The short answer
Often, yes, though the route needs planning. A converted loft puts a finished room between the roof and the dark space below, so the tube cannot simply drop straight down. It is run through the eaves void beside the room or boxed into a corner or cupboard, using rigid sections with as few bends as possible, and checked against fire and insulation rules.
Why a loft conversion changes the question
In an unconverted house, a sun tunnel drops through an empty loft from the roof to the ceiling below. A conversion fills that space with a bedroom or a study, and the simple route is gone.
The finished loft has a floor that carries people and furniture, sloping ceilings where the plasterboard follows the rafters, and insulation packed in behind it. The roof above the room is part of the room. A dark landing or bathroom on the floor below is, in plan, often directly under it. The tube from a dome on the roof to that space has to get past all of that without cutting up the new room or spoiling its insulation.
Crawley shows the pattern clearly. The town is full of 1950s to 1970s homes with lofts already converted into a bedroom, and the first-floor landing in those houses is commonly a windowless stair well. The converted loft has made the top of the house bright and left the middle dark. That is the situation a sun tunnel can help with, as long as the route is worked out properly. Our page on sun tunnels for hallways and landings covers the landing side.
The two routes that usually work
There are two practical ways through, and the survey decides between them.
Through the eaves void
A converted loft with sloping ceilings nearly always leaves a low space behind the knee wall, at the edge of the room where the roof meets the floor. That void is outside the living space and often unused. A dome set on the lower part of the roof slope, below the line of the conversion, can feed a tube that runs down through this void and into the ceiling below.
The advantage is that the tube stays out of the room entirely. The limit is the geometry. A dome low on the slope is a long way from the landing, and the tube needs a bend or two to get from the eaves to a point over the stairs. Every bend costs light, so the planning is about finding the shortest path. Our page on tunnel length, bends and how much light arrives explains why.
Boxed through the conversion
Where the eaves route is too far from the dark room, the tube can pass through the loft room itself, boxed in. A corner, the back of a built-in wardrobe, a chimney breast recess or a stud wall line can all hide a tube in a neat casing. The dome sits higher on the roof, the run is straighter, and more light arrives.
The cost is floor space and finish. The casing takes a slice of the room, and it needs plastering or boarding and decorating to match. It also means the work touches a finished room. For that reason it is best agreed early, ideally before the loft is fitted out, although a tube can be added afterwards where the room has a spot that will take it.
What has to be checked on the way down
A tube passing through a converted loft meets three constraints. None of them rules a tunnel out, and all of them shape the details.
Structure. The roof opening for the dome sits between rafters, and a conversion may have altered them. Where a rafter is in the way, the opening needs proper trimming. The floor the tube passes through is usually a fire-resisting floor, and the route may run beside a structural member. We look at the actual timber at the survey and do not guess from outside.
Fire. A converted loft generally relies on a protected stairway as its escape route. Anything that passes through the floor or the stair enclosure has to keep the fire protection intact. A tube or casing through that line needs to be detailed so it does not become a path for smoke or flame. Part B of the Building Regulations governs this, and our page on whether a sun tunnel affects fire safety in a loft explains it in plain terms. The work is installed to current Building Regulations and we handle the Building Control notification where it applies. See does a sun tunnel need Building Regulations approval.
Insulation. The loft room is insulated to keep heat in. A tube through the insulated roof or floor must not leave a cold bridge or a gap. The tube is wrapped, the opening is sealed and the insulation is made good around it, following Part L. Cold surfaces in an insulated space are where condensation starts, and sun tunnels, loft insulation and heat loss sets out the detail.
Choosing the tube and the dome for a long route
A conversion route is usually longer than a plain loft route, so the hardware matters more.
Rigid sections carry more light than a flexible tube, because the smooth reflective surface loses less at each reflection. Where a bend is unavoidable, a rigid elbow is better than a folded length of flexible tube. The trade is explained in rigid or flexible sun tunnels. A flexible section still has a place where the route has to snake round a joist, but it should be short and pulled fully taut.
A wider tube also helps, since it collects more and carries more down a long path. The dome and diffuser are chosen alongside. Because the loft bedroom sits under the same roof, noise is worth thinking about, and a dome chosen for calm in rain is written into the quiet spec with the rest.
One more check is whether the landing really needs a tunnel. If the dark space is directly under the loft stairs and a roof window could light the stairs themselves, that may serve better. The question is covered in can a sun tunnel pass through an upstairs room, which looks at the same problem from the other side.
Loft conversion questions
Can the tunnel be added after the conversion is finished?
Yes, where there is a route. The eaves void route causes the least disturbance, and a boxed route means opening and making good a finished wall or corner. It is simpler before the loft is fitted out, but it is not ruled out afterwards.
Will it use up space in the loft bedroom?
The eaves route uses none. A boxed route takes a narrow casing, sized by the tube, and we try to hide it in a corner or a wardrobe line where it costs the least.
Does the loft conversion need to be signed off first?
Not as a rule. The tunnel is its own piece of work, but the conversion's own records help us understand the floor and the escape route. If you have the drawings, bring them to the survey.
How long does it take?
A route through an eaves void is usually a shorter job than a boxed one, because there is less finishing. Our page on how long it takes to fit a sun tunnel describes a normal day, and the conversion adds what the survey finds. To begin, get a quote. The full service is on our sun tunnel installation page.