Rooflight and skylight installation in Sible Hedingham

Start with the roof structure

Cut roof or trussed rafters decides more about the price than the choice of unit does, and you can settle it yourself with a torch.

Rafters running from eaves to ridge with a horizontal purlin partway up and clear space between them is a traditional cut roof. Forming or widening an opening is ordinary carpentry, wide rooflights are possible, and the loft is convertible.

A repeating pattern of triangular frames with diagonal members crossing the space, joined by flat pressed steel plates, is trussed rafters. Rafter, ceiling tie and webs act as one engineered unit, so cutting any member sends load somewhere it was not designed to go.

With trusses at 600mm centres, a unit narrow enough to sit between two of them needs no structural work at all. Anything wider needs a designed trimmer and an engineer, which is routine and which is where the price steps up. It is also why a trussed loft cannot be converted without replacing the roof structure.

Broadly, properties here from before the 1970s are cut roofs and anything later is likely trussed. A photograph looking up in the loft answers it without an appointment.

Coverings

Concrete interlocking tiles across most of the twentieth century housing, with clay plain tile and slate on the older property, on pitches typically between 30 and 35 degrees.

Interlocking tiles are profiled and need a deep flashing kit rather than the flat kit used on slate. A flat kit leaves open voids under the tile channels where it crosses them, water gets under within a season, and because it enters below the flashing it shows up inside as a leak that appears to come from nowhere. It is the most common installation fault we find on other people’s work and it is invisible once the job is finished.

Ask any quoting installer which kit is specified for your covering by name and part number.

Where the daylight work is

Rear extensions, mostly, and loft rooms in the older cut roof properties.

On an extension the kerb decides whether the installation lasts: at least 150mm of upstand, the deck falling away from it so water cannot pond against the seal, and rigid insulation on the outer face of the kerb itself. That last item appears on almost no quotation and matters more than the glass specification does, because an uninsulated timber kerb punches straight through the roof insulation around the whole perimeter of the opening.

On a modest extension, two or three flat rooflights in a row light a long room more evenly than one large unit, cost less, and sit lower from outside. On a larger one with a flat ceiling and normal head height, a lantern gives volume the room does not otherwise have.

Replacement work

A growing share of what we do here, because a lot of units went into this village during the 1980s and 1990s and sealed units last fifteen to twenty five years.

Photograph the data plate on the sash before doing anything else. It is on the top edge of the sash or the frame beside the hinge, and on a centre pivot window rotating the sash brings it into view. Photograph rather than transcribe, because the characters are small and a mistyped code buys the wrong window.

Obsolete sizes are normal on anything of that age and entirely solvable, usually by adapting the opening to the nearest current size and making good the reveal, which leaves a standard size for the next thirty years. What nobody should do is force a unit into an opening it does not fit and pack the difference, which lasts about a year before the frame goes out of square.

Permissions and access

Most properties here are permitted development: no more than 150mm projection beyond the plane of the roof and not above the highest part of it. The exceptions are individually listed buildings, which need consent regardless of slope or visibility, and any property within the conservation area covering the older core where an Article 4 direction applies.

Access is generally good, with off street parking across most of the village and space to stand a tower at the rear. Tighter along the main street, where frontages sit close to the road and scaffold may need a highway licence.

The window with two jobs

Building Regulations require a means of escape from a habitable room in a loft, and in most conversions that duty falls on a roof window. It brings a minimum clear openable area, minimum opening dimensions, and a maximum height of the bottom of the opening above the finished floor so a person can actually reach it.

A centre pivot window is elegant and frequently unsuitable as an escape window, because the sash sits in the middle of the opening and obstructs it. A top hung unit that swings clear gives the full opening and is usually what gets specified. And setting a window high in the slope for a better view of the sky can put the opening out of reach for escape purposes.

Settle it at design stage rather than at order stage, because reversing it after the unit has arrived is expensive. Where an alternative escape route exists the requirement may be met elsewhere, and the roof window is then free to be chosen purely for light.

Getting the light right

Two smaller units spaced along the slope beat one large one in almost every loft. One large unit gives a bright pool and leaves the rest of the room darker by contrast; two read as ambient daylight. On a cut roof with a purlin, two narrower units are frequently easier to fit as well.

Splay the reveal rather than boxing it square. Cutting it back at an angle at head and sill opens the beam out and makes a modest window feel considerably larger. It costs a little more in plastering and it is the best value decision available on any installation.

Orientation decides the glass. A loft room under an uninsulated south or west facing slope is the classic overheating case, and solar control glass costs a modest premium at the point of order against a great deal afterwards.

Building Control

A loft conversion is notifiable whether or not planning permission is needed, and we handle Building Control where the work requires it. It appears as a named line on the quotation rather than as a surprise.