Rooflight Installation in Kennington

A village of converted lofts

Kennington sits immediately south of Oxford, on the road between the city and Radley, with Bagley Wood on the higher ground to the east and the river not far to the west. It is a village by name and by feel, but the housing is overwhelmingly of the middle of the twentieth century: estate-built semis, short terraces and detached houses laid out street by street after the war, with the older core a small part of the whole.

A good many of those lofts have since been taken on: some as full conversions with staircases and sign-off, some as rooms made without much ceremony and now being brought properly into use, and some still empty with a hatch and a ladder.

That spread makes rooflight installation in Kennington a different conversation from the one we have a few miles away. The enquiry rarely arrives as a request for more light on the landing. It arrives as a loft conversion, and the rooflight is one element of something larger. What we can usefully do is set out what the room has to satisfy before anybody chooses a unit, because that order saves people from buying twice.

When a loft becomes habitable

The distinction that governs everything else is whether the space is a loft or a room. It is not about how it is furnished. It is about what the space is intended to be used as, and once it is intended as a bedroom or a study, a different set of requirements applies to it.

Putting a rooflight into a cold, unlined loft is self-contained. The opening is formed, the structure around it made good, the unit set and flashed into the covering, and the loft carries on being a loft. The thermal line stays where it always was, at ceiling level.

Converting that loft is a different proposition. The thermal line moves from the ceiling up to the rafters. The floor has to carry people rather than boxes. The staircase and the route down from it become an escape route, which affects doors, linings and sometimes the whole stair enclosure. And the room itself needs a means of escape for when that internal route is not available. Several of those touch the rooflight directly.

We raise it early, because homeowners often have a unit in mind before we arrive, chosen from a neighbour’s roof. If that neighbour’s loft is storage and yours is going to be a bedroom, the two roofs are not answering the same question.

Escape, and what governs it

A roof window can serve as the means of escape from a loft room, and on the pitched roofs around Kennington it often does. When a rooflight is doing that job, three things about it stop being matters of taste.

Its size. The unit has to be large enough for a person to get out through, and that is a function of the aperture rather than the frame outline. A unit that looks generous in a brochure can present a smaller usable opening once the frame, the sash and the way it swings are accounted for.

Its clear opening. What counts is the unobstructed area available when the window is open, and the shape of that area as well as its extent. A tall narrow opening and a wide shallow one of similar area are not equally useful to somebody climbing out.

Its position. This is the one that catches people out. The height of the opening above the finished floor matters, because an opening set too high cannot be reached and used. The position relative to the eaves matters too, because a unit low on the slope brings the head of the opening down with it. Between those two constraints there is a band on the slope where an escape rooflight can sit, and it is narrower than most people assume.

We do not publish numbers for any of this, and be wary of anybody who quotes them off a website without having seen your roof. The governing dimensions follow from the Building Regulations as they apply to the room being formed, and the specification is confirmed at survey against your pitch, floor level and eaves.

Why the hinge matters

Here is a distinction that gets glossed over almost everywhere, and it is worth understanding before you choose.

A centre-pivot roof window rotates about a bar running horizontally across the middle of the frame. Opened, the sash sits half inside the room and half outside, and the pivot bar sits across the middle of the aperture. That is a good arrangement for ventilation and for cleaning the outer face from inside. What it does not give you is an unobstructed hole, because the bar and the lower half of the sash are in the way.

A top-hung unit is hinged at the head and swings outward from the bottom. The whole aperture below the hinge is clear, which is why top-hung operation is normally specified where a roof window has to serve as an escape window: the opening it presents is the opening you can get through.

Units exist that do both, with a top-hung escape function and a pivot action for cleaning, and those are frequently the sensible answer in a converted loft, though which you are looking at is not always obvious from a product code. We install VELUX, Fakro, Keylite and Roto rooflights, and we say which operation the room needs before anybody talks about finishes.

Insulation at the rafter line

Converting a mid-century roof means insulating between and under the rafters, and rafters of that period were sized to hold up a roof rather than to hold insulation. They are frequently shallower than the build-up now expected wants them to be.

There are ways around that and they all cost something. Insulation can be added on the underside of the rafters, which works but eats into the head height you were converting the loft to get. Rafters can be deepened, which is structural work, designed by somebody qualified to do it, with us coordinating around the result rather than determining it. Higher-performance boards carry more of the job in less depth at greater cost. And there is usually a ventilation path to preserve above the insulation, which cannot be filled in to buy back depth.

Where this lands on our part of the work is the reveal. The lining running from the frame out to the finished plaster has to carry the insulation continuously around the opening and keep the vapour control layer unbroken where it meets the frame. Get that wrong and warm damp air from the room reaches a cold surface behind the plaster. The owner sees water on the reveal and reads it as a failing window, when the window is doing what it was made to do.

Where light does most good

In a converted loft the floor area that counts is the part where you can stand up. Under a pitched roof that is a band down the centre of the plan, tapering away towards the eaves on either side, and the low ground at the edges becomes wardrobes, drawers and knee-wall storage.

That bears directly on placement. Positioned to wash the standing band rather than the storage strip, a modest unit does more than a larger one badly placed. Two units spaced along a slope usually beat one wide one for evenness, and on a room with a slope facing each way, glass on both sides gives light at more hours of the day.

Placement has to hold the escape position and the view from the street in the same hand. On the estate roads here the front slopes face other houses directly and are read as a set, so where the room allows it we put the working glass on the rear slope, and where escape pulls a unit onto the front we say so at survey rather than after the scaffold is up.

This is also where a rooflight earns its place against a dormer. A dormer buys standing room and on some plans it is the right answer, but it is a visible box the neighbours can see and it carries far more construction. Glass in the slope brings daylight into the part of the room you are converting it for, without altering the roof line.

Coverings and permitted development

The roofs here are mostly concrete interlocking tile, with clay plain tile on the older houses and some of the earlier estate work. Both are ordinary and well understood, and neither presents the difficulties that stone slate does further west in the county.

Concrete interlocking tile wants a flashing kit made for its profile. The interlock along the side of each tile means water is being managed within the covering as well as over it, and a generic kit adapted to fit is where these installations go wrong. The batten gauge either side of the opening has to be set out correctly and the underlay turned and dressed into the opening rather than cut back to the timber. Clay plain tile is double lapped, so the coursing has to be held true across the head and down both sides. Neither is difficult work. Both are precise work, and that precision is the difference between a dry opening and a wet one.

On planning, the position is generally straightforward. Rooflights on a house are commonly covered by permitted development where they do not project beyond the plane of the slope by more than the permitted amount and sit no higher than the ridge, with tighter treatment on principal elevations. Kennington falls under Vale of White Horse District Council rather than Oxford City, and the older core is worth checking address by address, since conservation area boundaries and Article 4 directions belong to the authority to confirm rather than to us to assert.

Coordinating a notified conversion

Building Control notification is ours. We handle it as part of the installation rather than handing you a form.

A conversion needs one extra step, and it is the step most often missed. The rooflight is one element of a wider notified job. Somebody is already running the conversion, whether a main contractor, an architect or the homeowner acting for themselves, and the structure, the stair, the fire separation and the insulation are being notified together. Our work has to sit inside that rather than alongside it, so we ask early who is running the job, who the building control body is, and what has already been submitted.

Where the escape function of a rooflight is being relied on, that reliance sits in somebody’s design. We are installers. We do not determine what the room needs, we do not sign off the conversion, and we are not the building control body. We install to the specification the job has settled on, say when a unit will not achieve what it is being asked to achieve, and coordinate so our opening is inspected within the same process as the rest.

What we establish on a Kennington enquiry. Whether the loft is becoming a habitable room or staying a loft. Whether a rooflight is being relied on for escape and, if so, where on the slope it can sit. What the rafters are and what depth is available once the insulation build-up is decided. Which slope, which orientation, and what the covering is.

We have been installing rooflights for fifteen years, we do new installations and replacements and nothing else, and our workmanship carries a ten-year guarantee with coverage and exclusions on their own page. Kennington sits inside the twenty five mile road radius we work to. Tell us what the loft is going to be, and we will tell you what the roof can give you.