Are energy efficient rooflights quieter too?

Keeping heat in and keeping noise out sound alike, and they are not.

Heat crosses a rooflight by conduction through glass and frame, by air moving in the cavity, and by radiation from one pane to the next. The parts that fight it are thin and mostly invisible: a low-emissivity coating on one pane surface, an inert gas in the cavity, a spacer bar that does not conduct, and a frame with a thermal break. None of those adds mass, and none damps vibration.

Sound crosses a rooflight differently. A pane is a light, stiff sheet that shakes when air pressure changes against it, and it passes that shake into the room. What stops it is mass, damping and a mismatch between the panes. A thicker sheet moves less. An interlayer bonded between two sheets absorbs the vibration. Two panes of different thickness do not ring at the same pitch, so they cancel each other's weak spots rather than joining forces.

So a rooflight described as energy efficient has told you about the first set of parts and nothing about the second. You could have a very warm unit that drums in the rain, and a very quiet unit that loses more heat than it should. Neither is a fault. They are simply two separate answers, which is why the question deserves asking at the quote stage.

A few choices help both, and those are the ones worth paying for.

• A second pane in the first place. Double glazing beats single for warmth and for sound, since there is more mass and an air gap between layers.
• A well-made edge and gasket. Continuous seals stop air leaking, which carries cold and also carries noise. A gap in a seal whistles in wind.
• A solid, insulated upstand. A dense kerb with insulation fitted tightly behind it keeps heat in and stops the frame behaving like a drum skin. Our page on insulating around a rooflight describes the detail.
• A frame that is stiff and well fixed. A rigid frame seats the glass without rattle, and a thermal break adds a little damping.

Triple glazing deserves a separate mention. A third pane helps the thermal figure, but it does not guarantee a quieter unit, because three similar panes and two similar gaps can resonate together. A double unit with a laminated acoustic inner pane can be calmer than a plain triple. Weight also rises with a third pane, which is covered in triple glazed rooflights and when the third pane earns its place.

There are two places where an efficiency choice does nothing for sound, or even works against it.

The first is the coating. Low-E and solar control coatings are a micro-thin layer on the glass surface. They change how heat and light pass through and leave the sound unchanged. Choosing a better coating will not make a rooflight quieter, so nobody should expect that from it. We explain the coating side in low-E coatings on rooflight glass.

The second is a very narrow cavity, sometimes picked to squeeze a slim unit into a tight upstand. A narrow gap can be fine for warmth, but it couples the panes together more tightly, so sound passes through more easily. The width is a compromise between the two jobs, and it is chosen rather than defaulted.

Polycarbonate is a different matter. As a lightweight sheet, it tends to be noisier in rain than glass, and our page on whether glass rooflights are more efficient than polycarbonate covers that comparison.

We begin by listening to the room, and the build follows from what it hears.

Around Crawley, the noise differs from street to street. A loft bedroom near the airport hears departures and arrivals, a kitchen extension near the A23 or the Brighton main line hears road and rail, and a flat-roofed kitchen anywhere in the 30 miles we cover hears rain. Each calls for a different emphasis. The bedroom wants the laminated acoustic pane and a tight seal. The kitchen wants a thicker outer pane and a solid kerb. All of them still want the coating, gas and warm edge that make the room comfortable in winter.

What we choose goes into the quiet spec that comes with every quote. It names the panes, the coating, the interlayer, the seals and the upstand, so you can see that warmth and quiet were both asked for. Our page on one glazing build for warmth and quiet walks through a full example. For the rest of the range, the energy efficient rooflights hub is the place to start.

We never quote noise figures, because a number on its own says little about a particular room. What we can do is name the glass and explain why it was chosen. The installation meets current Building Regulations, and the Building Control notification is ours to handle where the work is notifiable.

Will a thicker rooflight always be quieter?

A thicker outer pane helps, particularly for rain. It works best when the inner pane is a different thickness, and ideally laminated, so the two do not vibrate together.

Does argon fill change how a rooflight sounds?

Not in any way you would notice. Gas fill is chosen for heat retention. If you want to know what it does, read what argon gas does inside a rooflight.

Can I add quiet glass to a rooflight I already have?

The sound comes from the glass units, so the lasting fix is to replace them with an acoustic build. A blind softens the room a little but does not stop the glass shaking.

Is a flat rooflight or a lantern quieter?

It depends on the glass and the upstand far more than on the shape. See flat roof rooflight installation for that route, or get a quote and we will specify the build for your room.