Rooflight Installation in Banbury

Three periods in one town

Banbury reads as three building stocks laid over each other, and a rooflight installation in Banbury means something different in each.

The historic core is ironstone, a warm orange-brown local building stone quarried across this part of north Oxfordshire. It is not Cotswold limestone, and anybody who has driven west towards Chipping Norton will have noticed the walls change colour. The core carries the town’s oldest fabric, its designations and its tightest streets, and there the answer starts with what the building is rather than what the owner wants.

Around and behind that core sits the Victorian town. Banbury grew hard through the nineteenth century on industry and the railway, and the housing that came with it is terraced: brick, two storeys, slate, in long runs with rear yards and back entries. That is the stock the rest of this page is mostly about, because its roof arrangement is where the real specification decisions live.

Then there is the modern periphery, and it is large. Banbury has expanded a long way out in every direction, and those estates are ordinary contemporary housing with ordinary contemporary roofs. There the job is straightforward, and we say so rather than dressing it up.

The rear outrigger and its valley

Stand behind a Banbury terrace and the shape is familiar. The main roof runs the length of the terrace, parallel with the street, ridge to eaves front and back. Off the rear of each house a two-storey addition projects into the yard with its own roof, usually pitched, running at right angles to the main one.

Where those two roofs meet they form a valley: an internal angle running down the slope, with a plane of roof falling into it from either side. That angle is lined, most often in lead, sometimes with a purpose-made trough beneath the covering, and the courses of slate or tile are cut back to it on both sides.

The valley matters more than anything else on the roof because of what it is asked to do. Every other part of a pitched roof sheds water down a single plane and gets rid of it at the eaves. A valley takes the water off two planes, concentrates it into one narrow channel, and carries the combined volume the full length of it. That is far more work than the slope beside it, in a detail that also accommodates the covering being cut, the two planes moving independently, and debris collecting in the angle.

That is why a valley is the part of an older roof most likely to be nearing the end of its life, and why it is the first thing we look at on a terrace survey here. It is also why its presence changes the conversation about where a rooflight can reasonably go.

Where on the slope it goes

People generally arrive with a room in mind and a rough idea of the wall it sits against. What settles the specification is the position of the opening on the slope, and near a valley that is a genuine engineering decision rather than a preference.

A rooflight interrupts the flow of water down a plane. Water arriving from above is split around the unit by the side flashings and then has to run down the covering below the opening and away at the eaves. The run of roof below the unit is doing real work, and so is the run to either side.

Put an opening close to a valley and two things happen at once. The run available for water to spread out again is reduced, and the flashing on the valley side is throwing water towards an angle already carrying two roof planes. Neither is acceptable, and the answer is set out at survey rather than improvised on the roof. A flashing must never discharge into a valley or across it, the courses between the unit and the valley have to keep their laps, and there must be enough plane between the two for water to behave normally.

The honest position is that on this kind of roof, position matters as much as the unit does. Sometimes that means a smaller opening set further up and across, sometimes the other side of the same slope, and sometimes it means the slope the owner had in mind is not the one that works.

The lower back-addition roof

The two-storey outrigger frequently has something else attached: a single-storey lean-to over a rear scullery or bathroom, or, very commonly here, a later flat roof where an older lean-to was rebuilt or the addition widened.

That lower roof is a different job from the main slope, and often the better place for glazing. The room beneath is usually the kitchen, a utility or a bathroom, the darkest and most used part of the ground floor. It sits well away from the valley above, and being lower it makes access and working simpler.

A flat roof takes a different kind of unit. Glass is set on a kerb standing proud of the finished surface rather than dressed into courses of slate, the covering is turned up the kerb and terminated under the frame, and the fall of the deck is designed so water leaves the area around the unit rather than gathering against it. Where the existing deck has no useful fall, that is built in as part of the work. The build-up matters as much as the glass: insulation, vapour control and where the warm side sits are settled before anything is ordered.

Party walls and scaffold room

Terraced housing brings constraints that have nothing to do with the roof covering and everything to do with the neighbours on both sides.

A terrace is a shared structure. Party walls run up between the houses, chimney stacks usually stand on the party line, and rafters commonly bear on shared plates. Forming an opening means working between rafters within your own roof, and the setting out respects what the structure is doing rather than where the room would like the light. Where a stack sits on the party wall and the slope beside it is short, the useful area is smaller than it looks from the yard.

Access is the other half. The front of a Banbury terrace is generally straight onto the pavement with parking pressure along it, and the rear is a yard reached through the house or from a back entry. Scaffold has to stand somewhere, and on rear elevations here that somewhere is often over or beside a boundary. Where the standing, the ties or the working platform involve a neighbour’s ground, that is agreed in advance and in person, not discovered on the morning the scaffold arrives.

We plan that before quoting, because it changes the programme and the price, and the neighbour hears about it with a date attached.

Ironstone and making good

In the historic core the walling material becomes part of the specification. Banbury ironstone is a ferruginous limestone, warm orange-brown, and it is visually distinctive enough that a mismatch is obvious from across the street.

It is also relatively soft and porous. Weathered faces erode, and in exposed positions the stone can spall, losing its outer face in flakes. So anything disturbed is handled carefully, because a stone that comes out sound can be broken in the barrow and there is no like-for-like substitute on a merchant’s shelf. Salvaged material is worth more than new: where stone comes down it is set aside, kept dry, and put back.

Most rooflight work does not involve the walls at all, and it is worth saying so plainly rather than inflating the difficulty. Where it does, it is usually at a verge, around a stack, or where a reveal is formed at the head of a stair. In those cases the making good is judged on how it looks once it has weathered a season, not on the day the scaffold comes down.

Roof coverings in the core vary more than the walls do, so what the flashing has to do is established on site. On a designated building the visual quality of the finished detail is part of what is assessed, and the unit is chosen to suit that rather than the other way round.

Cherwell, and the newer edges

The local planning authority here is Cherwell District Council, not Oxford City Council. Anything you have read about Oxford’s conservation areas or its street-level directions is a different framework and does not apply to a house in Banbury.

What can be said generally is that Banbury has conservation area coverage over its historic core, along with listed buildings within and around it. Both designations are matters of public record and both are worth establishing for a specific address rather than assuming from the look of a street. Article 4 directions, which withdraw particular permitted development rights, are a tool any authority can use, so whether one applies at a given address is a question to check in either direction. Where a determination is needed it belongs to the authority, not to us.

Out on the newer edges, none of that is usually in play. The estates around the town are built with concrete interlocking tile on battens over an underlay, prefabricated trusses at regular centres, consistent pitch and a uniform covering. A rooflight goes into that kind of roof cleanly, with a flashing kit made for the tile profile and the underlay dressed into the opening. Trussed roofs have one real limit: the diagonal webs are structural and are not cut without a designed alteration, so lighting a loft is simple while converting one is a bigger project with the glazing following the structural work.

What we establish in Banbury

The sequence on a Banbury job is the same every time, and it starts before any product is discussed.

The address and what attaches to it. In the core that means designations and it can change the answer completely. On the estates it takes a few minutes and clears the way.

The roof arrangement, in full. Not just the slope you have in mind. Where the back addition sits, where the valley runs, where the stacks are, where water currently goes and how the lower roofs are formed. On a terrace this is the part that decides the job.

The structure and the build-up. Rafter depth and spacing, condition of the covering, whether there is an underlay, and what insulation and vapour control the finished room needs. On a replacement, the state of the existing opening and upstand, because a new unit set onto an unsound upstand inherits every fault there.

Access, scaffold and the neighbours. Where it stands, who needs to know, and how long the roof is open.

The specification, then the price. Flush conservation detailing where the building calls for it, a standard unit where it does not, glass chosen for the orientation of that slope, and the opening method chosen for how the room is used. We install VELUX, Fakro, Keylite and Roto units, and we specify what the roof needs.

One honest note on geography. Banbury sits at the outer edge of the twenty five mile road radius we work to from Oxford, so it is a longer run than Kidlington or Abingdon and we plan the days around that rather than pretending distance does not exist. The offer is the same as everywhere else: new installations and replacements only, the Building Control notification handled as part of the job, and a ten-year guarantee on our workmanship with its coverage and exclusions set out on its own page. Fifteen years of installing rooflights sits behind it.