Velux Blackout Blinds: Fitting Full Darkness to a Roof Window

Velux blackout blinds fit inside the frame of a roof window and run in side channels that trap light at the edges, delivering true darkness rather than a dim glow. The single thing that decides fit is the size and type code stamped on the window itself, and getting that code right matters more than the fabric you choose.

[toc]

Most guides skip straight to fabric and never tell you where to look for that code. This article starts with the plate on the frame, then explains why the side channels, not the cloth, are what actually gives you full darkness in a room lit from directly overhead. Velux is a brand name for roof windows, and blackout blinds are made to suit those frames as well as other roof-window makes.

Key Takeaways

• The code decides everything: the size and type code on the frame plate is what tells you which blind fits; measuring alone is not enough for a roof window.

• Channels beat fabric for darkness: velux blackout blinds are only as dark as their side channels, because a flat blind leaks light down both edges.

• Find the plate before you buy: the code sits on the top of the sash, usually visible when the window is swung open.

• Overhead light is relentless: a roof window faces the sky directly, so any edge gap shows far more than it would on a vertical window.

• Thermal and blackout overlap: a channelled blackout blind also cuts heat loss and summer glare, so the darkness upgrade earns its keep year round.

Why the size code decides the fit

A roof window is not a standard rectangle you can simply measure and order. Each one is built to a set size and type, and the blind is engineered to clip into that exact frame. Order by guesswork and the side channels will not line up, which is the fastest way to end up with light leaking down the edges.

The code is a short string of letters and numbers that names both the model type and the size. It tells the supplier which bracket positions to expect and how long the channels need to be. Once you have it, ordering becomes precise rather than hopeful, which is exactly what you want for a blind that has to seal all four edges.

This is where velux blackout blinds differ from a normal window blind. On a vertical window you can fudge a few millimetres; on a roof window the frame does the locating, so the code is the whole game. If your window is an unusual shape or age, our guide on choosing blinds for skylights and odd-shaped windows walks through the trickier cases.

Where the code plate sits and how to read it

Open the window and look at the top edge of the sash, the part that swings. On most roof windows there is a small metal or printed plate there, tucked along the head of the frame, and it stays hidden until you rotate the sash open. That plate carries the code.

Read it in two halves. The first group of characters names the window type, and the following group names the size, usually a letter and number pairing that maps to a fixed width and height. Write the whole code down exactly as it appears, including any spaces, because a single wrong character points you at the wrong blind.

If the plate has faded, you can measure the pane and the frame as a cross-check, but treat the code as the primary source whenever it is legible. For velux blackout blinds the code is faster and safer than a tape measure, and it removes the edge-gap risk that plagues skylight blinds ordered on measurements alone.

Why side channels deliver darkness, not fabric

Here is the point almost every article misses. Blackout fabric blocks light passing through the cloth, but it does nothing about the two strips of daylight that pour down the sides of a flat blind. On a vertical window you might tolerate that. On a roof window, with the sky directly above, those strips light the whole room.

Side channels are the answer. They are slim tracks that run down each edge of the window and capture the side of the blind as it travels, closing the gap the fabric cannot reach. This is the mechanism that turns a merely dark blind into a genuinely dark one, and it is the reason channelled skylight blackout blinds cost more than a plain pull-down.

So when you compare products, look past the fabric name and check how the edges are sealed. A premium cloth in an unchannelled frame still leaks; a modest cloth in good channels performs. Our blackout blinds range is built around that edge-sealing principle rather than fabric alone.

Choosing the fabric once the fit is sorted

With the code found and the channels understood, fabric is the enjoyable part. Blackout cloth comes in a spread of colours and weights, and on a roof window the colour you see most is the reverse, since you look up at the back of the blind from below. A pale reverse keeps a small loft room feeling lighter when the blind is down for a nap.

Weight and structure matter for more than darkness. A honeycomb construction traps a layer of air across the pane, which is why our honeycomb blackout blind does double duty as insulation and as a light block. Under a roof that bakes in summer and bleeds heat in winter, that trapped-air layer is a practical gain.

If your main worry is temperature rather than sleep, weigh the fabric choice against dedicated thermal blind fabrics too. Many households want both, and a channelled blackout in a honeycomb weave gives you darkness and insulation from a single blind rather than layering two.

Fitting the blind so the darkness holds

Fitting a roof-window blind is a bracket-and-channel job, and the order of operations decides how dark the result is. You fix the top brackets first, clip in the headrail, then run the side channels down each edge so they catch the blind for its full travel. Skip or misalign the channels and you undo the whole point.

Take your time squaring the channels to the frame. If they sit even a couple of millimetres proud or twisted, the blind either binds as it moves or leaves a hairline of light down one side. On velux blackout blinds this is the single most common fitting fault, and it is entirely avoidable with a level and a steady hand.

Check the seal at the bottom too. A well-fitted blind meets the base of the window with the fabric held inside the channels the whole way down, so there is no triangle of light at the sill. Test it in daylight before you consider the job finished, because a night check hides exactly the gaps you are trying to close.

Flat roof skylights and awkward openings

Not every overhead window is a pitched roof window. Flat roof skylights sit horizontally and often use a different frame and blind mount, so the same code-first logic applies but the fixing detail changes. Check what the manufacturer specifies for the flat unit rather than assuming a pitched-window blind will transfer.

For flat roof skylight blinds, the darkness challenge is the same and if anything sharper, because a horizontal pane catches the midday sky head on. Channels still do the sealing work, and a blackout or honeycomb cloth still does the blocking, but you may need a tensioned or cassette system suited to the horizontal run.

Whatever the shape, the principle holds across all blinds for velux windows and their flat-roof cousins: find the code or the exact frame spec, seal the edges with channels, then choose the fabric last. Get that sequence right and the odd shape stops being a problem, so browse the full skylight blind range with your window code to hand and match the channels to your exact frame.

Frequently asked questions

How do you fit velux blinds?

You fit them to the window frame using the supplied top brackets, then clip the headrail into place and run the side channels down each edge of the sash. Fix the brackets square, seat the headrail level, then align the channels so they capture the blind along its full travel. Test the blind in daylight to confirm the edges seal with no light strip down either side. Working slowly on the channel alignment is what separates a dark result from a leaky one.

How do you measure for velux blinds?

Start with the size and type code on the plate at the top of the sash, since that is the reliable way to identify the blind. If the code is missing or faded, measure the visible glass and the frame as a cross-check, following the manufacturer's stated points. Always treat the code as the primary source, because roof-window blinds are made to fit specific frame sizes rather than cut to a free measurement. Note the code exactly, spaces and all.

Do velux windows come with blinds?

Roof windows are usually supplied as the window unit only, with blinds sold separately so you can pick the light control you want. That means a new window rarely arrives with a blackout blind fitted. When you buy the blind afterwards, use the frame code to match it precisely, and choose a channelled blackout option if full darkness is the goal, since the channels rather than the glazing are what block edge light.