Are sun tunnels worth it?

The good cases are a landing at the heart of a house, a bathroom with no outside wall or a cloakroom under the stairs. These rooms are small, they sit under a roof and a window there could face a neighbour's brickwork anyway. A dome up top, a tube dropping through the roof space and a ceiling diffuser bring them daylight without touching a wall. A sun tunnel also lets a bathroom keep its privacy, since there is no glass looking in.

That is the strong case. A top-floor landing with a short drop to the roof is the easiest of all, because the tube is short and loses little on the way down.

A sun tunnel passes on the daylight that reaches the dome, and it cannot make more. On a bright day it lifts a corridor. On a grey one, the effect is gentler. A dome on a north-facing slope, or one in the shade of a taller house or a tree, gets less than a dome on an open south-facing roof.

The tube also gives up a little light along its length. Every metre and every bend takes some, and a rigid tube can send light on over a longer distance than a flexible one. So a short, straight run is worth more than a clever product. There is no sky to look at either. For that, you need glass you can see through, which means a roof window or a rooflight.

A loft bedroom with a sloping ceiling asks for a roof window, which gives sky and daylight both. A flat-roofed kitchen extension that stays dim in the middle suits a flat roof rooflight or a roof lantern, because those bring in far more light than a small tube can. A sun tunnel is the right size for a stairwell, a short corridor or a small bathroom.

The same house can use two of these. A lantern over the extension and a sun tunnel over the landing behind it each do the job they suit.

The dome wants a place on the roof that sees as much sky as it can, clear of a chimney stack, a dormer cheek or the shadow of a taller neighbour. Moving it along the slope can also shorten the run to the ceiling, and a shorter run delivers more light. On a tiled or slated roof, the units around the base can be lifted and laid back round it, while on a flat roof the covering can be dressed up to the base and sealed. The junction between dome and covering is the part that has to stay watertight, so the survey looks at it closely.

At night the tube has nothing to carry, since the dome collects daylight and there is none, so the diffuser shows only as a pale disc overhead while the room relies on its own lamps. That is worth knowing for a landing you use before breakfast in December. A downpour may also be heard through the dome, which matters if the tube ends above a bedroom.

Whether the spend makes sense depends on the route, the roof and the ceiling, and our answer on what a sun tunnel costs to fit explains what moves the figure. We give a price only after a free survey, as a fixed written quote.

Rules are part of the sum as well. In Wales a dome is a roof alteration, so the Class C limits of 150 mm beyond the original slope and no higher than the highest part of the original roof are the starting point. A house on protected land or a listed house can bring in a planning application or listed building consent. The answer on planning permission for sun tunnels goes through them, and we raise the question at the survey where it applies to your house.

Start with the room. If it is small, it sits under a roof and its only problem is a lack of daylight, a sun tunnel is a fair candidate. If the room is big, if you want a view or if a loft bedroom needs fresh air and sky, look at the other products first. We install and replace every one of them. Book a free survey through the survey form, or send a photo of the dark room to WhatsApp 07880 284133 first.