Rooflight and skylight installation in Tetbury, planned before anything is ordered.

Listing density in the core, and the assumption worth checking early

The centre of Tetbury has an unusually high concentration of listed buildings for a town of its size, and the practical effect is that a good number of enquiries here concern a building that is listed even though the owner assumed it was merely in a conservation area. Those are different regimes. Conservation area status is area-based and works through the planning system. Listing is building-specific, applies inside and out, and creates a consent that is required regardless of whether planning permission is.

Two extras catch people. Listing reaches structures within the curtilage that were there before July 1948 and in the same ownership at the date of listing, which takes in coach houses, stores and outbuildings behind the frontages. And the internal work matters as much as the external: the plastered reveal, the loss of riven battens, the removal of lime mortar torching from the underside of the roof, and any alteration to hand-cut timbers are all part of what consent covers.

Steep pitches on the older roofs, and what they do to the geometry inside

Cotswold stone slate is laid steep because it is a small unit with a modest lap, and pitches of 45 to 55 degrees are normal on the town’s older roofs. Two things follow inside.

First, the reveal becomes a tall box rather than a shallow one. A window in a 50 degree slope sits with its head a long way above the floor, and the vertical lining above it throws light much deeper into the room than the same unit in a 30 degree roof would. That is an advantage worth designing for rather than a side effect. Second, reaching the opening handle from standing height stops being realistic on anything set high in the slope, which is where a rod-operated or an electrically operated unit earns its place. Detail on the powered version is on electric rooflight installation.

A steep pitch also means more of the unit is visible from any ground below than the same window on a shallow roof, which is a genuine factor in how an officer assesses a proposal rather than a technicality.

Shops, storerooms and the floors above the antiques trade

A large part of the town centre is in commercial use at ground level with a floor or two above it, and the upper floors in this town are more often used as storage or showroom space than they are in a comparable residential core. That produces a particular kind of enquiry: an owner wanting daylight into an upper room that has one small window in a gable and nothing else.

The work is shaped by the occupancy as much as the building. The floor below the working area may hold stock that has to be moved or sheeted before anything is cut. Access is through a shop or a rear yard shared with a neighbouring business. And the useful working hours are often outside the trading day, which affects the programme and is agreed in writing beforehand rather than negotiated on the first morning. The roof is never left open overnight regardless, so the day’s outside work is planned to a point where the covering is whole.

Attics under stone slate, and the headroom that decides the project

People often come to a rooflight thinking about light and discover that height decides it. A stone slate roof at 50 degrees over a narrow plan gives a tall, sharp void with a decent ridge height and very little floor area where a person can stand upright.

The arithmetic is worth doing before anything else. Measure the ridge height above the existing ceiling joists, subtract the depth of a new floor structure, subtract insulation and a finished ceiling at the rafter line, and see what is left in the middle. Where the answer is workable, rooflights set into the slope are the right way to light it, and they are also the alteration a conservation officer is most likely to accept in this town because they change the roof outline not at all. Where the answer is not workable, the honest thing is to say so before drawings are paid for. That is a statement about the building.

Torching, and the detail agreed before the scaffold goes up

Many of the older roofs in the town have no underlay at all. The joints between the stone slates were sealed from below with a lime mortar torching, often mixed with animal hair, applied to the underside of the covering between the battens. It has worked for a very long time and it cannot be put back exactly as it was once disturbed.

The replacement detail therefore gets agreed in advance, usually as a breather membrane on counter battens local to the opening, and on a listed building it forms part of the method statement submitted with the application rather than a decision taken on the scaffold. That is one of the reasons pre-application advice is worth the fee here: an officer will say early what treatment they will accept, and that answer arriving before the work starts is worth many times what it costs.

Where a sun tunnel does better than a roof window in a Tetbury cottage

A sun tunnel is a small dome on the roof, commonly around 350mm across, running a reflective tube down through the void to a diffuser in the ceiling below. It disturbs a fraction of the covering that a roof window does, and on a town centre roof where every course taken back is a cost and a consent issue, that fraction matters.

It suits a windowless internal bathroom, a landing, a stair head or a deep-plan back room, all of which the town’s older houses have in quantity. It gives daylight rather than a view and it does not ventilate, so it is a different product rather than a smaller roof window. On a prominent slope in a designated area it is sometimes the only proposal that will get through, and the comparison is set out on sun tunnels and where they beat a rooflight.

What the survey records on a Tetbury roof, and how a figure follows

The order goes out against measured facts. On a stone slate roof in this town the survey records the covering, its thickness and the measured gauge over several courses, the pitch off a digital level, whether the roof is torched and in what condition, the rafter positions and depths, any purlin, strut or collar in the way, valley positions on a multi-range roof, the designation position for the address, and the access and licensing route for scaffold.

Those answers decide the unit, the lead schedule, the reclaimed stone order, the breakage allowance and the programme. The commercial route is the same as everywhere Severn works. Send photographs of the roof and the room, the covering if you know it, and the address to info@severnskylightsgloucester.co.uk, and an indicative range comes back by email. After the survey there is a fixed price, itemised so it is clear what is unit, labour, scaffold, lead and Building Control, and it holds unless the scope changes at the customer’s request. The costs page explains how a range becomes a fixed price, and conservation rooflight installation covers the unit that most Tetbury roofs end up wanting.