Adding a Velux or roof window is one of the most effective ways to bring natural light into a loft, whether you’re planning a full conversion or just improving an existing loft space. Here’s what’s actually involved.
Do you need planning permission?
For most homes, fitting a roof window doesn’t need planning permission. That’s because it falls under permitted development rights. A dormer is different, though. According to the Planning Portal’s guidance on loft conversions, a dormer on a wall that fronts a highway needs an application. A rear dormer is usually permitted, provided it stays within the volume limits. That’s 40 cubic metres of extra roof space for a terraced house, or 50 cubic metres for a semi-detached or detached one, and it must not exceed the height of the existing roof ridge.
Conservation areas add another layer. Dormers specifically require planning permission if the property sits inside one, even where a plain roof window wouldn’t. Since so much of Twickenham, Richmond and St Margarets falls within a conservation area, it’s always worth checking before you commit. See our guide to roofing in a conservation area for more detail.
Roof window vs dormer
A roof window (a Velux is the best-known brand) sits flush with the existing roof slope. It lets light in without changing the shape of the roof. A dormer, by contrast, projects out from the roof, creating extra headroom and usable floor space inside. That makes it a better choice if you’re planning a full loft conversion rather than just improving light in an existing loft.
What installation involves
Fitting a roof window means cutting an opening in the roof structure, fitting a supporting frame, and flashing the window in to keep it fully weathertight. This last step matters as much as the window itself, since a poorly flashed roof window is a common cause of leaks. A dormer is a bigger job again. It involves new stud walls, a flat or pitched dormer roof of its own, and matching the external finish to the rest of the property.
Choosing the right roofer for the job
Both jobs involve creating a new opening in an otherwise weathertight roof. Because of that, it’s worth using a roofer who fits roof windows and dormers regularly, rather than as an occasional add-on. Our guide to choosing a trustworthy roofer in South West London has questions worth asking before you commit to anyone for this kind of work.
We fit Velux roof windows and build dormers across Twickenham, Richmond upon Thames and Teddington.
Related reading
- Storm Damage to Your Roof: What to Do and How Insurance Works
- Choosing a Trustworthy Roofer in South West London: 10 Questions to Ask
- Roofing in a Conservation Area: Rules for Richmond, Twickenham & St Margarets
- How Much Does a New Roof Cost in Twickenham & Richmond? (2026 Price Guide)
- Flat Roof Repair vs Replacement: Which Do You Need?
- EPDM Rubber vs GRP Fibreglass vs Felt: The Best Flat Roof Material for London Homes
- How to Tell If Your Roof Needs Replacing: 8 Warning Signs
- What to Do When Your Roof Is Leaking: An Emergency Checklist