Perforated Sheet as an Exterior Facade Material
Perforated metal sheet, also called perforated plate or perforated screen, is sheet metal punched or drilled mechanically to produce a regular pattern of round holes, slots, hexagons or decorative shapes. For exterior architecture it is used as a cladding skin that shades the facade, admits daylight and air, screens plant equipment and gives a building a distinctive rhythm without adding significant dead load.
Perforated panels are equally suitable for new construction and for recladding out-dated buildings, where a ventilated perforated screen can modernise the appearance while leaving the original envelope in place. Because the panels are made from steel sheet, they accept galvanizing, powder coating and fluorocarbon coatings, and in weathering steel they can be left bare so that a stable protective patina develops.
Material, Coating and Hole Pattern Options
| Option | Range |
|---|---|
| Base material | Galvanized steel, weathering steel, carbon steel, aluminium, stainless steel, copper |
| Hole shape | Round, square, hexagonal, cross, triangular, oblong and decorative patterns |
| Hole arrangement | Straight, side stagger, end stagger |
| Surface treatment | Hot dip galvanizing, zinc coating, powder coating, fluorocarbon coating, anodizing |
| Pitch and hole diameter | Made to the pattern required by the project |
For outdoor facades the two most common specifications are galvanized steel sheet with a powder or fluorocarbon topcoat for a uniform colour, and weathering steel sheet supplied bare or with a clear treatment so that the surface patina performs the protection function.
Typical Panel Specifications
| Material | Hole pattern | Hole size, mm | Thickness, mm | Coating |
|---|---|---|---|---|
| Galvanized steel | Hexagon | 50 | 1 | Powder or fluorocarbon |
| Galvanized steel | Hexagon | 50 | 2 | Powder or fluorocarbon |
| Galvanized steel | Hexagon | 20 | 3 | Powder or fluorocarbon |
| Galvanized steel | Round | 25 | 3 | Powder or fluorocarbon |
| Galvanized steel | Oblong | 6.6 x 15.5 | 2 | Powder or fluorocarbon |
| Galvanized steel | Triangle | 50 | 1.5 | Powder or fluorocarbon |
| Galvanized steel | Oblong | 80 x 12 | 1 | Powder or fluorocarbon |
| Weathering steel | Round or hexagon | Made to order | 1.5 - 6 | Bare or clear sealed |
| Stainless steel | Round | 30 - 60 | 3 | Powder or fluorocarbon |
Panels are normally supplied as flat sheets cut to the module size of the facade, or in coil for continuous roll forming. Where a curved facade is required, the sheets are rolled to the specified radius before coating. Thickness is generally kept equal to or below the hole diameter so that the punching operation produces clean, accurately formed holes rather than torn or distorted openings.
Open Area, Light and Ventilation
Open area is the single parameter that connects the visual pattern to the technical performance of the cladding. It is calculated as the ratio of the total hole area to the plate area over the same pitch, and for round holes on a 60-degree staggered pattern it can be approximated by multiplying 90.69 by the square of the ratio of hole diameter to pitch. The value directly controls how much daylight passes through, how much solar gain is intercepted, how the facade looks from a distance, and how much air movement the screen allows for car park or plant room ventilation.
Low open area, roughly 20% to 30%: a solid architectural appearance with strong solar shading.
Medium open area, roughly 30% to 50%: balanced daylight, privacy and ventilation.
High open area, above 50%: maximum airflow and transparency, typical for screens and enclosures.
Because the panel carries the wind load, open area also affects structural design: a higher open area reduces the wind pressure on the sheet but leaves less material to resist it.
Fabrication, Fixing and Quality Inspection
Punching on CNC turret presses for standard patterns, laser cutting for large holes, curved layouts and one-off designs.
Sheets can be bent, rolled and framed after perforating; the coating is normally applied after forming so that cut edges are also protected.
Galvanizing followed by powder or fluorocarbon coating gives a two-layer system for coastal and industrial atmospheres.
Panels are fixed to aluminium or steel sub-frames as a rain screen, with stainless steel fasteners and isolation washers to avoid bimetallic contact.
Weathering steel panels should be allowed to drain and dry; standing water and trapped debris prevent the patina from stabilising.
Inspection of perforated sheet covers hole diameter and pitch, open area, sheet thickness, flatness, hole edge quality and coating thickness and adhesion.
Packing is in rolls with cartons for coil, or in pieces on wooden or steel pallets for flat sheets, with waterproof protection for transport. Routine cleaning of coated panels with water and a neutral detergent is normally enough to maintain the surface; bare weathering steel needs no cleaning unless salts or pollutants accumulate.
FAQ
Q: What is perforated steel sheet?
It is steel sheet that has been mechanically punched or drilled to create a pattern of holes, slots or decorative shapes, supplied flat, in coils or formed into panels.
Q: Which materials are used for exterior facade panels?
Galvanized steel, weathering steel, carbon steel, aluminium, stainless steel and copper are all used, with galvanizing, powder coating or fluorocarbon coating for protection and colour.
Q: How is open area calculated?
Open area is the total hole area divided by the plate area over the same pitch; for round holes on a staggered pattern it is close to 90.69 multiplied by the square of hole diameter divided by pitch.
Q: Why must sheet thickness not exceed the hole diameter?
Keeping thickness at or below the hole diameter allows the punch to form a clean hole, which protects the accuracy of the pattern and the appearance of the facade.
Q: Can perforated weathering steel be left unpainted?
Yes, in exposed facades that drain and dry freely it develops an adherent patina; in permanently wet or polluted positions a coating is preferred.
