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Choosing U Channel
Installation Guide
Which Glass Partition Channel Size Do I Need?
25mm, 30mm or 50mm — how to pick the right one for your opening, and how to calculate your glass sizes.
If you're fitting a glass partition yourself or ordering glass to go with our channel systems, you need to know which channel size to use. Get this wrong and your glass won't fit — or it'll rattle around with too much clearance.
There are three sizes to choose from: 25mm, 30mm and 50mm. They all work the same way, but the size you pick depends on how straight your opening is and how slimline you want the finished look.
Our Recommendation: Go With 30mm
For the vast majority of installations, 30mm channel is the one to use. It's still slimline enough to look neat, but it gives you that bit of extra tolerance — usually around 5mm — to deal with ceilings, floors and walls that aren't perfectly level. And let's be honest, they rarely are. It's what we include in all of our glass partition kits as standard.
The Three Channel Sizes
Each size gives a different amount of tolerance between the glass and the channel. Pick based on how true your opening is.
25mm
Ultra Slimline
The slimmest profile. Looks very neat and minimal, but only works well if your ceiling and floor are dead straight across the full width.
Leaves very little room for error — if your opening is even a few mm out, the glass may not slide in.
Best for: perfectly straight openings where you want the thinnest possible channel.
30mm
Recommended
The sweet spot. Still slimline enough to look good, but with enough tolerance to handle the minor variations you get in most buildings.
If your ceiling drops a couple of mm across the span, or the floor isn't dead flat, 30mm will handle it without any issues.
Best for: most installations. It's what we recommend unless you have a specific reason to go smaller or larger.
50mm
Maximum Tolerance
The most forgiving size. Use this if your opening is noticeably out of true — maybe an older building where the ceiling has a visible slope, or a floor that dips.
Also worth considering if you simply prefer the look of a chunkier channel profile.
Best for: openings that are significantly out of level, or if you prefer a more substantial frame look.
U Channel vs 2-Part Channel
You'll use both types in a typical installation. They serve different purposes depending on where they're fitted.
U Channel
Ceiling / Top
A single-piece profile that the glass slides up into from below. Used along the ceiling to hold the top edge of the glass panels. Simple to install — fix it to the ceiling, then slide the glass up into it.
2-Part Channel
Walls / Sides / Floor
A two-piece system: a base channel that fixes to the wall or floor, and a clamping section that clips over the top. You fix the base first, position the glass, then clip the front section on to lock everything in place.
How to Calculate Your Glass Size
Once you've chosen your channel size, use these calculations to work out the correct glass dimensions. Get these right and your glass will sit properly with the right amount of clearance.
Glass Panels (fixed panels, not doors)
Measure the height of your opening from floor to ceiling, then subtract the amount shown below. This gives you the panel height that will sit neatly in the channel with the right amount of clearance.
| Channel Size | Glass Panel Height | Example (2400mm ceiling) |
|---|---|---|
| 25mm | Opening height minus 20mm | 2400 − 20 = 2380mm |
| 30mm | Opening height minus 25mm | 2400 − 25 = 2375mm |
| 50mm | Opening height minus 40mm | 2400 − 40 = 2360mm |
Door Panels
Doors need extra clearance at the bottom for the hydraulic hinges. Take the ceiling height, subtract the channel size, then subtract a further 22mm for the hinge clearance.
| Channel Size | Door Panel Height | Example (2400mm ceiling) |
|---|---|---|
| 25mm | Ceiling height − 25mm − 22mm | 2400 − 25 − 22 = 2353mm |
| 30mm | Ceiling height − 30mm − 22mm | 2400 − 30 − 22 = 2348mm |
| 50mm | Ceiling height − 50mm − 22mm | 2400 − 50 − 22 = 2328mm |
The 22mm accounts for the gap needed for the hydraulic floor hinge mechanism. The bottom of the glass door will be 13mm from the floor and 9mm is allowed for the gap at the top.
Already Have Glass? Work Backwards
If you've already got your glass panels and need to figure out which channel size to order, measure the gap between the top of the glass and the ceiling. Then match it to the closest size below:
- Gap is around 20mm — you need 25mm channel
- Gap is around 25mm — you need 30mm channel
- Gap is around 40mm — you need 50mm channel
If your gap falls between sizes, always go up to the next size — a little extra room is much better than glass that won't fit.
Available Colours
All three channel sizes (25mm, 30mm and 50mm) are available in all four colours. Bespoke RAL colours are also available on request.
Silver
RAL 9006
Black
RAL 9005
White
RAL 9010
Anthracite
RAL 7016
Common Questions
What size U channel do I need for a glass partition?
For most installations, 30mm channel is the best choice. It gives you a slimline look while allowing enough tolerance if your ceiling, floor or walls are slightly out of true. Use 25mm only if your opening is perfectly straight and you want the slimmest possible profile. Use 50mm if your opening is significantly out of level or you prefer a chunkier look.
What's the difference between U channel and 2-part channel?
U channel is a single-piece profile used on the ceiling to hold the top of the glass. 2-part channel is used on the walls, sides and floor — it has a base channel that you fix first and a clamping section that clicks over the top to hold the glass. Using 2-part on the sides makes installation much easier because you can set the base, position the glass, and then clip the front section on.
Can I use 25mm channel on a ceiling that isn't perfectly level?
It's not recommended. 25mm channel only gives you a few millimetres of tolerance after the glass and gasket are in place. If your ceiling drops even slightly across the span, the glass may not fit or could look uneven. In most real-world installations, 30mm is the safer choice because it handles minor variations while still looking slimline.
I already have glass — how do I choose the right channel?
Measure the gap between the top of your glass and the ceiling. If the gap is around 20mm, go for 25mm channel. Around 25mm gap, go for 30mm. Around 40mm gap, go for 50mm. If you're between sizes, always round up — it's easier to pack a slightly larger channel with extra gasket than to force glass into a channel that's too small.
What colours do glass partition channels come in?
All our channels are available in Silver (RAL 9006), Black (RAL 9005), White (RAL 9010) and Anthracite (RAL 7016). All four colours are in stock across all sizes and both U channel and 2-part channel types. If you need a bespoke RAL colour, get in touch and we can arrange that on a custom order basis.
Do I need gasket with the channel?
Yes. The glazing gasket sits between the glass and the channel. It holds the glass firmly in place, stops it rattling, and creates a neat finish. You'll need two lengths of gasket for every 3m length of channel — one for each side of the glass.
Ready to Order?
Buy individual channels if you know what you need, or save time with one of our complete partition kits — available with or without glass.
All channels in stock · Next day delivery available · 0800 772 3992