A Velux or rooflight loft conversion keeps the existing roof shape and adds windows set into the roof slope. It is usually the cheapest and quickest type of loft conversion, and rarely needs planning permission, but it only works if the loft already has enough head height: typically at least 2.2m from the top of the ceiling joists to the underside of the ridge.
Last reviewed 22 September 2026. Based on our research into official and published sources, listed at the end of this page.
What is a velux or rooflight loft conversion?
Rather than changing the roof structure, a rooflight conversion strengthens the floor, insulates the roof and adds windows that sit in line with the roof slope. "Velux" is a brand name often used for any rooflight window.
Because there is little structural work, it is the most affordable option and usually the fastest to build, but it adds less usable floor space than a dormer, because the roof still slopes.
Which houses suit it
Any house with a roof that is already tall enough inside. Many newer homes have trussed rafter roofs, which make any loft conversion more involved.
How much does a velux or rooflight loft conversion cost?
In Berkshire, expect roughly £26,000 to £39,000 to build a typical 30m² velux or rooflight conversion, before VAT and fees. Elsewhere in the UK the typical range is £23,000 to £30,000. These are research-based estimates, not quotes.
Velux or rooflight: typical build costs in Berkshire
Conversion type
Floor area
Typical build cost
Build time
Velux or rooflight
30m²
£26,000 to £39,000
4 to 6 weeks
Ranges, not quotes. Build cost only: excludes VAT, professional fees, planning and building control. Last updated September 2026.
Add VAT, drawings, a structural engineer, building control and any party wall costs to get a total. Use the calculator for your own size and finish, or read the cost guide.
Planning and building regulations
Rooflights usually do not need planning permission. They are allowed if they stick out no more than 15cm from the roof slope and are no higher than the highest part of the roof. Rooflights on a side roof slope must be obscure-glazed and non-opening below 1.7m.
Unlike dormers, this right is not excluded in conservation areas, but an Article 4 direction can remove it on some streets. Building regulations approval is still needed.
Whatever the planning position, every loft conversion needs building regulations approval, covering structure, fire safety, stairs and insulation. See our planning guide and building regulations guide.
Pros and cons
Pros
Usually the cheapest type of loft conversion
Minimal structural work and a faster build
Rarely needs planning permission
Keeps the roof's existing look
Cons
Less extra floor space, because the ceiling still slopes
Needs enough head height to start with
Harder with modern trussed roofs
How long it takes
Checkatrade's typical build time for a velux or rooflight conversion is 4 to 6 weeks on site, after design, approvals and any party wall process. See the process and timeline guide.
Rooflight conversions rarely need planning permission, because the outside of the roof barely changes.
Frequently asked questions
How much does a velux or rooflight loft conversion cost?
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In Berkshire, a typical 30m² velux or rooflight conversion costs roughly £26,000 to £39,000 to build, before VAT and fees, against £23,000 to £30,000 elsewhere in the UK. These estimates come from published cost guides; your quotes will depend on your roof and the specialist.
How much head height do I need for a Velux loft conversion?
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As a guide, at least 2.2m from the top of the ceiling joists to the underside of the ridge beam at the highest point. A specialist will measure and check the roof structure.
Do Velux windows need planning permission?
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Usually not, if they stick out no more than 15cm from the roof and are no higher than the top of the roof. Side-facing rooflights must be obscure-glazed and fixed shut below 1.7m. An Article 4 direction can change this on some streets.
Is a rooflight conversion cheaper than a dormer?
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Yes, usually by a large margin, because it keeps the existing roof structure. The trade-off is less usable floor space.
This guide is general information to help you plan. It is not legal or professional advice: check your own project with your council or a qualified professional.
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