When I get three offers for the same façade and the gap between the extremes is 40%, the first one I look at isn't the cheapest. It's the most expensive — because that's usually where you can see what's missing from the others.
ACP is a sandwich panel: two sheets of aluminum with a core between them. The entire difference in price, durability and fire classification comes down to two variables: what the core is and how thick the aluminum is. An offer that says "4 mm ACP cladding" describes the total panel thickness and says nothing about either of them.
The core decides whether the job is legal
PE means a full polyethylene core. Cheap, with the best flatness, easy to work, and combustible. Polyethylene burns with a high heat release. In a ventilated façade, the cavity behind acts like a chimney and spreads the flame vertically faster than the building structure would. FR has a mineral core with a reduced polymer content and improved fire reaction — an intermediate position, not an equivalent of A2. A2 has a predominantly mineral core, classified A2-s1,d0 per EN 13501-1: negligible contribution to a fire, low smoke, no flaming droplets.
My recommendation on public, commercial or crowded buildings is A2, no alternatives. Not out of professional caution — the P118/1-2025 code, in force since 10 May 2025, requires class A1 or A2-s1,d0 for the elements of ventilated façades and curtain walls and for exterior thermal insulation, across an extended range of buildings: educational facilities, healthcare facilities, residential buildings over 20 m and, regardless of height or use, any building on which photovoltaic panels are installed.
That last category is the one everyone underestimates. If you run a network and don't control what gets installed on the roof three years from now, you've already chosen the fire-reaction class — you just don't know it yet. For low height regimes, the code allows lower classes. The cost difference between FR and A2, however, stays well below the cost of a later reclassification, and A2 removes an entire category of discussions from the start: at permitting, at insurance, at franchise audit.
PE-core ACP is still installed on buildings where it has no business being. It happens because it's cheaper, because it looks identical on handover day and because no one opens the panel to check. An A2 panel and a PE one are visually indistinguishable after installation. The difference shows only once. The document that settles this is the panel manufacturer's declaration of performance, with the fire-reaction class stated explicitly, matched to the batch actually delivered. Not the generic data sheet on the importer's website.
Why cheap façades ripple
A 4 mm panel can have aluminum sheets of 0.30, 0.40 or 0.50 mm. The rest is core. At 0.30 the rigidity is insufficient and the deformation is visible — it's the thickness of cheap imported panels. 0.40 is the acceptable threshold for commercial façades. 0.50 becomes necessary on large panels, southern exposure or areas with high wind load.
The effect is called oil canning: the rippling of the surface, like a slightly bulged sheet. It doesn't appear at installation. It appears after the first summer, when the temperature difference between the exposed face and the core produces stresses that a 0.3 mm aluminum can't absorb. In a network, the consequence is more troublesome than on a single building: the southern façade looks different from the northern one, at the same location, and the handover photo no longer resembles the building. The aluminum sheet thickness is requested explicitly in the offer. If the answer to the question is "4 mm," your contact is talking about the panel.
The structure is the build, the panel is the finish
The aluminum structure is compatible with the panel — the same expansion coefficient, no galvanic couple. Galvanized steel is stiffer and cheaper, but it requires proper separation at contact with the aluminum, otherwise galvanic corrosion appears right at the fixing points. Both are correct, executed correctly. Non-galvanized steel, or steel protected only by paint, is not a third option.
Expansion is where you see whether someone calculated or estimated. The panel doesn't work at air temperature but at the temperature of its own surface: in winter, on a northern façade, it drops toward -25°C; in summer, on a southern one with a dark finish, it slightly exceeds +50°C. The realistic assumption is therefore a 70°C variation. Aluminum expands about 1.6 mm per linear meter over this range — on a 12-meter span, roughly 2 cm of movement between the annual extremes. The structure must allow this movement through fixed points and sliding points distributed correctly. Fixed rigidly everywhere, the stress discharges where it can: it ripples the panel, ovalizes the holes, shears the rivets. The joint width follows the same calculation, not aesthetics — a joint sized for an underestimated variation closes in summer and forces the panels into each other.
Anchoring depends on the real substrate, not the assumed one. A plug sized for concrete, installed in AAC, has a load capacity several times lower. It's the most frequent cause of failure under wind load. And on tall buildings, at corners and eaves, suction loads are several times higher than in the general field of the façade — the spacing between brackets is calculated there, not carried over from the field.
Fixing the panel
Cassetted, the panel is routed, folded and turned into a tray with edges, fixed mechanically to the structure. It allows expansion, has its own rigidity and, important for a network, allows a single panel to be removed and replaced without touching the rest of the façade. Direct-riveted means a flat panel, fixed with rivets through the visible face. Cheaper, the rivets stay visible and, if the holes aren't oversized for expansion, the panel deforms. Structural bonding requires controlled temperature and humidity conditions at application, rigorous surface preparation, certified adhesive and traceability. On site, these conditions aren't met. The result appears in three to five years, through local detachment. I don't use it and don't recommend it. When an offer is significantly below the others, the fixing system is the first place to look for the explanation.
What shows from three meters
A correctly executed façade is recognized by details, not by the large surfaces. Joints of constant width across the whole façade, aligned vertically and horizontally — a joint that varies from one module to the next jumps out immediately. Corners routed and folded from the same panel; a joint from two pieces produces a visible line and a point of infiltration. Top and bottom edges closed, with a drip edge, otherwise the core stays exposed and water gets in. Connections to the joinery solved with sills and profiles, not with generously applied silicone. And an observation that contradicts expectation: existing buildings aren't flat. Deviations are corrected from adjustable brackets, in the structure. When they're corrected by forcing the panel, the result shows on the face of the façade.
Ventilation and its trap
The air layer between panel and wall, open at the base and at the coping, isn't a technical bonus. Without it, condensation builds up behind, the structure corrodes, and the thermal insulation, if any, loses its performance through dampness. With it, moisture is removed, the thermal load on the wall drops and the system's lifespan increases. The same cavity accelerates the vertical spread of a fire. From this it follows that a ventilated façade with a PE core is the most dangerous configuration possible — and one that does get built. On a ventilated façade, A2 isn't a preference of the contractor. It's the requirement of the code.
The administrative part, per location
Cladding a façade changes the building's exterior appearance and, in most cases, requires a building permit. It isn't maintenance work, however often it's treated that way. Before contracting, you check the building's zoning status, the fire-safety requirements applicable to the building category and the need for an ISU permit, and the panel's conformity documents — DoP, technical approval, fire-reaction certificate. For a network, these checks aren't done once and aren't extrapolated. Zoning status differs from one city to another and, in practice, from one street to another. An Expansion Manager who gets the answer "it's the same as the others" just once should ask for proof, because it isn't.
What stays verifiable
An ACP façade looks identical on handover day, whatever the composition. The differences appear after the first summer, in the third year, or at the first ISU inspection. What separates it from a poorly executed one isn't the finish, but four decisions made before the first panel reaches the site: the fire-reaction class, the aluminum sheet thickness, the structure sizing and the fixing system. All four become invisible after installation. All four are verifiable in the offer, on paper, before you sign anything.
WOX FAD executes ACP cladding and ventilated façades for multi-location networks nationwide, with per-location technical documentation — a DoP matched to the delivered batch, the structure specification and the anchoring details matched to the real substrate.
If you're currently evaluating offers for a façade or a network of locations, send us the documentation and you'll receive the complete offer, including the panel class, the aluminum thickness and the structure sizing.