Conservation Rooflight Installation
Slim cast frames set flush, for stone slate, listed and conservation roofs.
the Cotswolds
Rooflight and skylight installation in Northleach, and the roof it has to sit in.
Northleach: small wool town, stone slate throughout. What that changes about getting glass into a roof is the whole of this page.
- Covered from Gloucester
- 15 years on Gloucestershire roofs
- 10 year workmanship guarantee
- From Gloucester by road
- 15 to 30 milesApproximate, and inside the 30 mile radius
- Dominant roof stock
- Cotswold stone slate in diminishing coursesWhat the covering is decides the detail
- The usual constraint
- Conservation consent and matching the stoneSettled at survey, before anything is ordered
- Local character
- small wool town, stone slate throughoutRecorded for Northleach specifically
In Northleach
Rooflights we fit around Northleach
Roof Window Installation
Roof windows trimmed into slate, clay and concrete tile without proud flashing.
VELUX Window Installation
VELUX fitted alongside Fakro, Keylite and Roto, chosen to suit the roof.
Electric and Opening Rooflights
Actuated openers, rain sensors and controls, wired and commissioned.
Energy Efficient Rooflights
Specified on U-value and g-value for the way the roof actually faces.
Replacing a Failed or Misted Rooflight
Misted and tired units taken out, and the opening made good underneath.
The local detail
Fourteen things worth knowing about Northleach roofs, worth reading before the survey.
Northleach is small, it is old, and its roofs are unusually consistent. Where a Gloucester street can hand you clay tile, Welsh slate and concrete interlocking within fifty yards, the historic part of this wool town is close to unbroken Cotswold stone slate. That single fact settles most of the technical argument before a survey is booked, and it moves the difficulty of the job away from identifying the covering and onto sourcing material, sequencing the coursing and getting the consent right. Severn Skylights Gloucester travels out from the city to work here, and the county-wide picture of where the company goes is on the areas pages. What follows is what actually changes on a Northleach roof.
A town where the covering is more or less a known quantity
Most survey work starts with identification. Not slate, but Welsh slate at a stated size with a measured headlap. Not tile, but a clay plain tile at a double lap or a concrete interlocking at a 75mm minimum. In the historic core of Northleach that stage is short, because the answer is nearly always stone slate, and the useful measurements are the ones underneath it.
What still has to be established is the thickness range across the slope, the gauge at the height where the opening will sit, whether there is any underlay or only torching, what the battens are, and how sound the fixings are. Those five answers decide the flashing schedule, the material order and the programme. A covering that is easy to name is not a covering that is easy to work, and this one is the most demanding in the county.
On Northleach roofs Conservation consent and matching the stone.
Diminishing courses, and the gauge that changes every course up the slope
Cotswold stone slate is not a repeating module. The slates are graded by size and laid largest and thickest at the eaves, reducing progressively towards the ridge. Every course is a different depth from the one below it and the gauge changes continuously, which is why the old yard names for the sizes survive, running from Cussomes at the eaves through Muffities and Wivetts to the small slates near the ridge.
For a rooflight, that has two consequences. The head flashing has to be sized to whatever the gauge happens to be at that particular height in the slope, not to a standard figure, so the lead is cut on the scaffold rather than taken from a bundle. And the reinstated courses have to pick the diminishing rhythm back up exactly, or the finished roof shows a rectangle of uniform coursing around the window that reads as wrong from the lane even to somebody who could not say why.
What the survey lifts and measures on a Northleach slope
The order is written from measured facts. On a stone slate roof there are more of them than on any other covering in the county.
- Slate thickness sampled at more than one height, because it changes up the slope.
- Measured gauge over several courses at the intended opening position, and the pitch off a digital level on the actual slope.
- Whether the roof is torched from below, and the condition of the mortar.
- Batten type and condition. Riven battens are historic fabric in their own right on a listed roof.
- The presence or absence of underlay, and if present, its age and state.
- Rafter positions and depths, and any purlin, strut, collar or ashlar piece in the way.
- Fixings: whether the slates are pegged, nailed, or a mixture from previous work.
- Existing openings on the slope and on neighbouring buildings, because they set the pattern an application will be judged against.
- The designation position for the address, and whether curtilage listing is in play.
- Access, and where a scaffold can stand.
the Cotswolds
Diminishing courses mean the slate at the ridge and the slate at the eaves are different sizes. An opening has to be set out against that, not against a tape measure.
The covering
Cotswold stone slate laid in diminishing courses on torched battens, the covering that decides the whole detail.
Cotswold stone slate in diminishing courses, which is what the survey is looking at before it looks at the glass.
Reclaimed stone, sourcing time, and why the date follows the material
Stone slates break. Some are already cracked, some are bedded hard into old mortar, and the thick courses low on the slope are heavy enough that a dropped one is done. So every opening in a stone roof needs a quantity of replacement material, matched for thickness, size and weathering colour.
New stone reads bright against a covering that has been weathering since the eighteenth century and stays visible for a decade or more, which is why reclaimed material is worth the wait and why a conservation approval frequently requires it by condition anyway. The programme runs material first and date second. Sourcing the right sizes in the right thicknesses can take weeks, and a date agreed before the stone is found is a date that will move. That gets said at the point of quoting rather than discovered later.
The wool town plan, and the long ranges behind the street
Northleach was laid out with narrow plots running back from a market place, and the buildings grew backwards along them. Behind a single frontage there is often a main range, then a lower rear wing, then a former store or workshop, at different heights and different dates, sometimes with a lead valley gutter where two roofs meet.
That plan produces the town’s characteristic problem: rooms that are a long way from any external wall with a window in it. A back parlour, a stair head or a first floor landing in the middle of a deep range can be genuinely dark at midday. It is also why the argument for daylight from above is strong here rather than cosmetic. The constraint is the valley. A valley gutter takes water off both slopes with a limited fall, and any position is set out from the valley outward, keeping the flashings well clear of it.
Cottages on the old road, and the slope facing the traffic
The town sits on the old east to west route across the wolds, and a run of its buildings front directly onto it. On those, the visible slope and the slope with the useful roof are frequently the same one, which is the least comfortable position a rooflight proposal can be in.
Three things help. A conservation unit with a slim steel frame, a single central glazing bar and a dark factory finish set as near flush as a 25mm covering allows. Modest size, and two small units rather than one large one, because total glazed area on a visible slope is what officers tend to cap. And alignment with the openings already on the elevation below, which reads as part of the building rather than as something added to it. Where none of that gets a proposal over the line, a sun tunnel disturbs a fraction of the covering and is often acceptable where a window is not. The unit itself is covered on conservation rooflight installation.
The covering
Cotswold stone slate laid in diminishing courses on torched battens, the covering that decides the whole detail.
Cotswold stone slate in diminishing courses, which is what the survey is looking at before it looks at the glass.
Barns, coach houses and the curtilage question on the edge of the town
Around Northleach and out along the Coln valley there are stone farm buildings, coach houses and outbuildings that have been converted or are being considered for conversion. A rooflight is almost always part of that, because a barn has a large roof and very few openings in the walls.
Two points come up repeatedly. Listing extends to structures within the curtilage of a listed building that stood before 1 July 1948 and were in the same ownership at the date of listing, so a stone barn a hundred metres from a listed farmhouse can itself be listed by association without appearing on the national list under its own name. And barn conversions carried out under the agricultural to residential prior approval route have no permitted development rights for roof alterations at all, while conversions granted by full planning permission very often carry conditions capping the number, size and type of rooflights. Those conditions sit on top of everything else and are worth reading before a unit is chosen.
A conservation unit in a 25mm covering
A standard manufactured roof window and its flashing kit are made for a covering a fraction of the thickness of Cotswold stone slate. Put one into a roof where the slates run 20 to 30mm and it sits proud, casts a shadow line all round, and reads as a modern object bolted to an old roof from anywhere with a view of the slope.
A conservation rooflight exists for exactly this. Cast or pressed steel frame, one central glazing bar, low profile, designed to sit almost flush in a thick slate roof. Sizes are modest by comparison with a manufactured roof window, which suits what officers here will accept anyway. Where a genuinely flush appearance is required, a sub-frame or a recessed detail may be needed as well, and that is worked out against the measured slate thickness rather than assumed. The behaviour of thinner natural slate coverings, which some later Northleach roofs carry, is on rooflights in natural slate roofs.
The lead apron on an irregular stone slate
A pressed flashing kit relies on the covering being dimensionally consistent. Stone slate is not, so the weathering around an opening in a Northleach roof is lead, cut and dressed by hand on the scaffold.
The set is an apron at the cill dressed down over the course below, side soakers interleaved course by course and each one cut to the depth of the course it serves, and a head flashing dressed under the course above. Code 4 lead for most of it, code 5 where it is exposed. Head laps of at least 150mm, more where the run is shallow. And every piece fixed at the head only, so it can expand and contract along its length: lead nailed down both sides tears along the fixing line within a few winters. Dressing lead onto an irregular stone surface takes longer than clipping a kit into a tile profile, and that time is in the price rather than hidden in it.
On stone slate the flashing is a material quantity worked out from the measured coursing, not a boxed kit picked off a shelf.
Torched battens are the reason a stone slate roof is opened carefully and closed properly.
Hand-cut structure under an old roof in this town
Under the covering, the older roofs here are hand-cut: common rafters, one or two purlins carried on principals or on the gable walls, collars, and sometimes ashlar pieces at the eaves. Nothing is at a modern spacing and nothing is a standard size.
Trimming into that is a different exercise from trimming a Victorian roof with regular rafters. The clear rectangle between the purlin and the collar is measured on site and often decides the unit size on its own. Where a rafter has to be cut, doubled trimmers go across the head and cill of the opening and the load transfers into the rafters either side, which now carry more than they were built for. Over one bay that is routine. Over two or three it is a calculation, and where the building is listed the added complication is that notching or replacing historic timber is itself part of what consent covers. Reversibility is a persuasive argument in an application here, and it is worth designing for.
Insulating the reveal in a roof that has no underlay
A traditional stone slate roof with torching and no membrane was never intended to be airtight, and it breathes through the covering. Introducing a modern insulated reveal into it is where a lot of otherwise good work goes wrong.
The insulation runs continuously around the frame, tight with no voids, and the vapour control layer is taped to the frame rather than trimmed short of it. Where a breather membrane replaces disturbed torching, it has to be dressed so that any water crossing the covering, which some always does, lands on the membrane and runs down outside the frame rather than into the new construction. And the ventilation path above any insulation between the rafters is kept clear at 25mm, because forming an opening is one of the easiest ways to block it and create a cold spot in the roof directly above the new window.
Two small units rather than one large one
This comes up on nearly every stone roof enquiry and it is worth setting out as a principle rather than a compromise. Two modest openings spread along a slope give more total glass than one large one, light a room far more evenly, and each sits within its own structural bay so no designed trimmer is needed.
They also read better on the elevation and they tend to land better with an officer, because the objection to a rooflight on a historic roof is usually about the size of the single interruption rather than the presence of glass. The cost difference is smaller than people expect once the scaffold is up, because the scaffold, the lead work and the making good are the substantial parts and a second small opening shares all three.
Weather, sequence, and the roof closed every evening
The wolds are open and Northleach sits high enough to feel it. Work on a stone roof is more weather-dependent than work on a tiled one, because the stripped area is larger, the material is handled twice, and lead is dressed by hand in whatever conditions the day gives.
The sequence follows one rule: the roof is never left open overnight. An opening is not started unless it can be closed and made watertight the same day, and if the forecast turns during the morning the outside work stops at a point where the covering is whole. Where two units are going in, the sequence runs from the top of the slope downwards so every evening ends with a closed roof. That governs how a stone job is programmed rather than the other way round, and it is the reason a Northleach installation takes longer than the same unit on a concrete tile semi in the city.
Conservation here is not a formality. It is the reason the stock still looks like this.
What a Northleach figure is built from, and how to start
No figures are published, and the reason is straightforward: a conservation rooflight into diminishing courses on a listed cottage on the old road, with hand-carried scaffold and matched reclaimed stone on order, is not the same job at any price as a narrow window between two trusses on a modern house. A published number would be wrong for both.
What drives it here is the covering and its making good, the quantity and availability of reclaimed stone, whether structural trimming is needed against a purlin, the lead schedule taken from the measured coursing, access and scaffold, any pre-application and consent work, and how far the internal reveal and plaster are taken. Then two figures in this order. An indicative range by email, from photographs of the roof and the room, the covering and the address, sent to info@severnskylightsgloucester.co.uk. Then, after a survey, a fixed price, itemised so it is clear what is unit, labour, stone, lead, scaffold and Building Control, holding unless the scope changes at the customer’s request. The costs page sets out that process, the consent landscape is on conservation areas and listed buildings in Gloucestershire, and the written guides go further into individual questions.
Also covered: the Cotswolds