Length answer
Sun tunnel length: how far can the tube run?
There is no single maximum, because three things set the sensible length: how wide the tube is, how many bends it takes and how much sky the dome can see. How each one works.
The answer
A sun tunnel can run as far as the maker's kit allows, but light fades with every metre and every bend, so shorter and straighter is always brighter. Each product has a published longest run, and past a certain point the ceiling panel looks dim. For a long route, a wider tube or a roof window may do the job better. We judge this at the survey.
What decides how long a tube can sensibly be?
Width, wall finish and the number of bends. A wide, polished tube carries light further. A narrow or ribbed one fades faster. Each manufacturer publishes a longest run for each kit.
Light inside a tube loses a little at every bounce off the wall. A longer tube means more bounces, so less light reaches the ceiling. Nothing stops a tube being extended; the question is when the result stops being worth having.
Width of the tube
A wider tube lets in more light at the dome and keeps more of it as it travels, so it can run further than a narrow one. A bigger tube also needs a bigger roof cut and a larger ceiling panel, so it must fit the house as well as the light you want.
Wall finish
A mirrored rigid wall is the best carrier. A ribbed flexible wall gives up more on the way down, so its useful length is shorter. Our guide to rigid and flexible tubes compares the two.
The maker's limit
Every kit is sold with a longest recommended run, and past that point the performance falls away. We fit within that limit and tell you where on the scale your route falls. A route near the limit still works, only with a softer glow than a short one.
How much does each bend cost in light?
A bend is like adding extra length: it uses up part of the run you have. Two or three bends can leave a tube with a fraction of its straight-line reach, so we avoid them when we can.
Think of each bend as swallowing a length of tube. A route that needs an offset to dodge a beam may be the equivalent of a much longer straight run.
Why bends bite
Where the tube turns, the light hits the wall at a steeper angle and more of it is lost or sent back up. A gentle bend loses less than a sharp one, and a tube pulled taut loses less than one allowed to sag. Rigid elbows are better than a flexible tube folded over on itself.
Moving the dome instead
Before adding a bend, we look at whether the dome can slide along the slope, or the diffuser can shift on the ceiling, to give a straighter drop. A move of a hand's width to clear a rafter is often cheaper in light than any bend. The room and the roof need to agree, which is why we look at both at once.
When a bend is unavoidable
In some houses a structural member, a chimney or a duct sits in the only possible line. Then a single well-made offset is acceptable and the tube is kept short elsewhere to make up for it.
What shortens a good run
- A beam, duct or tank in the straight line
- More than one bend between dome and ceiling
- A narrow tube on a long drop
- A ribbed flexible wall left slack or kinked
- A diffuser placed a long way off the dome's line
How long is the run in a Tyneside home?
It varies with the house. An upstairs flat or a top-floor landing usually has a short drop; a room in the middle of a house, with another storey above, has no route at all.
The distance from roof to ceiling comes from the building, so it helps to picture the common house types.
Upstairs Tyneside flats
Beneath the roof of an upstairs flat, a landing or inner bathroom has only a short stretch of loft above it, which makes for a bright run. Down below, the flat above takes the main roof, so only a back offshoot with its own low roof offers a route.
Terraces and semis
On the top floor, the drop through the loft is generally short. The longest runs come where a room sits below a deep loft or a floored attic. A room on the floor beneath that, with a storey in between, cannot be reached unless the route passes through another space, which we do not do.
Extensions
Over a one-storey extension the roof is thin, which keeps the tube brief and the glow strong. That is why a tunnel can suit a utility or a pantry at the back of a house better than a room in the middle of it.
What can I do if my route is long?
Choose a wider tube, shorten the run by moving the dome, add a second smaller tunnel, or use a glazed rooflight. A long route should be solved with the right product, not by adding length.
If the survey shows a long drop, there are four honest ways forward, and which one is right depends on the room.
Wider tube
A wider tube is the first thing to try, because it carries more light further. It needs a bigger roof opening and a larger ceiling panel, which may or may not suit the space.
Better position
Moving the dome or the diffuser to shorten the drop is often free of any extra cost to the light. We try this before anything else.
Two smaller tunnels
Two tubes of short length can light a long hallway better than one tube of long length. Each has its own roof opening, so the planning route and the Building Control notification cover both. On a flat, planning permission is needed from the council for each new opening, and we handle the Building Control notification where the work is notifiable.
A different product
If the room is large or the drop is deep, a roof window or flat rooflight over the room may be the better tool. Our guide to choosing between them covers that call, and the sun tunnels page gives the wider picture.
Length and brightness, briefly
Does a longer tube mean a darker room?
In general, yes. More length means more bounces and less light at the ceiling. A tube within the maker's limit still gives a useful glow, but it will be softer than a short one. The survey tells us what to expect for your route.
Can I extend a tunnel later if I change the room?
Sections can be added in principle, but each addition shortens the light, and a change to the ceiling or loft may need the route reconsidered. It is better to plan the run once, with any later work in mind.
Does the dome's position change how far the tube can go?
Slightly. A dome with a clear view of the sky collects more light, which helps a longer run. Shade from a chimney or a neighbouring gable can reduce it, so we look at the roof around the dome as well as the route below.
Is there a minimum length for a sun tunnel?
Very short drops are fine; they give the brightest result. The practical need is for room to fit the dome base, the tube and the diffuser, which we check on site. Where the gap is shallow, a low-profile kit is used.