Energy efficient rooflights in Crawley, warm in winter and calm in summer

Glass loses heat faster than any insulated roof, and it faces the sky, which is the coldest thing your house ever meets. An energy efficient rooflight is one specified so that loss is small, the summer gain is managed and the edge detail does not undo the glass.

A well-insulated pitched roof or warm flat roof holds back heat through a thick build-up of board, quilt or foam. A rooflight replaces an area of that build-up with a few millimetres of glass and a cavity. Even the best glazing unit is a thinner barrier than the roof around it, so the rooflight will always be the coldest and the warmest spot in the ceiling, depending on the season. The job is not to pretend otherwise. The job is to make that spot as mild as the glass, the frame and the fitting allow.

You feel it in a few familiar ways. In January you sit under a skylight and the air above your head is cool, even though the radiator is working. Warm air rises, meets cold glass, cools and drops back down as a slow draught that has no gap to blame. Condensation gathers on the inner pane on still mornings. In July the same room can be too bright and too warm by mid-afternoon, because the glass lets solar heat in faster than a small room can lose it.

Winter asks the glass to keep heat in. Summer asks it to keep heat out. One rooflight has to do both, and solar control glass is how it manages the second half.

Solar control glass carries a coating that reflects or absorbs part of the sun's infrared energy before it enters the room. The g-value tells you how much gets through. A lower g-value means a cooler room on a bright afternoon. It usually also means a slightly tinted or slightly reflective look and a small reduction in daylight, which is the price of the benefit. Does that make a room darker? Does solar control glass make a room darker gives the answer: a little, and far less than a blind drawn against glare.

The need for it depends on where the glass faces and how big it is. A large south-facing or west-facing rooflight over a small room will overheat without help. A north-facing one might never need it. A modest rooflight over a stairwell barely matters. Solar control glass for rooflights explains the options and stopping a rooflight room from overheating turns it into a practical plan that also includes ventilation, blinds and external shading.

The glass that keeps heat in and the glass that keeps noise out overlap further than people expect. Where they do not, we explain the choice and write it down.

Laminated glass is two sheets bonded by a thin plastic interlayer. It is a safety glass, because it holds together if it breaks, and an acoustic glass, because the interlayer damps vibration. A thicker outer pane adds mass. A deeper or uneven cavity changes how the unit resonates. Every one of those choices affects thermal performance a little, for better or for worse, and the table below sets out how the common builds compare in plain terms.

A rooflight installed a generation ago is usually a single sheet, a basic double unit with an aluminium spacer, or a plastic dome. Replacing it is one of the more direct energy improvements you can make to a ceiling.

The question is always whether to renew the glass alone or the whole unit. If the frame is sound, thermally broken and in good order, a new sealed unit in the existing frame can be enough. If the frame is a simple metal section with no break, or the upstand is bare and cold, a glass-only change will disappoint, and we advise replacing the unit, the upstand finish and the lining together. Can an old rooflight be upgraded to be more energy efficient goes through the decision. Where a unit has already failed, with fog between the panes, our page on misted and failed rooflight replacement sets out the replacement route.

It helps to know what you are replacing. We look at the glass type and age, the frame material, the condition of the seals and the state of the upstand, and we record each one. That survey is the first page of the quiet spec. It also means the new rooflight is chosen against the real faults of the old one. A unit that was cold at the edge gets a warm edge spacer. A unit that overheated gets solar control. A unit that drummed in rain gets a laminated inner pane.

The survey is where an efficient rooflight is won or lost, because the specification comes from what we measure and listen to in your house.

We visit, look at the roof, the ceiling and the room, and note the orientation. We check the existing insulation, find the joist or rafter runs, look at any old rooflight and its upstand, and listen. A room under a flight path, beside the A23 or at the back of a terrace on the Brighton line tells us something the drawings will not. We then write the specification: the glass build, the frame, the upstand and the finish, with the reasons. That document is the quiet spec, and it comes with the quote.

The fitting itself is kept tidy. The old unit comes out, the structure is checked, and the new upstand is built and insulated. The unit goes in, sealed against the structure with the vapour control layer tied into the ceiling. The reveal is lined and made good inside. The work is installed to current Building Regulations, we handle the Building Control notification where it is required, and the job carries our 10-year workmanship guarantee, which you can read on our guarantee page.