Rooflight and skylight installation in Lechlade, surveyed first, and fitted once.

Georgian frontages on the Market Place, and the roof you cannot see

The market place and the streets running off it carry a good deal of eighteenth and early nineteenth century frontage: regular window rhythm, dressed stone or render, and in a fair number of cases a parapet or a coped gable running up past the eaves line.

A parapet changes everything about a rooflight. It hides the lower part of the roof slope completely from anybody on the pavement, which is the single most useful fact for an applicant in this town. A unit set low on a front slope behind a parapet may be invisible from the street while a unit two courses higher is fully exposed. The survey works out where that line falls, measured from the parapet coping down the slope, and the position is set from it rather than from the room. Photographs from the opposite side of the street, and from any point the roof is seen from at a distance, establish it properly.

Shallow slopes behind the wall, and the unit that has to change type

A roof concealed behind a parapet is often laid at a much shallower pitch than the frontage suggests, sometimes 5 to 15 degrees, because nobody had to look at it. A manufactured roof window is rated from about 15 degrees upwards and will not perform below that.

So on those slopes the unit becomes kerb mounted rather than in plane: a treated timber kerb built up off the deck, insulated on its outer face, with the covering dressed up and over it and a made-to-size flat roof rooflight set on top, its glass at a minimum of about five degrees so rain sheds and dust does not sit. The distinction between the product types, and why the trade words are not interchangeable, is on roof window or rooflight and the difference, and the kerb detail is on flat roof rooflight installation.

Riverside plots, boat yards and the flat roof facing the water

Along the river frontage there are single storey extensions, garden rooms, boathouses and workshop buildings, most of them flat roofed and most of them oriented at the water rather than at the street.

These are good buildings for daylight from above, and they are usually the least constrained work in Lechlade. The controlling numbers are the same everywhere: an upstand of 150mm measured from the finished waterproofing at the high point of the fall, a deck laid to a designed fall of around 1:40 so the finished fall stays no shallower than 1:80 after deflection, and the membrane dressed up and over an insulated treated timber kerb rather than turned up and stopped. Where an existing deck already ponds against the position somebody wants, the falls are corrected before any unit goes on, and that is said at survey rather than found later.

Permitted development on a Lechlade roof, and the 150mm that decides it

Most rooflights in a house go in with no planning application, and the limit that catches people out is the projection. An alteration to the roof of a house must not project more than 150mm beyond the plane of the existing roof slope, and must not be higher than the highest part of the existing roof.

Two Lechlade consequences follow. An in-plane roof window on a pitched slope is almost always inside the limit. A kerb mounted unit behind a parapet is a different matter, and the answer depends on whether the concealed roof reads as a roof slope of the house for the purposes of the class, which is a question for the authority rather than for an installer. Where a lawful development certificate is worth having, particularly with a sale in prospect, it is a modest fee and a short wait. The limits in full are on permitted development limits for rooflights.

Damp, river air, and what the survey reads in the roof void

A roof void in a low lying river town behaves differently from one on the wolds two hundred metres higher. Relative humidity is higher for more of the year, the void takes longer to dry after a wet spell, and condensation on the underside of a cold covering is a normal winter event rather than an unusual one.

Forming an opening can make that worse if the ventilation path is disturbed. There should be a continuous route from eaves to ridge with a clear 25mm air gap above the insulation between the rafters, and pushing insulation tight against the underside of the covering while forming a reveal blocks it, producing a cold spot directly above the new unit. Keeping that gap open, taping the vapour control layer to the frame, and specifying a vent flap in the head of the unit are three parts of the same job. More on condensation, ventilation and rooflights.

What moves the figure on a Lechlade job, and how it is fixed

No prices are published, because the range across this one town is too wide for a figure to mean anything. A conservation unit into stone slate on a market place frontage with a shared parapet gutter, and a narrow roof window between two trusses on a modern house at the edge of the town with a driveway to park on, are not the same job.

What actually drives it here: the covering, whether the slope sits behind a parapet and what the gutter does, whether the pitch forces a kerb mounted unit rather than an in-plane one, whether reclaimed stone has to be sourced, the designation position, structural work if any, access and how far material is carried, glass specification, and how far the internal finish is taken.

Then two figures in that order. An indicative range by email from photographs of the roof and the room, the covering and the address, sent to info@severnskylightsgloucester.co.uk. Then, after a survey, a fixed price, itemised, which holds unless the scope changes at your request. The Building Control notification is submitted and closed out as part of the job, the roof is never left open overnight, and the workmanship carries a ten year guarantee. Nearby Fairford has its own page, and the costs page explains the process end to end.