Rooflight and skylight installation in Layer-de-la-Haye

Cut roof or trussed rafters

The question that sets the price, and one you can answer yourself with a torch in two minutes.

Rafters running from eaves to ridge with a horizontal purlin partway up and clear space between them is a traditional cut roof. Rafter, purlin and ceiling joist each do a separate job, so 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 middle of the space, joined by flat pressed steel plates, is trussed rafters. Each is a single engineered component in which rafter, ceiling tie and webs are designed to work together, and cutting any member sends the load it carried somewhere it was not meant to go.

With trusses at the usual 600mm centres, a unit narrow enough to sit between two of them without touching either goes in with no structural work at all. That is the quick and inexpensive job. Anything wider needs a structural trimmer designed by an engineer, which is routine and which is the point at which the price steps up.

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

Coverings and the flashing kit

Concrete interlocking tiles across most of the twentieth century housing, with clay plain tile and peg tile on the older property and pantile on some agricultural buildings.

Interlocking tiles are profiled and need a deep flashing kit rather than the flat kit used on slate. An interlocking tile has a raised profile with a channel down it, and a flat kit designed to sit against smooth slate leaves open voids under those channels where it crosses the tile. Water gets under within a season, and because it enters below the flashing it appears inside as a leak that seems to come from nowhere.

It is the most common installation fault we find on other people’s work, it is invisible once the job is finished, and it is exactly where a cheap quotation saves money. Ask any quoting installer which kit is specified for your covering by name and part number.

Exposure toward the water

Properties on the reservoir side of the village get more wind than their inland position suggests, because a large body of open water gives wind an uninterrupted run.

Driving rain matters more for a roof window than total rainfall does, which puts the weathering job on the underlay collar and the flashing kit rather than on gravity. Specify the kit generously and correctly for the covering, and use stainless fixings rather than plated, which cost very little more and do not stain an exposed roof.

What we fit here

Roof windows into rear slopes for loft rooms and landings, which the cut roof properties take very well. Flat roof rooflights and lanterns over rear extensions, which a great many houses here have gained. Sun tunnels into internal bathrooms and hallways. And a growing amount of replacement work, because a lot of units went in during the 1980s and 1990s and sealed units last fifteen to twenty five years.

On any replacement, photograph the data plate on the sash rather than measuring. From that we can usually tell you what the unit is, whether the size is still made, and what the job costs, without anyone visiting.

Extensions and the kerb

Where an extension is involved 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. Ask directly whether it is insulated; it is the fastest way to tell who is detailing the job and who is fitting a unit.

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. Individually listed buildings need consent regardless of slope or visibility, and for a converted agricultural building it is worth reading the original permission, because conversions are frequently granted with permitted development rights removed by condition.

Access is generally good, with off street parking across most of the village and space to stand a tower at the rear. Two storey rear slope work needs scaffold, but it stands on private land, which avoids the highway licence.

Ventilation is the fix

Where condensation is the diagnosis, nothing done to the window solves it. Moving air does.

An opening at the highest point of a room lets warm moist air leave and draws drier air in through anything open lower down. That clears a room in minutes where a wall window alone takes hours, and it only works if something at low level is open as well.

Where the unit is above easy reach, a motorised opener with a rain sensor is worth the premium, because a window that closes itself when it starts raining is a window that actually gets left open. Where running mains cable through a finished ceiling would mean lifting floors and chasing walls, a solar powered opener needs no connection at all and goes in within a couple of hours.

What we will tell you before charging for a visit

Send a photograph of where the water appears and, if it is safe, one of the outside of the unit. Say whether it follows rain or cold mornings, and whether it can be wiped off. Between those we can usually tell you which situation you are in, and two of them need nobody to come out at all.