Guide · VELUX Window Installation
Choosing between the major roof window brands
Four manufacturers supply almost every roof window fitted in a British roof: VELUX, Fakro, Keylite and Roto. They build to the same standards, they weather the same way, and a well fitted unit from any of them will still be dry in fifteen years. The differences that matter are in accessory ranges, what comes in the box, stock depth in the UK and how the sizes are coded.
Sunspire fits all four. What follows is how they actually differ on a job, which differences are worth paying for, and what tends to decide it once a survey has looked at the roof.
The four names you will actually be choosing between
VELUX is Danish, has been making roof windows since the nineteen forties and is the reference product against which the others position themselves. Fakro is Polish, the second largest manufacturer globally, and has built its position on range breadth and a strong price. Keylite is Northern Irish and sells on including as standard what others charge for. Roto is German, with a long history in window hardware, and its roof window range reflects that engineering focus.
There are other names in the market, mostly rebadged or aimed at the trade shed. The four above are the ones with UK stock networks, published technical data and accessory ranges you can still buy from in a decade.
What is genuinely common to all four
More than the marketing suggests. All four build a laminated timber core, offer a white polyurethane version of the same section, glaze with a low emissivity coated double unit filled with argon as standard, and hang the sash on a pivot or a top hinge with a comparable set of catches.
All four publish whole window U-values tested to the same standard, so the numbers can be compared directly. All four supply a flashing kit specific to the roof covering, an insulation collar and an underlay collar. All four CE and UKCA mark their products. If you put four units of the same size and glazing side by side in a slope, most people could not tell you which was which from the garden.
Where the differences are real rather than marketing
Five places, in rough order of how much they affect a job. The size grid and its codes, because it determines what fits between your rafters. What arrives in the box, because it changes the comparison between quotes. The accessory range, because a blind is bought years later. Stock depth in the UK, because it sets the programme. And the glazing options at the top of each range, because that is where they diverge most.
Everything else, the frame timber, the hinge design, the gasket profile, is a matter of small preferences rather than outcomes.
VELUX, and the position it holds
VELUX has the deepest UK distribution and the largest accessory catalogue by a wide margin, and that is its practical advantage rather than any claim about the window itself. Blinds, awnings, motor kits, control systems, flashings for unusual coverings and combination kits are all held in stock across the country.
The size codes, the letter and number pairs like MK04 and CK02, have become the informal standard the whole trade quotes in, and even installers fitting other brands will describe an opening in VELUX terms. The range runs from basic manual units to triple glazed, solar powered and integrated smart home control. It is generally the most expensive of the four for an equivalent unit, and generally the easiest to get by Thursday.
Fakro, and what its range is built around
Fakro competes on breadth and price. The catalogue includes shapes and configurations the others do not carry: very large units, balcony windows where the sash opens into a rail, units with a lower fixed light extending the glass down the slope, and a good range of loft ladders and hatches from the same manufacturer.
The construction is sound and the technical documentation is thorough. Its centre pivot units use a pivot point set higher in the frame on some models, which is a genuine ergonomic difference on a low set window. Where a project wants an unusual configuration, Fakro is frequently the only one of the four that makes it as a standard product rather than as a special.
Keylite, and the parts included in the box
Keylite’s proposition is that the items other manufacturers sell as extras arrive with the window. In practice that has meant an insulating collar fitted around the frame at the factory, and a flashing supplied as part of the package rather than ordered separately.
That changes how quotes compare. A Keylite unit priced against a VELUX unit is not a like for like comparison unless the collar and the flashing have been added to the other side of the sum, and once they are the gap narrows or reverses. The factory fitted collar also removes a site operation and the chance of it being done badly, which is worth something on a job where the thermal detail around the frame is being taken seriously.
Roto, and the engineering behind its frames
Roto came to roof windows from window hardware, and it shows in the mechanisms. Its pivot arrangements and multi point catches are well engineered, and its frames include options with a pivot bar set high in the sash so the window can be operated comfortably from a low cill.
UK distribution is thinner than the other three and the accessory range is smaller, so it appears less often on domestic jobs. Where it earns specification is a project with a particular operating requirement, or a specifier who has worked with the hardware before and wants it again.
Sizes across brands, and why they do not swap
Each manufacturer runs its own grid of external frame sizes and its own coding for them, and while the common widths cluster around similar figures the exact dimensions differ by tens of millimetres. A structural opening formed for one brand’s unit is not automatically right for another’s.
This matters most on replacement, where an existing opening was cut for a unit made thirty years ago. How the codes are read, which number is the frame and which is the opening, and how to measure what you already have is set out on our page about roof window sizes and how they are coded. The rule for brand choice is simply that the brand is fixed before the opening is cut, not after.
Flashing kits, and the brand you are committed to
The flashing kit is made for the window it flashes. Frame sections differ, so the apron, the side sections and the head all mate to a specific profile, and a kit from one manufacturer will not weather another’s frame properly.
That is the real lock in. The window and its kit are bought together, and the kit is then chosen by what is on the roof: plain tile, profiled concrete tile, slate or a low profile pantile all take different kits, as set out on our page on flashing kits by roof covering. Every one of the four makes kits for every common British covering, so this narrows nothing at brand level. It simply means the decision is made once.
| VELUX | Fakro | Keylite | Roto | |
|---|---|---|---|---|
| UK stock depth | Deepest | Good | Good | Limited |
| Accessory range | Very wide | Wide | Moderate | Narrower |
| Included in box | Window, collars | Window, collars | Collar and flashing | Window, collars |
| Unusual configurations | Some | Widest choice | Core sizes | Core sizes |
| Typical unit price | Highest | Keenest | Competitive as a package | Mid to high |
Blinds, accessories and the system you buy into
A blind is usually bought after the window, sometimes years after, and it has to be the manufacturer’s own because it clips into brackets moulded into that frame. So the accessory range you are choosing is the one you will still be shopping from in 2035.
This is where VELUX is hardest to argue with. Blackout, pleated, venetian, roller, awning and solar variants exist for essentially every unit in the range and are stocked. Fakro’s range is broad and available. Keylite and Roto cover the main types. If a household is likely to want a specific blind in a specific fabric later, it is worth checking that it exists for the frame before the frame is ordered.
Spares and availability over a twenty year life
Roof windows outlive the range they belonged to. A handle, a hinge, a gasket or a sealed unit may be wanted in 2040 for a window fitted next month, and the question is whether the manufacturer will still supply it.
All four have a record of supporting older ranges, VELUX conspicuously so: components for units going back decades are still obtainable and the data plate inside the sash identifies exactly what you have. That is a genuine argument for the more expensive unit on a house somebody intends to stay in.
Warranty structure, and what to read before ordering
Warranties on roof windows are layered rather than single. There is typically one period for the window and its flashing, a shorter one for electrical components and motors, and a shorter one again for blinds and accessories. The lengths differ between manufacturers and they change from time to time, so the current published terms are the ones to read rather than anything quoted from memory.
Two conditions appear in all of them: the window has to be installed to the manufacturer’s instructions, and the flashing has to be the correct kit for the covering. Both are installation matters rather than product matters, which is why Sunspire’s own ten year workmanship guarantee sits alongside the product warranty and covers the part the manufacturer’s does not.
Compare quotes by what arrives on site, not by the price of the window, because a collar and a flashing on one line and not the other will swing a comparison by more than the brand does.
Glazing ranges, and how far each goes
The base specification across all four is a double glazed unit with a low emissivity coating and argon fill, toughened outer, laminated inner, giving a whole window U-value in the region of 1.2 to 1.4 W/m²K depending on size.
Above that the ranges diverge. All four offer triple glazing. VELUX and Fakro both carry solar control coatings, acoustic laminated interlayers and anti dew outer coatings across most of their sizes. The top specifications get down towards 0.9 W/m²K and below, at a weight penalty that affects handling and sometimes the structure. On a south or west facing Essex slope the solar control option is generally the more valuable upgrade of the two, because summer overheating under a roof is a bigger practical problem than winter heat loss through a modern unit.
Electric and solar options across the four
All four offer factory fitted electric units and retrofit motor kits. All four offer a solar powered version with a small photovoltaic panel on the sash head, which is the answer for an existing conversion where a cable would mean lifting a finished ceiling.
The differences are in control. VELUX has the most developed system, with room controls, rain sensors, integration with its blinds and app control as standard on current products. Fakro has a capable equivalent. Where a household wants several units, blinds and windows all acting together on a schedule, the depth of the control system is the deciding factor, and that is set out on our electric rooflight page.
Lead times, stock depth and the programme
On a common size in a common specification, all four are obtainable within days. The gap opens on anything less common: a larger unit, a solar control glazing option, a triple glazed unit or an unusual flashing.
VELUX generally recovers fastest because more of the range sits in UK stock. Fakro and Keylite are reliable on core sizes and can take longer on specials. Roto more often comes to order. Where a job has a fixed date, because a plasterer is booked or a scaffold is up on hire, the brand with stock is worth more than the brand with a slightly better catalogue number.
Matching an existing window already in the slope
Where one unit on a rear elevation has reached the end of its life and another has not, matching becomes the deciding factor and it overrides most of the above.
Frame sections, external cladding colour and the sightline of the sash all read from the garden, and a mismatched pair on the same slope is obvious. The data plate inside the sash of the old unit gives the manufacturer, the model and often the year, which is the starting point. Sometimes the honest answer is to change both, because a single new unit next to a twenty five year old one draws attention to the older one rather than blending with it.
What actually settles the choice on an Essex roof
In practice it comes down to three things. What the roof will take, since a trussed roof on the Great Notley or Beaulieu Park estates caps the width and only some ranges have a unit narrow enough with the glazing you want. What the programme allows, since stock beats specification on a job with a scaffold on hire. And what is already on the house, since matching an existing unit on the same slope is worth more than any specification argument.
Below all of that, the four are close enough that installation quality decides the outcome. The upstand and trimming, the underlay collar dressed correctly, the flashing lapped in the right order and the insulation collar closed around the frame are what keep the room dry and warm, and they are the same four details whichever badge is on the sash. That is the part covered by the workmanship guarantee on every VELUX installation we carry out, and on every Fakro, Keylite and Roto one as well.
Keep reading
More on velux window installation
Roof window escape openings and the rules
Read the guide →Roof window blinds and when to specify them
Read the guide →Roof window flashing kits by roof covering
Read the guide →Roof window sizes and how they are coded
Read the guide →Roof window ventilation flaps and filters
Read the guide →
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