Skylights and rooflights for moorland-edge stone houses in Meltham

What the layers do

Each extra sheet of glass adds a sealed gap, and argon or krypton in that gap passes heat on more slowly than air does. A thin low-emissivity coating on an inner face turns warmth back toward the room. A warm-edge spacer, in a plastic or composite material, stops the metal strip at the glass edge from becoming a cold line.

The frame matters too

A frame with a thermal break has two parts joined by an insulating strip, so cold on the outside does not run straight through to the inside. That keeps the inner edge of the frame warm enough to resist condensation, which can run down a cold frame onto the plaster.

A number to compare

The U-value is the rate at which a unit lets heat through, and a lower figure is better. Part L caps heat loss at 1.4 W/m²K through a roof window and 2.2 W/m²K through a rooflight when either is fitted or replaced in an existing house. A unit chosen for Meltham sits comfortably under those limits and so keeps more warmth than the old one.

Glare and summer

Cold is not the only test. A solar-control coating takes some of the sun's heat out of the light, which helps in a room facing south or west in summer. It is a choice for each room.

Our quote is written down and fixed, recording which room is being lit and the unit with its size, and because fitting or swapping a roof unit falls under the energy rules we notify Building Control.

Fitting it so the heat stays in

Insulation is packed round the frame and lapped onto the roof insulation, and the light well is lined and sealed. A gap in that insulation can cause more heat loss than the glass does, so the fitting counts as much as the unit.

Why the shape of the lining counts

That passage is the light well. If its sides run straight down, the light from the glass meets the lining at a steep angle and little reaches the floor. If they flare out toward the ceiling, the opening at the bottom is wider than the glass at the top, and the light spreads across the room. We cut the lining to flare, and a white finish bounces light on.

Sizing against the gap

A roof window has a size code, and the letter gives the width while the digits give the height. Rafters on either side of the gap frame the opening, so the size chosen has to suit the spacing we find in your roof. In an old stone house the rafters may not sit at regular centres, and the survey records how far apart they are before a size is picked.

Building the well

Timber trimmers frame the opening in the roof, and a short timber box forms the well between the frame and the ceiling. Plasterboard lines it, insulation sits outside it, and the reveal is plastered. The well has to be sealed at the top to stop warm room air meeting cold glass.

When the ceiling is lath and plaster

An old ceiling may be lath and plaster, and cutting through them throws up dust and can crack the plaster beside the cut. We score the line first and support the ceiling while it is opened. Floor and furniture get covered before any cutting, and the room is cleaned when we leave.

Light wells above a stair

A winding stair in a thick wall is a natural place for a roof window, because the well can sit directly over the stairwell. Light drops down the shaft to the turns that never had a window. We look from the loft hatch to check the stair lies under a clear stretch of roof.

Looking the address up

A map search tells us whether the house is listed, whether its street is protected as a conservation area and which authority covers the postcode. If the map leaves any doubt, we ask the planning office itself and wait for the answer before any unit is ordered.

The slope that faces the lane

Where the question is how the roof looks from outside, the slope counts. A unit on a back slope over a yard is far harder to see than one on the front, and a stairwell or landing can sometimes take its light from either side. That makes the rear slope the first place to look.

A unit that suits blue slate

The conservation rooflight is a slender black frame with the glass close to the slates and often a single bar down the middle. On blue slate or stone slate it reads as a dark line among the slates. Conservation officers often ask for that style, and it also suits a house that is not in a conservation area but is seen from the lane.

Old unit out, new unit in

Taking out an old rooflight and bedding a new one in the same hole disturbs a smaller area of roof than a fresh cut. The new unit still has to meet today's energy limits, and a listed house may need consent even for a swap, so the address check comes first either way.

A flat in a converted building

Flats sit outside the roof-alteration right that houses enjoy, so the council is asked before any work. The roof is shared by the whole building, and the lease shows whose agreement covers the roof.

Putting the answer in the paperwork

When an application is needed, the unit and its size are already fixed, so the council is asked about a definite product in a definite place. That keeps the application short and the reply specific.