Velux & Skylight Windows Explained: Installation, Cost and Care
Thinking about adding light to a loft conversion or replacing a tired, leaking skylight? Here’s what installation actually involves, what it costs, and how to keep one watertight for years.
Quick Answer
A roof window typically costs £600-£1,500 supplied and fitted depending on size and type, with installation usually completed in a single day. Proper flashing around all four sides is what keeps it watertight long-term.
What Skylight Installation Involves
Choosing the Right Position
Position is worked out around the roof pitch, the room below, and the rafters either side of the opening – getting this right at the planning stage avoids awkward compromises later.
Cutting the Roof Opening
The rafters are trimmed and a structural opening formed to the correct size, with the roof made weathertight again the same day.
Fitting and Flashing
The window unit is fitted, then flashed on all four sides with a flashing kit matched to your roof covering – this is the single biggest factor in whether a skylight stays leak-free.
Internal Finishing
Plasterboard reveals, insulation around the opening, and internal trims are finished to match the room.
Fixed vs Venting Skylights
A fixed roof window lets light in but doesn’t open – the cheaper option, and fine for most loft spaces. A venting (opening) skylight adds ventilation too, manually or electrically operated, at a higher cost but often worth it in a bathroom or a loft conversion used as a bedroom.
Common Skylight Leaks and Their Causes
Skylight leaks almost always come down to perished flashing seals rather than the window unit itself failing. Condensation on the inside of the glass is often mistaken for a leak – the fix for that is ventilation, not a repair. Blocked drainage channels around the frame are another common, easily missed cause.
Maintaining a Skylight
Keep the surrounding flashing and drainage channels clear of leaves and debris, check seals periodically for cracking, and clean the glass from inside where possible rather than climbing onto the roof.
Typical Skylight Costs
| Skylight Type | Typical Supplied & Fitted Cost |
|---|---|
| Fixed roof window | £600 – £900 |
| Manual venting roof window | £900 – £1,300 |
| Electric/remote venting | £1,300 – £2,000+ |
Frequently Asked Questions
Can I fit a skylight into any roof?
Most pitched roofs can take one, though very shallow pitches or already-crowded rafters need a proper survey first.
Do skylights leak more than the rest of the roof?
Not if fitted properly – failures nearly always come down to flashing that wasn’t dressed in correctly, not the window itself.
How long does installation take?
Most single skylight installations are completed in a day, including making good internally.
Related Reading
Skylights Merthyr Tydfil
Read moreVelux window installation and repairs across Merthyr Tydfil.
Roof Leak Repairs Merthyr Tydfil
Read moreFast leak detection and fix, including around skylights.
Lead Flashing Repairs & Replacement
Read moreChimney, valley and abutment flashing repaired to Code 4/5 standard.
Roof Maintenance Merthyr Tydfil
Read moreInspections and upkeep to catch problems early.
10 Signs Your Roof Needs Repair
Read moreThe warning signs worth knowing before they become urgent.
Thinking About a Skylight?
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