External Window Cills for Timber and Composite Windows

According to one of our customers, the main purpose of an external window cill is to provide a surface to rest his coffee mug on. A cill’s secondary purpose is to take rainwater away from the building to prevent it pooling at the base of the window and finding a route inside. Building regulations suggest it’s the latter that’s the most important but, either way, you’ll probably need a cill of some description underneath your windows.

In most cases, window cills are completely separate to the main window frame. It’s rare to find a window with them built-in. Since this is a separate item, it presents an opportunity for choice!

For plastic or aluminium windows, customers often opt for a “box cill” in the same material as the window. These cills have a set height and depth and are simply cut to the length of the window. However, for timber and alu-clad timber windows the answer is less obvious. It is worth considering all the options first. For any further questions about our product range and how you could tailor this to your home, please contact us.

Wooden Window Cills

It’s perfectly logical to think that a timber window should have a timber cill. It will match the appearance of the window frame in colour and material and traditionally, this is the go-to option.

Although, consider for a moment what the purpose of the window cill is. This is where every drop of the water running down the window is going to end up. That’s why you’ll often see a timber window that looks perfectly fine… apart from the rotting cill underneath.

So, maybe it’s worth looking into other options that help to prolong the life of the window as a whole.

Aluminium Pressings (Not Boxes!)

Before manufacturing the window, we subtract about 25mm from the height of the unit. This gives us space to insert a treated timber packer underneath the window which provides a surface for us to attach a thin section of powder-coated aluminum.

Using this, we can precisely measure the depth needed after installing the window, so the result is the neatest-possible cill section, as well as the added durability over timber.

Aluminium cills on an alu-clad timber window isn’t a huge stretch. But do they work aesthetically with timber? We match the RAL colour code and gloss level with the frames so the visible difference is unbelievably small .

However, these cills are not suitable for doors. If too much pressure is put on them (such as if they are stood on) they will just bend downwards.

Aluminium Boxes

Instead, aluminium boxes are much sturdier to go underneath doors due to their rigid construction. They’re more expensive than pressings and only come in select depth options but the advantage is their added strength.

In terms of their appearance, there are two options. Most customers opt to colour match the frames and cills together for a seamless look between the two.

Alternatively, some prefer the bare aluminium finish. This is often because it’s easier to fix any scratches. If someone scratches a colour-coded cill when walking over it, the only option to fix this is repainting. With bare aluminium, scratches can just be polished out.

Stone, Brick and Slate Cills

It is becoming more and more common for us not to supply any cills at all, especially for newbuilds. Building regulations still require a solution for taking water away from the building but there are some other solutions.

Stone, brick or slate cills all have a defined appearance that can create effective highlights throughout a build. If executed correctly, they can completely negate the need for cills from your window supplier.

Common Questions

Do I need window cills?

Yes, you will need some way to keep the water away from the pooling on a flat spot below your window or door. The type of cill however is up to you: aluminium or timber cills are supplied by us, but you may wish to look into stone, brick or slate solutions

Will my window cills match my windows?

Yes, we can match every product we have with a window cills of the same colour, gloss level and material

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