Slaithwaite skylights and rooflights for Colne Valley cottages, stone terraces and mill workshops

Graded courses

Stone slates are laid in courses that shrink in size from the bottom edge of the roof to the top, with the biggest, heaviest stones lowest down. An opening cuts across several courses, and each stone that comes off is kept and numbered in its place so the roof can be dressed back to the same pattern around the frame. Stone that cracks is matched from what is on the roof.

A flashing for a thick covering

The flashing kit has to suit the covering. Welsh slate lies thin and flat, tile has a profile, and stone slate is thick and uneven underneath, so the lead or kit dressed round the frame is shaped by hand to the stones either side. The standard kits differ from this, as the flashings for slate and tile guide describes.

What the roof carries

A stone-slate roof is a heavy covering for its rafters to carry. Making a new opening interferes with the roof timbers, so trimmers are fixed to carry the load round the unit, and we notify the work. A window narrower than the clear gap between two rafters avoids cutting either.

Planning in the valley

Planning for Slaithwaite sits with Kirklees Council. A house usually has permitted development rights for a rooflight on a roof slope, although a listed building, a flat or a property in a conservation area under an Article 4 direction can lose them. The conditions are gathered in the planning permission and building regulations guide.

Looking after the stones

Stone slates are lifted by hand and stacked in order near the opening, so none is broken by being walked on. Any stone that cracks is matched from what is already on the roof, and the courses are laid back in their original pattern, so the new frame sits in a roof that still reads as one surface from the road.

Energy figures for a new unit

A new roof window must reach a U-value of 1.4 W/m²K, or Window Energy Rating band B. A rooflight must reach 2.2 W/m²K. A single-pane rooflight of the old sort in a cottage roof falls a long way short of both.

Houses and commercial units differ

The permitted development rights for a rooflight on a roof slope belong to dwellinghouses. A workshop, a studio unit or an office does not have them, so the council is asked whether an application is needed. Where the building is a flat or a house, the planning guide sets out how the line falls.

Roofs of mill buildings

A mill roof may be pitched and slated or it may be low-pitched and clad in sheet or felt. A flat rooflight suits a low or flat roof, with a kerb built up above the surface and the covering dressed over it. On a pitched roof, a larger roof window or a row of units can light a long floor evenly. Roof structure in these buildings can be trusses instead of rafters, so a unit is sized to fit between the members where possible.

Choosing the glass

A workroom with a south-facing roof gathers heat, so solar-control glazing is worth considering, with a coating that limits the warmth passing through. A studio that needs steady, even light often does better with a roof window that faces away from the sun. Solar-control and other glazing options are compared under energy efficient rooflights.

Light for the middle of a deep floor

On a long floor, one large unit lights the area under it and leaves the ends in shade. A row of smaller units spaced along the roof spreads the daylight more evenly, and the spacing follows the trusses or rafters so each opening sits between members. The room below is looked at for desks, benches and machines, since those set where the light needs to land.

By the canal

Buildings beside the canal may sit in a conservation area or be listed themselves, and either one brings extra consent. A conservation rooflight is the type that suits a protected roof of stone slate or slate.

Reading a size code

Makers label roof windows with a code. In a code like MK04, the letter M gives the width and the digits 04 give the height. We never quote a code without checking it against the real rafters, since the same code means a fixed frame size and the roof must have room for it. The lettering follows a fixed pattern, as the VELUX size codes page shows.

Between the rafters

A unit that fits between two rafters needs no rafter cut and leaves the roof structure alone. Where the best position needs a wider unit, a rafter is cut and trimmed, and that work is notifiable. The opening is framed before the unit goes in, with the sheeting and insulation dressed round the frame.

Low eaves, high light

With low eaves, the best position for a window is high in the slope, where there is more headroom and the daylight falls across the floor. Two opening styles matter in a low attic. A top-hung sash hinges along its head, swings outwards and leaves the floor area under the opening clear. A centre-pivot sash rotates on a horizontal axis halfway up, and works well above a bed or a chest of drawers.

Where the opening sits in the slope

A window high in the slope gives headroom at the opening and daylight across the floor, and one low in the slope lights the floor edge but not the ceiling. In a low cottage roof, the position is picked from inside, standing in the room and looking up. The opening is then marked from the loft so it lines up with the rafters that carry it.

Old plaster and boarding

Cottage ceilings in the roof are often lath and plaster or boarding laid over the rafters. Cutting through them throws up dust, so the floor and the stair are sheeted first, and the edges of the cut are trimmed neatly as the lining goes in, so the plaster meets the old ceiling cleanly.

The finishing indoors

The lining of the opening is boarded, plastered and painted as quoted. On fitting day the slates are lifted, and the frame is flashed in. We file the Building Control notification ourselves.