All articles · 6 min read

What is sill height, and how high should a window sit?

Sill height is the distance from the floor up to the underside of the window frame. It decides how much you can see out, how much light reaches the lower part of the room, and whether the window can serve as an escape opening or have furniture placed in front of it.

What exactly does sill height mean?

The "sill wall" is the section of wall below a window — from the floor up to the underside of the window frame. Sill height is simply the vertical distance there. The lower the sill, the more you see while sitting down, and the more light reaches the lower part of the room. The higher the sill, the more wall there is for furniture, a radiator or a kitchen worktop under the window — but at the cost of less view and less light while seated.

The measurement is used both when planning a new window and when describing an existing one precisely enough for a contractor or window supplier to work from.

Typical sill heights — and why they vary

• Living spaces (living room, bedroom). Often 80-100 cm, so the window gives a view while seated but still leaves room for a radiator or a low bookcase underneath.
• Kitchen. Usually higher, because there is normally a worktop and cabinets to fit under the window — the sill height then follows the worktop height, often around 90 cm.
• Bathroom. Often higher than in living spaces, both for privacy and to leave room for a basin or storage below the window.
• Floor-to-ceiling windows and balcony doors. Sill height near 0 — but many places then require safety glass or a guard rail, because there is no sill wall to prevent a fall.

These figures are rules of thumb, not fixed answers. The local building authority may set specific requirements for sill height at balconies, French doors and escape openings — always check that before ordering a new window with a different sill height than the existing one.

Can I try out a new window before I order it?

Yes, in several ways. The simplest is to mark the new window's outline directly on the existing wall with painter's tape, so you can see the size in real life. The digital version is to place the window in a 3D model or on a photo of the room, with the width, height and sill height you are considering — that gives you a quick sense of how much light and view the new window actually delivers, before anything is cut out of the wall.

Both methods are good for judging proportions and placement. Neither can decide whether the wall can carry a larger opening, or whether a new window needs planning permission — that is covered further down.

How do you set a new window "to measurements" digitally?

When an opening needs to be planned precisely — not just sketched — there are typically four figures in play: width, height, sill height, and a horizontal position on the wall. The horizontal position can be set in three ways: centred on a point you tap, offset to the left or right of a reference point, or as a fixed distance from the corner of the wall. The last method is the most precise, because it does not depend on where you happen to tap, but on a measurement you can reproduce identically every time you open the drawing again.

How wide should an opening be if you remove a door entirely?

If you remove a door entirely and turn it into an open passage instead, the width is what decides whether the opening feels like a room of its own or a natural extension of the next one. A narrow opening, about the width of a door, keeps the sense of two rooms. A wide opening spanning almost the whole wall makes two rooms feel like one. There is no single correct measurement — it depends on the furniture, how much traffic passes through, and whether you want to keep two separate rooms or open them up. If furniture needs to be carried through, the practical minimum width is usually larger than it looks on a drawing — always measure your widest piece of furniture before fixing the width of the opening.

What can't a digital window plan decide?

• Whether the wall can carry a larger opening. That is decided by a building surveyor or structural engineer, never by an app or a drawing.
• Whether a new window or opening needs planning permission. It depends on the house, the area and what is being changed — ask the local building authority before you order.
• Requirements for escape and ventilation openings. Bedrooms often must have at least one window usable as a fire escape — a size and placement requirement that has to be checked locally.
• Energy requirements for the new window itself. Insulation performance and glazing type are a conversation with a supplier, not something a drawing shows.

What HouseSense does

In HouseSense you can stand in front of a wall in the 3D walkthrough and place a door, window or opening "to measurements" — with width, height, sill height and a position you choose yourself: centred on a point, offset to the left or right, or at a fixed distance from the corner. That gives you a quick picture of how the new opening looks in the room before anything is cut out of the real wall. The app does not decide whether the wall can carry the opening, and it does not know the local requirements for escape openings — that is still a conversation with a professional.

Should a professional be involved before you order?

Yes, as soon as the plan involves an opening in a load-bearing wall, a change to the facade's appearance, or an opening that must meet requirements for escape routes or daylight. A building surveyor or structural engineer assesses whether the wall carries load, and the local building authority decides whether the project needs planning permission. Use the digital trial to work out what you want — use the professionals to decide whether and how it can be done.