Structural and base materials · Metals
Aluminium (Sheet, Extrusion and Sections)
Covers what sets aluminium apart from the steel-based metals in construction: low weight, extruded profiles, applied finishes, marked thermal movement and contact sensitivity.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What aluminium is
Aluminium is a light, comparatively soft metal used in construction as rolled sheet and coil, as extruded profiles pushed through a shaped die, and as castings. Extrusion is what makes it distinctive: intricate profiles carrying channels, screw ports and thermal breaks can be produced in a single piece, which is why window, door and curtain wall systems are built from it.
It forms a tight oxide film in air, and that film gives it a base level of resistance. Most architectural aluminium is then finished further, either by anodising, which thickens and colours the oxide film electrochemically, or by powder coating or liquid painting, which puts a separate layer over it. The two routes weather differently, repair differently, and rarely match one another in the same nominal colour.
Two behaviours shape how it is detailed. It expands and contracts noticeably as temperature changes, so sheet, trims and framing are designed to move rather than to be held rigidly in place. And it is sensitive in contact: wet cement-based materials, some timbers and contact with other metals in damp conditions can all affect the surface, which is why isolation appears as a standard part of the detail.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- Aluminum (US spelling)
- Aluminium alloy
- Extruded aluminium
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Window, door and curtain wall framing built up from extruded profiles.
- Rainscreen cladding panels, cassettes and trims folded from sheet.
- Roof sheeting, flashings, copings, fascias and rainwater goods.
- Support rails, brackets and carrier components behind cladding.
- Balustrades, louvres and shading components on external elevations.
- Internal trims, thresholds and light framing where weight matters.
Consideration
Where it is commonly considered
- Where low weight matters, such as large panels or components positioned by hand.
- Where a complex profile can be extruded in one piece rather than fabricated from several.
- Where a wide range of applied colours and finishes is wanted on external components.
- Where an unprotected steel component would be difficult to maintain in the same position.
- Where thin, crisp sight lines are wanted around glazing or panel edges.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Where it would sit in direct contact with wet mortar, concrete or other alkaline materials.
- Where it would touch another metal in a position that stays damp for long periods.
- Where the surface will take heavy impact or abrasion, since it marks more readily than steel.
- Where a component is being asked to carry significant load without engineering input.
- Where long unbroken runs are proposed without a movement strategy in the detailing.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Thermal behaviour
- Aluminium expands and contracts appreciably as temperature changes, so long runs of sheet, trim and framing are detailed with slots, sliding clips and open joints that let the movement happen without buckling the metal or working the fixings loose.
- Weathering and exposure
- Anodised and coated finishes weather along different paths. Anodising is part of the surface and tends to fade or chalk gradually, while a coating can chip to expose the metal beneath, which then oxidises to a dull grey patch.
- Substrate dependency
- Contact with fresh cement-based materials, some treated timbers and other metals in damp positions can affect the surface, so isolating tapes, sleeves or washers usually appear in the specified detail rather than being optional.
- Appearance
- Powder coating gives an even colour across complex shapes, while anodising follows the metal itself and can show slight variation between extrusions, and between extruded and rolled components placed side by side.
- Repairability
- Coating damage can sometimes be touched in, but touch-up on a factory finish rarely matches under raking light, and damage to an anodised surface cannot be repaired in place in the same way at all.
- Installation dependency
- Because the metal is soft, over-tightened fixings, careless handling and hard tools mark it easily. Protective films are normally kept on until late in the programme and then removed within the period the supplier states.
- Maintenance
- Regular washing removes deposits that would otherwise hold moisture against the finish. Coating suppliers usually state cleaning expectations, and those vary by product, by colour and by how exposed the component is.
Exposure
Exposure and environmental conditions
- Is the component in a coastal or industrial atmosphere where deposits build up on the surface?
- Is the surface rain-washed, or sheltered so that dirt and salts sit on the finish?
- Will run-off from another metal or from a masonry surface pass across the aluminium?
- How much temperature swing will the component see in this orientation through the year?
- Will it be splashed by ground water, de-icing salt or irrigation at low level?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- Isolating tapes, sleeves or washers wherever aluminium meets another metal or a wet material.
- Fixing arrangements that hold the component securely while still allowing it to move.
- The carrier or support system behind cladding, which is designed as a set with the panel.
- Sealants and gaskets have to be compatible with the finish and are specified together with it.
- Where profiles form part of a thermally broken system, the break is integral to the product.
Appearance
Appearance and finish considerations
- Powder coating and anodising look different in the same nominal colour and are hard to mix.
- Extrusion lines and slight surface texture can show through thin or high-gloss finishes.
- Large flat panels reveal any waviness in reflected light, which is a fabrication question.
- Colour matching between sheet cladding and extruded frames usually needs samples of both.
- Edges, returns and folded details decide how crisp the finished component reads on the building.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- What finish is specified, and what exposure did the supplier have in mind for it?
- How is movement accommodated along long components and at their end conditions?
- Where does the aluminium touch other metals, and what isolation has been included?
- Is the finish likely to be damaged by following trades, and how is it being protected?
- How would a damaged panel or profile be replaced later, and is matching stock available?
Upkeep
Maintenance and repair considerations
- What cleaning products does the finish supplier consider appropriate for this surface?
- How often does this exposure suggest washing to keep deposits off the finish?
- Can chips in a coated finish be touched in, and how visible would the repair be?
- Who holds the finish reference so that a later replacement can be matched to it?
- What signs of surface deterioration are worth photographing and reporting?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- Protective film needs removing within the period the supplier states, before it becomes difficult.
- Fixings are chosen for compatibility with the metal as well as for their holding power.
- Cut ends and drilled holes in coated profiles expose bare metal and are treated as specified.
- Handling with clean equipment avoids denting a material that is softer than steel.
- Sequencing keeps finished aluminium away from wet cement-based work wherever possible.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The finish type, colour reference and the supplier's guidance for the intended exposure.
- Cleaning and maintenance guidance issued with the finish being supplied.
- Details showing how movement is accommodated within the specified system.
- Information on isolation where the aluminium meets other metals or masonry.
- Compatibility information for sealants and gaskets used against the finish.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Is the finish anodised or coated, and what led to that choice for this exposure?
- How does the detail allow the metal to expand and contract across long runs?
- Where does the aluminium touch another metal or a wet cement-based material?
- What isolation is specified at those contacts, and who is responsible for installing it?
- How will the surface be protected from following trades while work continues on site?
- What is the replacement route if a panel or profile is damaged after completion?
- Are sheet and extruded components being matched from the same finish batch where they meet?
- What cleaning does the finish supplier expect in a position as exposed as this one?
Blind spots
Commonly overlooked points
- Anodised and powder coated components in the same colour rarely match when seen side by side.
- Movement in long runs shows first at fixings and end stops rather than in the middle of a run.
- Protective film left on too long in sunlight can become very difficult to remove cleanly.
- Splashes of wet mortar or concrete on a finished surface need dealing with promptly.
- Aluminium marks under ordinary site handling in ways that heavier steel components do not.
What this page does not do
- Where aluminium carries load, sizing and adequacy are engineering matters for a qualified professional.
- Contact between aluminium and other metals, or wet alkaline materials, should be reviewed for the specific detail rather than assumed.
- Finish performance varies by product, by colour and by exposure, and belongs to the manufacturer's documentation rather than to a reference page.
Component forms
Building components commonly formed from this material
Elements this material is commonly used to make, named by the position they occupy in an assembly rather than by what they are bought as. This states common practice only — it is not a statement that this material suits any of these components in a particular building.
Related entries
Alternatives to consider
Entries that may be considered instead of this one for a similar job. Not a statement that they are interchangeable, or equal in any respect.
Related entries
Common comparisons
Entries met at the same decision but which behave differently, so the comparison is about the difference rather than a swap.
Related entries
Often used alongside
Entries commonly encountered together with this one. Co-occurrence only — never a claim that any combination is compatible or suitable.
Related entries
Used in
Entries this is commonly incorporated into as a constituent or layer.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Metals in Construction
Reference entries for the metals used in building — structural and light-gauge steel, galvanised and stainless steel, aluminium, copper, zinc, lead and reinforcement.
Browse all metals entries →