Why architects are turning to FRP grating

Architectural projects once used grating mainly as an extension of industrial platforms. More and more shading, facade screens, balustrades and decorative surfaces now use it, not because plastic is cheap but because of three designable properties: colour can run through the material, sections can be pultruded into almost any shape, and the surface does not rust in wet or saline conditions.

Compared with aluminium, FRP has low thermal conductivity, so a shading element does not become a thermal bridge the way an aluminium louvre can. Compared with steel, it needs no galvanising or paint maintenance, and a cut edge does not start to rust the way a broken galvanised layer does. The price is a low modulus, high thermal expansion and connections that must be designed for the material.

In architecture, FRP grating is usually a secondary element rather than a primary structure: shading, screens, infill panels, ceilings. Secondary elements still have to pass wind load, fire, weathering and safety checks. Listing those requirements first makes selection much easier than choosing a colour and adding structure later.

The corrosion resistance, light weight and electrical insulation of the material are set out in the main benefits of FRP materials

Shading: spacing, angle and view

The performance of a shading screen is set by three dimensions: blade spacing, blade depth and installation angle. Closer spacing and greater depth give more shade, but also less view and less daylight. Design usually starts with the view requirement, such as seeing the street when seated or the sky when standing, and works back to blade spacing.

Orientation sets the angle. On a south facade the solar altitude changes a lot, so horizontal blades at a suitable spacing can block high summer sun while admitting low winter sun; on east and west facades the sun is low and horizontal blades work poorly, so vertical blades or a screen are often used. FRP sections can be pultruded with the blade angle built into the die, without the folding that metal needs.

Colour affects surface temperature and thermal comfort. Dark elements run noticeably hotter in sun than light ones, so use dark colours cautiously on balustrades and shading close to people. Shading calculations should use the project's own weather data; this article gives no universal angle, because latitude, orientation and obstruction differ on every project.

Facade screens and decorative surfaces

Facade screens must take wind load. FRP grating is open, so air passes through, but the panels, the support grid and the connections still need calculation against local wind pressure; the larger the panel, the denser the support grid, and the more critical the number and position of connections. Do not treat permeability as freedom from wind load.

Tolerance and joint width decide the visual result. Pultruded profiles carry straightness and twist tolerances, moulded grating carries moulding tolerance; on a large facade these must be absorbed in the setting-out and the connections rather than demanding metal-grade accuracy from the material. Keep joint widths consistent and set out from one datum.

Fire and fall protection also apply. As an external wall element, a screen may fall under facade flame-spread requirements; as a high-level screen, it needs secondary protection against panels or fixings falling. The class and construction are set by the building code, the facade consultant and the fire engineer.

Colour, gloss and ultraviolet light

FRP colour comes from pigments and weather resistance from the combination of resin, pigment and UV stabiliser. Light colours, inorganic pigments and a good surface veil usually weather better; dark colours and bright organic pigments fade faster under strong UV. The darker the colour, the hotter the surface and the faster the resin ages, which is why dark elements need extra confirmation.

Gloss changes before colour does. Chalking, loss of gloss and slight whitening are early signs of surface resin ageing; they do not mean structural failure, but they affect appearance and cleaning. The design can accept a matte finish as the long-term state, or specify a surface veil and gelcoat to hold gloss longer.

Samples must be judged in the light of the site. A small colour chip in an office and a large facade read as two different colours, and the same pigment shifts in a different resin. For colour approval, make a full-size or near full-size mock-up and compare it with adjacent materials in the natural light of the project location.

Structural profiles and connections

Architectural FRP profiles are mostly pultruded: square and rectangular tube, angle, channel and purpose-made blade sections. Pultrusion puts fibre along the length, so longitudinal strength is high and transverse strength low; connections and holes should stay out of transverse tension. Where load runs in several directions, use multiaxial fabric or moulded nodes.

A low modulus means deflection governs. A shading beam of the same span may deflect several times as much as steel, so support spacing follows deflection rather than strength; long cantilevers also need checking for wind vibration and long-term sag under self weight.

Connections usually use stainless bolts, aluminium clamping blocks or purpose-made brackets. Isolate dissimilar materials to avoid galvanic corrosion; leave clearance in bolt holes rather than relying on tightening to locate the parts as steelwork does. Connections must also allow thermal movement, or the element will bow in summer or tear its fixings.

Non-conductive, non-magnetic and light

FRP does not conduct electricity, which has two direct architectural benefits: elements near electrical equipment, catenary or substations need no extra insulation, and metal parts in contact with FRP do not set up galvanic corrosion. It is also non-magnetic, which makes it preferable to steel in spaces that must avoid magnetic interference, such as some medical and laboratory areas.

Light weight matters most in refurbishment. For the same screen or shading element, an FRP section imposes less lifting and anchorage burden and adds less load to an existing structure or roof. Light does not mean the connections can be ignored: wind suction lifts light elements, so pull-out and shear capacity must be checked against wind load.

These properties do not replace engineering judgement. Metal accessories that need earthing, elements that need lightning protection and penetrations that need fire stopping must follow their own disciplines. The insulation of FRP says the material does not conduct, not that the whole assembly is electrically safe. Industry practice is described in the FRP grating applications by industry

Cleaning, graffiti and repair

Architectural facades are cleaned less often than industrial platforms but to a higher standard: no water marks, no colour change, no scratching. Use a neutral detergent and a soft brush; soften bird droppings and tree resin before removal rather than scraping with a blade.

Anti-graffiti coatings are common on stations, schools and busy buildings. They reduce paint adhesion but change gloss and feel and may affect colour matching on later local repairs. Confirm compatibility with the panel resin and carry out adhesion and removal tests on a sample first.

Repair depends on depth. Where only the surface has dulled, cleaning and polishing are enough; where the resin layer is broken but the fibre is intact, a matching resin repair and sanding can work; where fibre is broken or the section is cracked, replace rather than repair, because strength and weathering at a patch will not match the original.

Mock-ups, tolerance and inquiry

For an inquiry, give the location, element size, span, wind load, colour and gloss requirement, surface, connection method, fire class and expected service life. An artist's impression alone does not let a supplier judge section and connection.

On large projects, build a mock-up first. It should include typical connections, joints and edge details, not just one panel; leave it in place for a period and confirm colour, movement and cleaning before production.

Specifications, colours and section options are in the FRP grating specifications and options

• Set the view and shading target before blade spacing and angle.
• Check facade screen supports and fixings against wind load.
• Approve colour in site light on a full-size mock-up.
• Leave expansion and erection tolerance in every connection.