Heritage aluminium replicates the look of original steel windows using modern thermally broken frames, generally at lower cost and with far less maintenance than genuine steel.
Written by Windows in the Lakes · A trading name of Home Glazing Ltd
Original steel windows, common in inter-war and mid-century houses, have a distinctive slim, precise appearance that many homeowners want to keep or replicate when they renovate or extend. The genuine article, however, is prone to rust, poor thermal performance, and increasingly hard-to-source parts, which leads most homeowners to compare it against heritage-style aluminium as a modern replacement or match.
This guide compares the two directly for anyone deciding whether to repair or replace existing steel windows, or to specify heritage aluminium on an extension to match an existing steel-windowed house.
Genuine steel windows are prized for extremely narrow glazing bars and frames, a result of steel's high strength relative to its cross-section. Heritage aluminium systems were developed specifically to get as close as possible to that same slim profile using a thermally broken aluminium extrusion, and on many properties the visual difference from a normal viewing distance is negligible.
| Genuine steel | Heritage aluminium | |
|---|---|---|
| Sightline | Narrowest available | Very narrow, close to steel |
| Thermal performance | Poor unless specially upgraded | 1.2-1.4 W/m²K double glazed, meets Part L easily |
| Corrosion risk | Rusts without regular maintenance | Powder-coated aluminium does not rust |
| Repair vs replace | Existing units can sometimes be refurbished | New manufacture, not a refurbishment option |
| Typical cost | Refurbishment or bespoke replication, often high | £1,600–£3,200 per window, guide price |
| Weight | Heavy | Considerably lighter |
This is where the comparison is least close. Genuine single-glazed steel windows perform poorly by modern standards, and even double-glazed steel retrofits struggle to approach the U-values achieved by a modern thermally broken aluminium frame. Heritage aluminium comfortably exceeds the Part L requirement of 1.4 W/m²K, typically achieving 1.2-1.4 W/m²K double glazed, making it the clear choice wherever thermal performance and ongoing running costs matter.
Refurbishing genuine steel windows, including de-rusting, re-glazing and painting, can be a specialist and costly undertaking, and does not usually deliver a significant improvement in thermal performance even when done well. New heritage aluminium typically costs £1,600-£3,200 per window supplied and installed, and needs no repainting or rust treatment over its service life, only an occasional wipe down and a check of hardware and seals.
Outside of these specific cases, heritage aluminium is generally the more practical choice for most homeowners wanting the steel-window look without steel's drawbacks.
From a real Windows in the Lakes project
West Yorkshire · 32 windows · 4 doors
A live self-build programme with 36 openings across four elevations, all in newly dressed stone, several of them non-standard shapes — triangular gables and a full-height narrow light — with no tolerance for cumulative setting-out error across the elevation.
Early involvement with the builder to agree structural opening sizes, then a full measured survey of every opening after the stonework was complete and before manufacture. Georgian bar layouts were drawn as a set rather than window by window, so bar spacing aligns horizontally across each elevation, and the non-standard gable and side-light units were manufactured to survey.
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