What Are Internal Windows? Crittall-Style Explained

An internal window is exactly what it sounds like: a window fitted inside your home rather than in an outside wall. Instead of looking out at the garden, it looks from one room into another, borrowing light and opening up the space. They have become a real favourite in recent years, especially the black-framed Crittall-style look, and this guide explains how they work and where they suit a home.

What is an internal window?

An internal window, sometimes called an internal glazed partition or a borrowed-light window, is a fixed or opening pane set into an interior wall. It lets natural light pass from a bright room into a darker one, such as a windowless hallway, a landing or a home office carved out of a larger space.

They come in a few forms:

• A single window set into a wall, like a hatch or a picture frame of glass.
• A part-glazed partition that divides a room while keeping it feeling open.
• A full glazed screen, often floor to ceiling, that separates a kitchen from a dining area or a hallway from a living room.

Most internal windows are fixed, since they do not need to open for weather or security. Some designs include an opening section for airflow between rooms.

The Crittall-style look explained

When people picture an internal window today, they usually picture Crittall style. Crittall is a long-established British maker of steel-framed windows, and the name has become shorthand for that distinctive look: slim frames, often in black, divided into a grid of smaller panes.

The appeal is easy to see. The thin frames and gridded glass give a smart, industrial-meets-period feel that suits everything from a Victorian York terrace to a modern open-plan kitchen. True steel Crittall windows are premium products, but the same style is widely available in aluminium and other materials at a range of price points, so you can get the look to suit your budget.

For homeowners who love slim black frames, our aluminium windows share the same clean sightlines, and if you are working with a period property, our heritage aluminium range is designed to sit sympathetically in older homes.

Where internal windows work best

Internal windows earn their keep in a few common situations:

• Dark hallways and landings. Borrowing light from a bright room next door lifts a gloomy corridor without any structural work outside.
• Broken-plan living. A glazed screen zones a big open space, so a kitchen and a snug feel separate but still connected.
• Home offices. Partitioning off a work corner with a glazed screen keeps light flowing while giving you a bit of quiet.
• Internal rooms with no outside wall. En-suites, box rooms and utility spaces can feel much less boxed in.
• Period homes. In many York terraces, a Crittall-style screen between the front and back reception rooms is a classic way to add light and character.

Things to think about before you fit one

Internal windows are mostly about looks and light, but a few practical points are worth weighing up.

• Privacy. Clear glass shares the view as well as the light. Reeded, frosted or fluted glass keeps brightness while blurring what you can see through, which is handy for offices and bathrooms.
• Sound. A glazed partition passes more noise than a solid wall. If quiet matters, consider a door in the screen or a thicker glass spec.
• Structure. Cutting an opening into a load-bearing wall needs proper support. Always get advice from a builder or structural engineer before removing part of any wall.
• Regulations. Depending on the wall, the room use and fire safety, some internal glazing work can come under Building Regulations. Rules change, so check the current requirements with your local authority or a competent installer before you start.
• Glass safety. Glazing at low level or near doors usually needs to be toughened or laminated safety glass.

What do internal windows cost?

Cost depends hugely on size, frame material and whether you are fitting a single window or a full glazed screen. As a rough 2026 guide, a modest internal window might start in the low hundreds of pounds, while a large Crittall-style partition with several panes can run into the low thousands, before any building work to create the opening. Steel frames sit at the top end, with aluminium and lighter alternatives more affordable. These are ballpark figures only, so get a quote for your exact design.

If you like the idea and want to price it up, request a free quote and we will talk through frame options, glass and finishes for your space.

FAQs

What is an internal window used for?

It shares natural light between rooms and helps a space feel more open. People fit them to brighten dark hallways, zone open-plan rooms, partition home offices and add light to internal rooms with no outside wall.

What is a Crittall-style internal window?

It is an internal window with slim frames, usually black, divided into a grid of smaller panes. The look is named after Crittall, a British steel window maker, and is now available in aluminium and other materials too.

Do internal windows need Building Regulations approval?

Sometimes, depending on the wall, fire safety and whether you are cutting into a load-bearing structure. Rules change, so check the current requirements with your local authority or a competent installer before starting work.

Can you see through an internal window from both sides?

Yes, if the glass is clear. If you want light without a full view, choose reeded, fluted or frosted glass, which keeps the brightness while blurring what you can see through.

Want to see slim-framed styles and finishes in one place? Download our latest brochure, or request a free quote and we will help you plan the look.