Can you replace just the glass in a rooflight?

Pitched roof windows

Some have a sealed unit held by a removable glazing bead, so the glass can be changed with the frame in place. On others the glass is bonded into the sash as one component and the sash is replaced instead.

The code on the data plate tells us which yours is.

Flat roof rooflights

Usually not. On most modern flush glazed units the glass is structurally bonded to the frame as a single component, and there is no serviceable way to separate them. Replacement means the whole unit.

When replacing the glass is right

Frame under about fifteen years old, sound, with working hinges and seals. Then new glass restores the window and the saving is real.

When it is a false economy

On an older frame. A twenty five year old window has hardened seals, worn hinges, a finish at the end of its life and thermal performance two generations behind current.

New glass in that frame gives you modern glazing in a worn window, and the draughts and stiffness remain. The labour and access are nearly identical either way, and most of the cost of this job is getting to the window rather than the component.

Never

Into a frame with timber decay. It is money thrown away, because the frame will have to be replaced within a few years and the new glass goes with it.

Drilling and drying

Some companies drill a misted unit, dry it and fit vents. It clears the visible misting for a while. It does not restore the seal, the argon is gone, and the unit continues to breathe moist air. We do not offer it on overhead glazing.

Sometimes, and it is often not worth it

Whether it is possible depends on the model. Whether it is sensible depends on the age of the frame.

When it is possible

Some pitched roof windows have a sealed unit held by a removable glazing bead, so the glass can be changed with the frame in place. On others the glass is bonded into the sash as one component, and the sash is replaced rather than the glazing.

On most flat roof rooflights the glass and frame are a single bonded unit and the answer is no.

The data plate tells us which, which is why we ask for a photograph of it before anything else.

When it is worth doing

The arithmetic is straightforward once you accept that most of the cost of this job is getting to the window rather than the component. The access, the setting up, the protection and the making good are nearly identical whether you change the glass or the whole unit.

Frame under fifteen years and sound: replace the glass. You get modern glazing in a frame that has plenty of life left.

Frame over twenty years: replace the window. A unit of that age has hardened seals, worn hinges, a finish near the end of its life and thermal performance two generations behind current. New glass in that frame buys you the shorter of the two lifespans.

Any timber decay: replace the window, always.

The upgrade opportunity

Where the glass is being changed anyway, the marginal cost of solar control glazing or an acoustic laminate is small, because the labour and access are already being paid for.

Coming back for the glass alone later costs nearly as much as the original job.

What not to do

Drilling and drying a misted unit. The visible misting clears, the seal is not restored, the argon has gone and is not coming back, and the unit then deliberately breathes outside air with a spent desiccant.

At height, the labour to do that is most of the labour to replace it properly. We do not offer it.

Flat roof units

Generally a whole unit replacement, and the good news is that dropping a new unit onto a sound existing kerb is one of the quicker jobs we do. The expensive part of a flat roof rooflight is forming and insulating the kerb, and that is already done.

Which units can be reglazed

Most mainstream pitched roof windows. The sealed unit sits in the sash held by gaskets and beads, and it can be removed and replaced by somebody who knows the system. Manufacturers supply replacement units against the size code.

It is a genuine option and considerably cheaper than a whole window.

Which cannot

Flat rooflights and structural glass walk on units, in the great majority of cases. The glass is structurally bonded to the frame with silicone under factory conditions, and that bond cannot be remade on a roof. The whole assembly is replaced.

Any unit where the frame is the actual problem. Rotten timber, a failed hinge, a distorted sash or a perished gasket is not improved by new glass, and a new sealed unit in a tired frame is money spent on the wrong component.

And any model old enough that replacement units are no longer made to that size.

The judgement, by age

Under about fifteen years with a sound frame, reglazing is usually right.

Over about twenty, the hinges, gaskets and mechanism are approaching the end of their lives too. New glass buys a few years before everything else needs doing, and the access cost is identical either way.

Since access is frequently the largest line on the job, that arithmetic matters more than the price difference between glass and window.