Skylights and rooflights for stone mill cottages in Queensbury and the hill villages around it

The roof comes first

Before a unit is chosen, the roof has to be understood: what it is built from, how it is supported, and how much of its weight it can lose to an opening. A large old roof may be carried on iron, steel or timber trusses, and an opening between them is framed to suit.

Choosing the unit for a working space

• A flat roof rooflight where the roof is flat or near flat.
• A rooflight that opens electrically for a high ceiling, giving ventilation without a ladder.
• A roof window where part of the building has a pitched slope and a lower ceiling.

When the mill is listed

Parts of Black Dyke Mills are listed at Grade II, among them the principal mill blocks and the chimney. A listing brings consent of its own, which is sought before the work starts, and the answer on style and size comes from the conservation officer. The written quote is fixed for the unit and where it goes, so the consent application describes something definite.

Light for the rooms underneath

Some old mill rooms are so wide and deep that the windows in their walls leave a band of floor in the middle unlit. A row of rooflights above that band gives an even spread across a bench or a desk, and the openings can line up with the structure so no truss is cut.

Reaching the roof safely

A mill roof can be large and a long way up, and some old coverings are brittle. We plan the access at the survey and tell you what is needed before work starts, whether scaffold, edge protection or crawling boards. If you know the roof covering is old cement or sheeting, tell us at the start, because brittle sheets are walked on only with boards laid across them.

What the rules ask

For a roof window, the energy rules in Part L cap heat loss at 1.4 W/m²K, or an equivalent Window Energy Rating band. A rooflight, lantern included, may reach 2.2 W/m²K. Those are upper limits, so a unit can do better, and rooflight U-values and Part L explains the two figures.

Picking from the options

Three things do most of the work on a cold hillside. A low-emissivity coating on the inner face of the glass sends heat back towards the people in the room. A warm-edge spacer between the panes stops the edge of the unit becoming a cold line. In a thermally broken frame, a gap in the metal stops the cold outside carrying through to the inside face.

Triple glazing adds a third pane, and gas between the panes improves the figure further. Whether that is worth having depends on the room: a bedroom that is slept in all night may suit it better than a hall. Our comparison of double, triple and solar-control glazing lays the options out.

Condensation on cold glass

Cold glass in a damp room collects water on the inside face, which is a different matter from fogging between the panes. Better glazing keeps the inner pane warmer, so there is less to condense. A kitchen or a bathroom benefits most.

Weather side or sheltered side

On an open hillside, the slope that takes the weather also takes the sun. A window on the weather side meets the wind head-on, so its seal and flashing matter, while one on the sheltered side is easier on the frame. The room's needs come first, and the slope is picked with that in mind.

Fitting that keeps heat in

The best glass loses its advantage if the gap around the frame is not insulated. The reveal is lined, the gap packed and the finish plastered as the quote says, so no draught finds a way round the frame. A rooflight in the wind needs a good seal at its flashing, and the covering around it is lapped to suit.

If an old single-glazed rooflight is already in the roof, the change is easy to feel. The room usually holds its warmth better, and the glass on a cold morning is no longer so chilly to touch.

How the tunnel works

A dome on the slope collects the daylight. A tube with a mirror finish carries it across the loft space, and a diffuser panel in the ceiling shares it out over the room below. It is small, which means it can pass between rafters without a larger opening, and it costs less in structure than a roof window.

Rigid or flexible

Rigid tubing keeps the light moving along a straight, shiny wall. Flexible tubing is ribbed, and every ridge catches some of the light, so it is better kept for a short run with a bend. Rigid and flexible sun tunnel routes sets out when each makes sense.

Tile or stone slate overhead

Later Queensbury houses may be roofed in concrete tile, and older ones in slate or stone slate. A tile roof takes a dome with a flashing shaped to the tile profile, so water runs off the tiles and over the collar without finding a gap. A stone-slate roof is heavier and more brittle, so the dome is dressed into it by hand and the sound slates are kept.

Through the loft

The tube has to find a path from the slope to the ceiling around the water tank, the pipework, the rafters and any boarding. The route is walked in the loft before the dome is placed, because a bend, however gentle, costs light. Where a joist must be cut for the route, the work becomes structural.

Which room gets the tunnel

If both the hall and the landing are dim, the landing is usually the better choice, as the light then falls down the stairwell as well. In a bungalow the hall is the obvious room, because the roof is directly overhead.

Daylight from a tunnel is soft and even, and in a small hall it reads as a gentle brightening rather than a spot of sun. One tunnel lights one room well. A second one can be added for a second room, and the quote names each unit and where it goes.