Period properties, conservation areas and buildings that once had steel windows present a specific problem: the customer wants the slim, elegant look of the original, but modern thermal rules and the practicalities of maintenance rule out putting old single-glazed steel back. Heritage aluminium is the answer that satisfies both — and, increasingly, the conservation officer too. Here's how to spec it.
The short answer
Heritage aluminium replicates the slim sightlines of original steel (Crittall-style) windows while delivering modern double glazing, security and thermal performance. It's the go-to for replacing steel windows and for conservation-area work where a chunky replacement would be refused.
Why steel windows are a problem to replace like-for-like
Original steel windows have beautifully slim frames, but they're single-glazed, prone to rust, cold, draughty and a nightmare to maintain. Putting new single-glazed steel back rarely makes sense: it won't meet thermal expectations and it carries the same maintenance burden. But swapping to standard uPVC or bulky aluminium loses the very thing that makes the building look right — the delicate frames and multi-pane layout. That's the gap heritage aluminium fills.
How heritage aluminium gets the look right
Aluminium is a structural metal, so it holds a slim, square profile that standard uPVC can't. Heritage systems push this further with narrow frames and sightlines engineered to match original steel, and they recreate the details that sell the illusion:
- Slim frames and mullions close to the proportions of the steel original.
- Fine glazing bars — either structural or applied — to recreate the multi-pane (Georgian or Crittall) grid.
- Period ironmongery — monkey-tail handles, peg stays and casement fasteners in heritage finishes.
- Matt heritage colours in any RAL, so black, off-white or a conservation green can be matched exactly.
Modern performance behind the period look
Underneath the slim profile it's a fully modern window: thermally broken aluminium with double (or slim-profile double) glazing, so it meets the Approved Document L requirement for replacement windows, and it can be specified to PAS 24 security. For very tight conservation sightlines, slim-profile sealed units keep the glazing cavity narrow so the glass line still looks authentic without dropping to single glazing.
Conservation areas and listed buildings — the consent question
This is where the job can stall, so raise it early. In a conservation area or on a listed building, replacing windows can need planning permission or listed-building consent, and the conservation officer will care about sightlines, the glazing-bar pattern, the opening style and the finish. Heritage aluminium's appeal to them is precisely that it can match the original far more closely than standard replacements — but the customer should confirm the consent position with the local authority before committing. Getting a sample or detailed sightline drawing in front of the officer often smooths approval.
How to steer the conversation
- Replacing old steel windows: heritage aluminium is the natural match.
- Conservation area / listed: check consent first, then spec to match sightlines and bar pattern.
- Wants authentic timber instead: hardwood is the alternative heritage route — offer both.
- Modern thermal + period look: thermally broken frame, slim-profile double glazing.
- Always: match colour, glazing bars and ironmongery — the details are what sell the look.
We supply heritage-profile aluminium windows matched to original steel sightlines, with the glazing-bar and ironmongery options conservation work needs. Where a customer wants the traditional route instead, we also carry hardwood windows — so you can put both options in front of them and let the building decide.
