive roof window supplier, and the one itemised SupaLite quote published lists a VELUX window on its own line. For each window, the roof quote should list:
- Make, model and size, and whether it is a roof window or a rooflight
- Whether it opens, and by hand, electric motor or solar
- The flashing kit
- The U-value, and whether it was calculated vertical or horizontal
- Whether the price includes VAT
- Whether the building control approval for the roof covers it
As part of a roof replacement
When the window is one line of a whole new roof, the bigger number is the roof: start with the cost of replacing the roof. Once the roof and its windows are specified, get quotes for your roof with each window on its own line.
Wall glazing is a different job
Failed or draughty windows in the conservatory walls are priced separately: see what it costs to replace conservatory windows. For every other job on a conservatory, start at conservatory cost.
Price your job in six questions
No phone number until the final step, and no email needed to see an estimate.
Rather skip the questions? Ask for a conservatory roof quote against a size you already know.
Questions people ask first
How much do conservatory roof windows cost?
Can you put a lantern roof on a conservatory?
How much does it cost to install a lantern roof in a conservatory?
Do I need permission for a roof lantern?
Are roof lanterns worth it?
Do VELUX windows need building regulations approval?
How much does it cost to install a rooflight?
Figures last checked 14 September 2026. Prices come from five UK cost publishers, VELUX's own cost article, a lantern supplier, a trade reseller and one shop. Where a price rests on one publisher we label it Thin, and where a publisher states no VAT position we say so.
Find out what yours costs
Six questions, about sixty seconds, and an estimate built from published UK figures with every source shown. Then up to four local installers can quote you, if you want them to.