Sun tunnel installation in Cambridge, daylight for dark corners

Walk into the middle of a Cambridge terrace on Mill Road, in Romsey or along the streets off Chesterton Road and you meet the same problem. The front bedroom has the bay, the back bedroom looks over the garden, and the landing between them is a dark rectangle lit only by whatever spills through open doors. The stairs run up the party wall, so the hall below is dark too. Neither space touches the rear slope in a way that suits a roof window, and on some of these houses the landing sits under the loft rather than under the roof itself, with a metre or more of void between ceiling and rafters. That is the classic place for a sun tunnel: a small dome on the slope, a tube dropped through the loft, and a disc of daylight on the landing ceiling that means nobody reaches for a switch at 11am.

The same logic holds in other housing across the city. A 1930s semi in Cherry Hinton or Arbury usually has a side hall with a tall stairwell and a small landing window that faces the neighbour's wall a couple of metres away. A flat-roofed block at Eddington or an apartment in Trumpington Meadows may have an en-suite or a utility cupboard in the centre of the plan with only an extract fan for company. A village bungalow in Histon, Cottenham or Sawston has a long central corridor with rooms off both sides and a big, empty roof void above it. Each of these is a place where a window is impossible and a rooflight would need a light well so deep that it becomes a sun tunnel in all but name.

Rooms where a tube does its most useful work:

• Halls, landings and stairwells in terraces, semis and chalet bungalows. Our guide to sun tunnels for halls and landings works through stair layouts and where the diffuser should sit so the treads are lit.
• Internal bathrooms, en-suites and shower rooms, often paired with an extract fan or a ventilation kit.
• Walk-in wardrobes, dressing rooms and box rooms, where true daylight makes it much easier to tell navy from black. See can a sun tunnel light a walk-in wardrobe.
• Kitchens with a dark back corner, utility rooms and larders. The answer on whether a sun tunnel can go in a kitchen covers steam, grease and extractor positions.
• Garages and workshops, where a tube gives daytime light without the cost of glazing a wall. The answer on putting a sun tunnel in a garage covers the simpler build-ups involved.

A tube is a way of moving daylight, not a way of framing a view. It gives light, not sky: you will not see clouds pass or watch rain on the glass. Where the room sits directly under the slope and a view up to the sky would be welcome, a roof window almost always gives more light and more pleasure for the opening. Where there is loft, ceiling void or a second storey between the room and the roof, the tube wins. Our guide to a sun tunnel vs a skylight lays the two side by side, and at the survey we say which one the room actually needs.

Cambridge helps. The city sits at about 52 degrees north on some of the flattest land in England, with no hills to cast a shadow across a roof in the afternoon. At midday in late June the sun stands around 61 degrees above the horizon; in late December it reaches only about 14 degrees. A dome on a clear south slope collects direct sun through the middle of the day in every season, and on the flat Cambridgeshire horizon that low winter sun is not blocked by a ridge of high ground as it would be in a valley town. The things that do block it here are closer to home: a neighbour's chimney stack, a taller rear outshot next door, a three-storey block on the corner, or one of the big street trees on the Victorian avenues.

Orientation shapes the light that reaches the diffuser. A south-facing dome gives the brightest result and the most variation through the day. East-facing gives a strong morning and a softer afternoon, which suits a landing people use when they get up. West-facing does the reverse, lighting the hall for the return home. A north slope gives the lowest output but the steadiest, since it collects diffuse light from the open sky rather than direct sun. A sun tunnel can still be worthwhile on a north-facing roof, especially with a larger tube and a short run, and the answer on fitting a sun tunnel to a north-facing roof explains the trade-off honestly.

On many terraces the choice is not purely about orientation. The front slope faces the street and, in a conservation area, may be the slope the planners care about most. The rear slope of the main roof might be partly shaded by the two-storey back addition. The roof of the back addition itself, often a lean-to or a shallow pitched slate roof, can be the sunniest and least visible option, with a short, steep tube down into a first-floor bathroom. Our guide on where to put a sun tunnel on the roof works through these choices, and the principles behind them are set out on our page about how we plan the light.

We also keep clear of the zone either side of a party wall. Building Regulations guidance on fire spread between houses asks that the roof covering for 1.5 metres either side of a compartment wall meets a high external fire rating, which is why we avoid placing a dome in that strip. On a narrow terrace this can pin the dome to the middle third of the slope, and we draw that into the light plan before the survey is finished.

Domes are made of clear, impact-resistant acrylic or polycarbonate, sometimes with a shaped inner lens that helps bounce low sun down the tube. The dome sits on a raised base, and the base sits on a flashing kit that laps under the courses above and over the courses below, in the same way the flashing of a roof window does. Kits are made for profiled tiles, flat tiles and slates, and for flat roofs, and the choice has to match what is on your roof rather than what was easiest to buy.

Cambridge roofs vary more than people expect. The Victorian terraces of Petersfield, Romsey and De Freville are mostly Welsh slate, thin and brittle, laid on battens with a tight lap. Cutting a neat opening in slate and dressing a flashing into it is careful work, and the answer on fitting a sun tunnel to a slate roof explains how the slates around the dome are cut, holed and refixed. 1930s and post-war houses in Cherry Hinton, Arbury and the villages often have plain clay tiles or concrete interlocking tiles, each of which needs a different flashing profile. Village cottages in Grantchester, Barrington or the older parts of Linton may have handmade clay plain tiles, where matching and reusing the originals matters for appearance as well as for the weather.

Pitched-roof sun tunnel kits are generally designed for a range of slopes, commonly from about 15 degrees up to about 60 degrees, and the elbow at the top of the tube lets the dome stand upright while the tube angles back into the loft. Our guide to sun tunnels for pitched roofs covers low-pitch and steep-pitch details.

Flat roofs take a different kit: a dome on an upstand collar that is sealed into the membrane, whether that is single-ply, EPDM, GRP or felt, so that water runs round it. This is common over the flat-roofed rear extensions on terraces and over apartment roofs in newer developments. A flat roof also allows a completely vertical tube, which is the best route of all for light. The detail is in sun tunnels for flat roofs, and where a flat roof is going to be replaced anyway, it makes sense to fit the tube at the same time so the collar is built into the new membrane.

Because the light arrives at the diffuser after many reflections down a long tube, the direct heat of the sun stays mostly on the roof. The dome warms, the air in the upper part of the tube warms, but the ceiling disc does not throw a hot beam onto the floor the way a south-facing pane can. That makes a tube a comfortable choice for a landing or bathroom at the top of the house, where heat collects in July. The answer on whether sun tunnels let heat in goes through the physics without the lecture.

Winter works the other way. The dome and the top of the tube are cold, and the air in the room below is warm and, in a bathroom, full of moisture. If that moist air reaches a cold surface, it condenses. The defences are straightforward and all of them are part of a proper installation:

• a sealed or double-glazed diffuser at the ceiling, so room air does not enter the tube;
• sealed joints along the tube, taped with the manufacturer's foil tape;
• an insulating sleeve round the tube wherever it passes through the cold loft;
• loft insulation made good tight to the tube at ceiling level;
• good extract ventilation in the room itself, which is required in any bathroom.

The answer on whether sun tunnels cause condensation explains what happens when one of these is missed. On a replacement job, drips from an older tube are usually a sign of one of them, and a new, correctly sleeved tube solves it rather than moving it.

Cloudy days are the other seasonal question, and a fair one in the East of England. A tube carries diffuse daylight as well as direct sun, so an overcast sky still produces light at the diffuser, softer and cooler in tone, much as a north-facing window still lights a room on a grey day. The answer on whether sun tunnels work on cloudy days gives a realistic picture.

The signs are easy to see. A dome that has turned cloudy or yellow passes less light and is losing its impact resistance. A flexible tube that has sagged between its supports, or was installed with a long slack run, loses light at every fold. A diffuser with water staining, a dark ring or moisture behind the lens tells you the seal or the insulation has failed. A disc that was always dim may simply have been the wrong size or on the wrong slope in the first place.

When we replace a sun tunnel, we start as we would for a new one: which slope, which diameter, which route. Sometimes the original ceiling position is right and the roof position can be reused, and the job is a straight swap of dome, flashing, tube and diffuser. Sometimes a better slope or a wider tube makes a far bigger difference, and it is worth moving the dome or enlarging the ceiling opening to a 350mm diffuser while the ceiling is being made good anyway. Where the old flashing was dressed into a slate or tile roof, the slates or tiles around it are lifted and refitted with the new kit. The answer on how long sun tunnels last covers the typical life of each part, and if the problem is a failed rooflight rather than a tube, our misted and failed rooflight replacement service deals with those.

The day follows a set order. We protect the stairs, landing and any floor under the ceiling opening with dust sheets, then set up roof access, using ladders and roof ladders for most two-storey houses and a tower or scaffold where the roof is higher, steeper or over a conservatory. Inside, the position of the diffuser is marked and checked against the joists, and the ceiling opening is cut from below with dust extraction. In the loft, the route is confirmed and the insulation pulled back.

On the roof, the tiles or slates at the dome position are lifted, a neat opening is cut between the rafters, and the flashing kit is dressed in and the coverings refitted around it. The dome goes on, and from that moment the roof is weathertight again. Back in the loft, the upper elbow, the rigid sections and any flexible link are joined, sealed and supported, the insulating sleeve goes on, and the loft insulation is made good round the tube. Finally the diffuser ring is fitted to the ceiling and any small gaps round it are filled and decorated to match where agreed.

By mid-afternoon you can stand on the landing and see the result, which in a dark terrace is usually the moment the house feels different. The answer on how long sun tunnel installation takes covers the variations. Every installation is fitted to current Building Regulations and covered by our 10-year workmanship guarantee.

Before any of that, the survey and the written light plan set out the dome position, the tube diameter and route, the diffuser type and any extras, with the reason for each. It is the same approach we take across every service on our skylight and rooflight installation homepage. To start, book a light survey or message us on WhatsApp.