Conservation Rooflight Installation
Slim cast frames set flush, for stone slate, listed and conservation roofs.
the Cotswolds
Rooflight and skylight installation in Stow-on-the-Wold, planned before anything is ordered.
Stow-on-the-Wold: hilltop town, exposure, stone slate. 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
- hilltop town, exposure, stone slateRecorded for Stow-on-the-Wold specifically
In Stow-on-the-Wold
What we fit on Stow-on-the-Wold roofs
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.
Walk-On Rooflight Installation
Structural glass rated to stand on, over rooms below a terrace.
Sun Tunnel Installation
Daylight into landings and bathrooms with no roofline to work with.
Roof Lantern Installation
Flat roof glazing sized to the room and detailed into the kerb it stands on.
The local detail
Fifteen things worth knowing about Stow-on-the-Wold roofs, before you cut one open.
Stow-on-the-Wold sits on top of the wolds at around eight hundred feet, higher than any other town in the Cotswolds, on an exposed hill where several old routes meet. That position is not scenery as far as a roof is concerned. It is a set of numbers: more wind, more driving rain, more uplift on the covering, colder nights, and occasional snow that lies when it has already gone from the vale. Every one of those changes something about how a rooflight is detailed here compared with the same unit fitted in Gloucester. Severn Skylights Gloucester travels out to the wolds tops from the city, toward the outer edge of the thirty miles by road it works within, and the coverage picture is on the areas pages.
Eight hundred feet up, and the exposure that drives the detailing
Exposure is a design input, not an atmosphere. British practice grades a site by how much wind-driven rain it receives, and a hilltop with open country around it sits in a more severe category than a sheltered valley twenty miles away. Standard details are written for moderate exposure, and a severe site wants the margins increased.
In practical terms that means deeper laps on the covering around an opening, wider side flashings, more attention to how the head flashing is turned at its ends, and a stricter view of the fixing pattern. None of it is exotic. It is the same details done with more generous dimensions, worked out from the exposure and the measured pitch rather than taken from a default. The one thing that does not survive a hilltop is a detail that was only just adequate on paper.
Driving rain from the south west, and the laps that go past the minimum
The prevailing weather arrives from the south west with very little between the Severn Vale and the top of the wolds to slow it down. Rain does not fall vertically onto a roof here for a good part of the winter. It arrives at an angle with pressure behind it, and it climbs.
That is why laps go up. On a slate covering, a headlap of 100mm is the general figure on a moderate pitch in a sheltered position, and roofs on exposed slopes are commonly found running 115 or 125mm. The consequence at a rooflight is direct: the interleaved soakers down each side lap each other by the same figure the covering does, so an increased lap means deeper soakers and more lead per course. That is a material quantity taken from the measured lap rather than a guess, and it is one of the reasons the same unit costs a little more to weather here than lower down. The covering method in full is on rooflights in natural slate roofs.
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.
Wind uplift on a hilltop roof, and what holds a stone slate down
Wind does not push a roof covering down. It lifts it, because air accelerating over a ridge drops in pressure above the slope while the pressure underneath stays higher. Uplift is worst at the verges, at the ridge and around any interruption in the plane, which is exactly what a new rooflight is.
Cotswold stone slate resists it mainly by weight, and there is plenty of that: slates commonly 20 to 30mm thick with a roof loading well over 100 kilograms per square metre. But weight alone is not the whole answer at an edge. The slates immediately around a new frame have lost part of their bearing on their neighbours and some have been cut down to width, so they need a positive fixing rather than reliance on friction. Cut pieces are re-pegged or re-nailed where there is sound material to take it, and held with a clip where there is not. On this hill that is not a refinement. It is the difference between a covering that stays where it was put and one that starts to lift at the corner of the opening in the first hard winter.
Every slate cut down beside a new frame has lost part of its fixing, and on an exposed slope each one gets a positive replacement.
The market square, the plots behind it, and where the roofs are seen from
The town is arranged around a large market square with narrow alleys running off it and long plots stretching back behind the frontages. The buildings on the square present their principal elevations to a wide open space with nothing in front of them, so those roofs are seen from further away and from more angles than a roof on a narrow street ever is.
Behind them, the plots produce the same layered arrangement found in the other wool towns: a main range, a lower rear wing, a former store or workshop, sometimes with a lead valley between two roof planes. Those rear roofs are lower, enclosed and much less exposed to view, and they are usually where a proposal is strongest. The valley itself is the constraint on position, because a valley gutter carries water off both slopes with limited fall and a flashing terminating into one is a detail that gets tested by every storm. Positions are set out from the valley outwards.
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.
Snow on the wolds tops, and the load a hilltop roof already carries
Snow lies here when it has cleared elsewhere in the county, and it drifts against anything that stands above the plane of a roof. A kerb-mounted unit on a shallow roof, or the upstand of a lantern on a flat rear extension, is exactly the kind of obstruction that collects a drift on its windward side.
Two things follow. The structural check on any opening takes the imposed load into account alongside the dead load of a very heavy covering, which matters most where a rafter is being cut and trimmers are carrying into the rafters either side. And on a flat roof, an upstand is measured properly from the finished surface of the waterproofing at the high point of the fall, because 150mm is the figure at which standing water, drifted snow and driven rain stop climbing. Measured from the deck instead of the finished surface, or from the low corner instead of the high point, that margin quietly disappears, and on this hill it is the margin that is doing the work.
Fixing a frame into an exposed slope
A rooflight frame is fixed to the roof structure, not to the covering, and on an exposed site the quality of that fixing is worth more attention than usual. The frame brackets go into sound timber at the specified spacing, into the trimmers formed for the opening rather than into a batten, and the timber is checked with a moisture meter first because a soft trimmer takes a fixing that looks right and holds nothing.
The other half of it is the weathering above the frame. A head flashing on an exposed slope is turned up at its ends into welts rather than left as a flat sheet, so wind cannot get under a free edge and work it loose. Lead is fixed at the head only along its length so it can expand and contract, because lead nailed down both sides tears itself along the fixing line, and cracked lead along a nail line is one of the most common findings when an old unit comes off a roof up here.
Fixed unit or opening unit where the wind is constant
People arriving at a rooflight tend to assume they want one that opens. On this hill the question is worth thinking about properly.
| Unit type | Where it suits a Stow roof | What to weigh |
|---|---|---|
| Fixed | High in a slope for daylight only, or where the room already has escape and ventilation | Fewest gaskets and moving parts on an exposed elevation, and the lowest long-term draught risk |
| Centre pivot, manual | Within reach in a converted attic | The sash rotates into the room when open, which needs clear space below it |
| Top hung | Where a view out and an escape opening are both wanted | The open sash presents a larger area to the wind and wants closing in a gale |
| Electrically operated with a rain sensor | Out of reach above a stair or a double-height space | Closes itself when the weather turns, which on this hill is a practical benefit rather than a gadget |
| Conservation type, steel frame | Any visible stone slate slope in the historic core | Sits near flush in a thick covering, and modest sizes suit what officers accept |
Where a roof window forms the escape opening from a room in the roof, a fixed unit will not satisfy it: the clear openable area must be at least 0.33 square metres with a minimum of 450mm in both height and width, and the bottom of that opening between 800 and 1100mm above the floor. More on the powered option is on electric rooflight installation.
Cold nights, and the condensation risk in an attic up here
A hilltop attic gets colder at night than the same room lower down, and the coldest surface in it after a new installation is the glass. Warm moist air rises, meets that glass, and condenses. On a clear cold morning a roof window can run with water while every other surface in the room is dry, and that is physics rather than a fault.
The controls are the same three everywhere and they matter more here. Background ventilation through a vent flap in the head of the unit, left open rather than shut. Purge ventilation, meaning opening the unit properly for a few minutes, which clears a humid room faster than anything else. And reveal geometry: a vertical lining above the window to throw light deeper into the room, a horizontal lining below it so warm air from a radiator washes up the face of the glass, insulation continuous and tight around the frame with no voids, and the vapour control layer taped to the frame rather than trimmed short of it. The ventilation path above the insulation between the rafters is kept clear at 25mm as well, because forming an opening is one of the easiest ways to block it.
Glass for a cold, bright, exposed position
Two properties matter more on this hill than they do in a sheltered town. The first is the U-value, because the room is losing heat through the glass on a great many more cold nights. A current manufactured roof window runs around 1.0 to 1.4 W/m2K against something nearer 2.8 to 3.0 for a unit from the 1990s, and triple glazing goes lower again, which is worth the weight in a hilltop attic used as a bedroom.
The second is the outer pane. There is very little shelter from the sun up here either, and a south or west facing slope on a small attic room heats fast, so a solar control coating that brings the g-value down from around 0.5 to roughly 0.25 to 0.3 earns its place. Safety glazing is not optional in a roof: toughened outer, laminated inner wherever there is habitable space, a stairwell or a bath below. Laminated glass also cuts rain noise noticeably, which on an exposed roof taking driven rain for weeks at a time is not a small thing. The figures are on energy efficient rooflights.
Torched battens are the reason a stone slate roof is opened carefully and closed properly.
Stone slate on the wolds tops, and the making good it needs
The covering in the historic parts of the town is Cotswold stone slate: graded and laid in diminishing courses, largest and thickest at the eaves, reducing up the slope, hung on riven battens, often with a lime mortar torching underneath and no membrane.
An opening cannot be cut into it and closed up around a frame. The courses above are stripped back, the frame is set, and the courses are re-laid downwards, re-establishing the diminishing gauge so the finished slope reads correctly. Slates break coming off, so reclaimed material is sourced to match thickness, size and weathering colour, and the sourcing sets the date rather than the date setting the sourcing. The weathering is lead cut and dressed on site, because no pressed kit will bed onto an irregular slate that thick, and the torching replacement detail, usually a breather membrane on counter battens, is agreed in advance rather than decided on the scaffold.
The later housing off the square, and its hipped roofs
Away from the historic core there is interwar, post-war and modern housing, and it is a different job with a different constraint. The interwar and post-war houses are largely hipped, at 30 to 35 degrees, in concrete interlocking tiles over cut structure with purlins and struts. Structurally those are among the most straightforward roofs to work on, because rafters can be trimmed and the flashing kit is made for the tile.
The problem is the shape. On a hip the slope narrows towards the corner, so the usable rectangle is much smaller than the roof looks from the garden, and once a purlin across the middle and a binder in the ceiling are taken into account the clear zone on a typical rear hip is often around 1.2 metres of vertical run across two rafter bays. People arrive wanting one large window and the roof will only take a shorter one. The better answer is usually two units in adjacent bays: no structural design needed, more glass in total, and a more even spread of light than one unit in the middle. Newer houses on the outer edges are trussed rafter construction instead, where an opening either fits between two trusses or needs a designed trimmer, as set out on rooflights in a trussed roof.
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.
Scaffold on a hill, and the days work does not start
Wind stops roof work before rain does. There is a point on any exposed site at which handling a sheet of glass, a lead roll or a scaffold board stops being reasonable, and on a hilltop that point is reached more often than in a sheltered street. It is better to say so at the point of agreeing a programme than to lose a day and explain it afterwards.
Scaffold on an exposed elevation is tied and braced accordingly, and any sheeting on it acts as a sail, which affects how it is specified. In the town centre there is the separate matter of a scaffold standing on a footway, which needs a licence from the highway authority with its own lead time. Behind the frontages, access along a plot or through an alley often means components are carried in rather than offloaded at the building, and a made-to-size lantern’s glass may need extra hands or a lift. All of that is looked at at survey and priced from what is actually there.
Consent on a Stow roof, and the pattern that gets approved
The planning authority is Cotswold District Council, the historic core is a conservation area with a substantial body of listed buildings inside it, and the surrounding country carries national landscape designation. Conservation area status controls what an application is judged against and can remove permitted development rights where an Article 4 direction applies. Listing creates a separate consent required for anything affecting the building’s character, inside and out, and visibility is not the test for it.
The approvable proposal here looks much as it does elsewhere in the district: a modest, dark, near-flush conservation unit on a rear or concealed slope, aligned with the openings on the elevation below, sized down rather than up, with matched reclaimed stone for the making good and lead formed on site. Two small units frequently land better than one large one. A proposal on a slope facing the square is a harder conversation, and pre-application advice with photographs and a named unit is worth the fee before anything is ordered. The full authority-by-authority position is on conservation areas and listed buildings in Gloucestershire, and the unit itself on conservation rooflight installation.
the Cotswolds
Torched battens are the reason a stone slate roof is opened carefully and closed properly.
Building Regulations on a wolds-top conversion, and the notification that closes it out
Forming a new opening in a roof is notifiable work and so is replacing a unit in most circumstances. Four parts of the regulations touch a job in this town more often than the rest.
- Structure. Trimming a hand-cut rafter under a very heavy stone covering, on a site where snow load is a real figure, is where a calculation goes in with the application rather than being assumed.
- Fire safety. Where a roof window forms the escape opening from a room in the roof, the clear openable area, its minimum dimensions and its height above the floor all have to be met, and the unit is chosen against that before it is ordered.
- Conservation of fuel and power. The limiting standard for a replacement roof window is 1.4 W/m2K, and the continuity of insulation around the reveal is checked under the same requirement, which on an exposed roof is the part that actually matters.
- Ventilation. Purge ventilation to a habitable room means an openable area of at least one twentieth of the floor area, and a unit with a background vent flap contributes to both purge and background provision.
The application is submitted, the inspections are booked and the completion certificate comes back to the homeowner in their name. It is the paperwork a buyer’s solicitor asks for, and finding it missing at the point of sale is a worse problem than dealing with it now. Where the building is also listed, the listed building consent stands alongside it and is required regardless of whether planning permission is.
On Stow-on-the-Wold roofs Conservation consent and matching the stone.
What a figure for a Stow-on-the-Wold roof is built from
The exposure shows up in the price in specific places rather than as a general uplift: deeper soakers and more lead from the increased lap, additional fixing to the cut slates around the frame, a heavier structural check where snow load and a very heavy covering meet a cut rafter, and a programme with weather contingency in it.
Everything else is the familiar list. The covering and its making good, the quantity and availability of matched reclaimed stone, whether trimming runs into a purlin, scaffold and access, any pre-application and consent work, glass specification, and how far the internal reveal and plaster are taken. Send photographs of the roof and the room, the covering if you know it, and the address to info@severnskylightsgloucester.co.uk for an indicative range by email. A survey follows, then 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 route, and the written guides answer individual questions in more depth.
Also covered: the Cotswolds