Choosing between the major roof window brands

Range and availability

The largest manufacturer has the widest size range and by far the best parts availability. That matters twice: when matching an existing opening, and in fifteen years when a seal or a handle needs replacing.

Smaller manufacturers make good windows and hold fewer sizes, and parts for a discontinued model can be difficult a decade later.

Flashing systems

The genuinely important difference. A mature flashing system has kits for every covering and profile, combination kits for multiples, low pitch kits, and recessed options.

A narrower system may not have a kit for your covering, and that is when installers improvise. Improvised flashing is the source of most of the leaks in this trade.

Price

Mid range manufacturers are typically meaningfully cheaper for a comparable specification, which on a job fitting four windows is real money.

Compare like for like: glazing specification, frame material, and whether the flashing kit is included, because it often is not.

Where we would spend more

On a replacement, where matching an existing opening is the whole problem, range wins. On a window you expect to keep for thirty years, parts availability wins. On a coastal property, coating specification matters more than brand.

Where we would not

On a garage, an outbuilding or a utility space, a mid range unit correctly flashed is entirely sensible.

What actually decides the outcome

The right flashing kit for the covering, the underlay collar fitted properly, the insulation collar not omitted, and the opening trimmed correctly. Get those right with any decent window and it will be fine. Get them wrong with the best window made and it will leak.

The honest starting point

Every mainstream manufacturer makes a competent roof window. The differences between the major brands are real and they are smaller than most people expect, and they are far smaller than the difference between a well installed window and a badly installed one.

Almost every rooflight problem we are called to is an installation problem rather than a product one. The name on the frame has very little to do with whether the window leaks.

So the useful question is not which brand is best, but which brand suits this particular job, and there are five things that genuinely differentiate them.

1. Size ranges and continuity

The one that matters most on a replacement.

Manufacturers work to their own size codes, and those codes describe the structural opening rather than the glass. Ranges are revised every decade or so, and a size discontinued by one maker may still be current with another.

Where you are replacing an obsolete unit and the opening is genuinely awkward to alter, tight against a purlin, a steel, a party wall or a historic timber, the brand that still makes that dimension is the right brand, whatever your preference otherwise.

A manufacturer that has kept its size codes stable over decades also makes life easier in twenty five years, which is worth something on a window you are buying now.

2. Accessory ecosystems

A genuine practical advantage and one people underrate.

Some ranges have extensive clip in blind options: blackout with side channels, pleated, venetian, external awnings, all matched to the model and size code, fitting exactly and going on without tools.

Those cost far less than a made to measure blind fitted to a plaster reveal, and a blackout blind in side channels genuinely blacks out where a reveal fitted one leaks light at the edges.

If blinds matter in the rooms you are glazing, particularly bedrooms, the accessory range is a legitimate reason to choose one manufacturer over another.

3. Availability and lead times

Stock sizes held in the country arrive in days. A specialist product arrives in weeks.

On a job with a fixed date, a builder’s programme or a room that needs to be usable, that is decisive, and it is worth asking rather than assuming.

Where a stock size from one maker can be delivered next week and a made to measure unit from another arrives after the date you need, the first one is the better window for that job.

4. Specialist capability

Where the field narrows considerably.

Conservation rooflights, walk on glazing, very large bespoke units and lanterns all come from a smaller number of suppliers, and there the choice is about capability rather than preference.

On a listed building, the question is which manufacturer makes a unit with the profile, proportion, glazing bar and finish that will be consented, and whether they make it in the size the historic timber leaves available.

Several mainstream makers now offer conservation variants within their own ranges, which brings the accessory and size advantages with them. Whether one satisfies a particular officer is a question for that officer, and it is worth putting in a pre application conversation with the product named.

5. Mechanism and detail

The differences you notice in use rather than on paper.

How the handle feels. Whether a centre pivot unit locks positively in the cleaning position. Whether a dual action design is offered, opening top hung for use and pivoting for cleaning, which on a high level window with an escape duty removes a real trade off.

Whether the ventilation flap and filter are easy to get at, because a filter that is awkward to reach is a filter that never gets cleaned.

None of that shows in a specification comparison and all of it shows over twenty five years.

What does not differentiate them much

Thermal performance. Any current double glazed unit with a low emissivity coating, argon fill and a warm edge spacer lands at 1.2 to 1.4 whole unit. The spread between reputable makers is small, and it is dwarfed by whether the kerb was insulated or the insulation collar fitted.

Weathering, provided the right kit is used. Every manufacturer makes flashing kits matched to slate, profiled tile and pantile. What matters is that the correct profile is specified and fitted, not whose name is on it.

Longevity. Sealed units last fifteen to twenty five years across the board, because they are all doing the same job in the same conditions.

What actually determines the outcome

Five things, none of them about the brand.

The right flashing kit for your covering, specified by name and part number.

The underlay collar dressed and lapped so the roof membrane drains around the opening rather than into it.

The covering reinstated over the flashing, never under it.

The frame set square in both directions, so the sash closes evenly for twenty five years.

And the insulation collar fitted, so the reveal does not run cold enough to condense.

Get those right and almost any decent unit will run for twenty five years. Get any of them wrong and the best window on the market will leak.

How we specify

By what the job needs rather than by a standing preference.

On a listed building, a manufacturer whose conservation product will be consented. On an obsolete opening, whichever maker still offers that dimension. On a stock replacement, usually matching what is already there, because the opening and the accessories are already sized for it. On a bedroom where blackout matters, a range with a good clip in blind system.

The quotation names the manufacturer, model and size code so you know exactly what you are buying, and you are welcome to ask why that one. Where the answer is that another brand would suit better for a reason we have not thought of, we would rather hear it.

The questions worth asking instead

Which flashing kit, by name, for my covering. Whether the insulation collar is included. What the whole unit U-value is rather than centre pane. What the workmanship guarantee covers and for how long. And who handles a manufacturer’s warranty claim if the unit fails.

Those five tell you more about how the installation will perform than any brand comparison will.

The comparison that reorders shortlists

Ask every manufacturer for the same five figures, at the actual size you are buying, and put them side by side.

Whole unit U value. Not centre pane. The gap between the two varies by manufacturer and widens as the unit gets smaller, so a brand that looks best on centre pane may not be best on the number that describes reality.

The g value, which tells you about summer comfort as well as winter gain.

Spacer type. Warm edge or aluminium, stated plainly.

Warranty terms, and specifically what is covered on the sealed unit as distinct from the frame, whether labour is included, and whether the cover survives if you fit it yourself.

Whether your size is a stock size in that range, which decides lead time and the cost of every accessory for the next twenty five years.

The consideration that outlasts the specification

Accessory availability over the life of the window.

Blinds, flashing kits and insulation collars are all range and size specific. A well established manufacturer with wide distribution means those parts will still be obtainable in fifteen years when you need a new blind or a replacement flashing.

On a smaller or newer brand that is a genuine risk, and it is a stronger argument than any single performance figure.

The same applies to actuators on powered units. A motor from a discontinued proprietary system can be very difficult to source.

Consistency on one roof

Where several windows are visible together from the same room, buy them from the same range.

Frame proportions, sash depth within the frame, handle position and the way the lining meets the plaster all differ between manufacturers. From the ground that is usually invisible. From inside the room it is noticed every day.

What not to decide on

Headline claims without the underlying number. Any manufacturer can quote an impressive centre pane figure.

And price alone, where the cheaper unit is a basic specification. The access is being paid for once, and the difference between a basic sealed unit and a well specified one is small against the total cost of the job.

The practical shortlist

Establish which manufacturers hold your size as stock. Compare the five figures at that size. Check accessory availability. Then choose, and record the model designation and size code with the house paperwork.

Availability through the trade

A consideration that does not appear in any comparison table and matters on the day.

Widely distributed ranges are held by local merchants, which means a damaged component or a wrong item can be replaced within days rather than weeks.

A specialist product from a smaller manufacturer may be excellent and may also mean a fitter waiting a fortnight for a replacement gasket with the roof already open.

Ask what your installer actually fits regularly. Familiarity with a system produces better work than reading the instructions on the day.

The twenty five year view

Whatever you buy, you or somebody else will replace the sealed unit in fifteen to twenty five years, and want a blind before that.

Both of those depend on the manufacturer still existing, still supporting the range, and still holding the size.

That argues for a mainstream manufacturer on anything you intend to keep, and it is a stronger practical argument than a marginal difference in a published U value.

Recording the choice

Manufacturer, model designation, size code, finish and glazing specification, with the house paperwork.

It turns the next replacement from a survey into a phone call.