Rooflight Installation in Deddington

Ironstone, and the colour that has to be respected

The village sits on the Northamptonshire ironstone belt, which runs up from north Oxfordshire into Northamptonshire and gives Deddington, Adderbury and Bloxham their deep orange-brown walls. It is a marlstone, iron-rich, and it weathers to a colour nothing else in the county quite matches.

That colour matters for a rooflight in one specific way. Ironstone buildings carry a narrow range of roof coverings, and the eye reads the combination as a whole. A dark grey conservation unit on a Welsh slate roof over ironstone walls sits quietly. The same unit on a stone slate roof reads differently, because the stone slate is a warm grey-brown rather than a cold blue-black. Where a designation is engaged, and in the middle of Deddington it often is, the finish of the unit is part of what is being assessed rather than an afterthought.

The other consequence is structural. Ironstone rubble walls are thick, and the wall plate sits on a substantial bed rather than on a narrow modern skin. That is generally helpful, since there is bearing to work with, but it means the roof structure often meets the wall in a way that is not obvious from below.

The Market Place, and frontages that hide their roofs

The centre of Deddington is a conservation area, with the Market Place and the streets running off it carrying a high proportion of designated buildings. The frontages are what the designation was drawn around and they are what people photograph.

The roofs behind them are frequently a different age entirely. A Georgian ironstone frontage in a village like this is very often a refacing, applied when the fashion changed, to a building that was already old. The roof behind may have been re-pitched at the same time, or left as it was and hidden. Either way the front elevation is close to useless as a guide to what is above it.

So the survey here starts in the roof space and stays there for a while. Hand-cut rafters of uneven section, a purlin at an unexpected height, a pitch that changes partway up a slope, evidence of a former ridge line: all of these are common and all of them change what can be fitted and where.

Three roof ages in one village

Broadly there are three, and they are worth being able to tell apart.

The oldest are the pre-Georgian roofs, hand-cut, with irregular rafters and no underlay beneath the covering. These carry stone slate or, where a later re-covering has happened, plain clay tile. Openings here are formed between rafters wherever the spacing allows, and the spacing is irregular enough that the position often has to move by a few hundred millimetres from where the customer imagined.

Then the Georgian and Victorian roofs, more regular, often Welsh slate arriving on the railway, with a shallower pitch than the stone roofs they replaced. These are the easiest of the older stock to work with.

Then the twentieth-century houses around the edges of the village, on concrete interlocking tile over trusses, with felt beneath the battens. These are ordinary work with a proprietary flashing kit and no designation attached, and they are usually finished in a day.

Stone slate, and the arithmetic of diminishing courses

Where a Deddington roof carries stone slate, the coursing is graded: large stones at the eaves, reducing steadily to small ones at the ridge. Each course has its own size and its own place, and the roof was set out that way when it was laid.

Cutting an opening into a graded roof therefore means recording where every stone came from before it is lifted, and putting each one back into the course it belongs to. A stone returned two courses out of place breaks both the visual grading and the weathering, because the laps were calculated for that position.

Stone slate is also heavy, considerably heavier than slate or plain tile, so the structure carrying it is doing more work than it looks. Removing a section of covering changes the loading on the rafters around it temporarily, and reinstating it changes it back. On a roof already carrying a lot of weight on old timber, that is a survey consideration rather than a formality.

The permission position

Deddington falls under Cherwell District Council, which is the authority for planning and for listed building consent here. If you have been reading Oxford City Council’s guidance, it does not apply.

Inside the conservation area, a rooflight on a slope facing a highway will normally need permission, and one on a rear slope out of public view often will not. That is the general shape and the detail turns on the individual designation.

On a listed building, consent is engaged wherever the unit goes, including the rear, including a slope nobody can see. This is worth stating plainly because the opposite belief is widespread. Listing covers the whole building, not the elevation somebody drew the boundary around, and a rooflight inserted without consent is an unauthorised alteration that will surface during a sale.

Outside the conservation area, on the twentieth-century stock, most rear-slope work is permitted development and needs nothing but a Building Regulations notification.

What gets accepted on the designated buildings

Where a unit is accepted on a listed or conservation-area roof in Deddington, the specification is predictable.

It sits flush with the plane of the covering rather than proud of it, which means the covering is re-dressed around it rather than a frame being sat on top. It is finished dark, usually black or a very dark grey. It is modest in size, and there are usually fewer of them than the owner first proposed. It commonly carries a single vertical glazing bar, so that it reads as a Victorian cast-iron light rather than a modern panel.

Position matters as much as product. A unit tucked below a ridge on a rear slope, in line with others, attracts far less attention than one placed centrally on a visible plane. Where an officer is going to look at anything, they will look at whether the alteration reads as part of the roof or as an object on it.

Ironstone and the weathering detail

The perimeter work on these roofs is hand-formed lead rather than a kit, because there is no proprietary flashing made for a graded stone slate roof and there never will be.

That means soakers worked in course by course, side flashings dressed to the profile of the stone, an apron lapping over the covering below and a head flashing tucked under the course above. Lead in bays no longer than about 1.5 metres so it can move with temperature, fixed at the head only. Patination oil brushed on the day it is fitted, or the first rain will streak white carbonate down an ironstone roof where everybody can see it.

This is slow work and it should be priced as slow work. A quotation for a Deddington stone roof at the same rate as a concrete tile estate house has not understood the job.

Insulating an old roof without ruining it

Lighting a loft in one of the older cottages usually means insulating that part of the roof at the same time, and the depth available is the constraint.

Hand-cut rafters are often shallow by modern standards, and there is rarely room to achieve current standards between them alone. The answer is a build-up designed for the depth that exists, with a continuous vapour control layer sealed to the rooflight frame, rather than packing insulation in and hoping.

Getting this wrong in an old cottage produces condensation on the cold side of the build-up within a winter, and the owner reads running water as a failing roof when the roof is doing nothing wrong. In a building with no underlay beneath the covering, the roof void behaves differently from a modern one and the vapour control layer is doing more work, not less.

Access on the older streets

Buildings on the Market Place and the older lanes stand close to the road, with little or no frontage and limited parking. Scaffolding often has to stand on the highway or the footway, which needs a licence from the county council and has its own lead time.

That is a cost and a programme item, and it belongs on the quotation rather than appearing later. On the outlying modern housing, none of it applies and a tower reaches most roofs from a garden.

The outbuildings, which are often the better opportunity

Ironstone villages are full of former agricultural buildings: stables, cart sheds, granaries and barns behind the street frontages, many of them now converted or waiting to be.

These are frequently the easier place to get good daylight, and sometimes the only place. A barn roof has a large uninterrupted plane, a generous pitch, and a structure of substantial timbers with wide spacing, so an opening can go where the room wants it rather than where the rafters permit. The roof is often out of public view behind the main building, which changes the planning conversation considerably.

Two cautions. A converted outbuilding within the curtilage of a listed building is usually caught by the listing itself, even where nobody thinks of it as a listed building, so consent is engaged. And barn roofs on old timber often carry no underlay and considerable movement, so the survey has to establish what the structure is actually doing before anything is cut into it.

Roof pitch, and what the ironstone belt inherited

Roof pitch here follows the covering the building was first built for, and that is worth knowing because it governs which units can be fitted at all.

Stone slate needs a steep pitch to weather properly, typically around 45 to 50 degrees, because the stones are laid with generous laps and water has to be moving. Roofs originally built for stone are therefore steep, and a steep roof is good news for a rooflight: water runs off it quickly, the flashing detail is forgiving, and almost any unit will be within its minimum pitch.

Where a stone roof was later stripped and re-covered in Welsh slate, which happened widely in the nineteenth century, the pitch usually stayed as it was. So a great many Deddington roofs are slate at a pitch steeper than slate needs, which is the most forgiving combination in the county.

The exception is a later rear addition, often a single-storey outshot at a much shallower pitch. Those are the roofs where a standard unit may fall below its minimum pitch, and where a model designed for shallow slopes becomes necessary rather than optional.

What we fit, and what we decline

New rooflights and replacements of failed units, in houses and in the converted outbuildings that are common around the village. Conservation-grade units where a designation calls for them, and standard units where it does not, specified for the slope rather than ordered to match each other.

What we do not take on is remedial roofing. On a stone slate roof at the end of its life, the honest answer is that the covering needs attention from a roofer before anybody puts a new unit into it, and we will say so rather than fit a good rooflight into a poor host.

Getting a realistic answer

Four things get you a useful reply: where in the village the building is, what the roof is covered with, whether it is listed or in the conservation area, and which room you are trying to light. Deddington is about twenty minutes from Oxford and comfortably inside the twenty-five miles of road we cover.

If you do not know whether the building is designated, say so and we will check it. It is the fact that most changes the answer, and it takes a minute to establish from the address.