Sun tunnel installation in Exeter

A sun tunnel has three working parts. At the top is a dome, clear or lightly textured, that sits on a flashing and gathers daylight. Below it runs a tube with a highly reflective inner surface, which carries that light down by bouncing it from wall to wall. At the bottom a diffuser, a frosted or prismatic disc in a trim ring, spreads the light across the ceiling. Some makes add a second layer of glazing at the diffuser to cut heat loss.

Because the tube is narrow and the dome small, a sun tunnel works where a roof window cannot: a room in the middle of the house, a bathroom with a loft above it, or a landing two rooms away from any outside wall. It needs no rafters cut in many cases, because a standard tube is made to fit between them. That keeps the structural question simple and the roof work short.

The rooms that take one best are the ones people pass through or use for a short while and want to feel bright without switching on a lamp. The common cases in Devon houses are these.

Hallways and landings

The 1930s semis of Heavitree and Pinhoe, and the Victorian terraces of St Thomas and Newtown, often have a landing or stair hall with no window at all. A sun tunnel above the landing lights the stairs and the doors off them.

Bathrooms and en suites

An internal bathroom, or an en suite built into the roof space of a new home in Cranbrook or a converted loft, is the classic candidate. We cover this in sun tunnels for bathrooms, landings and hallways.

Cloakrooms, utility rooms and walk-in wardrobes

These small rooms usually sit against the centre of the plan, where daylight never reached. One small tunnel is enough.

Bungalow corridors

The long, windowless corridor in a bungalow in Exmouth or Dawlish suits a tunnel or two, because the roof is close above the ceiling and the run is short.

Where the room is large, where you want to see the sky or where you need fresh air, a rooflight or a roof window does a different job. Our guide to a sun tunnel or a rooflight sets out how to choose, and our roof window installation page covers the larger opening.

The roof end is where a sun tunnel is won or lost for weather. The dome sits on a flashing, and the flashing must match the roof it goes into. A sun tunnel is not a single product for every roof, and the right flashing for a plain concrete tile is wrong for a Delabole slate roof or a flat roof with a felt covering.

Plain and interlocking tiles

Tile roofs use a flashing with a flexible skirt that moulds over the profile of the tile, or a tile-specific flashing plate. Double Roman and pantile profiles each need their own type, and the sizes differ from one manufacturer to the next. The surrounding tiles are cut back, relaid and bedded so that the line of the roof is not disturbed.

Natural slate

Slate needs a flashing that sits under the slates above, with soakers or an apron below, and the opening is cut around slate courses without breaking more than a few. We take care here because slate roofs on older Devon homes are not cheap to disturb and their battens, laths and nails are often old.

Flat roofs

On a flat roof, the dome sits on a small kerb, called an upstand, which is insulated and dressed with the roof covering, whether that is felt, GRP fibreglass or EPDM. The kerb lifts the dome clear of standing water, and its height is set by the roof falls and the covering. Our guide to sun tunnels on flat and pitched roofs covers the differences.

Where the roof faces matters little for a sun tunnel, but where the dome sits on the slope does. A position near the ridge gives the dome clear sky and keeps it clear of snow and leaf fall, while a position low on the slope near the eaves sits in the shade of the tree or the neighbouring gable. The dome is a plastic, usually acrylic or polycarbonate, with a UV stable surface, and some are made with a double skin to reduce heat loss and condensation inside the dome itself.

Whatever the roof, the flashing is the line where the work will either last or fail, which is why it sits inside our 10-year workmanship guarantee. The weathering we fit is covered for the length of that guarantee, and the written quote names the flashing type and the roof covering it suits.

This is the part you see every day, and the one that most often looks like an afterthought. The diffuser sits in a trim ring, the ring sits against the ceiling, and around the ring there is a ceiling that has been cut. A clean job here is a flat disc, a collar that sits tight to the plaster, and a ceiling that runs unbroken to the edge of it.

A sun tunnel is usually a round opening, but the finish is as much about the plaster as the circle. Cutting through a plasterboard ceiling is straightforward and tidy. Cutting through a lath and plaster ceiling in a Georgian house in Southernhay or a Victorian terrace in St Leonards is different, because the plaster is held by keys pushed between the laths, and a careless cut sends a crack across the ceiling. We score the plaster, support it from above and cut the opening with the laths held, so the plaster around the hole stays sound.

Where the opening is cut, the plaster edge is made good before the trim ring goes on. On plasterboard, the edge is sealed and taped and the gap between ring and ceiling is filled, sanded and left ready for paint. On lime plaster, in an older home with a lime ceiling, we make the edge good in lime rather than gypsum, because the two behave differently with moisture and gypsum beside lime can crack as the lime moves. The distinction is covered in our guide to how a rooflight is finished inside.

The depth of the tube above the ceiling affects the finish too. A sun tunnel does not have the deep splayed reveal of a rooflight, so there is nothing to splay, and the best finish is a flat, flush collar. On a ceiling that is thick, as in some older houses, a short length of tube is lined or collared down through the thickness so that the diffuser does not sit recessed into a hole. In a coved or textured ceiling, the ring needs a level surface to sit on, and we form one.

Paint makes the last difference. A white diffuser ring looks right on a white ceiling and wrong on a cream or coloured one, and a ring that is a different white from the ceiling stands out in the afternoon sun. Some rings can be painted and some cannot, and we say which at quote stage. If the ceiling is going to be repainted, we tell you whether to leave that until the plaster has dried and the ring is fitted, so that the paint line runs tight and clean.

Most sun tunnels on houses need no planning application. A dome in the roof of a dwellinghouse is usually permitted development under Class C of Part 1 of Schedule 2 to the General Permitted Development Order, provided it projects no more than 150mm beyond the plane of the roof and sits no higher than the highest part of the roof. Sun tunnel domes are low, so on a pitched roof they fall inside this. A flat roof kerb with a dome may stand taller, and we measure it against the 150mm limit at survey.

The exceptions are the usual ones. Flats and maisonettes do not have householder permitted development, so the flat's owner and freeholder need to be asked. A conservation area allows Class C but an Article 4 direction can remove that right, and a listed building always needs listed building consent for an external change, including a small dome. Inside a national park such as Dartmoor, some rights are restricted. Where it varies, we say so and suggest you check with the local planning authority, which is Exeter City Council, East Devon, Mid Devon or Teignbridge District Council, Torbay Council or the national park, depending on the house.

Building Regulations are a separate matter. Cutting a new opening that trims roof timbers is building work, and Building Control may treat a sun tunnel like a rooflight under Part L of the Regulations, which covers the conservation of fuel and power. Where Part L is applied, the reference is the limiting U-values in the 2021 edition of Approved Document L Volume 1. How a tubular unit is treated varies, so we confirm the position with Building Control rather than assume it. Where the work is notifiable, we handle the Building Control notification for you. Whether a given tunnel needs trimming of timbers depends on the tube diameter and the rafter spacing, and we confirm what applies at survey rather than assuming.

A few rooms bring extra points. A sun tunnel in a room used as a bedroom does not take the place of an escape window, because a tube cannot be climbed through. Where a bathroom is fitted, the ventilation rules in Part F still apply, and a sun tunnel provides no ventilation of its own, so the extractor fan remains. The planning and regulation points for every product we fit are set out on our services page, and the finish schedule records which apply to your job.

A sun tunnel is among the least expensive ways to add daylight, but the price still moves with the job, and a written quote that lists the parts is the only reliable guide. We give no figures here because the price depends on your roof and your ceiling, and a survey is the way to find it. For general market ranges, the costs page gives indicative figures with the caveat that our own prices come from a survey.

The factors that matter are these. The first is the product: the diameter, the tube type, the dome and whether the diffuser is double glazed. The second is the roof: pitched or flat, tile or slate or felt, and how steep. The third is the run: the length of tube, the number of bends and whether the loft has to be cleared to reach it. Fourth comes the ceiling: plasterboard, or lath and plaster, or lime, with a thick or coved edge. After that come the extras: scaffolding if the roof is high or awkward, a light kit, a wiring job and any Building Control fee.

The cost of making the ceiling edge good, and leaving it ready to paint or painted, is a real share of a sun tunnel job

Finish is what quotes most often leave vague. The cost of making the ceiling edge good, and leaving it ready to paint or painted, is a real share of a sun tunnel job, because the tube is small and the finish is nearly all of what you see. Our quote shows it as its own line in the finish schedule, so you can compare like with like if you ask for other quotes.

It is a one-page written note for your room.

Not by much. A sun tunnel is a small opening and has an air gap between the dome and the diffuser, and some are made with double-glazed diffusers and double-skinned domes. The cold stretch of tube in the loft is the weak spot, which is why we seal the ceiling end and insulate the tube where the loft is cold. Fitted that way, a sun tunnel adds less heat loss than a roof window and rarely causes any trouble.