Rooflight and skylight installation in Abberton

Open water, and what it does to a roof

A large body of open water gives wind an uninterrupted run at anything on its lee side, so properties around the reservoir are more exposed than their inland position would suggest.

What matters for a roof window is driving rain rather than total rainfall. Wind driven water is pushed under a covering rather than running down it, which means gravity is doing much less of the weathering work and the details are doing much more.

Two details carry almost the whole burden. The underlay collar, dressed and lapped so that water reaching the membrane passes around the opening rather than into it. And the flashing kit, which must be the correct profile for the covering and generously lapped. A universal kit adequate in a sheltered position will let water past on an exposed roof, and it is exactly where a cheap quotation economises.

Stainless fixings rather than plated cost very little more and do not bleed rust down an exposed roof. On larger units and anything that opens, wind loading is worth checking against the site rather than assuming a catalogue figure.

The building stock

Cottages and farmhouses of some age, several listed, alongside twentieth century housing. The older buildings frequently combine several building periods in one roof, extended and altered over generations.

Every dimension is measured off the building at the position the unit will occupy, because a rafter spacing measured in one bay may be different in the next. Where historic timber is part of a listing, an opening is positioned to avoid it rather than cut through it, and the survey establishes where a rooflight can go before anybody discusses what it should be.

Coverings are handmade clay plain tile and peg tile on the older property, with pantile on some agricultural buildings and concrete interlocking tile on the twentieth century housing. Each needs its own flashing kit and they are not interchangeable.

Consent

Listed building consent is required for a rooflight on a listed building, always, on any slope, whether or not anyone can see it. The listing covers the whole building inside and out and there is no small works threshold.

Where a property is unlisted and outside any designation, permitted development normally applies: no more than 150mm projection beyond the plane of the roof and not above the highest part of it, with additional restrictions on side elevations facing a boundary.

For converted agricultural buildings, read the original permission, because conversions are frequently granted with permitted development rights removed by condition and those conditions run with the property.

Orientation, with a view worth having

Where a property looks toward the water, the orientation question becomes more interesting than usual.

A rooflight set lower in the slope gives a view out and lets light reach further into the room. Set higher it gives more sky, more even light and better privacy. Where there is something worth looking at, lower is usually right, and it is worth deciding deliberately rather than defaulting to whatever is easiest to fit.

The glass follows the direction the slope faces rather than the view. North gives even, cool, glare free light all day with no solar gain, and should be specified for thermal performance alone. South and west want solar control glass as standard, and west is frequently worse in practice than south because low afternoon sun arrives when the building has already been warming for hours.

The twentieth century housing

Ordinary work. Concrete interlocking tiles, pitches around 30 to 35 degrees, cut roofs on the earlier properties and trussed rafters on the later ones.

Establish cut or trussed from a loft photograph, because it decides more about the price than the choice of unit does. Trusses limit opening width to the 600mm spacing unless a designed trimmer is installed by an engineer, and they mean the loft is not convertible without replacing the structure.

Access

Good, with space around most properties for a tower or scaffold on private land and no highway licences to arrange. The practical constraint is more often the route for a delivery vehicle down a narrow lane than the working position itself.

What eventually fails

The sealed unit, at fifteen to twenty five years, when the perimeter seal finally gives up after decades of daily thermal cycling. That is the end of the unit’s life rather than a fault.

The actuator on a motorised window, at ten to fifteen years. It is the shortest lived component and it is a serviceable part that unbolts and is swapped for a fraction of the cost of a new window.

Nothing else, if the installation was right. Frames, flashings and glass have no moving parts and no reason to fail early on a job that was detailed properly.

Our guarantee

Ten years on the workmanship: the flashing, the underlay collar, the frame fixing, the insulation collar and the making good. Alongside it sits the manufacturer’s warranty on the product, which is separate cover from a separate party.

It does not cover accidental or storm damage, failure of the wider roof, lack of the routine maintenance above, or condensation caused by an unventilated room. Where the cause of a problem is genuinely ambiguous we will not charge you for the visit to establish it.