This charming home in Harpenden Hertfordshire, has the original windows fitted within hardwood frames, which is very typical of early generation double glazing. We’ve improved the security, energy efficiency and interior comfort with latest generation Alitherm Heritage Windows. A substantial overall improvement, whilst keeping to the original look of the house.

White Alitherm Heritage Windows in Hardwood Subframes.

This project in Harpenden, Hertfordshire involved replacing original steel windows while carefully retaining the existing hardwood subframes.

Our customer was clear outset. While the old steel single glazed windows had reached the end of their life, the existing hardwood subframe look was essential to the building’s appearance and could not be lost. And these hand-crafted oak frames, black outside and light oak inside were still in fantastic condition.

The customer wanted to:
• Eliminate draughts and improve thermal comfort
• Replace failing steel windows with modern aluminium
• Retain the look of traditional oak subframes
• Keep the character of the property intact
• Improve both internal and external appearance

Rather than forcing a standard replacement solution, we helped retain the look of the house, whilst respecting the original hardwood frames with one of the tried and tested window brands for this type of product. Smart Systems Alitherm Heritage Windows. At the same time we at LB Window Systems developed a bespoke approach that combined modern aluminium performance with traditionally styled steel-look detailing.

The original steel windows were cold, inefficient and prone to draughts, a common issue with early steel systems. However, the surrounding timber subframes formed an important architectural feature, visually framing each opening and tying the windows into the brickwork. At the same time, wood is a natural insulator, providing a warm to the touch feel outside.

Properly cared for, there is no reason hardwood subframes cannot last as long as the windows. In this case, they outperformed the original steel!

Slimline and Cutting-Edge Alitherm Heritage Windows

We specified an Alitherm aluminium heritage window system, carefully integrated into the existing oak timber subframes. The aluminium windows sit cleanly within the oak, combining the slim sightlines and strength of aluminium with the warmth and depth of timber. This image shows the original wood frames with the old metal windows removed:

This approach is particularly effective where original steel windows are being replaced, as it respects the original design intent while delivering modern performance. And even better, Alitherm Heritage windows come with a dedicated odd or equal leg outer frame specifically designed to fit into hardwood frames.

Why aluminium into hardwood subframes works

Early generation aluminium double glazing was frequently fitted in hardwood subframes. As well as this, there are countless conservation areas around the UK where the original design (windows in hardwood frames) has to be respected. Aluminium therefore, whether standard or part of our steel look collection, are the best solution. Moreover, products like Alitherm are not only designed for hardwood frames, but also for stone surrounds.

Aluminium windows offer excellent longevity, minimal maintenance and significantly better thermal performance than historic steel frames. When paired with hardwood subframes, they also allow:

• Traditional proportions to be retained
• Deeper reveals and shadow lines to be preserved
• A warmer visual transition between window and brickwork
• Greater design flexibility for heritage-style properties

The Alitherm Heritage system is arguably the best selling in the UK today and tried and tested over many many years. Arguably it is the best suited to this kind of window replacement project. Slim profiles in classic white RAL 9910 gloss finish, like the original steel, that do not overpower the timber framing while providing modern sealing and glazing performance.

A noticeable improvement inside and out

The difference was immediate. The homeowner noticed a dramatic reduction in draughts, particularly in the hallway, which had previously been exposed to cold air movement from the steel frames.

Internally, the kitchen and living spaces feel more refined and cohesive, with the oak frames adding warmth while the aluminium windows bring crisp definition to each opening.

Externally, the windows now sit comfortably within the façade, maintaining the character of the property rather than altering it.

Customer feedback

“They look amazing; very smart. We have already noticed a big difference in the hallway with no drafts from the windows. The kitchen looks much smarter inside and out too. We are so very pleased with our lovely new windows, thank you!”

Steel-Look and Heritage Windows and Doors in London and the HOme Counties

This Harpenden project is a strong example of how aluminium windows in hardwood subframes can be used to sensitively upgrade older properties. The combination delivers the best of both worlds: traditional appearance where it matters, and modern performance where it counts.

Replacing steel windows does not have to mean losing character. With the right window brand, proper craftsmanship and a professional installation, aluminium can enhance rather than detract from a building’s original design.

At LB Window Systems, we specialise in tailored aluminium window solutions, including heritage and hybrid installations where timber detailing plays a crucial role. This project shows how careful design and experience can deliver a result that feels both authentic and future-proof.

Contact us today to discuss your project.

Project details

Location: Harpenden, Hertfordshire
Property type: Residential home with original steel windows
Products installed: Alitherm aluminium heritage windows with period leaded glass and pear drop heritage handles.
Subframes: Original lack outside, light oak inside hardwood subframes
Project type: Replacement of original steel windows