Glass Window Cills - Toughened Glass Window Sills, Cut to Size

A toughened glass window cill is the simplest way to finish a window reveal in something that will not swell, stain, chip or need repainting. We supply glass window sills cut to your exact millimetres in 8mm toughened safety glass, from 500mm to 2000mm long and 100mm to 250mm front to back, in clear or sandblasted frosted. Clear lets the paint, plaster or tile underneath read through and almost disappears. Frosted gives an even, matt surface and takes the shine off, though on a cill it will not hide what is underneath. Polished edges and a 5mm radius on all four corners come as standard, toughened to BS EN 12150 and impact classified to BS EN 12600. The size bands here step in 100mm of length and 50mm of width, far finer than the bands on our cut glass panels, which is why a long shallow piece costs a good deal less ordered as a cill than as a panel.

What is a glass window cill for?

The internal shelf at the bottom of a window reveal gets called a lot of things: a cill, a sill, a window board or a cill board. In timber or uPVC it is the part that marks first, swells when a window is left open in the rain, and ends up repainted every few years. In glass it stays flat, does not absorb anything and wipes clean.

The jobs we see most often are bathroom and shower reveals where water sits on the surface, kitchen windows above a worktop, cills over a radiator where timber dries out and splits, and bay windows where the customer wants the ledge to disappear rather than frame the view. It also works well as a plain display ledge in a shop or showroom, and as a replacement for a cracked stone or tiled cill where cutting out the old one is the hard part and the new surface wants to be thin.

Why glass instead of a timber cill board?

Two things sell these, and both are practical rather than decorative.

The first is water. A glass cill does not care about it. Behind a kitchen sink, where a timber board goes dark along its front edge and a painted one blisters and peels within a couple of years, glass simply gets wiped down. The same goes for a bathroom window, a utility room, or anywhere a window gets left open in the rain.

The second is plant pots. People stand plants on a window ledge, the pots sit in water, and sooner or later that water finds its way into the board underneath. Ring marks, swelling, lifted paint. You can stand a wet pot on a glass cill all year and the worst you get is a water mark you wipe off.

After those two it is the small things. It cleans in seconds, it never needs repainting, and it does not chip along the front edge the way a timber nosing does. It is also thin, so where you are replacing a cracked stone or tiled cill you are not fighting to make a thick new board fit a reveal that was never sized for it.

How to order the right size

The sizes on this page are bands, not fixed sizes. Pick the next band up from your own cill, so the band is equal to or larger than your glass in both directions, then send us your exact sizes and we will confirm them back to you before anything is made. The cill is then made to your measurements rather than to the band size.

• Length bands run from Up to 500mm through to Up to 2000mm in 100mm steps. A 1430mm cill goes in the Up to 1500mm band, and we make it at 1430mm
• Width is the measurement from the window frame to the front edge, in bands up to 250mm. Anything deeper than 250mm is quoted individually, so send us the sizes and we will price it
• Up to 500mm is the smallest band. We will happily make a 400mm cill, so pick the Up to 500mm band and give us your exact sizes
• Set the quantity to the number of cills you need at that size. Different sizes need adding to the basket separately
• Longer than 2000mm, shaped, notched around a pipe, or with a cut-out for a window handle? Those are priced individually through our bespoke service

Measuring the reveal

Measure the opening in three places along its length and work to the smallest figure, because reveals are rarely parallel. For the width, measure from the face of the frame to where you want the front edge to sit, and decide whether you want the glass to finish flush with the wall or to project slightly and throw a shadow line. A 2mm to 3mm gap each end gives you something to work with when you set it; a cill cut tight to the opening will not go in.

Why toughened glass cannot be cut down afterwards

Once glass is toughened it cannot be cut, drilled, notched or edged. The toughening process puts the glass into tension, so every hole, cut-out and polished edge has to happen before it goes through the furnace. A cill that is 5mm too long is scrap rather than something to trim, which is why we work to the exact measurements you send us and confirm them back before the order goes to the furnace.

If you are not certain of the opening yet because plastering or tiling is still to come, wait and order once the reveal is finished. A fortnight of patience costs nothing; a remake costs the price of the glass again.

Clear or frosted: which should you choose?

Clear is the right choice when the surface underneath is already what you want to see. Over a painted or plastered reveal it reads as a hard, wipeable layer rather than a shelf, and over tile or stone it protects the surface without hiding it. It is also the honest choice if the cill is in a bay or a feature window and you do not want to interrupt the light.

Frosted is sandblasted on one face, and it is worth being straight about what that does on a cill. Frosted glass hides by distance, not by contact. Press your hand flat against a piece of frosted glass and you see it clearly, almost as though the frosting were not there. Lift it 50mm off the glass and it becomes much harder to make out. A frosted shower screen has air behind it and holds back detail, but a cill is bedded straight onto the reveal, so the surface underneath is in contact with the glass and will still read through it.

So on a cill, frosted is for the look rather than for cover. It gives an even, matt, slightly milky surface, it takes the shine off, and it softens small marks rather than hiding them. If the reveal underneath is in poor condition, make it good before the glass goes on, because frosted will not cover it. And if you genuinely need what is underneath hidden, frosted is the wrong choice, so talk to us before you order rather than after.

Otherwise the two behave identically: same toughened glass, same edgework, fitted in exactly the same way. Tell us which face you want sandblasted if it matters for your installation. Most people have the frosting underneath so the top surface stays smooth and easy to wipe.

How are the edges and corners finished?

Every cill gets polished edges on all four sides and a proper 5mm radius on all four corners as standard, not the dubbed corner knocked off by hand that a lot of suppliers will quote you. That matters more on a cill than it does on a panel, because a window ledge is at hand height and gets touched, leaned on and wiped every day. A flat polished arris is comfortable to the hand and does not catch a cloth.

Our full edge and finish standards are set out on the material finishes page, and the glass quality standards page explains what is and is not acceptable in a toughened panel.

Is 8mm toughened glass strong enough for a window sill?

Yes, for a supported cill. The glass is toughened to BS EN 12150 and impact classified to BS EN 12600, which is the safety glass standard you want anywhere a person could come into contact with a glazed surface. Toughened glass is several times stronger than ordinary annealed glass of the same thickness, and if it ever does break it goes into small blunt granules rather than shards.

The important condition is support. A cill is designed to sit on a continuous bed along its length, not to span an opening like a shelf on two brackets. Supported that way, 8mm is ample for plant pots, ornaments, a cup of tea and the occasional person sitting on it. If you are planning to use it unsupported over a gap, or to stand on it, tell us what you have in mind before ordering and we will say what we would normally supply. There is more background on thickness in our toughened and laminated glass guide.

Fitting a glass cill

It is a simpler job than most people expect. A glass cill is bedded onto what is already there rather than fixed through it, so there are no holes to drill and no fixings on show. What decides whether it looks right is the surface underneath.

Get that surface clean, dry and flat before the glass goes anywhere near it. Most of the cills we supply sit on a painted reveal, which is exactly what they are meant to sit on, but flat matters more than pretty. Glass will bridge a hollow and rock on a high spot, and a cill that rocks will eventually crack where it is bearing. Knock off any nibs of plaster or paint, fill any dips, and check it with a straight edge rather than by eye. It is also worth getting the paintwork how you want it, because with either finish you will see it through the glass.

Once the surface is right, fixing is usually nothing more than a bead of silicone around the perimeter to hold it in place. Run it continuously rather than in dabs, set the glass down onto it, and keep the weight off it until the silicone has gone off. Leave a couple of millimetres at each end rather than butting the glass hard into the plaster, and seal that gap with a flexible bead so the cill is not pinched as the opening moves.

Do not try to drill it or trim it on site, because toughened glass cannot be worked once it has been through the furnace: the piece that arrives is the piece you fit. Two people for anything over about 1200mm. The glass is strong across its face and vulnerable on the edges and corners, which is where nearly every breakage starts.

How do you clean a glass cill?

Warm water, a drop of washing up liquid and a microfibre cloth will do it, finished with a dry cloth or a squeegee to stop water marks. A proprietary glass cleaner is fine for the top surface. For limescale in a bathroom, a dilute white vinegar solution left for a few minutes will lift it.

Do not use a scouring pad, a bladed scraper, or anything abrasive, and keep cement, plaster and grout off the glass while the room is being finished, because all three are difficult to remove once they have gone off. Frosted glass holds a greasy mark more readily than clear, so it benefits from being wiped in one direction rather than circled. There is more on looking after our glass products on the product maintenance page.

Lead time and delivery

Glass is cut and toughened to your sizes, so allow 2 to 4 weeks from the point your sizes are confirmed. Dio-Met has been supplying architectural metalwork and structural glass since 1991, 35+ years, and we buy our glass from UK processors working to BS EN 12150.

Cills travel boxed rather than on a pallet. Check the glass over before you sign for it, and see our delivery information page for the full terms.

Related

• Bigger pieces in the same glass: 8mm clear toughened glass panels and 8mm frosted toughened glass panels
• The full range of thicknesses and finishes: cut to size glass
• Anything longer than 2000mm, deeper than 250mm, shaped or notched: bespoke and made to measure

A note on specification

The guidance on this page reflects what we typically supply for jobs of this kind, and is offered in good faith to help you order the right thing. It is not a structural specification and it is not a substitute for project-specific design. Spans, support, loadings, substrates and exposure all vary from site to site, and the final specification for your project remains the responsibility of you, your designer, your structural engineer or your building control body. We supply to the sizes and specification you give us. If you are unsure, send us the details before ordering and we will tell you what we would normally supply for a job like yours.