Rehau Rio vs Cortizo Cor 70: uPVC or Aluminium Flush Casement?

Flush casement windows have become the default choice for homeowners who want the clean, traditional look of a timber window without the upkeep. Two systems dominate the enquiries we get for this style: Rehau Rio in uPVC and Cortizo Cor 70 Hidden Sash in aluminium. We fabricate and install both in-house from our Uxbridge workshop, so this comparison is written from the bench rather than a brochure. It sets out where the two systems genuinely differ and which fits which project.

What Each System Is

Rehau Rio is a uPVC flush casement built on Rehau's multi-chamber profile, engineered so the opening sash sits flush with the outer frame rather than proud of it, giving a run of windows a uniform, timber-like appearance. Cortizo Cor 70 Hidden Sash achieves a similar visual result in aluminium: the opening sash is concealed behind the outer frame so opening and fixed lights read identically from outside. The two systems solve the same design problem in different materials, and that material choice is the real decision most homeowners are making.

Sightlines and Appearance

Both systems are built specifically to hide the opening sash, so on a straightforward comparison of "does it look flush", the answer for either is yes. Where they diverge is frame depth and finish. Aluminium generally allows a narrower overall frame for a given structural strength, so Cor 70 sits among the slimmest flush casement frames we fit, while Rio's uPVC profile is a little deeper to achieve the same strength and weatherproofing. On a period property, that extra depth on Rio often reads as more sympathetic to an original timber sash; on a contemporary rebuild, Cor 70's narrower aluminium line tends to suit the brief better.

Thermal Performance

Both systems reach an A-rated energy category on a typical specification, with the exact figures confirmed at survey once glazing and hardware are chosen. uPVC's multi-chamber construction gives Rio strong inherent insulation without a separate thermal break; Cortizo's aluminium profile relies on a thermal break built into the frame to achieve comparable performance. In practice, glazing specification tends to move the numbers more than the frame material itself, so neither system has a fixed thermal advantage over the other at this stage.

Security and Hardware

Both Rio and Cor 70 Hidden Sash are specified with multi-point locking hardware as standard, and both can be built to meet current UK security expectations for a domestic window; the exact certification available depends on the configuration ordered and is confirmed at survey. Neither system trades away hardware quality to achieve its flush appearance.

Colour and Finish

Rio is available in a wide range of foiled uPVC finishes, including woodgrain effects that suit period properties closely matching the material of an original sash. Cor 70 is finished in Cortizo's powder-coat range across the full RAL colour spectrum, including a dual-colour option for a different finish inside and out. If a heritage colour match matters more than material authenticity, both ranges have options worth discussing at survey.

Maintenance

uPVC is effectively maintenance-free beyond routine cleaning, and Rio's foiled finishes are engineered to resist fading over the long term. Aluminium is similarly low-maintenance day to day, and Cortizo's powder-coat finish is built to hold its colour for decades without repainting. Neither system asks for more upkeep than the other; the difference is one of feel and finish rather than ongoing effort.

Which We Recommend

For a period property, a like-for-like replacement, or a project where budget is a bigger factor than absolute sightline, Rehau Rio is the sensible default. It gives a genuinely flush, traditional appearance in a material that needs no ongoing maintenance. For a contemporary extension, a full rebuild, or anywhere the brief calls for the narrowest possible frame and a material that pairs naturally with aluminium doors elsewhere on the elevation, Cortizo Cor 70 Hidden Sash is worth the conversation at survey.

We fabricate and install both Rehau Rio and Cortizo Cor 70 Hidden Sash in-house at our Uxbridge workshop. Every installation is FENSA registered and carries a 10-year CPA insurance-backed guarantee.

Frequently Asked Questions

What is the main difference between Rehau Rio and Cortizo Cor 70 Hidden Sash?

The main difference is material. Rehau Rio is a uPVC flush casement, while Cortizo Cor 70 Hidden Sash is an aluminium flush casement. Both hide the opening sash for a uniform appearance, but the material affects frame depth, finish options and how each reads against a period or contemporary elevation.

Is aluminium or uPVC better for a flush casement window?

Neither is universally better. uPVC such as Rehau Rio tends to suit period properties and like-for-like replacements where a traditional, maintenance-free frame is the priority. Aluminium such as Cortizo Cor 70 tends to suit contemporary extensions and rebuilds where the narrowest sightline and a material that matches aluminium doors elsewhere is the priority.

Will Rehau Rio or Cortizo Cor 70 pass conservation area planning?

Both can be specified with finishes and detailing suited to conservation area requirements, but acceptability always depends on your local planning authority and the specific conservation area guidance in force. We recommend checking with your council or discussing this with us before ordering.

Which system has the slimmest sightlines?

Cortizo Cor 70 Hidden Sash generally achieves a narrower overall frame than Rehau Rio because aluminium allows a slimmer profile for the same structural strength, putting it among the slimmest flush casement frames we fit. Rio's uPVC profile is a little deeper to achieve comparable weatherproofing and strength.

Do both systems come with the same guarantee?

Yes. Every Rehau Rio and Cortizo Cor 70 Hidden Sash installation we carry out is FENSA registered and backed by the same 10-year CPA insurance-backed guarantee, whichever system you choose.