Architectural and secondary steelwork in Dubai: coatings, fixings and movement

What this guide covers

Part F applies to buildings and to structures or appurtenances connected to a building, and villas and townhouses are designed to Part K.⁸ The building envelope, which Part E covers, is the physical barrier between the conditioned inside and the exterior, and crown extensions of the façade that screen rooftop plant count as part of it.⁹

Coating system, coating life and maintenance

The Engineer’s steelwork specification states the steel grades and the protective paint systems, which must be durable and compatible with Dubai’s climate. Coatings are specified to BS EN 12944 as a minimum, with additional requirements for their susceptibility to ultraviolet degradation, and the specification states the inspection and maintenance requirements and defines the expected coating life.¹

For villas, Part K repeats the requirement for durable, climate-compatible systems to BS EN 12944 as a minimum with ultraviolet protection, but does not repeat the sentence on inspection, maintenance and coating life.¹⁰ Part E requires the whole envelope to be designed and specified to limit environmental degradation over the building’s design life.¹¹

On façades, the UAE Fire and Life Safety Code does not allow bitumen, bituminous products or flammable agents as anti-corrosion or waterproofing coatings on primary substrates, whether metal or concrete, because bitumen spreads building envelope fires.¹²

The American Galvanizers Association (a US industry body; its guidance is not a UAE rule) stresses that a duplex system, paint or powder over galvanizing, needs the fabricator, specifier, painter and galvanizer to talk before galvanizing. Surface conditions that are acceptable for the zinc coating under ASTM A123, such as roughness, small dross inclusions and zinc runs, can spoil topcoat adhesion, so where the galvanizer and the paint or powder applicator are different parties they should settle, before coating, who is responsible for avoiding post-treatments, smoothing, cleaning, profiling and, for powder coating, outgassing.¹³

For architecturally exposed steel, the same guide notes that runs, roughness and excess zinc acceptable under ASTM A123 may not be acceptable on feature elements. It recommends vents and drains placed for the galvanizer’s handling orientation, designated lifting points, not mixing thicknesses, steel chemistries or surface conditions, blast cleaning before galvanizing, weld wire with a silicon content close to the base steel, and grinding thermally cut edges.¹⁴

Inspecting hot-dip galvanized secondary steel

The AGA inspection guide (US industry guidance) explains that, in the US, zinc coating requirements come from ASTM A123 for structural steel, pipe, tube, bar and assemblies, from A153 for small parts and fasteners centrifuged after galvanizing, and from A767 for reinforcing bar, and notes that ISO 1461 is the standard most used in Europe; in all cases inspection takes place at the galvanizing plant before shipment. The time to first maintenance is directly proportional to the thickness of the zinc.¹⁶

Where ASTM A123 is specified, the minimum average coating depends on the material category and the measured steel thickness. In the AGA summary of that standard, for example, structural steel 6.4 mm and thicker needs coating grade 100 (100 µm), and pipe and tubing 3.2 mm and thicker needs grade 75 (75 µm); the table gives the other categories and thinner steel.¹⁷

Coating thickness is sampled, not measured on every piece; the number of specimens depends on the lot size and is set in the ASTM specification. An article with 1032 cm² (160 in²) of surface or less is one specimen: it gets at least five widely dispersed readings, its average may be as low as one grade below the minimum for its material category, and the average of all the specimens tested in the lot must reach that minimum. A larger article, or one with more than one material category or steel thickness, is a multi-specimen product and is judged on its own sample. For a large article, three continuous local sections of equal area make up the sample, each with at least five widely dispersed readings; each section’s average may be one grade below the minimum, but the average of the three must reach the minimum for the material category, so a thicker article elsewhere in the lot does not make up for a thin one. Each material category or thickness in a fabrication is a separate specimen, judged against its own minimum. Further tests are typically done only when there is a question or concern about a particular part: adherence is then checked by running a stout knife smoothly along the surface, without whittling or gouging, and, where embrittlement is suspected, a small group of products may need testing to ASTM A143.¹⁸

Visual inspection, without magnification, covers every part inside and out, including contact points, welds, junctions and bends, before the steel leaves the galvanizer. A bright, spangled or matte grey appearance has no bearing on corrosion protection, and the coating weathers to a uniform matte grey.¹⁹ The finish must be smooth, uniform and continuous, and a surface condition is a reason to reject only if it will shorten the coating’s corrosion life. Bare spots are a defect: small ones can be repaired in the galvanizing shop, and their size or number decides whether the part is rejected. Parts rejected for reasons other than embrittlement can be repaired, or stripped and regalvanized.²⁰

In the plant, repairs are limited to the smaller of 0.5% of the article’s accessible surface or 22,500 mm² per ton of piece weight; for larger areas the part can be stripped, regalvanized and resubmitted. In the field there is no size limit. ASTM A780 gives three repair methods, zinc-based solder, zinc-rich paint and zinc metallizing, and any touch-up must give at least 50.8 µm in one application.²¹

In service, the guide lists the places to inspect: crevices at overlaps, between fasteners and where zinc meets wood or concrete; contacts with dissimilar metals, where the zinc corrodes preferentially and isolation with plastic or rubber grommets, or painting the cathode, stops the couple; flat areas where water pools, which can be drained with holes where possible; and previously touched-up areas, which often corrode faster.²² Brown staining over a coating that still reads on a thickness gauge is cosmetic; tightly stacked, wet bundles can develop wet storage stain, so bundles are vented; weeping welds can be sealed with epoxy or caulk; and the surrounding zinc gives some cathodic protection only to bare areas about 1 to 5 mm wide, depending on the electrolyte, so bare areas should be touched up to ASTM A780.²³

Fixings and connections

The building envelope must carry all its static and dynamic loads, including dead, imposed, thermal, seismic and wind loads, to the building structure without fracture or permanent loss of performance. It must be securely fixed with both vertical support and horizontal restraint, allow where necessary for differential movement between cladding and structure such as settlement and inter-storey drift, and use durable materials: its fixings must resist corrosion, suit the local environment and exposure, and last at least as long as the envelope’s design life.²

Fixings are chosen on proven performance, usually from manufacturer test data under an ETA, BS, EN or ASTM standard, with strengths from tests in a base material representative of the one they anchor into, allowing for weaknesses such as cracked concrete or voids in masonry. The design must address what happens if any single fixing fails, and fixings must not be welded.³ Part K sets the same rules for villas.²⁴

The envelope must also carry, without losing performance, a horizontal load on panels or framing members to Section 4.5.1 of ASCE/SEI 7-16; 0.6 kN/m² or a 1 kN vertical load, whichever is more onerous, on internal ledges, horizontal framing members and horizontal surfaces; and loads from cleaning cradles, anchor points, equipment and operators. In our reading, the 0.6 kN/m² and 1 kN values are for those ledges and horizontal members, and guards follow the Section 4.5.1 or B.4.2.5.2 route below. Envelope parts protecting a drop of more than 760 mm are either designed for the Section 4.5.1 forces or given a guardrail, and balustrades and guardrails at balconies, terraces, roofs and changes in level over 760 mm must conform to B.4.2.5.2.²⁵

B.4.2.5.2 requires guardrails where a walking or standing surface is 760 mm or more above the finished floor, with listed exceptions such as the loading side of loading docks and the audience side of stages and raised platforms. The guardrail is at least 1,200 mm high above the floor or the lowest stepping feature; openings must not let a 100 mm sphere pass; horizontal climbable elements are not allowed in the bottom 865 mm; any gap at the floor is no more than 100 mm; and the balcony, handrail and guardrail assembly has to resist the loads in ASCE/SEI 7-16.²⁶

On villas, Part K instead requires the envelope to sustain and transfer, without loss of performance, a single concentrated load of 0.89 kN to Section 4.5.1 of ASCE/SEI 7-16, or to be provided with a guardrail, and requires balustrades and guardrails at balconies, terraces, roofs and changes in level greater than 760 mm to conform to K.5.2.5.2, which was not read for this guide.²⁷

For structural connections, welding design and procedures follow AWS D1.1 or BS EN ISO 15614. Welding should not be done on site; if it cannot be avoided, the method of work, with the necessary certificates and tests, is submitted for approval, and the welders must be accredited. A connection must never be detailed to rely on welds and bolts sharing the load at the same time.⁴ Post-installed anchors into reinforced concrete may support steelwork where cast-in anchors are impractical, designed to ACI 318-19 for every conceivable failure mode.²⁸

The AGA design guide recommends galvanized fasteners for galvanized assemblies, with bolted assemblies sent to the galvanizer dismantled. Nuts are tapped oversize after galvanizing, and welded studs may need reheating and brushing to clear excess zinc, so alternatives to welded studs are worth considering.²⁹ Moving parts such as shafts, shackles and drop-handles need at least 1.5 mm radial clearance for the added zinc. Hinges should be loose-pin and galvanized separately and, where possible, bolted on after galvanizing, with adjacent edges ground before galvanizing to give at least 0.8 mm clearance.³⁰

For slip-critical joints the design rule is Section J3.8 of AISC 360, the specification the Code names for structural steel.³¹ AISC 360-16 gives the Class A mean slip coefficient of 0.30 to hot-dip galvanized surfaces only when they are roughened; un-roughened galvanized surfaces are not listed in Class A or B, so on our reading their coefficient has to be established by tests.³²

The AGA design guide, which is US industry guidance, takes a different view: it treats unprepared galvanized faying surfaces as Class A with a mean slip coefficient of 0.30, advises against wire brushing to roughen them, and reaches higher values with zinc-rich paint over a chemically pretreated surface. It also says galvanizing on the contact surfaces of bearing-type joints does not reduce their design strength, and recommends a washer under the turned part to protect the coating during tensioning.¹³

Euro Inox guidance (European industry guidance, not a UAE rule) says that where other metals meet stainless steel outdoors they must be separated by a non-metallic barrier such as neoprene or nylon, because stainless is the more noble metal and a small, less noble part in contact with a large stainless area corrodes faster.³⁴ The guide Cold-formed and stainless explained covers stainless grades and fasteners.

Thermal and structural movement

Structures must resist self-straining forces from expansion and contraction. Details that relieve those forces may be used where practical, provided they do not break an assumed load path, and permanent ones must be durable with provision for maintenance.³⁵

Thermally induced forces are derived from the actual restraints and the temperature changes over construction, seasons and days. For steel members and members exposed to solar radiation the range should equal the maximum temperature swing; ±25 °C may be assumed for protected steel, but for exposed steelwork the Engineer assesses the range and the forces case by case, allowing for construction stages, exposure and when the steel is locked into its final configuration.⁵

The envelope itself must take the changes in size and shape of its parts caused by service temperatures, and by the difference between inside and outside temperatures, without losing performance.³⁶ Movement joints are provided where needed for the expansion or deflection of above-ground structures.³⁷

SCI’s portal frame guide (UK Eurocode guidance, cited here for the principle) takes steel’s coefficient of thermal expansion from BS EN 1993-1-1 (not held here) as 12 × 10⁻⁶ per K up to 100 °C, about 1.2 mm per degree over 100 m. A member free to expand is not stressed, a fully restrained one develops axial stress, and bracing at both ends of a run creates axial forces in the members between.³⁸

Envelope components must not be damaged by deflection under the worst load combination, and deflections must be fully recovered. The allowable deflection depends on the material and on the spacing and method of attachment, and the values in Table E.1, which follow the CWCT standard, are generally acceptable: for example span/200 between attachment points for storey-height assemblies other than masonry up to 3 m span, and span/90 between supports for opaque infill panels in secondary framing, excluding glass, of non-brittle materials such as aluminium or steel, with the manufacturer’s recommendation also sought. Deflection limits for the main structure are in F.8.³⁹

Façade cladding in Dubai: what the Municipality circular adds

Dubai Municipality’s Circular 12-12-1 of 2025, dated 2025/07/03 and addressed to all engineering consultants and contractors in Dubai, was issued after fires and falling cladding on some tall buildings. It rests on the Dubai Building Code and Local Order No. 3 of 1999 and follows Circular 215 of 2016. Consultants must design façade cladding, including aluminium panels, to the Civil Defence requirements; meet Part E of the Code, including the material specifications and a durability and service life not less than the building’s design life; meet the UAE Fire and Life Safety Code, including fire stoppers; show every detail of the fixing to the main structure on the drawings submitted to the Municipality; recheck projects already under construction and resubmit to Civil Defence where anything is missing; and supervise every stage of installation.⁶

Contractors must install to the approved drawings and specifications, obtain the consultant’s and Civil Defence’s approval of the cladding materials, get the consultant’s approval at every stage, and carry out the inspections and tests that show conformity, under the consultant’s supervision. All tests and approvals for the materials and fixing methods are documented at every stage and produced on request. When the completion certificate is applied for, the consultant and the contractor sign an undertaking of joint liability for the safety of the cladding and any later defects, on the Municipality’s form. The circular took effect on issue and applies to buildings under construction as well as new projects.⁷

The UAE Fire and Life Safety Code requires the consultant’s façade submission to include system listings, material certifications, drawings, sections, installation methods, insulation, thermal barriers, panel railing, cavity fire barriers, primary substrate details and fixing details, and requires the installers and fabricators to be qualified and approved by Civil Defence and the Municipality.⁴⁰

Secondary steel checklist: canopies, screens, balustrade posts and cladding supports

Scope and limits