An aluminium clad wood window has a solid or engineered timber frame on the room side and an extruded aluminium shell on the weather side, so you get the warmth and insulation of wood indoors and a coated metal skin that does not need repainting outdoors. It suits villas, hotels, heritage-style apartments and coastal homes where a plain aluminium frame feels too cold and an all-timber frame needs too much upkeep. Metline supplies the aluminium cladding profiles, clips and coated finishes to timber-window makers and projects worldwide.
A clad window is a timber window with a protective metal jacket. The timber does the structural and thermal work and gives the interior its look; the aluminium shell keeps rain, ultraviolet light and wind-driven grit away from the wood. Because the two materials each do the job they are best at, a well-made clad window can outlast both a painted timber window and a basic aluminium window in the same climate.
The idea came from northern Europe and North America, where timber windows were traditional but repainting the outside every five to eight years was expensive. Fixing a metal cap to the exterior faces removed most of that maintenance while keeping the timber inside. Modern systems use precision extrusions clipped to the timber with a ventilated gap behind them, so the wood can breathe and any moisture that gets behind the cladding drains away rather than soaking the frame.
Clad windows are sometimes confused with two related products. A wood-clad aluminium window is the reverse: an aluminium (often thermally broken) structural frame with timber trim fixed to the room side. A composite or hybrid window may combine timber, aluminium and a polymer or foam insulating core. All three aim to show wood indoors and metal outdoors, but they behave differently under load and heat, so it pays to know which one a quotation actually describes.
Every clad system has the same four layers, read from the room outwards. Understanding them helps you judge quality, because most failures in clad windows start where one layer meets the next.
| Layer | Typical material | What it does | What to check |
|---|---|---|---|
| Interior timber frame and sash | Finger-jointed, laminated (glulam) pine, spruce, larch, oak, meranti or modified timber | Carries the glass and hardware loads, provides insulation and the visible interior finish | Laminated, kiln-dried stock at 10 – 14 % moisture; factory-applied finish on all faces |
| Glazing and seals | Double or triple insulated glass units with warm-edge spacers; EPDM or TPE gaskets | Controls heat loss, solar gain, noise and air leakage | Gasket continuity at corners, drained glazing rebate, spacer type |
| Ventilation and drainage gap | Air space of a few millimetres between timber and cladding, with drainage slots | Lets any moisture behind the cladding drain and evaporate instead of being trapped against the wood | The gap must be open at the bottom and never sealed solid with silicone |
| Aluminium cladding | Extruded 6063 or 6060 alloy, typically 1.2 – 2.0 mm wall, coated | Weather shell: sheds water, blocks UV, resists impact and gives the exterior colour | Extruded rather than roll-formed sheet, mitred and corner-cleated or welded corners, coating standard |
The cladding is fixed with plastic or nylon clips that slide into a groove in the extrusion and screw into the timber. Clips let the aluminium expand and contract independently of the wood: aluminium moves about 2.3 mm per metre for every 100 °C change in temperature, while timber hardly moves with heat but swells and shrinks with humidity. Rigid fixing of one to the other would force one material to crack or buckle over a few seasons.
Corners are where cheap cladding gives itself away. Quality systems use mitred extrusions joined with internal corner cleats, crimped or bonded, or factory-welded corners on sashes. Butt-jointed, roll-formed sheet with exposed sealant joints may look the same on delivery but tends to open up, admit water and stain the timber within a few years.
Roll-formed cladding is shaped from thin coated sheet, often around 0.6 – 0.8 mm. Extruded cladding is pushed through a die and is usually two or more times thicker, holds sharper profiles and resists denting far better. For long-life projects, specify extruded cladding.
Window cladding needs an alloy that extrudes into thin, detailed shapes with a smooth surface for coating. That is why almost every system uses the 6xxx series, and in particular 6063 and its European near-twin 6060. Strength requirements are modest because the timber carries the loads; what matters is surface quality, dimensional accuracy and coating adhesion.
| Alloy and temper | Typical tensile strength | Typical yield strength | Why it is used |
|---|---|---|---|
| 6063-T5 | 185 MPa | 145 MPa | Standard cladding and bead alloy; excellent surface for powder and PVDF |
| 6063-T6 | 240 MPa | 215 MPa | Where cladding also carries fixings or long spans, such as mullion caps |
| 6060-T5 / T6 | 175 – 215 MPa | 130 – 170 MPa | European equivalent to 6063 (EN AW-6060), very good anodising response |
| 6005A-T6 | 270 MPa | 225 MPa | Heavier structural reinforcing sections in large lift-and-slide or fixed units |
Values are typical published figures for extruded sections; EN 755-2 and ASTM B221 specify the guaranteed minimums by wall thickness.
Coating choice decides how the window looks after fifteen or twenty years in the sun, so match it to the exposure:
Resins with at least 70 % PVDF give the best colour and gloss retention. Tested to AAMA 2605 in North America and to the top class of Qualicoat or GSB in Europe. The right choice for coastal, high-altitude and tropical sites.
The most common finish worldwide. Standard-durability powders meet Qualicoat class 1 or AAMA 2603/2604; super-durable powders (Qualicoat class 2) hold colour much longer in strong sunlight.
An oxide layer grown from the metal itself in clear, bronze or black. Specify at least 20 µm (Qualanod class 20) for exterior use, and 25 µm near the sea.
Sublimation printing over powder coat reproduces oak or walnut grain on the exterior for heritage or rustic projects.
Fine textures hide handling marks and minor dents; metallic effects need clear topcoats outdoors.
Because cladding and timber are finished separately, any RAL or custom colour outside can be paired with any stain or paint inside.
The timber species affects cost, stability, colour and how well the frame takes stain. Engineered (laminated, finger-jointed) sections are now standard in good clad windows because they twist and check far less than solid boards.
| Species | Character | Stability | Best suited to |
|---|---|---|---|
| Scots pine / Nordic spruce | Pale, even grain; takes paint and stain well | Good when laminated | Cost-effective residential projects, painted interiors |
| European larch | Warm reddish tone, naturally resinous and durable | Good | Alpine and cold-climate homes, natural oiled finishes |
| European or American white oak | Strong figure, hard surface, premium look | Very good when laminated | Villas, hotels and high-end apartments |
| Meranti / sapele (certified) | Medium-red hardwood with fine grain | Very good | Warm, humid climates and mahogany-style interiors |
| Walnut, cherry and other hardwoods | Dark, decorative | Good | Feature windows and bespoke residences |
| Thermally modified or acetylated timber | Enhanced durability and reduced swelling | Excellent | Humid and coastal sites, long-life projects |
Ask for timber from legally harvested, certified sources (FSC or PEFC) where your project or national rules require it, especially for public buildings and projects targeting green ratings. Interior finishes are normally water-based lacquers or hard-wax oils applied in the factory before glazing, so that every face of every component is sealed. Site-finished timber tends to leave end grain and rebates unprotected.
Interior colour options typically include clear lacquer, light and dark stains, white or RAL-matched opaque paint, and brushed or wire-textured surfaces for a more rustic look. Request a finished sample of both the timber and the cladding colour before approving production.
Almost every opening style can be built as a clad window. The table on the left of most system catalogues starts with these:
Side-hinged sash opening outward (common in the UK, Asia and North America) or inward (common in continental Europe). Compression seals give excellent air and water tightness.
Inward-opening sash that tilts at the top for secure ventilation or swings fully open for cleaning. The standard European clad window and ideal for high-rise residential.
Hinged at the top, opening outward so the sash sheds rain while ventilating. Often combined with fixed lights below.
Vertically sliding sashes for traditional elevations; clad versions replace old timber sash windows with far less maintenance.
Horizontal sashes on tracks for wide openings; lift-and-slide hardware raises the sash off its seals to glide, then lowers it to seal tightly.
Non-opening lights in large sizes, plus arches, trapezoids and circles that are difficult in plain aluminium but natural in timber.
Projecting assemblies of casement and fixed units joined by structural mullions, popular in residential renovation.
Entrance, French, folding and lift-and-slide doors built with the same timber-and-cladding principle, so doors and windows match.
Transoms, sidelights and stacked fixed-over-opening assemblies coupled into one frame for a consistent sightline.
A clad window should be tested as a complete unit, not judged from material data. The standards below are the ones most often written into specifications. Ask for the actual test report or declaration of performance for the size and configuration you are buying.
| Property | Europe and many export markets | North America | Typical range for good clad windows |
|---|---|---|---|
| Product standard | EN 14351-1 (CE / UKCA marking) | AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS) | Full test report for the unit type |
| Air permeability | EN 1026 test, EN 12207 classes 1 – 4 | ASTM E283 | Class 4 (EN), or ≤ 0.3 cfm/ft² |
| Watertightness | EN 1027 test, EN 12208 classes 1A – 9A, E750+ | ASTM E547 / E331 | Class 7A – E900 for exposed elevations |
| Wind load resistance | EN 12211 test, EN 12210 classes A/B/C 1 – 5 | ASTM E330 (performance grade) | Class B4 – C5, or design pressure to suit the building height |
| Thermal transmittance | EN ISO 10077-1/-2 or EN 12567-1 (Uw) | NFRC 100 (U-factor) | Uw about 0.8 – 1.6 W/m²·K depending on glass |
| Acoustic insulation | EN ISO 10140 test, EN ISO 717-1 rating (Rw) | ASTM E90 / E1332 (STC, OITC) | Rw about 32 – 45 dB depending on glass build-up |
| Security | EN 1627 resistance classes RC1N – RC3 | ASTM F588 forced entry | RC2 for accessible ground-floor windows |
| Exterior coating | Qualicoat, GSB, Qualanod | AAMA 2603 / 2604 / 2605 | PVDF or super-durable powder on exposed sites |
Thermal performance is where clad windows earn their price. Softwood has a thermal conductivity of roughly 0.13 W/m·K and 6063 aluminium roughly 200 W/m·K, so a timber frame core without a thermal break already insulates well. Most of the remaining heat loss is through the glass and its edge, which is why triple glazing with warm-edge spacers and argon fill takes a good clad window down towards 0.8 W/m²·K, a level required for passive-house projects in cold climates.
| Factor | Aluminium clad wood | Thermally broken aluminium | Painted timber | uPVC |
|---|---|---|---|---|
| Interior look | Natural wood | Metal (any colour) | Natural wood | Plastic, foiled wood effect |
| Exterior maintenance | Very low (wash only) | Very low | Repaint every 5 – 8 years | Low, but colours fade |
| Frame insulation | Very good | Good (depends on break width) | Very good | Very good |
| Slimness and large spans | Good | Excellent | Fair | Fair (steel-reinforced) |
| Behaviour in high humidity | Good if drained and sealed | Excellent | Needs care | Excellent |
| Fire behaviour | Timber chars slowly; aluminium non-combustible | Non-combustible frame | Combustible | Combustible, softens with heat |
| Recyclability | Aluminium fully recyclable; timber renewable | Fully recyclable | Renewable | Limited |
| Relative cost | High | Medium – high | Medium | Low – medium |
In short, choose a plain thermally broken aluminium window when you want the slimmest frames, the largest glass and a modern metal interior, or when the budget is tight. Choose aluminium clad wood when the interior design calls for real timber, when thermal comfort near the frame matters, or when the project replaces traditional timber windows and must keep their character. Our thermal break aluminium windows page covers the metal-only route in detail.
Clad windows are almost always made to measure, but early budgets and replacement surveys are easier with reference sizes. The figures below are common rough-opening dimensions used in residential planning; final sizes come from site measurement and the project drawings.
| Window type | Rough opening (W × H) | Approx. metric size | Typical use |
|---|---|---|---|
| Double-hung | 24 × 36 in | 610 × 915 mm | Bathrooms, small bedrooms |
| Double-hung | 32 × 60 in | 813 × 1524 mm | Bedrooms and living rooms |
| Double-hung | 36 × 72 in | 914 × 1829 mm | Tall rooms and views |
| Sliding | 48 × 36 in | 1219 × 914 mm | Kitchens and side walls |
| Sliding | 72 × 60 in | 1829 × 1524 mm | Master bedrooms, wide views |
| Casement | 24 × 36 in | 610 × 915 mm | Above a sink, bathrooms |
| Casement | 36 × 72 in | 914 × 1829 mm | Bedrooms and tall openings |
| Fixed / picture | 48 × 48 in | 1219 × 1219 mm | Feature walls, stair landings |
| Fixed / picture | 72 × 72 in | 1829 × 1829 mm | Large view windows in villas |
Maximum sash sizes are limited by glass weight and hardware rating rather than the timber. Triple glazing weighs about 30 kg/m² or more, so a large tilt-and-turn sash may need heavy-duty hinges or a change to a fixed light with a smaller opening vent. Confirm hardware capacity for any sash above roughly 1.2 m wide or 100 kg.
Good practice
Consider another frame when
Timber reacts to its surroundings. Storing clad windows outdoors on site, or installing them into a building that is still drying out after wet plastering and screeding, can raise the moisture content of the frame and lift the interior finish. Keep units wrapped, raised off the ground and ventilated until the building is closed in.
In replacement work, measure the structural opening after removing old frames where possible. Clad windows can be supplied as full-frame replacements, with the opening stripped back to the masonry, or in some markets as insert units that sit inside a sound existing frame. Full-frame replacement allows the wall junction to be insulated and sealed properly and usually gives better long-term results.
Wood interiors that match floors and joinery, with a durable coloured exterior on every elevation.
Tilt-and-turn and casement units that bring comfort and acoustic performance to city flats, including replacement of old timber windows.
Warm, natural interiors that support the guest experience, with low-maintenance exteriors near coasts and mountains.
PVDF or anodised cladding protects the timber from salt spray and intense sun.
Timber profiles and glazing bars that respect traditional elevations while meeting modern energy rules.
Triple-glazed clad windows reach very low Uw values with warm interior surfaces.
A typical villa package combines tilt-and-turn bedroom windows, a large fixed living-room light and a lift-and-slide door to the terrace, all in oak inside and a dark grey PVDF exterior. A typical apartment renovation uses pine-framed casements with white paint inside and a powder-coated exterior matched to the building colour, delivered floor by floor according to the window schedule.
Compare quotations on a like-for-like basis: same Uw, same glass build-up, same cladding thickness and coating standard, same hardware brand class. Two windows that look identical in a brochure can differ widely in what sits behind the cladding.
They are worth it when you want a real timber interior with very little exterior maintenance, or when replacing traditional timber windows in a way that keeps their character. Over 25 – 30 years the avoided repainting and the better thermal comfort usually offset much of the price difference. If neither the wood interior nor the low upkeep matters to you, a thermally broken aluminium window is better value.
None. "Aluminum clad" is the American spelling and "aluminium clad" the British and international spelling for the same product: a timber window with an aluminium exterior shell.
Not in a properly designed system. The cladding is held off the timber on clips with a ventilated, drained gap, so any water that gets behind it runs out through slots at the bottom. Problems arise when cladding is sealed tight to the wood or the drainage slots are blocked with sealant.
With extruded cladding, a durable coating and factory-finished timber, 40 years or more is a reasonable expectation. The interior timber finish may need light refreshing every 10 – 15 years in sunny rooms, and seals and hardware should be checked and adjusted periodically.
Usually 6063-T5 or 6060-T5/T6 extrusions, chosen for their smooth surface and excellent coating and anodising response. Heavier reinforcing sections in large doors may be 6063-T6 or 6005A-T6.
Yes, with the right choices: a stable laminated or modified timber, a fully sealed interior finish, a PVDF or anodised exterior, and installation only after the building interior is dry. In permanently wet interiors such as pool halls, an all-aluminium window is the safer option.
Send your window schedule, timber and colour preferences and destination. We will reply with cladding profile options, finishes and a delivered quotation.
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