The short answer
Yes. Passing through a loft is what most sun tunnels do. The dome sits on the roof, the tube crosses the loft space and the diffuser sits in the ceiling below. It works well through an ordinary cold loft, takes more thought through a loft full of storage or services, and is not the right answer where the loft has been converted into a room.
The details that matter are what is in the way, how the tube is insulated and how the ceiling is finished.
What the loft has to offer
A tube needs a clear path from the roof slope to the ceiling. In a cold loft that usually means a gap between two rafters at the top and between two ceiling joists at the bottom, with open space between them. Because the rafters slope and the joists run level, the tube is normally fitted vertically or at a slight angle, with the roof opening and the ceiling opening in line.
The wider the tube, the more clearance it needs. Before fitting, we check that the route sits between structural timbers. We do not cut through trusses or joists to make way for a tube, because they carry the roof and the ceiling.
What gets in the way
Lofts are rarely empty. The obstacles we look for are:
- a cold water tank or its pipework, and the overflow;
- electrical cables, which may need to be moved by a qualified electrician;
- extractor fan ducts from bathrooms below;
- chimney breasts and their flaunching;
- trusses, braces and purlins, which a modern roof has in a pattern that leaves less free space than an older one;
- boarding put down for storage.
Some of these can be avoided by moving the tunnel. A shift of half a metre can take a tube clear of a tank. Some can be worked round with a bend, though each bend costs light. And some cannot be moved, in which case a different position or a different product is the sensible choice.
Cold lofts and converted lofts are different
In a cold loft, with insulation laid on the ceiling joists, a tunnel is a simple fit. The insulation is cut back around the tube and the tube is wrapped in its own insulation, so no cold section is left that could attract condensation. We explain why that matters in do sun tunnels cause condensation.
In a converted loft, where the sloping ceilings and the walls of a room are insulated at rafter level, there is no void for a tube to cross. The dome would sit directly above the room, and what you want is a roof window, which lets in light and a view of the sky. Our page on roof window installation covers that route.
A third case is a landing or stair below a loft room. The tube then passes through the floor of the loft room and the ceiling structure of the room beneath, and may need boxing in. That is workable, but it is a job for a survey, not a guess.
Insulation, fire and the ceiling
A tube through a loft crosses the thermal line of the house, so the insulation has to be continued around it. Without that, there is a cold gap through the ceiling that loses heat and can produce condensation. The tube is wrapped, and the loft insulation is packed up to the wrap.
The ceiling is the other consideration. Cutting a round hole through a ceiling puts a break in the plasterboard or lath and plaster, and in some houses that ceiling forms part of the fire separation between floors. Where that applies, the tube and its ring need to be detailed to keep the separation in place, and we check the position against the guidance in Approved Document B at survey. Treat that as something to confirm for your house and not a general rule.
In an older home, the ceiling needs even more care. Cutting lath and plaster without support can crack the plaster around the hole, and a lime ceiling wants lime used round the new edge. We finish the edge to match the ceiling, with a clean arris round the diffuser ring and a straight paint line. Our finish schedule records how that is done for each room.
Reaching the loft to fit it
A tube is fitted from both sides at once: the roof opening and dome from outside, the ceiling ring and diffuser from inside, with the tube joined and wrapped in the loft between them.
The fitter needs to get a tube, a dome and the tools into the loft and move around safely. A loft with a small hatch, no boarding and a low pitch is slower and harder to work in. We note the access at survey, and where a loft is boarded for storage, we may need the boards lifted or the space cleared locally, and we discuss that with you beforehand.
Dust from cutting the ceiling is managed, with the room protected below and the room left clean afterwards.
How long a tube can be through a loft
The depth of the loft sets the length of the tube, and length sets how much light reaches the room. A tall loft void, as in some Georgian houses around Southernhay or St Leonards, gives a long tube and a dimmer result than a shallow one. Our answer on how long a sun tunnel can be gives the full picture.
Next step
If you want to know whether a tunnel can cross your loft, send a photo of the loft hatch and the room below with your request, and ask for a quote. We will survey the loft, measure the route and tell you plainly whether a tunnel suits, and what it will look like when finished. Where it doesn't suit, we will say so and suggest a better product. The planning and Building Regulations position for the dome is on our sun tunnel installation page.