Rooflight Installation in Goring-on-Thames

The gap, and what it is built from

Goring sits where the Thames cuts between the Chilterns and the Berkshire Downs, with steep wooded valley sides rising on both banks. The chalk that forms those hills produces flint, and flint is what the older buildings here are made of: knapped or whole, coursed or random, usually with brick at the corners, around the openings and in bands through the wall.

That brick is not decoration. Flint is an awkward building material with no natural bed and no flat faces to speak of, so brick is used wherever the wall needs regularity and strength: quoins at the corners, jambs and arches around windows, and lacing courses running through to tie the whole thing together.

Understanding that division tells you a great deal about how the building works, and it is the key to the rest of this page.

How a flint wall carries a roof

A flint wall is built as two faces with a rubble core between them, the whole thing bonded with a generous amount of mortar. It is strong in compression, which is why it has stood for centuries, and comparatively weak in tension, in bending and against any load that arrives sideways.

The roof sits on a wall plate: a timber running along the top of the wall, spreading the load of the rafters into the masonry below. In modern construction the wall plate sits on a level blockwork skin, bedded and strapped, and the load path is predictable.

On an old flint building it frequently is not. The top of the wall may be uneven, the plate may be bedded on whatever levelled it at the time, and it may be embedded in the wall rather than sitting on it. Straps tying the roof to the wall, which modern building takes for granted, may be absent entirely.

Why this only matters for larger openings

For an ordinary rooflight fitting between two rafters, none of the above is engaged. The rafter is cut, trimmers go in above and below the opening, and the load that rafter was carrying is redistributed into its neighbours. Everything stays within the roof structure, and the wall sees no change at all.

The picture changes when the opening gets wide enough that several rafters are cut. Now the trimmers are carrying more, the rafters either side of the opening are carrying more than they were designed for, and the additional load travels down them to the wall plate and into the wall.

On modern blockwork, that increase is generally absorbed without comment. On a flint and rubble wall, concentrating load at a point it was not built to receive is how mortar joints open and how a face bulges, sometimes years later.

So the honest rule here is that small is straightforward and large needs designing, and the threshold is lower than it would be on a Victorian brick terrace.

What a survey establishes

Five things, and they are all found by looking rather than assuming.

Whether there is a wall plate at all, and what condition it is in. Old plates in damp walls can be soft where nobody has looked for a hundred years.

Whether the roof is restrained laterally. A roof spreading under its own load pushes the tops of the walls outward, and flint walls are poor at resisting that. Existing spread is visible as leaning at the eaves and as cracking at the corners, and where it is present it changes the whole project.

Whether the rafters bear properly on the plate or have slipped.

What the wall actually is above and below the plate, since flint buildings often have brick in the upper courses precisely because somebody needed regularity there.

And where any existing structural alterations sit, because these buildings have usually been changed before and the previous alteration is not always benign.

Fixings into flint, and what not to do

Where anything has to be fixed to a flint wall, and occasionally a rooflight installation needs it, the method matters more than the fixing.

A flint face is hard and the mortar between is soft, which is the opposite of brickwork. A mechanical fixing driven into a flint will not hold, because the flint is glassy and brittle and will simply fracture. A fixing into the mortar joint holds only as well as the mortar, which in a lime-mortared wall is deliberately soft.

Where a fixing is genuinely required, it goes into the brick dressings or into a resin anchor properly set, and it is designed rather than improvised. Percussion drilling into a rubble wall is how a core gets disturbed and how a face is loosened, and once disturbed it does not go back.

The practical implication for most rooflight jobs is a preference for solutions that stay within the timber structure and never touch the wall at all, which is achievable far more often than not.

Steep valley sides, and access

The other consequence of the geography is that a good many Goring properties sit on ground that falls sharply, on plots that step down towards the river or climb away from it.

That affects access rather than structure. A mobile tower needs level ground within its adjustment range, and on a stepped garden that often does not exist, so the answer is a scaffold founded on jacks and sole boards or stepped to suit the fall. It takes longer to erect, costs more, and needs the ground beneath it to be capable of taking a concentrated load.

Retaining walls are common here and they are frequently old. A scaffold founded beside one puts a lateral load into a structure that was never designed for it, which is a matter for the survey rather than the morning of the job.

Lime mortar, and why it is not a detail to modernise

Old flint walls are built in lime mortar, which is softer than the flint and deliberately so. It allows the wall to move slightly without cracking, and it allows moisture to leave through the joints rather than through the stone.

Where later work has introduced cement mortar, the wall stops breathing at that point and moisture is driven to leave elsewhere, usually through the face of the flint, which then spalls. It is a common problem on buildings repointed in the twentieth century.

This is not a rooflight matter and it is worth understanding because it explains why an installer working on an old flint building should be leaving the masonry alone rather than making good with whatever is in the van. Any work that does touch the wall should match what is there.

The designation position

Goring falls under South Oxfordshire District Council. There is a conservation area over the older core, a number of listed buildings within it, and the whole area sits within the Chilterns National Landscape, formerly designated as an Area of Outstanding Natural Beauty.

On a listed building, consent is engaged for a rooflight anywhere on it, including a rear slope out of public view. In the conservation area, a slope facing a highway will usually need permission and a concealed one often will not.

The landscape designation is worth understanding correctly, because people expect it to prohibit more than it does. It does not add a consent requirement for a domestic rooflight, and it does not remove permitted development rights on its own. What it does is raise the weight given to landscape and visual impact in any application that is made, which in practice matters most for proposals visible on the valley sides from a distance.

Where a rooflight sits comfortably here

Rear slopes on lower additions and outshots, screened by the main roof, are the least contentious and frequently the most useful, because the rooms under them are often the darkest in the house.

On the main slopes of a designated building, the familiar expectations apply: flush rather than proud, dark finished, modest, positioned low, aligned with anything already there.

And on the later housing away from the historic core, it is ordinary work: concrete interlocking tile over trusses, a profile-specific flashing kit, most rear-slope work permitted development and notifiable under Building Regulations.

Spreading the load instead of enlarging the opening

Where a room needs more daylight than a single small unit gives, and the wall will not take a large opening comfortably, the answer is usually arithmetic rather than engineering.

Two modest units in adjacent rafter bays deliver more usable daylight than one large one of the same total area, because light arriving from two positions fills the room more evenly and removes the hard shadows a single source produces. Each opening stays within its own bay, no rafter carries an unusual load, and nothing reaches the wall.

They also give better ventilation, since two openings can flow where one cannot, and on a slope with any sun they allow one to be specified for light and the other for the view, which a single compromise unit cannot do.

The visual argument matters too, and it works in your favour on a designated building. A matched pair, aligned at head and cill, reads as a deliberate composition. One large unit reads as an intervention. Officers respond to the first far more readily than the second.

Where the room genuinely needs one large opening, that is a designed solution with an engineer’s involvement, and it should be priced and programmed as such rather than approached as a bigger version of an ordinary job.

Chalk, water and the ground

One local factor worth knowing, because it turns up in surveys here.

Chalk drains quickly, so the valley sides are generally dry, but the ground at the bottom near the river behaves quite differently and can hold water. Properties on the lower ground carry the higher humidity that goes with that, and the older ones have solid walls with no effective damp course.

For a rooflight the relevance is the same as anywhere on the river: a house running wetter throughout delivers air to the glass carrying more moisture, so condensation appears earlier in the season and lingers. It argues for a warm-edge spacer, an opening unit rather than a fixed one where the room allows, and a vapour control layer sealed continuously to the frame.

It also argues for separating the problems properly. Damp at ground level and condensation at roof level are two different faults with two different remedies, and treating them as one is how money gets spent in the wrong place.

The work we take on

New rooflights and replacements of failed units, in the flint and brick stock, the later housing and the converted outbuildings. Openings sized to stay within the roof structure wherever that is possible, and a designed solution where it is not.

What we do not do is masonry work, remedial roofing or re-covering. Where a survey shows the roof is spreading or the wall head is in poor condition, that is a structural matter for somebody else to put right before a rooflight goes in, and we will say so rather than proceed and add load to it.

What we need to know

Where in the village the building is and whether it sits above or below the road. What the walls are built of, and what the roof is covered with. How large an opening you have in mind, because on a flint building the size is the question rather than an afterthought. Whether the building is listed or in the conservation area.

Goring is inside the twenty-five miles of road we cover, and the authority is South Oxfordshire.