Fitzwilliam skylights and rooflights for terraces and semis under tile and slate

Reading the roof from outside

From the garden we look at the tile profile, the spacing of the courses, the state of the ridge and the point where the roof runs down to the gutter. A roof that has been re-tiled in the past may have a different tile on one slope, and that shows up as a change in colour or in the shape of the edges.

Battens and rafters

Tiles hang on battens, and the battens sit across the rafters. The opening for the frame is framed between two rafters, and the battens above and below it are cut back and refixed to the new framing. The rafter spacing in your roof is measured on the day, and it settles which window sizes fit without extra timber.

The flashing kit

A kit for deep tiles has a different apron from a kit for flat slate, so the wrong one leaves open gaps at the sides of the frame. The explanation of flashings for slate and tile shows why the profile matters. The tiles are relaid up to the flashing with the overlaps restored, which is what carries water past the frame.

Tiles that break on the way off

Concrete tiles can crack when they are lifted, particularly at the edges near old fixings. We keep the sound tiles for relaying and match any that break to the tile on the roof. A few spare tiles in the loft, left from an earlier roof, are worth pointing out when we survey.

Cut tiles near the ridge

Near a ridge or a hip, tiles are cut and the courses are shorter, which narrows the room for a frame. A window set a little lower on the slope sits among full tiles and is quicker to weather. Where the room below forces the position up the slope, we plan the cut tiles first and check the flashing can still lap them properly.

Lining and finish indoors

Below the frame, the opening is lined with insulation and plasterboard and then plastered. The light well is cut to flare slightly so that the daylight spreads across the ceiling and the upper wall.

What the droplets mean

Water on the face of the glass inside the room is condensation. It collects when the glass is colder than the dew point of the air around it, and it runs down the sash in cold weather. It is not the same as fog between the panes, which would mean the perimeter of the sealed unit had let go.

Why the glass runs cold

An old single-glazed window or a basic double-glazed one has a cold inner face. Modern units are made to warm that surface: a warm-edge spacer round the glass, a gas fill between the panes and a frame with a thermal break all keep the inside face closer to room temperature. Each of these parts raises the temperature of the inner face, and rooflight condensation is covered in more detail.

Moving the damp air out

Better glazing reduces the problem and does not remove it, because the water still has to go somewhere. A window that opens a notch, a vent in the frame, an extractor in the bathroom and a door shut while the shower runs all take damp air away. A roof window that can be opened wide in the morning clears the room fast.

Blinds and curtains

A blind pulled down over the glass traps the cold air between the blind and the pane, and that makes the glass colder than before. If a blind stays down all night, the glass may collect more water than it does with the blind open. A blind is still worth having for summer sun, and the habit to change is leaving it closed through the cold hours.

Looking at the lining

The lining round the opening is plasterboard or plaster, and it also gets cold. Staining or blackening there tells us that moisture has been collecting for a while. On the survey we check the lining and the insulation behind it, since a thin or gapped layer leaves a cold strip round the glass.

The light well

A light well is a boxed-in shaft through the loft, from the rafters down to the plastered opening in the landing ceiling. We build it from timber and plasterboard, insulate its sides and plaster it. The shape of the well changes the light on the landing, and the roof window light wells and reveals are described in more detail.

Window or tube

A roof window gives the most light and also opens. A sun tunnel gives less light for a smaller hole, and it suits a landing with a short or hipped slope above it. Over a stairwell that runs up under the ridge, the roof window is the better fit, a case set out in the notes on stair and landing roof windows.

Brightness at the foot of the stair

A well that opens at the landing also lights the stair below it, because the daylight spills down the flight and reaches the hall. A pale paint on the walls of the stair carries it further, and a glazed door at the foot lets some reach the ground floor.

Permission

Wakefield Council handles planning for Fitzwilliam, and a rooflight on the rear slope normally falls within permitted development; the guide to planning and Building Regulations lays out the conditions.

Which slope lines up with the landing

In a semi, the front and rear slopes of the roof are the same size, and the stair is usually nearer one of them. We pick the slope that lines up best with the landing, which keeps the light well short and its sides steep enough to throw the light downward.

When the roof is opened

The landing and stair are covered with sheets, the tiles come off, the frame goes in and is flashed, the light well is built and plastered. Because the opening alters the roof, the work is notifiable.