Cortizo Cor 70 Hidden Sash Windows: The Flush Aluminium Casement

Most aluminium casement windows give away which panes open. The opening sash sits proud, so a run of windows shows a mix of thin fixed frames and thicker opening frames. The Cortizo Cor 70 Hidden Sash system removes that tell: the opening sash is concealed behind the outer frame, so opening and fixed lights read the same from outside. This guide explains what that buys you and where the system fits.

What Is a Hidden Sash Window?

On a conventional casement, the opening sash is a visible frame that sits in front of the outer frame. On a hidden sash design, that opening frame is tucked behind the outer frame so only a slim, uniform face shows outside. The result is a clean, flush elevation where every window in a run looks identical whether it opens or not. Cor 70 is Cortizo's 70-series window platform, and the Hidden Sash variant is the one to specify when a flat, consistent sightline is the goal.

Uniform Sightlines Across the Elevation

The main reason to choose Cor 70 Hidden Sash is visual consistency. Architects and homeowners who want a minimal, contemporary elevation dislike the stepped look of a standard casement, where opening lights are visibly heavier than fixed ones. With the sash concealed, a bank of windows presents one continuous slim frame line across the whole opening. On a modern render-and-glass elevation, or a period home where you want restraint, that uniformity is what makes the windows look considered rather than off-the-shelf.

Slim Frames Without Losing Strength

Aluminium's structural strength is what lets Cortizo keep the visible frame slim while still carrying large glass units, and the Hidden Sash construction holds that slimness even on the opening lights. It is among the slimmest flush aluminium casements we fit, though the exact sightline on your job depends on the sash size and glass weight worked out at survey. The upside is more glass and more light for a given aperture, with frames that stay quietly in the background.

Thermal Performance

Cor 70 is a thermally broken aluminium system, meaning an insulating barrier separates the inside and outside of the frame to cut heat loss and reduce the cold-bridging older aluminium was known for. Combined with warm-edge, high-performance glazing, the system achieves the low U-values expected of a current premium aluminium window and meets Building Regulations for replacement windows comfortably. Our thermally broken aluminium explainer covers how that construction works if you want the detail.

Security and Everyday Use

The system carries multi-point locking and takes toughened or laminated safety glass specified to the opening, giving the security a premium home should expect. In everyday use the concealed sash operates as a normal casement: it opens on quality hardware and seals against a weather gasket, so you gain the look without losing function. As always, the hardware and glass spec is confirmed at survey rather than sold as a fixed bundle.

Where Cor 70 Hidden Sash Fits Best

Choose Cor 70 Hidden Sash when the elevation matters: contemporary new builds and extensions, architect-designed homes, and period properties being upgraded where you want slim, uniform frames rather than a stepped casement look. It pairs naturally with Cortizo sliding doors and bifolds on the same project so windows and doors share one frame language. If your priority is simply a warm, well-made aluminium casement and the flush look is not essential, a standard Cor 70 casement is the more economical route.

Fabricated and Fitted by Vitrum Solutions

Vitrum Solutions cuts, machines and assembles Cortizo profile into finished windows at our Uxbridge workshop, then installs them with our own team. Every installation is FENSA registered with a 10-year CPA insurance-backed guarantee. See the Cortizo windows range, the full Cortizo system, the wider aluminium range, or request a free survey. Our Cortizo aluminium windows review covers the platform in more depth.

Frequently Asked Questions

What is a Cortizo Cor 70 Hidden Sash window?

Cor 70 Hidden Sash is an aluminium casement window where the opening sash is concealed behind the outer frame. From outside, opening and fixed lights look identical, giving a flush, uniform elevation rather than the stepped look of a standard casement. Cor 70 is Cortizo's thermally broken window platform.

Why choose a hidden sash window over a standard casement?

A hidden sash window gives consistent sightlines across a whole run of windows, because you cannot tell which panes open. That uniform, slim-framed look suits contemporary and architect-designed homes, and period properties where restraint matters. A standard casement, where opening sashes sit proud, is the more economical choice when the flush look is not a priority.

Are Cor 70 Hidden Sash windows energy efficient?

Yes. Cor 70 is a thermally broken aluminium system with an insulating barrier through the frame, and combined with warm-edge high-performance glazing it achieves the low U-values expected of a premium aluminium window and meets Building Regulations for replacement windows. The exact figure depends on the glass specification agreed at survey.

Are Cor 70 Hidden Sash windows secure?

Yes. The system carries multi-point locking and accepts toughened or laminated safety glass specified to the opening. The concealed sash operates on quality hardware and seals against a weather gasket, so the security and function match a standard premium casement while the look stays flush.

Who fabricates and installs Cortizo windows near West London?

Vitrum Solutions fabricates the Cortizo range in-house at our Uxbridge workshop and installs across West London and the surrounding counties with our own team. Every installation is FENSA registered with a 10-year CPA insurance-backed guarantee.