HPL Dry Façade

What “compact” means, and why it is the whole product

There are two things called HPL and they are not the same object.

Laminate is a thin decorative sheet — the same kraft-and-resin construction, but 0.7 to 1.2 mm thick — bonded to a substrate. The substrate is chipboard, MDF or plywood, and the substrate is what gives the board its strength. This is kitchen worktop material. It cannot go outside, because the substrate is the weak point and moisture will find it.

Compact laminate has no substrate. The whole panel is the laminate: dozens of kraft layers impregnated with thermosetting resin and pressed together under heat and pressure into one homogeneous solid. It is self-supporting. There is nothing inside it to fail, because there is no inside — the panel is the same material all the way through.

• Laminate on a board A thin decorative sheet bonded to a substrate that carries the strength. Moisture finds the board, and the board swells.

• Compact laminate Dozens of resin-impregnated kraft layers pressed into one self-supporting solid. There is no board inside it to fail.

Sections through a cut edge. Layers not to scale.

That is what the “compact” in compact laminate means, and it is the reason this material works as a façade at all. The specification line reads exterior-grade compact laminate to EN 438-6, and all three parts of it are load-bearing:

• Compact — homogeneous, self-supporting, no substrate.
• Exterior-grade — formulated and surfaced for UV and weather. Interior compact laminate is the same construction and will not survive outdoors.
• EN 438-6 — the part of the laminate standard that covers exterior-grade compact panels, which is what makes “HPL” a specification rather than a word.

Design note 01, and the most common failure on this system

The existing note says: interior HPL will not survive external exposure; specify exterior-grade, and fire-rated where the building height requires it.

This is the most frequent specification failure on this material, and it is easy to make because interior and exterior compact laminate look identical in a sample box and differ substantially in price. The failure does not show for two or three years. Then the surface chalks, the colour goes, and the panels have to come off.

HPL against the alternatives

Every figure in this table is published on this site, on the specification panel of the system it belongs to. Nothing here is estimated.

• Perforated metal 4 – 9
• Aluminium composite 5.5 – 7.6
• HPL 8 – 14
• Ceramic 22 – 45
• Stone 75 – 110

020406080100120

Lighter to the left

Published ranges from each system’s specification. Ceramic, Stone, ACP, Perforated metal.

HPL or ACP — the comparison people actually search for

They look like alternatives and they behave differently in four ways.

Appearance. ACP is a coated metal panel: flat, metallic or solid RAL colour, and it reads as metal because it is metal. HPL reproduces timber, stone and concrete convincingly, because the decorative layer is a printed paper fused into the panel rather than a coating on a surface. If the elevation wants wood, HPL wins and it is not close. If it wants metal, buying HPL that imitates metal is buying the imitation of something you could have had.

Shape. ACP is two thin aluminium skins on a core, so it can be routed, folded and rolled into cassettes, returns and curves that no rigid panel will make. HPL is a rigid homogeneous board. It cuts; it does not form. A design with curved corners or deep folded returns is an ACP design.

Surface durability. This is the one that goes the other way. ACP’s colour is a coating — PVDF 70/30 or FEVE — and a coating is a layer that can be scratched through to the aluminium beneath. HPL’s decorative layer is fused into the panel under heat and pressure rather than applied to a surface, and the cured face is hard, so everyday scuffs stay in the surface instead of exposing bare metal. At ground-floor level, in car parks, on schools, on anything people touch or lean bicycles against, that difference is the whole argument.

Fire. ACP with an A2 mineral core reaches A2-s1,d0. Standard HPL is B-s1,d0, and reaching A2-s1,d0 requires the FR grade, which costs more. On a building where the code requires A2, ACP starts there and HPL has to be specified up to it. On a building where the code requires A1, neither of them qualifies and the honest answer is ceramic or stone.

Movement: the reason HPL is detailed differently

Design note 02 says HPL moves more than ceramic or stone, that fixing holes are elongated and joint widths are sized for the panel format. This is the single most important engineering fact about the material, and almost every HPL façade failure traces back to it.

It moves for two reasons, not one. Like every material it expands and contracts with temperature. Unlike ceramic or stone, it is also hygroscopic — it takes up and gives off moisture with the humidity around it, and it changes dimension when it does. Its movement is therefore seasonal as well as daily, and it is larger than a purely thermal material’s.

It does not move equally in both directions. Compact laminate is made from layers of paper laid in a direction, and it moves more across that direction than along it. Which means the panel’s orientation is not neutral: the same panel rotated ninety degrees needs a different joint allowance on each edge. The coefficients are a property of the specific panel and come from the manufacturer’s data — take them from there rather than from a rule of thumb.

• Two causes It moves with temperature like everything else, and with humidity, which ceramic and stone do not.

• More across the layers than along them So orientation is not neutral: the same panel turned ninety degrees needs a different allowance on each edge.

• One fixed point, every other hole oversized One tight hole locates the panel; the rest let it slide past its fixings. Two fixed points and it bows, then cracks.

Elevations. Movement exaggerated; the coefficients come from the panel manufacturer.

Three consequences, all of them non-negotiable.

1. Every fixing hole is oversized, and every panel has exactly one fixed point. One hole is a tight fit and locates the panel. Every other hole is elongated or oversized so the panel can slide past its fixing. A panel restrained at two points cannot move, and a panel that cannot move will bow, then crack.
2. The rivet must not clamp the panel. This is the detail that gets built wrong most often. A façade rivet for HPL has a collar that sets a fixed standoff, so it holds the panel against the rail without squeezing it. Installed with an ordinary rivet, pulled tight, the panel is locked and the movement goes into the panel instead of into the joint. It looks correct on the day of installation and fails in the first full season.
3. Joint width is sized from the panel format, not from the drawing. A larger panel moves more in absolute terms, so it needs a wider joint. Choosing the joint width for appearance and then choosing a large panel is the wrong order.

• Collar rivet The collar sets a fixed standoff, so the rivet holds the panel to the rail without squeezing it, and the oversized hole lets it move.

• Ordinary rivet, pulled tight The panel is clamped and cannot move, so the seasonal movement goes into the panel. Correct on the day, failing by the first full season.

Sections through a fixing. Clearances exaggerated.

Rivet or concealed fixing

Design note 03: visible coloured rivets are the economical route; concealed undercut fixings give a clean surface but need panel thickness. Expanded:

• Colour-matched visible rivet The economical route, at 6 – 8 mm. Set out deliberately, the rivets read as texture rather than as fixings.

• Concealed undercut Anchors in factory-drilled holes in the back of the panel. Nothing on the face, but it needs the upper end of the thickness range.

Elevation and sections. Simplified.

The visible rivet is not a compromise. On a large elevation the rivet pattern becomes part of the discipline of the façade — a regular field of small points, colour-matched so they read as texture rather than as fixings. Pretending they are not there is what makes them look wrong; setting them out deliberately is what makes them look intentional.

Edges, cutting and the core

Design note 04: cut edges show the core; where this matters, panels are ordered to size rather than cut on site.

The core of a standard compact laminate panel is dark brown-black — the kraft layers with their cured resin. Cut an edge and you see it. The important nuance, and the one that reassures people unnecessarily worried about it:

A cut edge is an appearance issue, not a durability one. The panel is homogeneous and non-porous through its full thickness, so a cut edge is the same weather-resistant material as the face. It does not need sealing to survive. It just does not match.

Three ways to handle it:

• Order panels to finished size. The factory edge is clean and the core is only seen where it was always going to be seen.
• Specify a colour-through panel, where the core is manufactured to match the face. Available on many decors, and it costs more.
• Design the edge to be seen. On a light panel the dark edge reads as a shadow line at every joint, and on a well-set-out elevation that is a better result than trying to hide it.

• A cut edge The standard core is dark brown-black. It is the same weather-resistant material as the face — it simply does not match.

• Colour-through core The core is made to match the face. Available on many decors, and it costs more.

• An edge designed to be seen On a light panel the dark edge reads as a shadow line at every joint — often a better result than hiding it.

Oblique views of a panel corner.

What not to do is cut panels freely on site and hope. It also matters for the fixing holes: a hole drilled off-position on site cannot be moved, and the panel is then either wrong or scrap.

Fire class: what B-s1,d0 and A2-s1,d0 actually say

The specification gives B-s1,d0 standard; A2-s1,d0 in FR grade to EN 13501-1. Three separate pieces of information are packed into that string.

The letter is the material’s contribution to fire. A1 is non-combustible. A2 is limited combustibility. B and below are combustible, with decreasing performance. Standard HPL is B. FR-grade HPL is A2. Ceramic, for comparison, is A1 — a class neither HPL grade reaches.

s is smoke. s1 is the best of three: very limited smoke production.

d is flaming droplets. d0 is the best of three: no flaming droplets or particles.

1. 1 · The letter: contribution to fire A1 non-combustible, A2 limited combustibility, B and below combustible.
2. 2 · s: smoke s1 is the best of three — very limited smoke.
3. 3 · d: flaming droplets d0 is the best of three — none.

EN 13501-1 reaction-to-fire classes. The positions are the published classes of the systems named.

So B-s1,d0 describes a combustible material with the best available smoke and droplet behaviour. That is a meaningful specification on many buildings, and it is not the same thing as A2.

The part that decides the project. Most codes set a building height above which external wall materials must be A2 or better, and on residential buildings that threshold is often low. It varies by country and it has been tightened in many of them. Check the threshold before the grade is chosen, because it does not adjust the design — it eliminates the standard grade outright, and the FR grade is a different price.

Substructure

The specification says aluminium rail; timber only where code permits. The qualification is the point.

Timber battens are cheaper and are still used behind rainscreens in some markets. But a ventilated cavity is a continuous vertical air path up the face of a building, and putting combustible material inside it changes the fire behaviour of the whole assembly, not just of the battens. Many codes now restrict or prohibit it above a certain height, and some prohibit it outright on certain building types.

Aluminium rail, on adjustable brackets, is the default here for that reason and for a second one: aluminium does not move with humidity, so the substructure stays dimensionally stable while the panels do the moving. A timber substructure moves too, in the same direction and at a different rate, and then the joint has to absorb both.

The cavity itself — its depth, its drainage, its base and head details and its cavity barriers — is common to every system in this family and is covered in full on Ceramic Dry Façade. The published cavity depth for HPL is 20 – 50 mm, open at base and head.

What to decide, and when

1. 01

   Concept

   Building height against the code’s fire-class threshold. This decides standard grade, FR grade, or a different material — before any decor is looked at.

2. 02

   Scheme

   The panel grid, set against the 1,300 × 3,050 mm sheet (see cost, below). Panel orientation, because movement is directional. Rivet or concealed.

3. 03

   Tender

   The EN 438-6 exterior grade, in writing. Decor and whether it is colour-through. Joint width, sized to the panel format.

4. 04

   Production

   Fixed and sliding point layout, one fixed point per panel. Rail and bracket setting-out. Panels ordered to finished size.

What drives the cost

1 · The grade

Standard versus FR is a step change, not a percentage. It is decided by the building’s height and the applicable code, so it is not a negotiable line — but it should be known at concept, because a project that budgets for standard grade and discovers it needs FR has a real problem.

2 · How the panel grid divides the sheet

The largest saving available on this material, and it is free.

HPL arrives as a sheet of 1,300 × 3,050 mm. Every panel is cut from it, and everything not used is waste that was paid for. A panel grid chosen for appearance, with no reference to the sheet, can leave a third of every sheet on the floor.

A grid chosen to divide it cleanly leaves almost nothing. Allowing a few millimetres for the saw cut and a trimmed factory edge:

• About 640 × 1,010 mm → 2 across × 3 down = 6 panels per sheet
• About 1,290 × 600 mm → 5 full-width panels per sheet
• About 640 × 1,510 mm → 4 panels per sheet

• Grid chosen for appearancePanels that ignore the sheet leave a band of paid-for offcut on every one.

• Six per sheetTwo across the width, three along the length.

• Five per sheetFull-width panels, five along the length.

• Four per sheetTwo across, two along — the long format.

Sheets drawn to one scale. Exact panel sizes depend on the saw kerf and edge trim — confirm the usable sheet with the supplier.

Set the elevation grid from the sheet and the material cost falls without a single design compromise that anyone will see. Do it at scheme stage; after the elevations are fixed it is not available.

3 · Decor and finish

Solid colours are the base. Wood, stone and concrete reproductions cost more. Metallic decors cost more again. Double-sided panels cost more than single-sided, and are only needed where both faces are seen — soffits, fins, reveals, balcony undersides. Specifying double-sided across the whole elevation because some of it is exposed is a common and expensive default.

4 · Colour-through core

A real premium, and worth it only where cut edges will be seen at close range. On an elevation where the joints read as shadow lines anyway, it buys nothing.

5 · Fixing method

Visible rivet is the economical route. Concealed undercut adds factory drilling to every panel and usually requires the upper end of the thickness range, so it raises both the fixing cost and the panel cost.

6 · The substructure

As on every ventilated façade, a large share of the cost and invisible when finished. Driven by panel weight, format, wind load, cavity depth and how far out of plane the wall is. HPL’s low weight helps here — it is one of the material’s genuine economies, and it is why the system suits overcladding and lightweight frames.

7 · Elevation complexity

Reveals, returns, soffits and interfaces. Flat area is the cheap part, on this system as on every other.