Compare your skylight and rooflight options side by side

The method

Five measures, the same for every option

A skylight quote that names one product leaves you with a yes or a no. Two or three suitable units on one page, described in the same terms, give you a choice you can reason about. We are independent of any single manufacturer, so we pick the units that fit your roof and your room, from more than one maker where the roof allows it, and write them up on five measures in a fixed order.

Under the options you will find the unit we would choose, with a line on why. Sometimes that is the dearer unit, because the room will use what it adds; sometimes it is the simpler one, because the extra would go unnoticed. Either way the facts sit in front of you and the choice is yours. To get yours, book a free survey.

Every option on a Forge quote is described on glass, frame, opening, lead time and price.

Product types

Each type of skylight on the same measures

The first comparison is between product types, because the roof often narrows the field before anything else does. A flat roof takes flat rooflights, lanterns, walk-on glass and some sun tunnels; a pitched roof takes roof windows, conservation rooflights and sun tunnels. Within those groups there is usually more than one sensible answer.

Our guide to the types of skylight goes further into each product, and our answer on whether a skylight can go in any roof covers the structural checks we make at the survey.

Flat roofs

Flat rooflight or roof lantern

This choice comes up on kitchen and garden-room extensions time and again. A flat rooflight is a single pane on a low kerb, so it reads as a clean opening in the ceiling and costs less for the same size of hole. A roof lantern rises above the roof in a pyramid or ridge of glass, which adds height and a sense of occasion to the room below and catches light from more directions, at a higher price and usually a longer lead time when made to measure.

Neither one is the right answer everywhere. A low ceiling under a flat roof often suits a flat rooflight, which keeps the line of the room calm, while a deep extension with a dining table at the far end can gain a lot from a lantern. Our answer on choosing a roof lantern or a flat rooflight goes through the common cases, and the roof lantern sizes guide helps with proportion.

Glass

Double, triple and coated glass

Glass is the measure with the most options and the one where the numbers matter. Under Part L 2021, Table 4.2 for existing homes, a rooflight must reach 2.2 W/m²K, and a roof window must reach the window limit of 1.4 W/m²K or WER Band B. Every unit we put on a quote meets the limit for its type, and we write the maker's stated figure next to it so you can compare.

Coatings sit on top of that choice. Solar control glass reduces the heat that builds up under glass facing the afternoon sun, and self-cleaning glass helps rain carry dirt off a sloping pane. A laminated inner pane holds together if the glass breaks, which some makers fit as standard. Our guide to double and triple glazed rooflights compares the two in depth, and the answers on solar control glass and self-cleaning glass say where each one earns its place.

Frame

Aluminium, uPVC and timber

The frame decides how a skylight looks from inside and how much of it you see. On flat roofs and lanterns the choice is usually between aluminium and uPVC; on pitched roofs, roof windows come in pine, white-painted timber or a white polyurethane-coated timber core, with an aluminium or coloured cladding outside.

For lanterns, our aluminium or uPVC lantern guide weighs those two frames against each other, and our frameless flat rooflights guide covers the minimal-frame look against framed units.

Opening

Fixed, manual or electric

A fixed unit gives the same daylight as an opening one of the same size for less money, and it has no moving parts. An opening unit brings fresh air in at the highest point of the room, where warm air gathers. Manual openers suit glass you can reach with a pole or a handle; electric openers suit high ceilings and lanterns, and usually come with a rain sensor that closes them when it rains.

On a pitched roof the question is the hinge. A centre-pivot roof window turns in the middle and opens from a handle on its top rail, so it is easy to clean from inside and suits a window set within easy reach; a top-hung window opens outward from the top with its handle at the bottom and leaves a clear opening below, which suits a window set higher in the slope or one you stand at. Our guide to top-hung and centre-pivot roof windows compares them, and the manual or electric rooflight guide covers the powered options. For loft rooms, our answer on roof windows as a fire escape states the Approved Document B position: an escape window serves only a storey within 4.5m of ground, so a loft conversion on a two-storey house needs a protected stair.

Makes

Comparing one maker's unit with another's

VELUX, FAKRO and Keylite all make pitched roof windows in a range of standard sizes, with flashing kits for tiles and slate, blinds made for their own frames and electric versions. Flat rooflights and lanterns come from a wider group of makers, each with its own frame profiles, glass build-ups and upstand options. We name the maker on each option as a fact about the product, and we compare units the same way whoever makes them.

Between two roof windows of similar size the differences tend to be in the details: how the frame finishes inside, which glass comes as standard, the shape of the handle, how the flashing kit sits in your covering, and how long the maker usually takes to supply that size and finish. VELUX size codes are a common reference point; in a code such as MK04 the letter is the width and the digits are the height, and our VELUX sizes guide explains how to read one. When you are replacing an old roof window, a current unit from the same maker often drops into the existing opening, and another maker's unit may need a slightly different opening, which we measure and show on the quote.

Our answer on how VELUX, FAKRO and Keylite compare goes into the makes in more depth, and the guide to replacing an old VELUX window covers like-for-like swaps against upgrades.

Lead time

Stock sizes and made-to-measure units

Lead time is the measure people forget until a builder asks when the unit will arrive. Standard sizes held by a maker or a merchant often arrive sooner; made-to-measure glass, unusual colours, triple glazing on some ranges and walk-on glass usually take longer. We write each option's lead time as the maker's typical range, stated as such, because the maker sets it and it can move. Our answer on how long skylights take to arrive explains what lies behind the ranges.

Price

What each step up costs

The price row is the last on every option, and the one that makes the others concrete. Moving from double to triple glazing, from fixed to electric, or from a flat rooflight to a lantern each adds to the fitted price; seeing the figures next to each other lets you decide whether the step is worth it for your room. Parts of the job that stay the same for every option, such as access and the inside finish, are shown once, so you can see that the unit is what moves.

Our guide to what shapes skylight and rooflight costs explains each driver in more detail, from size and glass to scaffold and Building Control, without inventing prices that would not fit your roof.

A worked example

Three options for a loft bedroom

Here is how a quote might look for a new roof window in the rear slope of a loft bedroom with a tiled roof. The options and their details depend on the roof we find; the format is the same on every job.

In a room like this we might pick option B, because a top-hung window lets you stand at the open frame and the triple glazing suits a bedroom that faces north. If budget leads, option A gives the same light for less. If the house is in a conservation area, option C may suit the street better, and we check the position for the address; the council decides. Planning for a roof window usually falls under permitted development, subject to the conditions in our rooflight planning guide.

Choosing

Questions that settle a choice

• Will you open it? If the room has a window or door nearby, a fixed unit may give you everything you need for less.
• Can you reach it? A window set high in the slope suits a top-hung window with its handle at the bottom, and one out of reach suits an electric opener.
• Which way does it face? Glass that takes the afternoon sun is where solar control earns its cost.
• When is the build booked? If the date is fixed, the option with the shorter typical range may suit.
• What does the room need to look like? A lantern changes the feel of a room; a flat rooflight keeps the ceiling calm.

• Five measures for every option
• More than one maker where the roof allows
• Our pick, with the reason

Whichever you choose, we fit it to current Building Regulations, handle the Building Control notification where the work is notifiable, and back it with our 10-year workmanship guarantee plus the maker's own warranty on the unit. Book a free survey and we can set your options out side by side.