How noisy is an electric rooflight?

The sound an electric rooflight makes in use is the actuator driving the sash open or pulling it closed. On a modern unit that is a low electric whirr, steady rather than sharp, and it lasts only as long as the travel. A roof window opening to its full vent position takes somewhere between twenty and forty seconds, so you are listening to the motor for well under a minute and then it stops.

Put a number on it and a good actuator sits around 40 to 45 decibels measured a metre away. For reference, a quiet library reads about 40, normal conversation about 60, and every ten points on the scale is roughly a doubling of loudness. So the motor is close to the bottom of what you notice indoors, and it is a mechanical hum rather than a rattle or a grind. In a room with the television on you would struggle to hear it start.

The one moment it is most audible is the last second of closing, when the sash pulls down onto its seals and the motor works briefly against the gasket to compress it. That firm shut is what makes the unit weathertight, so it is doing its job, but it is the part of the cycle people register. Better units ramp the motor speed down at the end so the sash settles rather than thumps.

Ask someone who has lived under a rooflight what they hear and they will almost never mention the motor. They will mention rain. Glass is a hard, flat surface angled at the sky, and a heavy shower drumming on it carries into the room below far more than the same rain would through a tiled roof with a loft and ceiling underneath it. This has nothing to do with whether the unit is electric or manual. It is the glazing.

Two things govern how loud rain sounds through the glass. The first is the thickness and make-up of the panes. A sealed unit with two panes of different thickness, say a 4mm outer and a 6mm inner, breaks up the sound at a different frequency in each pane and damps the drumming better than two identical sheets. The second is whether the outer or inner pane is laminated. Laminated glass has a plastic interlayer bonded between two thinner sheets, and that interlayer is very good at soaking up sound energy. A unit with a laminated pane can knock several decibels off rain noise, which is the difference between rain you notice and rain that wakes you.

If a bedroom or a home office is going under the glass, this is the specification to push on, and it is worth doing at the point of ordering because the glass is not something you change afterwards without swapping the whole unit. The good news is that a laminated inner pane earns its keep twice over: it is also the safety glazing that Building Regulations Part K asks for on an overhead unit, so you are often paying for the acoustic benefit anyway.

Electric rooflights open in one of two ways, and they do not sound the same.

• Chain actuators push the sash open with a rigid chain that folds away into a slim housing on the frame. They are compact and common on roof windows. The sound is a light mechanical clicking as the chain links feed out, softer than it sounds on paper, and the housing sits inside the room so nothing is exposed to the weather.
• Spindle or linear actuators use a threaded rod or a telescopic arm and tend to go on larger flat-roof units and lantern vents. They are a smoother, more continuous hum than a chain, and because they are usually asked to move a heavier sash they run for a little longer per cycle.

Where the motor is mounted matters as much as which type it is. A motor fixed to a rigid, well-packed frame is quiet, because there is nothing for it to vibrate against. A motor bolted to a sash that is not properly bedded into its upstand can transmit a buzz into the surrounding structure, and that structure-borne sound travels further than the airborne hum. This is an installation point rather than a product one. A unit that hums through the ceiling is usually telling you the fixing or the packing is loose, not that the motor is faulty.

Southend-on-Sea faces south across the Thames Estuary, and that open aspect changes the weather a roof takes. There is little in the way to the south, so a south-facing rear extension or loft here catches wind-driven rain square on when a shower comes in off the water. Rain that would fall vertically onto an inland roof arrives at an angle here and hits the glass harder, which is exactly the situation where a laminated acoustic pane pays for itself.

The same open southern aspect is why we specify the glass on these roofs the way we do in the first place. A south-facing rooflight is a solar collector as well as a sound surface, so the unit going in usually wants a solar-control coating to hold down summer heat and glare, and the laminated build that quietens the rain sits happily in the same sealed unit. You end up asking one piece of glass to do three jobs at once: control the sun, cut the glare off the water, and damp the rain. That is the thinking behind our electric skylight installation work, and the reason we start with orientation before we talk about the opening mechanism at all.

If noise is your worry, focus the conversation on the glass, not the motor. Ask for a laminated pane on the room side, ask whether the two panes are different thicknesses, and ask for the unit’s weighted sound reduction figure if the supplier has it. Those three things decide how quiet the finished rooflight feels far more than the badge on the actuator does.

Then think about where the unit is going. A hum you would never notice over a kitchen can matter over a bed, so it is worth telling whoever specifies the rooflight what the room below is for. If the roof faces south, ask for the solar-control and acoustic questions to be answered together rather than one after the other, because the same glass usually settles both. You can read how the sun side of that works on our energy-efficient skylight installation page, and see where the numbers land on our skylight installation costs page.

If you would like us to spec it for you, tell us the orientation, the rough opening size and what the room is used for, and we will come back with a glass and a mechanism to suit. Ring 01702 898232 or request a quote, and we will look at the whole roof rather than just the opening in it.