Upgrading the glass while the roof is open

What to take while you are there

Solar control, on anything facing south or west. The most consequential upgrade available and the one most often skipped. Adding it later means new glass.

A warm edge spacer, if the quoted unit does not already have one. Stops the band of edge condensation on cold mornings.

Acoustic or asymmetric glass, over a bedroom. Rain on glass is audible and this cannot be changed later without changing the glass.

Self cleaning, on anything you cannot reach with a pole.

Obscured glass, where a bathroom is overlooked.

What is not worth it

Triple glazing, in most cases. It moves the U-value from about 1.2 to about 0.8, costs substantially more, weighs more and transmits less light.

The same money on an insulated kerb and a properly sealed vapour control layer does more for how the room feels.

The other things to do while it is open

These matter as much as the glass and cost very little at this moment.

An insulation collar, if the original had none. Very common on older installations, and the explanation for reveal condensation people have lived with for years.

Sealing the vapour control layer to the new frame.

Splaying the reveal where it is being reformed, which throws noticeably more light into the room.

The principle

Anything requiring the roof to be open costs a fraction now and a whole job later. Anything that does not can wait.

The cheapest upgrade you will ever be offered

Most of the cost of a rooflight job is getting to the window: the access, the setting up, the protection, the strip out and the making good. The glass specification is a modest part of the total.

That means the marginal cost of better glass at the point of order is small, and the cost of coming back for it later is nearly the whole job again, because the labour and the access are identical either way.

What is worth adding

Solar control glass, on any unit facing south or west. The single most valuable upgrade available, because overheating is the most common regret about rooflights and it cannot be fixed afterwards without replacing the glazing or fitting external shading.

Do not add it on north facing units, where there is no direct sun and it would only make a good room slightly darker.

Acoustic laminate, over a bedroom or a study. Rain on a roof window is louder than people expect and a specialised interlayer damps it substantially.

Obscure glazing, in a bathroom or ensuite, particularly where the property is overlooked from higher ground. It solves privacy permanently without a blind that would get wet.

A warm edge spacer, which should be standard rather than an upgrade. If a quotation does not say, ask.

What is worth doing at the same time

Not just glass. Anything that needs the same access.

The other windows on the slope. Units fitted at the same time fail at about the same time, and access is a fixed cost shared across everything done in the same visit. If two of three have misted, the third is not far behind.

A capped electrical cable to the rooflight position, even if you are fitting a manual unit. Twenty minutes at first fix, and it turns a future motor upgrade from a disruptive job into a cheap one. Photograph where it is before the ceiling closes.

Blinds, ordered with the window so they are matched to the model and fitted on the same visit.

Kerb insulation, or the insulation collar, which is not an upgrade so much as something that should be there anyway.

Upgrades that do not pay

Triple glazing, in most cases. Modest thermal gain at the cost of weight, daylight transmission and a good deal of money, and it does very little about solar gain.

Solar control on a north facing slope. Self cleaning glass on a near flat unit, where rain does not run and the coating does very little.

The rule of thumb

If it would need the roof opened again to add later, decide it now. If it can be added from inside at any time, it can wait.

Why this is the moment

The cost of a rooflight job is not mostly the unit. It is the access, the covering off and back on, the carpentry, the flashing and the making good. All of that is being paid for once.

The difference between a basic sealed unit and a well specified one is a modest addition to a job that is already happening, and it buys twenty five years of better performance.

Doing it later means doing all of the surrounding work again.

The upgrades that do pay

A warm edge spacer. The single best value item on a rooflight, because a small unit has a great deal of perimeter and the spacer is a large part of the edge loss. It is also what decides where condensation first appears.

Solar control glazing on any south or west facing slope, and on any horizontal unit. The g value is the number, and overheating is the most common regret people report.

Laminated glass where security matters, over a stairwell, or in a garage or outbuilding. It holds together when attacked rather than clearing the opening.

Self cleaning coating on any unit that is difficult to reach. It extends the interval rather than removing the task, and on a steep roof it works well.

An acoustic laminate under a flight path or beside a busy road. Rain noise on a rooflight is a genuine complaint and this is what addresses it.

What is worth adding that is not glass

The insulation collar, the blind, and the electrical supply if a powered unit is even a possibility later. All three are cheap now and awkward afterwards, and the cable in particular means opening a finished ceiling if it is deferred.