Window Sills in Ireland: Granite vs Concrete vs Cast Stone

A window sill does more work than most people give it credit for. It throws rainwater clear of the wall, protects the masonry under every opening, and sets the tone for the whole front of the house. Whether you call it a window sill, a windowsill, a cill or a window ledge, picking the right one comes down to three things: the material, the profile, and the size that suits your wall build-up.

We've been manufacturing and supplying sills from Rathcoole since 1981, so this guide covers what we get asked most often by homeowners, builders and self-builders across Ireland.

What does an exterior window sill actually do?

An exterior window sill sits under the window frame and slopes gently outwards. Its main job is to catch the water running down the glass and frame and shed it away from the face of the building, so it doesn't soak into the wall below or find its way back inside. In a climate as wet as ours, that matters. A poorly sized or cracked sill is one of the most common sources of staining and damp around windows.

A good external sill also gives the opening a solid, finished look. Granite and cast stone sills in particular are a big part of how a traditional Irish house front reads from the road.

Granite vs concrete vs cast stone window sills

We stock all three materials in our window sill range. Each one suits a different budget and finish.

Granite window sills

Our natural granite sills are cut from silver granite. Granite is a dense natural stone, so it's naturally more resistant to staining and weathering than concrete, and it keeps its colour and finish for decades. It's the premium choice and the one people go for when they want the sills to be a feature.

• Silver Granite Window Sills – 220x140 for standard openings
• Silver Granite Window Sill – 350x140 for deeper walls and longer openings
• Silver Granite Bay Sill, available in left and right hand
• Silver Granite Window Sill Stools to finish the ends

Cast stone window sills

Cast stone sills are made in our own yard and come in three finishes: Cast Granite, Cast Sandstone and Cast Portland (a clean white). They give you the look of natural stone at a lower price, and because they're cast to order you can match them to surrounds and string courses in the same finish.

Popular sizes include the Cast Stone Window Sill – 265x140 for standard blockwork, the 300x140 and 350x140 for walls with cladding or stone facades, and the Cast Stone T-Frame Sill – 225x140 for timber frame builds.

Concrete window sills

Precast concrete sills are the hard-wearing, cost-effective option and the go-to for many builders. Our concrete sills are reinforced with three 12mm steel bars, so they're strong enough for long openings and won't crack under the weight of the wall above during the build. Once painted or rendered in, they give a clean, traditional finish.

The range runs from the compact Concrete Window Sill – 250x100 up through the 265x140, 300x140 and 450x140.

Quick comparison

Sill profiles: standard, stooled, T-frame and bay

Beyond the material, you'll need the right profile for the way your house is built.

• Standard sills are the straightforward option for most block-built houses.
• Stooled sills have raised flat sections at each end (the stools) where they build into the wall, giving a neater finish at the reveals. See the Concrete Stooled Sill – 265x140 and Cast Stone Stooled Sill – 265x140.
• T-frame sills are made for timber frame houses with an outer leaf of brick or block. Try the Concrete T-Frame Sill – 225x140 or the lighter 215x80 T-Frame Sill.
• Bay sills are angled to suit bay windows, like our Silver Granite Bay Sill.

How to choose the right window sill size

Sill sizes are listed as depth x height in millimetres, so a 300x140 sill is 300mm deep (front to back) and 140mm high. Length is then chosen to suit the opening.

A few rules of thumb when measuring:

• The sill should be longer than the window opening so the ends can be built into the wall at each side.
• It needs to project far enough past the finished wall face (after render, cladding or stone) for water to drip clear of the wall.
• Measure the full wall build-up, including insulation and any external finish, before choosing a depth.

If you're unsure, send our team your window schedule or drawings and we'll help you pick the right size. Many of our sills can also be made to order in non-standard sizes.

Matching sills with surrounds, string courses and capping

Sills look best when they're part of a consistent scheme across the front of the house. We make and stock matching pieces in granite, cast stone and concrete, including window surrounds, granite string courses, quoin stones and wall capping. Finishing the boundary with matching pier caps ties the whole frontage together.

Looking after your window sills

Granite, cast stone and concrete sills all need very little maintenance. A wash with water and a soft brush once or twice a year is usually enough. Granite can be sealed every year or two to help keep off staining and green growth. For step-by-step advice, read our guide on how to clean granite window sills without damaging the stone.

Lead times and delivery

Concrete sills are made to order and are generally ready in 3 to 5 working days. Cast stone sills generally take 3 to 10 working days, depending on the size of the order. Stocked items are delivered nationwide, usually within 1 to 3 working days. Builders and contractors ordering regularly can apply for a trade account for discounted pricing.