Can a rooflight go in a thatched roof?

A slate or tile roof is a thin skin on battens, and a rooflight is set into it with flashings that overlap the slates. Thatch is a thick, soft layer of straw or reed laid over the rafters and held down with spars, sways and fixings. There is no hard surface to flash against, and the thatch cannot simply be cut with a saw and sealed with a strip of lead.

Instead the thatcher forms a frame in the thatch and dresses the coat of straw or reed back to the edge of the rooflight, so that rain runs off the thatch onto the frame and over it, not behind it. The detail depends on the type of thatch, the pitch and the age of the coat. It is specialist work, so the thatcher needs to be involved from the first visit.

Thatch is also a combustible roof covering. That shapes where a rooflight can go and how the opening is built, which is covered further down.

Permitted development normally covers a rooflight in a house roof, within two limits: it may stand no more than 150mm proud of the roof plane, and it may not rise above the ridge line. Thatch complicates that, because the roof plane is a thick, rounded surface and a cottage may not have permitted development rights at all.

• Listed buildings. A thatched cottage that is listed needs listed building consent for external alterations. A new opening in a thatched roof is a change the conservation officer will look at closely, and consent may be refused or limited to a particular position and size.
• Conservation areas. Class C permitted development still applies unless an Article 4 direction has removed it. Thatched streets in East Devon villages are a likely place for one, so check.
• National parks. Inside Dartmoor or Exmoor, some permitted development rights are restricted. Ask the national park authority before you assume anything.

Whether the council is Exeter City, East Devon, Mid Devon, Teignbridge or another, the answer is to ask the local planning authority before work starts. Our guide to rooflights, planning permission and Building Regulations in Devon sets out the general position, and our page on conservation rooflights and planning covers the listed and conservation area side in more detail.

Cutting a new opening into a roof that already exists counts as building work. The rafters are trimmed and the window has to meet Part L, so Building Control must be told, and we make that notification for you. In thatch, fire adds a second layer of care.

Approved Document B treats thatch as a roof covering that needs particular thought, and the rules on thatched roofs near boundaries are stricter than for other coverings. Rooflights themselves have to be placed with that in mind, and the construction around the opening matters too. Keep the opening clear of chimneys and flues. Your Building Control officer is the person to confirm what the roof needs.

It is also worth telling your buildings insurer before anything is cut. Thatched houses are often insured with specialist policies, and a change to the roof is the sort of thing the policy wording expects you to mention.

The best fit is a small, low-profile unit set between existing rafters, so the structure needs the least alteration. A conservation-style rooflight with a slim, flat frame sits close to the thatch and reads as a small detail on the roof, where a chunky modern frame would draw the eye. For the style itself, see our conservation rooflights page.

• Size. Keep it modest, and between rafters if the spacing allows. A wide opening means trimming rafters and a bigger gap in the coat for the thatcher to dress.
• Position. A rear or side slope is easier to consent than the front elevation, and it keeps the unit away from the ridge, the eaves and any chimney.
• Frame. A flat, slim frame, dark or painted to suit, looks least out of place against straw or reed.

This is where thatch is unlike anything else. The roof build can be very deep, so the distance from the glass to the ceiling inside is often much longer than in a tiled house. The lining that spans it is a real feature of the room, not an afterthought.

A straight shaft through that depth gives a dim, tunnel-like opening. A splayed lining, wider at the ceiling than at the glass, turns it into a deep reveal like those at a cottage window, and it spreads what daylight there is. Our answer on what a splayed rooflight lining is explains the shape.

The ceiling matters too. Cottage ceilings under thatch are commonly lath and plaster, lime plaster or boards, and cob walls often sit below them. They need care when a new opening is cut, and lime plaster is the right finish where the house has lime. Our answer on fitting a skylight in a lath and plaster ceiling describes how that is handled. The finish schedule we write with the quote records the roof build, the lining shape and the finish for the room.

Start with the consent question, not the product. If the house is listed or in a conservation area, speak to the local planning authority and, for a listed house, expect to submit drawings and a heritage statement. In parallel, talk to the thatcher who looks after the roof, since the age and condition of the coat affect where an opening can go and whether the work is best timed with a re-thatch.

Then ask us to survey the roof and ceiling. We measure the rafters and the roof depth, look at the ceiling below and write a finish schedule for the room, so the thatcher, the council and you all see the same plan. Ask for a quote and send a few photos of the roof and the room if you can.

Sometimes a thatched slope is simply not the right spot. A listed cottage may be refused, or the roof may be due a re-thatch soon and best left alone. The light can often come from elsewhere: a rooflight on a slate or tile slope of a rear extension or porch, a flat rooflight over a single-storey addition, or a new window in a gable wall. They leave the thatch untouched.

If you are unsure which route suits your house, a survey will tell you, and our answer on Building Regulations covers what approval each option needs.