Vertical Blind Slats Replacement: Measuring, Matching and Fitting

A vertical blind is a headrail with a row of carriers running along it. Inside the headrail, a long shaft turns every carrier at once when you twist the wand or pull the bead chain, which rotates the vanes from edge-on to closed; a government master specification from Alberta describes the bead chain turning all louvres together through a full 180 degrees. A separate cord or the wand draws the carriers along the rail, so the vanes stack at one side or split to both.

The carriers are linked by small spacer links that set the gap between vanes as they draw across. The US Unified Facilities Guide Specification for window blinds notes that the length of these links is related to the louvre width, so vanes are evenly spaced and overlap properly when closed. That is the first reason replacements must be the same width as the originals.

At the bottom, each fabric vane carries a weight in a pocket or clipped on, and a light chain often links the weights so the vanes move together and do not twist apart in a breeze. Knowing these parts makes it much easier to see what has actually failed: the vane, the carrier, the chain, or the mechanism. You can turn the vanes on a virtual window in our vertical blinds simulator to see the movement before you take anything apart.

Start with the width, because it has to match exactly. Lay a vane flat and measure straight across. The width most commonly specified is about 3½ inches, roughly 89 to 90 mm; the US federal specification describes 90 mm (3½ in) as the usual choice and 50 mm (2 in) as an alternative for smaller windows. Wider vanes are also made. Do not assume: measure your own, because a vane a few millimetres wider or narrower will not overlap its neighbours correctly when the blind closes.

Then measure the drop. Take down an undamaged vane from the same blind and measure its full length, from the top edge of the vane to the bottom, including any stiffened top section with the hanging hole and any bottom pocket. Measure two or three vanes, not one, because fabric vanes can stretch or shrink a little over years in humid air, and the blind was made with a small clearance above the floor or sill that you want to keep.

Finally, note how the top attaches, as this decides which vanes will fit your carriers. Look at the hole or slot near the top of the vane, any plastic insert or hanger fixed to the vane, and how the weight at the bottom is held: in a sewn pocket, clipped on, or built into a PVC vane. Photograph the top and bottom of a vane beside a ruler; it saves guesswork when you order or ask us to match.

Vanes come in three main materials. Fabric vanes are woven polyester, usually stiffened so they hang flat. PVC vanes are rigid, wipe clean and ignore humidity, and are often embossed with a texture. Aluminium vanes are thin and metallic. Replacements should match the material first, because a PVC vane between fabric ones hangs and moves differently, catches the light differently and stands out from across the room.

Colour is the hard part. Vanes that have spent years in front of a bright window have faded or yellowed, so even a new vane in the original colour will not match exactly. Take an old vane with you, or send a clear daylight photograph next to a white sheet of paper, and compare samples against it in daylight rather than under a shop's lights. Match texture as closely as colour; an embossed PVC vane next to a smooth one is obvious even when the colours agree.

Then use placement to hide the difference. Put the new vanes where they are least visible: at the stack end that sits behind a curtain or a wall return, and move good old vanes into the most visible positions. If more than a handful need replacing, it is often better to replace the whole set of vanes and keep the headrail, so every vane matches and ages together.

Strong light does most of the damage. PVC breaks down under ultraviolet light: research on PVC photodegradation describes how UV exposure drives off hydrogen chloride from the polymer and leaves chains of conjugated double bonds, which absorb light and show as yellowing, while photo-oxidation weakens the material. Additives slow the process, which is why specifications for vertical blinds call for UV-stable or light-stable vinyl louvres. Without enough stabiliser, a white PVC vane facing the afternoon sun turns cream, then yellow, then cracks when it is bent.

Fabric vanes fade rather than crack, and their stiffening finish can break down so the vane curls or cups. Heat adds to it: vanes hanging close to west-facing glass take the low afternoon sun at full strength, and our guide to west-facing glare explains why that elevation is the hardest on any window covering. In the monsoon, humidity and still air let mildew spot fabric vanes that are left closed against damp glass for weeks.

So check where the damage is before replacing. If only the vanes nearest the door or the brightest pane have failed, replacing them makes sense. If every vane is brittle, new ones will fail the same way unless the window gets some protection: an external shade, a solar film, or a different blind for that opening.

On a sliding door in Goa, vertical blinds spend much of the year in a breeze, and the bottom weights and chain are what keep them in order. Each fabric vane needs its weight, so it hangs straight and drops back into line after a gust. The chain links the weights so the vanes rotate together and cannot wrap around each other. When a vane is replaced, the weight goes back in its pocket or clips on at the same height as its neighbours, and the chain is reconnected through it.

Hang the chain with the same slack between every pair of vanes, enough that the vanes can rotate fully without pulling on each other, but not so much that it droops in loops. Route it the same way on every vane, usually through the back of the weight or a clip at the bottom, so it does not show unevenly from the room. If the chain is rusty, replace it: a government blind specification calls for bead chains in nickel-plated brass or stainless steel, and near the sea a plated steel chain will rust and leave orange marks on pale vanes.

If vanes still swing and clatter after the weights and chain are sorted, the door may simply be open to too much wind for a vertical blind. Drawing the blind into its stack when the door is open helps, and the vertical blinds page covers stiffer PVC and aluminium vanes for breezy openings.

Vanes are the inexpensive, replaceable part. The headrail mechanism is not designed to be rebuilt in a living room, and some faults mean the blind has had its life. The commonest is failing carriers. They are moulded plastic, often nylon or acetal, and after years of sun through the glass and daily use their hooks and gears become brittle. One broken carrier can be swapped; when several are cracking, the rest are close behind.

Other signs: vanes that no longer all rotate together, which points to stripped gears or a worn tilt shaft; carriers that bunch up or spread unevenly when drawn, which means broken spacer links; a traverse cord that is frayed or has jumped its pulley; and a headrail that is bent, sagging between brackets or corroded at the ends. Any of these can sometimes be repaired, but on an older blind the cost and the risk of the next failure usually favour a new headrail with new vanes.

Child safety is a reason in its own right. The Royal Society for the Prevention of Accidents advises never fitting a blind with a looped cord or chain in a child's bedroom, using tidies, tensioners or cleats to secure cords and chains, with cleats at least 1.5 metres high, and notes that blinds installed before 2014 may lack built-in safety features. If your vertical blind has a loose looped chain and children in the house, replacing it with a wand-operated blind is a better use of money than new vanes.