Guide · VELUX Window Installation
Roof window blinds and when to specify them
Specify the blind when you order the window. Not because it is cheaper as a package, though it usually is, but because the parts that make a roof blind work sit inside the sash, and a window that arrives without the provision for them narrows what can be fitted afterwards.
A blind on a roof window has a harder job than a blind on a wall. It hangs on a plane that is somewhere between vertical and horizontal, so gravity pulls it away from the glass rather than against it, and it sits on the surface of the house that collects the most solar energy. This page covers the families of blind available, what each is actually for, how they are held to the glass, and the decisions that have to be made before the unit is ordered rather than after. The wider job is described on VELUX window installation.
Why a roof blind is built differently
Hang a fabric from a roller on a thirty degree slope and it will bow away from the glass within a few centimetres. Open the window and it swings. Add a warm afternoon and the fabric moves with the air.
The answer used by every serious maker is a pair of side channels running down the sash, with the fabric held in them along both edges. The blind then stays flat against the glass at any angle, moves in a controlled line, and holds position wherever it is stopped. Those channels are the reason roof blinds cost more than the equivalent wall blind, and they are the part that has to be planned for.
The provision inside the sash, and why it is ordered early
Modern roof windows carry pre-drilled fixing points, and in many cases a top cover profile, designed to take the maker’s own blind range. Where the window is ordered with the blind, the parts land together and the fitting is a fifteen minute job at handover.
Where the window has already been installed, the blind is still fittable in most cases, but the range narrows to what suits the fixing points that exist. Mixing a blind from one maker onto another maker’s sash is where the awkwardness starts, because the channels, the top cover and the pre-drilled positions are all proprietary.
The blind decision belongs on the order form with the window, not on the snagging list at the end.
The families available, and what each is for
There are five, and they solve different problems. Pleated blinds diffuse light without stopping it. Roller blinds in a light fabric cut glare. Blackout blinds in an opaque fabric with a coated backing stop light. Venetian blinds direct light and give a degree of control over where it lands. External awning blinds intercept solar energy before it reaches the glass at all.
Most rooms need one of the five, some need two working together, and specifying three because they were on the price list is how the top of a sash ends up crowded.
Pleated blinds, and the light they leave behind
A pleated blind is a concertina of translucent fabric that stacks into a slim head when it is raised. Down, it turns a hard rectangle of sunlight into an even wash across the room, which is what you want over a dining table, in a study, or anywhere a hard-edged bright shape on the floor is the actual complaint.
Because they stack tightly, a pleated blind clears the glass almost completely when it is up. Many are made to run in two directions on the same sash, so the shaded part can be moved to the top or the bottom of the window as the sun moves across the slope through the day.
Roller blinds, and what the fabric weight changes
A roller blind in a light fabric is the ordinary answer for a bedroom that does not need full darkness or a landing that wants softening. The fabric rolls onto a tube at the head, the side channels keep it flat, and a bar at the bottom holds it down.
Fabric weight is the specification that matters. Too light and the blind lifts off the channels when the window is open on a breezy day. Too heavy and it does not roll cleanly on a small tube. Makers publish a shading factor and a light transmission figure for each fabric, and those two numbers tell you more than the colour name attached to them.
Blackout fabrics, and where the demand comes from
A blackout blind uses an opaque fabric with a reflective coating on the outer face, run in channels tight enough that light does not spill down the sides. Fitted properly the room goes genuinely dark, which matters on an east-facing slope in June.
Bedrooms are where this is usually specified, and the detail of getting a loft bedroom dark, including what to do about the light gap at the head, is covered on roof windows in a bedroom and blackout. Elsewhere in a house a blackout fabric is also the right call for a room with a projector or a television on the wall opposite the slope.
Venetian blinds, and the control they give
An aluminium venetian in a roof window is the least common choice and the most useful in one specific situation: a room where you want daylight but not a view of the sky, or where light needs bouncing onto a ceiling rather than a floor.
The slats tilt as well as raise, so the blind sets the direction of the light rather than just the quantity. They work well in a home office where screen glare is the problem and full shading would mean turning a lamp on. They are noisier than fabric in a draught, and they collect dust on a horizontal-ish plane, which is worth knowing before choosing one for a high window.
External awning blinds, and why outside beats inside
Any internal blind stops light after it has passed through the glass, which means the solar energy is already in the room and the blind is warming up. An external awning blind is a mesh fabric held on the outside face, and it intercepts that energy before it arrives.
The difference in a south or west-facing slope in July is not marginal. An external mesh cuts a large share of the solar gain while still letting you see out through it, which internal blackout fabric cannot do. They are usually solar or electrically operated, because reaching an external blind by hand on a roof is not a daily proposition. On an exposed slope they are retracted in high wind, and better units do that automatically.
| Blind type | Primary job | Where it earns its place |
|---|---|---|
| Pleated | Diffuse and soften | Kitchens, studies, dining spaces |
| Roller, light fabric | Cut glare | Landings, living rooms |
| Blackout roller | Stop light | Bedrooms, media rooms |
| Venetian | Direct light | Home offices, screen glare |
| External awning | Stop heat before the glass | South and west slopes |
Shading against solar control glass
These are two different tools and they are not interchangeable. Solar control glass reduces gain permanently, all year, including in February when the gain would have been welcome. A blind reduces gain only when you deploy it.
The sensible pairing depends on the slope. On a north-facing plane, neutral glass and an internal blind for privacy or darkness is usually enough. On a south or west-facing plane, solar control glass carries the baseline and an external awning handles the peak. Specifying both a strong solar coating and heavy shading on a north slope gives a room that needs the lights on at noon. The glazing side of this is set out on energy efficient rooflights.
Steam, moisture and the fabrics that cope with it
A roof window over a shower, a bath or a hob sits in air that carries a lot of water. Standard blind fabrics absorb it, and a fabric that is repeatedly damp holds marks and eventually smells.
The specification for those rooms is a fabric with a moisture-resistant coating, or an aluminium venetian, which is unbothered by humidity and wipes clean. The other habit worth building is running the window’s ventilation flap while the room is in use, so the moist air leaves rather than condensing on the cold surface behind the blind. The flap arrangement is described on roof window ventilation flaps and filters.
Reaching it: hand, rod, motor or solar
Four ways to operate a roof blind, and the choice is mostly about height. A blind on a window whose bottom rail is at shoulder height is operated by hand, and that is the cheapest and most reliable arrangement there is.
Above about two metres, a telescopic rod hooks into an eye on the bottom bar. It works, and it becomes tiresome faster than people expect. Above two and a half metres, or on any window in a vaulted ceiling, a motorised blind is the honest answer. Mains-powered units want a cable at first fix; solar units carry a small panel and a battery on the sash and need no wiring at all, which is what makes them the usual retrofit answer.
Blinds on a motorised window
Where the window itself is electrically operated, the blind normally runs on the same control system and the same remote or app. That is worth setting up as one package rather than two, because two unrelated handsets for one window is an irritation that never goes away.
It also opens up sequencing: the blind closing at a set time, or on a temperature trigger, before the room has warmed up. On a west-facing slope over a living space, a blind that shuts itself at two in the afternoon in August does more for comfort than any amount of opening the window at six.
Fitting one to a window already in the roof
Retrofitting is normal and usually straightforward. The blind is matched to the window by its size code, the top cover is lifted, brackets go onto the existing fixing points and the side channels screw to the sash. On a modern unit it takes minutes.
Two situations complicate it. A window from a different maker to the blind, where the fixing points do not line up and a universal fitting kit is the compromise. And a window old enough that the range it belonged to has moved on, where the sash geometry has changed and current blinds do not match. In the second case the honest options are a universal blind or a new unit, and if the glass is also past its working life the second is often the better spend.
Measuring and ordering without getting it wrong
Roof blinds are ordered against the window’s size code rather than by measuring the glass, because the code fixes the sash dimensions exactly. Read the code off the data plate on the top bar of the sash, visible when the window is opened, and give it whole.
Where the plate is missing on an older unit, the outer frame is measured and matched against the maker’s chart. The coding system is explained on roof window sizes and how they are coded. What does not work is measuring the visible glass and ordering to that figure, because the channels sit outside it on the sash.
Two blinds on one window, and when that earns its place
Some sashes will carry two internal blinds at once, typically a pleated diffusing blind and a blackout roller, each in its own set of channels with a shared top cover. It is a real option and it is specified more often than it is needed.
Where it does earn its place is a room with two conflicting jobs. A loft bedroom that doubles as a study wants soft even light at eleven in the morning and complete darkness at eleven at night, and no single fabric does both. Where it does not earn its place is a room with one use, because the second blind adds cost, adds depth at the head of the sash, and takes a little more glass out of the view. Decide by listing what the room does at three different times of day.
Living with them, year to year
Fabric blinds want a light vacuum with a brush head once or twice a year and a damp cloth on any marks. The side channels collect dust and the occasional insect, and a wipe down the channel keeps the fabric running without dragging.
The parts that eventually wear are the small ones: a cord, a spring in the tube, a clip on a bottom bar. Those are available individually for current ranges, so a blind that has stopped holding position rarely means a new blind. What shortens a blind’s life more than anything is running it against a channel full of grit, which is a two minute job to prevent.
Keep reading
More on velux window installation
Roof window escape openings and the rules
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 →Roof window cill height and the view out
Read the guide →
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