Sun Tunnel Installation in Bristol Daylight carried down a tube to the room that has no window

The pages that follow suit anyone weighing it up for the first time. If the question is whether a tube loses warmth from the house, the answer on do sun tunnels lose heat goes into the detail. If you want the room to be aired as well as lit, read on to the chapter about bathrooms.

Dome and diffuser

The dome has a job beyond looking tidy. Many are shaped with a clear prism on the inside that bends low winter sun downward into the tube, where a plain dome would let it skim past. Others carry a fine outer layer that resists dirt, so the dome does not turn dull over the seasons. The diffuser at the ceiling is chosen for the room: a frosted one gives a soft glow, a clear prismatic one spreads the light wider across a long landing.

Some diffusers take a light fitting as well. A small ring of low-energy lamps in the diffuser means the same fitting gives daylight by day and electric light by night, with no second fitting on the ceiling. It is a small touch that makes a hallway feel designed rather than adapted.

Facing and shade

On a pitched roof the direction the slope faces changes how the day plays out. A south-facing dome catches strong light for most of the day and produces the brightest tube. An east-facing one gives a pleasant morning room. A west-facing one is at its best in the evening, which suits a hall or a kitchen. A north-facing slope is steadier and gentler. Trees and tall neighbouring walls matter more than the compass, and we look up from the roof for a few minutes at the time of the survey.

None of these is a poor choice. They produce different characters of light, and the room that uses it counts for more than the compass. An evening bathroom wants the west side. A morning landing wants the east. Where more than one slope is possible, we show the options at the survey and let the room decide.

A loft in a Victorian terrace around Southville or Totterdown is often roomy and fairly clear, with a cut roof and a straight drop, so rigid works well. A loft in a 1930s semi has trusses and a water tank to avoid, and a flexible tube may be the practical route. A loft that has been boarded for storage, or has a chimney breast running up through it, usually calls for a mix: a rigid run where the way is clear and a short flexible section to steer round the obstacle.

What we look at in the loft

1. The position of rafters, purlins and any trusses between the roof and the ceiling.
2. Cables, pipes and ducts that cross the straight line down.
3. The depth of insulation on the loft floor, which the tube has to pass through.
4. A clear route to the ceiling below that is free of beams and wiring.

These four checks decide the route, and the route decides the tube. If the straight line is clear we prefer rigid every time. If a rafter is in the way we can sometimes move the dome position along the slope by a hand's width and clear it, which keeps the tube straight. If that is not possible, we use flexible and explain how much light is traded for the bend.

Insulation along the tube

A tube passing through the loft crosses a cold space between the roof and the warm rooms below. A good tube is insulated or wrapped in the loft so that the warm room does not lose heat up the pipe, and the diffuser is sealed to the ceiling so that no warm air from the room leaks into the roof space. Both details are part of the fitting, not extras. Condensation can form on a cold surface wherever warm, damp air meets it, and an unwrapped tube over a steamy bathroom is a candidate. We wrap the tube in the loft for that reason, and the answer on whether sun tunnels lose heat describes it in more depth.

Tube length also decides the diameter we recommend. A short drop gets the best from a slimmer tube. A long drop benefits from a wider one, which keeps more light moving down. The size is set at the survey, once the route is known, and written onto the quote with the tube type beside it.

It is worth keeping expectations realistic. A sun tunnel does not open like a window, and a fan fitted into it does the same work a normal bathroom fan would. What the combination offers is tidiness and light: a single, round fitting on the ceiling, instead of a plain diffuser next to a separate fan grille. Clearing steam after a shower can help condensation disperse. It does not remove the need to wipe a mirror or leave the door ajar.

Where the air goes

Extracted air has to go somewhere safe. A bathroom fan must not discharge into the loft, where warm, damp air would settle on cold timber. It is ducted to the outside, through the roof or an outside wall. A kit that runs its exhaust alongside the tube can leave through the same flashing as the dome. Our team plans the route before the dome position is fixed, because the two decisions are linked.

If a bathroom already has a working extractor in a different spot, you may not need the kit at all. A plain sun tunnel will bring daylight, and the existing fan can stay. We say when we think the kit would be money better kept in your pocket.

Fresh air through the roof is what we are best known for, and a bathroom with a roof window above it is the stronger option where the roof allows it, since that opens fully. Where it does not, a sun tunnel with a kit is the sensible compromise. Our page on fresh air rooflights explains how we think about airing a house from above.

For typical UK market ranges, turn to our costs page. The guide to sun tunnel cost lists what usually moves the figure. Those ranges are guides to the market, and they are not our prices. Ours come from a visit, written down and itemised, so you can see what each line pays for.

What the visit includes

The survey is free and carries no obligation. We go onto the roof where it is safe to do so, and look at the covering, the slope and the shade. We go into the loft to see the route and measure the drop. We look at the room below and talk about where the diffuser should sit and what finish suits it. If a ventilation kit makes sense, we check for a power supply and a way for the air to leave. You then receive a written, itemised quote, and opening and ventilation options are shown on it so you can see what each would add.

Guarantee and aftercare

Our workmanship is guaranteed for 10 years, and the terms are written out on our guarantee page. If a dome ever fails or fogs in service, it is replaced as a whole unit, and a replacement of the full dome and collar is building work that we notify where required. A fogged dome with moisture between layers can be swapped without touching the tube.

Cleaning is simple. The dome is rinsed by rain and wiped from a ladder placed at the eaves when it needs it, and a soft cloth does the diffuser. The tube itself needs nothing. Nobody should walk on a dome, and we say so on the handover sheet. A soft brush on a long pole is enough if leaves gather round the collar in autumn, and there is no need to climb onto the roof for it.

Where we fit them

We fit sun tunnels across Bristol, Bath and the towns within 30 road miles. They suit the narrow terraces of Bristol, the stone houses of Bath, and the 1930s semis of Keynsham equally well, since each has an inner room that never saw a window. Wherever you are, the first step is the same: ask for a survey, and we will tell you straight whether a tube will do the job. If a larger unit would serve you better, such as a flat roof rooflight, we will say so.