Why slate suits a sun tunnel
A sun tunnel needs a small, round opening in the roof and a flashing that seals around it, and a flat covering like slate gives that flashing an even surface to sit on. The work is fiddly rather than difficult.
Profiled concrete tiles rise and fall across the roof, so a flashing has to follow their waves. Natural slate lies in thin, flat courses, which means the flashing plate can sit close to the roof and the dome reads as a small, tidy disc rather than a bump. On the Victorian and Edwardian terraces of Romsey, Petersfield and the streets off Mill Road, many roofs are still in slate, often on the rear slope over the back addition where a dark landing or bathroom sits below. Those are good candidates for a tubular skylight, because the loft run down to the ceiling is usually short.
The opening itself is small. Common tube diameters for homes run from around 250mm upward, so on a slate roof you are usually lifting a handful of slates rather than stripping a section. The tube passes between the rafters, and where a rafter is in the way the position moves along to the next bay rather than cutting the timber. How the tube, dome and diffuser carry the light down is set out in how sun tunnels work.
Slate flashings: what the kit has to do
The flashing is the part that decides whether a sun tunnel on slate stays dry, and it has to match both the roof covering and the pitch. Manufacturers generally make separate flashing kits for profiled tiles and for flat coverings such as slate.
Product ranges differ, so the specific kit always needs checking, but a pitched roof flashing for a sun tunnel usually has three jobs. It carries a collar that the dome fixes onto. It has an upper edge that tucks under the slates above, so water running down the roof passes over it. And it has a lower edge that lies over the slates below, so water leaves the flashing onto the roof, never behind it. On slate, a flat profile kit keeps the plate thin enough that the courses above lie down properly again.
Some kits are one moulded piece; others pair a rigid plate with a soft, formable skirt. On older or uneven slating, a roofer may prefer to dress lead soakers or a lead apron around the collar instead of, or as well as, the kit skirt. Which route suits your roof depends on the slate size, the headlap and how true the courses are, and it is something to confirm at the survey rather than assume.
Taking out and refixing slates
Most of the skill on a slate roof is in the slates themselves. They are brittle, they are nailed, and they have to go back so the roof looks as though nothing happened.
Slates are fixed with nails through each slate, either near the head or near the centre, so they cannot simply be lifted like clip-on tiles. The nails are cut with a slate ripper slid up under the course, and the slates come out one at a time. Around the opening, some slates are cut to fit the collar and the rest go back in their own places. Slates that cannot be nailed again, because the batten behind is now covered by the flashing, are held with a tingle (a small strip of copper or lead) or a slate hook, which is a normal way of refixing a single slate.
A slate or two can crack in handling, particularly on an old roof. That is why matching matters. Natural slate varies in colour, size and thickness from one quarry and one century to the next, so a reclaimed slate of the same size and tone is usually a better match on a Victorian roof than a new one. Asking about spares is sensible: some houses still have a few left in the loft from an earlier re-roof.
Natural slate, fibre cement and what to check first
Not every slate roof is natural slate, and the difference matters before any cutting starts. Artificial slates made from fibre cement behave differently and may need a different approach.
| Covering | Where you may find it | What changes |
|---|---|---|
| Natural slate, older | Victorian and Edwardian terraces | Brittle, varied sizes; match with reclaimed slate |
| Natural slate, newer | Re-roofs, some new homes | Even courses; a flat profile kit sits well |
| Fibre cement slate | Later re-roofs and estate homes | Cuts cleanly; older slates need testing first |
Fibre cement slates are thin and flat too, so the same kind of flashing kit generally suits them. The caution is age: fibre cement slates made before asbestos was banned in the UK in 1999 may contain it, so an older artificial slate roof should be tested before any slate is cut or drilled. That is a safety step, not a reason to give up on the sun tunnel.
It also helps to know what lies under the slates. Many older Cambridge roofs have no underlay, or a torn original felt, while newer roofs have a breathable membrane. The membrane is cut and dressed back into the flashing collar so any water that gets past the slates is still led outside. Where the loft side needs insulating around the tube, see can a sun tunnel go through loft insulation.
Where the dome goes, and the light it sends down
On a slate roof the dome position is chosen for the light first, then nudged to suit the courses and rafters. A dome a few slates higher or lower makes almost no difference to the light, but the slope it faces does.
A terrace's rear slope might face south west over the garden or north east towards the next street, and that changes how much direct sun reaches the dome through the year. A south facing slate slope gives the brightest tube in summer; an east or west slope gives morning or evening light; a north slope works mainly on sky light. We pick the slope, then place the dome so the tube runs as straight as possible to the ceiling, because each bend loses light. Choosing the slope is covered in more depth in where to put a sun tunnel on the roof, and the wider pitched roof picture, including longer runs through the loft, in sun tunnels for pitched roofs. Our approach to planning the light applies here as it does to any rooflight: know where the light will land before the roof is opened.
Questions people also ask
Will a sun tunnel on a slate roof need planning permission?
On many houses a sun tunnel is likely to fall under permitted development, as long as it does not project more than 150mm above the roof plane. Conservation areas and listed buildings are different, and a slate front slope on a terrace can be sensitive. See sun tunnels in a conservation area and whether sun tunnels need building regulations.
Does fitting on slate take longer than on tiles?
It can take a little longer, because slates are cut out and refixed one by one rather than lifted and dropped back. A straightforward single tube is still usually a one day job. What shapes the day is covered in how long sun tunnel installation takes.
Can the dome be kept low on a slate roof?
Within limits, yes. The flat profile flashing sits close to the slates, and some ranges offer lower domes. The dome still has to stand proud enough to gather light and shed water, so a fully flush finish is not how sun tunnels work.
Can I reuse my own slates around the flashing?
Usually, yes. Slates that come out whole go back in their own courses, and only those cut around the collar change. A reclaimed slate of matching size fills any gap left by a cracked one. To see what would suit your roof, book a light survey or read more on sun tunnel installation in Cambridge.
