Skylight Guides

The cards further down this page are sorted into seven groups, one for each of the main ways glass ends up in a roof. Around a dozen guides sit under each group, and every one of them also hangs off its parent page in the service list, so you can arrive from either direction.

• Roof lanterns. Pitched glass faces raised above a flat deck on a kerb. The guides here cover how the upstand is built and why it decides whether the thing leaks, sizing the frame against the room rather than against the roof, aluminium against timber, condensation on the inside of the glass, and how a lantern sits on the roofline of a 1930s semi without looking bolted on.
• Flat roof rooflights. Flush and near-flush units. Falls and standing water, warm roof build-ups, walk-on glass and where it earns its cost, single-ply against felt against GRP at the junction, and how many units a given extension actually needs before you are just adding heat.
• Pitched roof windows. In-plane windows in tile and slate. Flashing kits, trimming rafters, head height and where in the slope the window wants to be, escape sizes for a loft room, and what happens when you take out a twenty-year-old unit.
• VELUX roof windows. Reading a size code off the data plate, centre-pivot against top-hung, matching a flashing kit to your covering, replacing an old unit with the current equivalent, and the shading range.
• Energy and solar control. The group a south-facing roof makes unavoidable. G-value, U-value, Part L compliance, low-e coatings, warm-edge spacers, glare across a worktop or a screen, retrofitted shading, and ventilation treated as part of the glazing decision rather than a separate afterthought.
• Electric and opening rooflights. Power and cable routes, chain against spindle against linear actuators, rain sensors, stack ventilation, and how you get at a motor once it is four metres above the floor.
• Commercial rooflights. Non-fragile classification and roof safety, GRP replacement on an industrial roof, in-plane swaps without stripping the covering, phased bay working over an occupied floor, daylight factor in a warehouse, and automatic opening vents.

The library is more useful if you take it in stages instead of reading everything at once.

At the thinking stage, before any drawings exist, you want the guides that compare forms: lantern against flush unit, one large window against two small ones, glass against polycarbonate. These decide the shape of the job and they are cheap to change now and expensive to change later.

Once a layout is settled, move to the structural guides. Openings, trimming, upstand construction, deck build-up. This is the point where a rooflight either fits the existing frame or triggers a calculation, and knowing which one you are in changes both the programme and the budget.

Before anything is ordered, read the glazing guides. Glass is the part of a rooflight that cannot be changed afterwards without taking the unit out, so it deserves more attention than the frame finish and usually gets less.

Then the practical ones: what installation day involves, how long a unit takes to fit, access and scaffold, cleaning something you cannot reach from a window. Those are worth ten minutes the week before the work starts.

Every group has at least one guide about glazing, and that is deliberate. The same question keeps surfacing whatever the unit is, because Southend-on-Sea faces south across the Thames Estuary and a very large number of roof planes across south Essex look straight at an open sky with a reflective surface underneath it.

So the guides keep coming back to two figures. U-value, watts per square metre per degree, governs winter heat loss and is the number the regulations police. G-value, a decimal between 0 and 1, is the share of solar energy the glass lets into the room, and it is the one that decides whether a July afternoon is pleasant. Clear double glazing sits around 0.6. A good solar-control build-up lands near 0.3 while keeping light transmittance up around 0.6, so you lose the heat without losing the daylight. The solar-control guides go through that in full, and the group is worth reading even if you came here about a lantern or a loft window.

Regulation comes up on almost every page, so here is the shape of it in one place.

New and enlarged rooflights in a dwelling are notifiable under Building Regulations. Part L sets the thermal standard the unit has to meet, Part K covers safety glazing and guarding, which overhead means a laminated inner pane. We make the notification to Southend-on-Sea City Council, or to whichever authority covers your address, as part of the installation.

Planning is usually a shorter conversation. Rooflights on a house are generally permitted development where they sit below the ridge and stand no more than 150mm proud of the roof plane, with obscure glazing and restricted opening on side elevations below 1.7 metres. Flats, maisonettes, listed buildings and conservation areas fall outside that, and the Article 4 Direction covering the Leigh Cliff and Leigh conservation areas withdraws permitted development for roofing and window changes altogether, so an application is needed where it otherwise would not be.

Treat all of that as general guidance. Local designations vary street by street across the areas we cover, and the only reliable answer for a specific address comes from the local authority.

A written page can explain physics, regulations and typical values. It cannot see your roof, and there are four things it will never tell you.

What the deck is made of and what condition it is in, which you only know once a corner is lifted. Whether the structure below takes the opening you want without a new beam, which is arithmetic done against actual member sizes and spans, not a rule of thumb. How the plane really orients once you allow for a chimney, a neighbouring gable or a mature tree, because a compass bearing and an unobstructed sky are different claims. And how the unit gets on to the roof at all, which on a terrace with rear access through the house can be the single biggest item on a quote.

The point of reading any of this is not to specify your own rooflight. It is to make the quoting conversation a short one. Four questions do most of the work, and every one of them is answered somewhere in the library.

1. Which way does this plane face, and what is above it? Orientation before product, every time.
2. What is the G-value and the light transmittance of the glass being proposed? Two numbers, from the manufacturer’s data sheet. An energy rating is not a substitute for either.
3. Is the U-value quoted centre-pane or whole-unit? The whole-unit figure is the honest one and the one Building Control works to.
4. Who makes the Building Regulations notification? If the answer is you, that is worth knowing before you agree a price.

Read the group that matches your roof, check the cost ranges so the figures that come back have context, and then ask for a specification written plane by plane. Over fifteen years of installing skylights and rooflights across south Essex sits behind these pages, and every installation carries a ten-year workmanship guarantee, but the guides are here to be used whether or not you ever pick up the phone.