Three parts, three different lifespans
Asking how long a conservation rooflight lasts is really three questions: how long the glass unit stays clear, how long the frame finish protects the steel, and how long the flashing keeps water out. Each wears on its own clock.
The steel frame is the long-lived part. A conservation rooflight is modelled on the Victorian cast-iron rooflights still found on older roofs across Cambridge, and modern versions use slim steel sections that are galvanised and then powder coated. Kept dry at the joints and with the coating intact, the frame is usually the last component to need attention. Our guide to steel and aluminium conservation rooflights explains why steel is chosen for the slim profile in the first place.
The sealed glass unit is the part with a shorter working life. Double glazing relies on an edge seal that holds a dry gas fill between the panes, and a desiccant in the spacer bar soaks up the small amount of moisture that gets in over time. Once that desiccant is saturated or the seal lets go, mist and condensation appear between the panes, and the insulating value drops. Industry guidance commonly puts a quality sealed unit at around 20 to 30 years, and cheaper units can go sooner.
The flashing and the junction between the frame and the roof depend as much on the fitting as on the product. A well-dressed flashing kit on a sound slate or tile slope can last as long as the frame; a poorly fitted one shortens the life of everything around it.
| Part | What wears it out | Life, as a guide |
|---|---|---|
| Sealed glass unit | Edge seal and desiccant ageing | Commonly 20 to 30 years |
| Steel frame | Coating damage, standing water | Often longer than the glass |
| Flashing | Fitting quality, roof movement | Depends on the install |
| Opening hardware | Use, lack of cleaning | Varies by product |
What shortens the life of the frame and finish
Galvanising protects the steel and the powder coat protects the galvanising, so the finish only fails where one of those layers is broken. Early wear tends to start at a scratch, a cut edge or a joint that holds water.
The practical risks are ordinary ones. A frame scratched during installation and left untouched can let moisture reach the metal. Debris that collects at the bottom rail on a shallow slope keeps the finish damp for long spells. Moss and lichen growing off an old tile roof can hold moisture against the frame too. None of these is dramatic, but over twenty or thirty winters they matter. If corrosion is your specific worry, do conservation rooflights rust? goes into the galvanising and coating in detail.
Pitch also plays a part. Conservation rooflights are rated for a range of roof pitches, and a unit on a slope near the shallow end of that range sheds water and leaves more slowly than one on a steep Victorian roof. We check the pitch against the product rating at survey; the answer on what roof pitch a conservation rooflight needs sets out the usual range.
How the glass ages, and what the light tells you
The first sign of an ageing sealed unit is usually visible from the room below: a milky haze or droplets between the panes that you cannot wipe away. That is the edge seal, not the frame.
Orientation affects how hard the glass works. A south-facing slope, such as the rear roofs of some terraces in Romsey and Petersfield, puts the unit through bigger daily swings in temperature than a north slope, and repeated expansion and contraction is part of what ages an edge seal. A north-facing rooflight lives a gentler life. This is one reason we look at the sun path before choosing the glass: a south slope may justify solar control glass, which also keeps the room more comfortable in July. The answer on solar control glass in conservation rooflights covers the options, and our page on how we plan the light explains how orientation shapes the whole specification.
Laminated inner panes, low-emissivity coatings and warm-edge spacers all feature in current specifications, and they help the unit meet today's Building Regulations. None of them makes an edge seal permanent, so it is sensible to plan for a sealed unit that will eventually need renewing even if the frame carries on.
Renewing an older conservation rooflight
When a conservation rooflight reaches the end of its useful life, the usual course is to replace the whole unit with a current one of matching size and profile. That keeps the flush look planners expect and brings the thermal performance up to date.
Whether the glass alone can be swapped depends on the product. Some steel units are designed so the sealed unit can be changed; others have the glazing bonded in, and the whole rooflight is replaced. Replacing the complete unit also lets the flashing be renewed, which is often the part that has aged least gracefully. On older roofs we also check the condition of the surrounding slates or tiles and the timber trimmers, because a new rooflight should go into a sound opening.
In a conservation area a like-for-like replacement is often straightforward, but on a listed building any change to the roof needs listed building consent, even when the new unit looks the same. Our guide to listed building consent for rooflights sets out when that applies. If you are taking out an original Victorian unit rather than a modern one, read replacing cast iron rooflights. Replacement rooflights also have to meet current thermal requirements, and where the work is notifiable we handle the Building Control notification.
Getting the longest life from a new unit
The biggest factor you can control is the quality of the installation. A good product, fitted square, flashed correctly and protected from scratches during the work, starts its life with every layer intact.
- Choose a frame that is galvanised as well as powder coated, and ask what the manufacturer's product warranty covers and for how long.
- Match the unit to the roof covering and pitch, so the flashing sits properly on slate, plain tile or pantile.
- Keep the bottom rail clear of leaves and moss, especially under trees.
- Clean the glass and frame gently, without abrasive pads that cut through the coating.
- Operate opening units now and then so the hinges and stays do not seize.
We install to current Building Regulations and back our installation work with a 10-year workmanship guarantee. The product itself carries the manufacturer's own warranty, which is separate. To see the full service, visit our conservation rooflight installation page, or book a light survey and we will look at your roof, its orientation and the unit it needs.
Questions people also ask
Can a conservation skylight last as long as the roof?
The steel frame can come close to the life of a well-kept slate or tile roof, but the sealed glass unit usually will not. As a guide, expect to renew the glass or the whole unit at least once over the life of a roof covering.
Is a misted conservation rooflight a sign the frame has failed?
Not usually. Mist between the panes points to the sealed unit's edge seal. The frame may be sound, though replacing the whole unit is often the simpler route and brings the thermal performance up to date.
Do cheaper conservation-style rooflights last as long?
Not always. Thinner coatings, frames without galvanising and lower-grade sealed units can all shorten the working life. Compare the specification, not just the look, and see our costs guide for what drives the price.
Does replacing an old conservation rooflight need planning permission?
A like-for-like swap often does not, but it depends on whether an Article 4 direction applies or the building is listed. Check the position before ordering, since the answer changes the paperwork.
