Guides / Facade Systems
A square metre of wall does not tell you how much aluminium is on it, and that is the whole difficulty with a fin facade price. Depth and spacing settle it. A 200 mm blade at 300 mm centres hangs 1.33 m² of metal on every 1 m² of elevation; a 150 mm blade at the same centres hangs 1.00 m². Thickness, alloy, fixings, wind load and finish then decide the rest, and all of them are visible on the same drawing. This page works through those relations, so that a quote arriving next week can be checked rather than guessed at.
A fin facade has no per-square-metre rate, because the square metre of wall is not the unit the supplier buys. Coil, extrusion, coating and anodising are charged on the surface that gets treated, and a blade exposes two faces where the wall had one. Move the measurement to developed area and the pricing becomes arithmetic: developed area = 2 × depth ÷ spacing, multiplied by the elevation area.
What follows on this page is that arithmetic, plus the three things that sit on top of it. The thickness and alloy, which turn developed area into kilos. The wind load, which turns kilos into a subframe and a fixing schedule. And the finish, which is a separate process line with its own test standard. A quote that names all four can be compared with another; a quote that names none of them is a number about a different building.
Architects measure elevation area. Fabricators buy sheet, extrusion and coated surface. Those two quantities diverge the moment a fin projects from the wall, and the divergence is set by two dimensions that are usually drawn long before anyone asks for a price.
For a row of flat blades, each of depth d running the full height, at centres s, one square metre of elevation contains 1/s blades, and each blade presents two faces of area d. The developed area per square metre of wall is therefore:
developed area per m² of elevation = 2 × d ÷ s
| Blade depth | Centres | Blades per m | Developed area per m² of wall |
|---|---|---|---|
| 100 mm | 200 mm | 5.0 | 1.00 m² |
| 150 mm | 300 mm | 3.3 | 1.00 m² |
| 200 mm | 300 mm | 3.3 | 1.33 m² |
| 250 mm | 350 mm | 2.9 | 1.43 m² |
| 300 mm | 400 mm | 2.5 | 1.50 m² |
Arithmetic from the dimensions in the table: 2 × depth ÷ centres. Coated or anodised area is the quantity a finishing line invoices, so this column, not the elevation area, is what moves through the plant.
Two consequences are worth carrying into the enquiry. First, the spread in this table is 50 per cent between the shallowest and the deepest row at the same wall area, which is enough to explain most of the gap between two quotes that both claim to be per square metre. Second, the subframe follows the same geometry in the other direction: wider spacing means fewer brackets, deeper blades put more bending moment into each one.
Aluminium is bought by weight as well as by area, and the conversion between the two is a single constant: EN 1999-1-1 gives the density of aluminium as 2,700 kg/m³. One square metre at 2.0 mm is therefore 5.4 kg, at 2.5 mm it is 6.75 kg, and at 3.0 mm it is 8.1 kg.
| Developed area per m² | 2.0 mm | 2.5 mm | 3.0 mm |
|---|---|---|---|
| 1.00 m² | 5.4 kg | 6.8 kg | 8.1 kg |
| 1.33 m² | 7.2 kg | 9.0 kg | 10.8 kg |
| 1.43 m² | 7.7 kg | 9.7 kg | 11.6 kg |
| 1.50 m² | 8.1 kg | 10.1 kg | 12.2 kg |
Developed area × thickness × 2,700 kg/m³, rounded. These are the metal masses a structural engineer needs in order to check the rail and the anchors, and the same numbers a freight forwarder needs when the blades ship as a loose bundle rather than on a pallet.
Thickness is where a cheap quote usually hides. A blade drawn at 3.0 mm and supplied at 2.0 mm is a third less metal and, more importantly, two-thirds of the stiffness, so it deflects further under the same gust and needs more restraint points to keep the spacing even. The thickness band our own facade line works to is 0.6 to 3.0 mm, depending on the blade depth and the exposure, and both figures belong on the section drawing rather than in a covering email.
Most fin facades are one of two products wearing the same drawing, and the price difference between them is structural rather than commercial.
The choice tends to fall out of the section rather than out of a rate. A deep blade with a return, a channel for the bracket and an edge that has to stay straight over 4 m wants an extrusion. A wide, shallow blade in a standard alloy, where the finish is the visible feature, usually wants folded sheet, because the tooling disappears and the metal per square metre is lower.
One thing crosses over: the finish. Both routes end on the same coating or anodising line, so the finish cost per square metre of developed area is the same whichever way the blade was made. That is why a like-for-like comparison has to separate the blade from the finish before the numbers mean anything.
A blade row is a surface held out into moving air, and the brackets are what pay for it. The design pressure comes from EN 1991-1-4, which starts from the basic velocity pressure:
qb = ½ × ρ × vb², with ρ = 1.25 kg/m³
| Basic wind velocity | qb | What the number means on site |
|---|---|---|
| 24 m/s | 360 Pa | Sheltered inland sites, terrain category III |
| 27 m/s | 456 Pa | Common inland design value in western Europe |
| 30 m/s | 563 Pa | Open country, terrain category II |
| 33 m/s | 681 Pa | Coastal and exposed sites |
| 36 m/s | 810 Pa | Cyclonic regions and open-sea frontage |
Arithmetic from the formula above at 1.25 kg/m³. The design value on a project is the basic velocity pressure multiplied by an exposure factor that the code tabulates against terrain category, from category 0 at open sea to category IV in town centres, so the figure a bracket is sized on is higher than the column here. The column exists to show how sharply the pressure climbs with velocity: a 20 per cent rise in wind speed is a 44 per cent rise in pressure.
The consequence for the quote is not a small one. Brackets, anchors and the carrier rail are sized on that peak pressure, and the count per square metre is set by the blade spacing: blades at 300 mm centres with a carrier rail fixed at each floor slab 3.6 m apart work out at about 0.93 brackets per square metre of elevation, while blades at 200 mm centres on the same rail work out at 1.39. Anchor type then follows the substrate, and a concrete slab edge and a steel rail are two different details with two different prices.
This is the section where a facade quote most often turns out to be incomplete. Fin blades on their own are a metal price. The same blades with the carrier frame, the brackets, the anchors, the isolation washers and the setting-out drawings are a system, and the two are not comparable at any rate.
Depth costs metal, and metal costs money, so the useful question is how little depth the shading brief actually needs. For horizontal blades with no tilt, sunlight is screened once it comes in above an elevation angle of:
θ = arctan(centres ÷ depth)
| Depth | Centres | Screened above | Developed area |
|---|---|---|---|
| 150 mm | 300 mm | 63.4° | 1.00 m² |
| 200 mm | 300 mm | 56.3° | 1.33 m² |
| 200 mm | 150 mm | 36.9° | 2.67 m² |
| 250 mm | 250 mm | 45.0° | 2.00 m² |
| 300 mm | 200 mm | 33.7° | 3.00 m² |
Arithmetic from the formula above, for flat horizontal blades. Tilted or curved blades change the angle, and a louvre blade with a double bend is doing the same job with a different section. The developed area column is 2 × depth ÷ centres, so the row that screens the most sun also carries three times the metal of the shallowest.
Read together, the two columns are the design decision. A brief that asks for shade from a mid-afternoon summer sun needs a cut-off in the thirties, and that costs 3.00 m² of aluminium per square metre of glass. A brief that only wants to break up a blank elevation, with the sun already handled by the glazing, can be met at 1.00 m². Both answers are defensible; only one of them was asked for.
This is also the point at which a fin facade becomes cheap to change. Depth and pitch are drawing dimensions until the die is cut or the coil is ordered. After that they are a purchase order. Moving the cut-off from 45° to 56° on the same elevation removes a third of the metal, and it costs nothing to decide.
Aluminium moves with temperature more than steel does, and EN 1999-1-1 gives the coefficient as 23 × 10−6 per kelvin. On a 3.0 m capping rail, a 40 K swing between a cold morning and a sunlit afternoon is 2.8 mm of movement. That is not a large number, but it is larger than the gap between a fixed hole and a tight bolt, which is why rails and long trims are fixed through slotted holes and why the blade fixings are not all locked in the same direction.
The rest of the site problem is tolerance. A blade at 200 mm centres over a 30 m elevation has 150 positions, and setting-out error accumulates along the run unless the carrier rail carries the module and the brackets are adjusted rather than the blades. A supplier who asks for the fixing substrate before quoting is not adding a question to the process; the answer decides whether the frame is a set of individual brackets or a continuous rail, and those two are priced differently.
Where blades are supplied with their own axle and carrier frame, as on our wind-driven kinetic facade, the axle spacing and the restraint are set against the wind loading requirement of the structural engineer rather than against a catalogue grid. That is the same logic as a fixed fin row, with one more degree of freedom in the section.
The finish on a fin is applied to the developed area, twice over on a blade, and it is the only part of the build-up that is tested to its own standards. Three documents do most of the work in a specification.
The finish options on our own facade line run through PVDF, powder coating, anodising including copper and bronze tones, wood-grain, stone-grain and mill finish, and the same coating line serves the ceiling panels, so a facade and the soffits behind it can be delivered in one matched finish. Mill finish is the cheapest line and the one that shows handling marks first; on a blade row where both faces are read at an angle, that difference is visible from the street.
Anodising and coil coating are also priced differently from each other in a way that has nothing to do with colour. Coil coating is a continuous line and rewards quantity. Anodising is a bath process and rewards racking efficiency, so long blades that fill a rack are cheaper per square metre than short ones. Neither of those facts can be recovered from a finish name on a drawing.
Once the developed area, the thickness, the wind zone and the finish are agreed, a remaining gap has one of these behind it. All of them are checkable in the documents.
The wind pressure line catches people out because it is invisible in the price. A supplier who has assumed a sheltered inland site can price a lighter bracket and a longer rail spacing than one who has read the wind zone. Both quotes look complete, and only one of them will pass the structural check.
Six lines on a drawing do more than a page of description, because each one removes a decision the supplier would otherwise have to guess.
| Item | What to state | Why it has to be on the enquiry |
|---|---|---|
| Elevation and zones | Drawing with depth, centres and the extent of each fin zone in m² of wall | The developed area is computed from these two dimensions |
| Blade section | Profile drawing, or a note that the section is open to proposal | Decides extrusion or folded sheet, and whether a die is needed |
| Thickness and alloy | Thickness within the 0.6 to 3.0 mm band, alloy and temper | Sets metal mass, stiffness and the bracket spacing |
| Wind pressure | Design pressure from the structural engineer, or the site and terrain category | The subframe and anchors are sized on it, not on the blades |
| Fixing substrate | Concrete slab edge, steel rail, secondary frame, and the anchor type available | Changes the bracket detail and the setting-out method |
| Finish and colour | System (PVDF, powder, anodised, wood-grain, stone-grain), colour, and any exposure requirement | A separate process line with its own test standard and its own minimum quantity |
| Delivery basis | Destination, and whether the figure is material only or delivered | Freight on blades is a volume calculation before it is a weight one |
| Validity | The date the figure holds until, and the index it was built on | The metal component moves with the market |
The wind pressure and the substrate are the two that suppliers most often have to invent, and they are also the two that change the number most. Send them even when they are provisional, marked as such, and the reply will say which assumption it used.
This page is the geometry and the build-up. If the question is what a flat aluminium cladding sheet itemises, the ACP cladding guide covers panel, skin, core and coating, and the ACP sheet range carries the thicknesses and finishes. When the facade is meant to move rather than shade, the kinetic facade page sets out the flap system, its axle and its finish options.
Inside the building, the same arithmetic runs through the ceiling cost per square metre guide, which takes the division apart for a horizontal plane, and the weight per m² guide, which converts a build-up into the load the structure has to carry. Blade geometry appears in both worlds: the baffle ceiling and the ceiling and facade systems pages show how the same depth-and-spacing relation decides coverage on a soffit.
The documents a project can ask for before dispatch are listed on the certifications page, and how they are checked is described under inspection. For a landed cost, the container loading calculator answers the volume question that a blade bundle always turns into. Send the elevation with the depth, the centres and the wind zone on it, and the reply comes back as a scope with the developed area it was priced on. Send drawings and the destination, or use the contact page.
No single figure can be published, because a square metre of wall does not say how much aluminium is on it. Depth and spacing decide that: 200 mm blades at 300 mm centres give 1.33 m² of developed area per m² of wall, 150 mm blades at 300 mm centres give 1.00 m². Multiply by thickness and the density of aluminium, 2,700 kg/m³, to get the metal, then add the subframe, fixings, finish and freight. A quote is checkable once those four things are on the drawing; a rate without them cannot be compared.
Because the wall is not what the supplier buys. Coil, extrusion, coating and anodising are all charged on the surface that is treated, and a fin exposes two faces where the wall had one. The developed area of a blade row is twice the depth divided by the spacing, so a 200 mm blade at 300 mm centres carries 1.33 m² of surface for every 1 m² the architect measures on the elevation. Two quotes at the same wall rate can differ by a third before any question of margin, simply because one was built on wall area and the other on developed area.
They enter the same expression, twice depth divided by spacing, so a change in either moves the metal in proportion. What separates them is what they do to the design. Depth is also the lever for shading: with horizontal blades the sun is screened above an elevation angle of arctangent of pitch divided by depth, so 300 mm blades at 200 mm pitch screen from 33.7 degrees, while 150 mm blades at 300 mm pitch only screen above 63.4 degrees. Spacing changes how many brackets and how much carrier rail the subframe needs. Settle the shading angle first, then read the cost of the depth it demands.
It comes from EN 1991-1-4, and it is a site-specific number rather than a default. The code starts from basic velocity pressure, half the air density of 1.25 kg/m³ times the square of the basic wind velocity, then multiplies by an exposure factor that depends on terrain category, from category 0 at open sea to category IV in town centres. A basic velocity of 27 m/s gives 456 Pa before that factor; the same site at 33 m/s gives 681 Pa. The fins and their brackets are designed against the peak velocity pressure, and the fixing detail follows from it, which is why the wind zone has to be on the enquiry.
They are different products, not two prices for one product. An extrusion carries its own die, so a bespoke profile is a tooling cost paid once and amortised over the order, and the wall thickness is set by the die. A folded blade is cut from coated coil, so there is no die and the shape is limited by what a folder can do with the thickness. Extrusions are checked to EN 755-2 for mechanical properties, sheet and coil to EN 485-2. For a deep blade with a return and a fixing channel, the extrusion usually wins on tolerance and on fixing detail; for a wide flat blade in a standard alloy, folded sheet usually wins on metal per square metre.
The coating system has to be chosen for the exposure, and the test that gets quoted for it is neutral salt spray to ISO 9227. PVDF, powder coat and anodised finishes sit on different lines with different film builds, and the sea-front case is normally met by a multi-coat system rather than by a thicker single coat. Two other documents belong in the same conversation: the fire classification to EN 13501-1, which the project will ask for regardless of finish, and the coating approval scheme the applicator works to, such as QUALICOAT. Ask which of those three the quote is built on, because a finish name on its own does not fix the performance.
Six things: the elevation with blade depth, pitch and the extent of each fin zone; the blade profile or a section drawing; the aluminium thickness and alloy; the wind zone or the design wind pressure from the structural engineer; the fixing substrate, whether it is a concrete slab edge, a steel rail or a secondary frame; and the finish with the colour. Add the destination and the delivery basis, because freight on a fin facade is driven by volume, not weight. With those on paper the reply comes back as a scope rather than a rate, and it can be set against another supplier line by line.
The developed-area, mass, pressure and cut-off angle tables on this page are arithmetic from the dimensions and formulas printed beside them, and each can be recomputed. No unit price is published here: the figure depends on a developed area, a thickness, a wind zone and a finish that are specific to the project, and a rate written without them would be wrong for the next building.