Aluminium and steel are the two frame materials worth serious consideration on modern high-specification doors and windows. Aluminium dominates the volume market because it is lighter, warmer, easier to finish and easier to fabricate. Steel — specifically Jansen's fabricated steel systems — still wins in certain conditions where aluminium cannot compete. This article covers where each material has the edge and how to think about the choice for a Borehamwood residential project.
What each material actually is
Aluminium doors and windows use extruded aluminium profiles — hollow sections with an insulating thermal break bonded between the internal and external face. The industry has been engineering aluminium fenestration for over sixty years; systems like Schüco AWS and Cortizo's Cor Vision Plus-style Cor Vision are the current state of the art.
Jansen steel doors and windows use cold-rolled steel profiles, welded and finished. Modern Jansen systems include their own thermal-break equivalent — an insulated core within the profile — that brings the thermal performance close to good aluminium while retaining the material properties of steel.
Where steel wins
- Sightlines. Steel is stronger per unit of cross-section, so profiles can be slimmer. Modern Jansen sightlines are meaningfully thinner than the equivalent aluminium — the eye reads more glass, less frame.
- Pane size. Steel carries larger panes without deflection. Ultra-large fixed lights on architectural extensions often go to steel by default.
- Structural doors. Where a door is doing structural work — as sometimes happens on very large openings — steel is the more predictable choice.
- Fire-rated applications. Steel fire doors have a longer track record and often better tested performance than equivalent aluminium.
- Aesthetic longevity. Steel does not read as "budget" in twenty years the way early aluminium sometimes does.
Where aluminium wins
- Cost. Aluminium is meaningfully cheaper than steel on comparable spec, sometimes by 40-60%.
- Weight. Aluminium doors are lighter, easier to install, and put less load on the structure.
- Thermal performance. Modern aluminium systems still edge out modern steel on whole-window U-values, though the gap has closed.
- Colour and finish. Powder coating on aluminium comes in effectively unlimited RAL colours and is straightforward to touch up. Steel finishes are more restricted.
- Fabrication lead time. Aluminium fabricators are more numerous and turn projects faster.
- Maintenance. Aluminium is largely maintenance-free. Steel is durable but does need attention at the interfaces where its finish meets water.
The Jansen sub-category
Jansen is the reference name for high-specification residential and architectural steel systems in the UK. Their VISS, Janisol Arte and Janisol HI ranges cover different price points and applications. On a Borehamwood period-property or contemporary-architectural project where slim steel sightlines are the design driver, Jansen is usually the discussion. Approved installers like 5EC Aluminium carry Jansen credentials alongside their aluminium systems, and their published Jansen steel door installations covers what a proper steel installation looks like in this segment.
How to decide
A useful decision framework:
- What is the maximum single pane size? If it is under 2.5 x 2.5 m, aluminium handles it comfortably. Above that, steel starts to justify itself.
- How important are slim sightlines? If the aesthetic driver is "as much glass, as little frame as possible", steel wins. If sightlines can be normal for aluminium, aluminium wins on cost.
- What is the whole-project budget? Steel doors and windows can add 40-60% to the fenestration cost. On a project where budget is tight, aluminium is the honest answer.
- What is the aesthetic direction? Heavy, industrial, permanent — steel. Clean, modern, minimal — aluminium can do this too, but steel is often preferred.
- Where is the building? On listed and conservation properties, steel is sometimes the only acceptable specification. Aluminium may be excluded regardless of cost.
What we would not use to decide
- "Steel is more secure than aluminium." Not necessarily true — properly-specified aluminium PAS 24 doors are as secure as steel equivalents.
- "Steel lasts longer." Modern aluminium and modern steel both easily see 40+ year residential lives if installed correctly.
- "Aluminium always looks cheap." Depends entirely on the system, the fabricator and the installer.
Cost bands to expect
Rough guidance for a Hertfordshire residential project (2026 prices, indicative only):
- Standard aluminium doors and windows on a whole-house scope: £X per m² of glazed area.
- High-specification Schüco or Cortizo equivalent: 1.3-1.5x standard aluminium.
- Heritage-styled aluminium: 1.4-1.7x standard aluminium.
- Jansen steel: 1.8-2.5x standard aluminium.
These are supply-and-fit rough multipliers, not spot prices — but useful for scoping the budget decision at the design stage.
The honest answer
Most Borehamwood residential projects will do very well on aluminium. Where the specification calls for exceptional sightlines, very large panes, or a specific aesthetic that only steel achieves, Jansen is worth the premium. The tension between the two materials is real, and the wrong answer is committing to steel because it sounds premium when aluminium would deliver identical performance for meaningfully less. Choose on the specific need, not on the material's reputation.