Metal Roofing & Sheet Metal Wall Cladding Standard Requirements

The work covered by this document includes the workmanship, equipment, supplies and materials and in performing all operations associated with metal roof coverings including proprietary roof-lights, and sheet metal wall cladding. The Cladding system shall comply with the regulations of the local civil defense as regards force resistance and shall comply with the following criteria when tested in accordance with BS 476:

Combustibility: Class 0

Surface spread of flame: Class 1

Ignitability: Class P

Fire exposure: Class SAA

Material Requirements

• Polysobutylene butyl tape shall be Tremco 440, with width and size to suit the conditions
• Metal Filler – Polyester base type approved by the Company.
• No Asbestos Containing Materials (ACMs) shall be used for the Project
• Outer surface of the shading element used as roof cover or shades must have a minimum Solar Reflectance Index (SRI) of 29

Fabricated steelwork shall be inspected by the Company, and tests shall be carried out at the fabricator’s works, in accordance with the requirements of the Specifications.

Steel Roofing / Cladding

The roofing and cladding shall consist of outer and inner profiled steel sheets with an insulation blanket between them.

• Cover width: 1000mm
• Facing sheet: 7mm aluminium, alloy 3105, H46 temper, PVF2 colour finish. Coil manufacturer shall be ECCA and BBA certified
• Insulation: Rigid CFC free, 50mm Thermo core thick, factory injected class B2 fire rated polyurethane foam at overall 40kg/m3 density, with U value of less than 0.4 W/m2K.
• Liner sheet: 5mm gauge aluminium, alloy NS 31, H46 temper, lightly ribbed, Polyester RAL 9002 (Off White) colour finish. Coil manufacturer shall be ECCA and BBA certified
• Other requirements: Panels shall be foamed on a continuous online facility, finished with encapsulated side tapes and a concealed side lap return detail.
• Accessories: Primary fixings to be grade A2/AISI/316 stainless steel self tapping screws with saddle washers and matching colour caps. Contact between aluminum and steel to be avoided by using 75mm wide PVC tape.
• Flashing External flashing shall be manufactured from 0.9mm gauge aluminum sheet to match colour and finish of external weathering sheet.
• Flashing Internal flashing shall be manufactured from 0.5mm aluminum sheet to match the gauge, colour and finish of the internal liner sheet.

Insulated Eave Gutter

• Facing Sheet: 2mm aluminium, Unpainted Plain Mill Finish aluminium sheet
• Insulation: 50mm polyurethane board at 35kg/m3 density, cut to size
• Liner sheet: 7mm Aluminium polyester finish, colour to match roof liner
• Special requirements: Gutter shall be supported by colour matched 5mm thick GI support brackets at every 500mm and butt jointed at (maximum) every 3 meters. The water flow area shall be waterproofed using suitable material.

Vapor barrier: Shall be a multi-layer composite membrane with a aluminium core sandwiched between two layers of UV stabilized woven polypropylene reinforcing mesh. The vapour barrier shall provide a minimum water vapour resistance of 44,000MNs/g and have a maximum water vapour transmission rate of 0.05g/m2/day.10.5 Liner sheet. Shall be 1.5mm gauge RT 130/600 profile, polyester standard White colour finish reverse side (coloured finish shall face the internal area of the building) galvanized steel sheet. Sheet shall conform to ASTM 653, structural grade and be perforated with suitable perforation size to provide the specified acoustic rating.

Fixing Cladding: Cut sheets wherever necessary to give clean, true lines with no distortion. Remove burrs and any lubricant. Cut openings for outlets, vents, windows etc. to the minimum necessary size. Reinforce with trims as per cladding manufacturer’s recommendations.

Lay panels with exposed joints of side laps away from prevailing wind. Drill holes for primary fixings 1.5mm larger than the diameter of fastener. Ensure fasteners are not under or over tightened. Remove all swarf, dust and any other foreign matter before finally fixing panels into position. Check fastening on completion of installation and adjust if necessary to ensure water tightness and that sheets are not buckled or distorted.

Site Fabrication and Installation Requirements

Installation shall be carried out only by a contractor approved by the manufacturer, in strict accordance to the manufacturer’s recommendations. Roofing contractor shall check that structure is in a suitable state` to receive cladding before commencing fixing. Subcontractor must confirm in writing his acceptance to main contractor and consultant. Support structure tolerances shall be as per cladding manufacturer’s recommendations.

The cladding panels shall be designed, fabricated and installed to withstand all movements of the building structure under all design loads or combination of loads without damage or any reduction in the performance of the cladding panels. Attention is drawn to the Structural Engineer’s Specification, which describes the requirements and the tolerances of the support structure and surrounding elements.

All necessary expansion and movements joints shall be designed to accommodate the maximum movements that can be derived from the specified and determined design loads and movements.  Under maximum movements the joints shall meet all the performance requirements of the Performance Specification. The psychometric conditions under which, condensation shall not form on the building interior surfaces of framing members or any part of infill panels. In-situ welding is not permitted, without prior acceptance of the Engineer.

Design Life: The cladding panels shall be designed to withstand weather conditions based on a 50 year return period (from Meteorological data) taking account of extremes of wind, temperature, solar radiation, sandstorms, hail, rain and all other relevant factors.  The expected service life of the cladding panels is a minimum of 20 years.

Thermal Movement

• All components shall be designed to resist thermal movement resulting from: the maximum and minimum surface temperature differentials, maximum annual range, diurnal range, absolute highest and lowest temperature for mid-winter and mid-summer and surface temperature in accordance with the recommendations f BS 5427.
• The surface differential temperature range for components of the Roof Coverings shall be taken as 1ºC and 55ºC.
• The annual range of external air temperature is generally about 45ºC.
• The 24 hour range of external air temperature is generally about 20ºC.
• The highest recorded temperature is 50.5ºC and the lowest recorded temperature is 1ºC.
• The design shall cater for all temporary and permanent conditions envisaged for the works.
• In addition, the components shall be capable of accommodating changes in dimension and shape of its components resulting from varying surface temperatures between the outside and inside of the building, without any reduction in the specified performance.

Protection: All fabrications and assembled units shall be protected against damage, corrosion and disfigurement during handling, installation and subsequent site operations. Protective coverings shall be applied before dispatch to site and shall not be detrimental to products, finishes or installation procedures.

Fixing Anchor Installation and Adjustments

• Ensure that fixing anchor cast-in inserts are positioned in accepted locations and that insert cavities are protected from entry of concrete.
• Site drill or cur into structure only in approved locations
• Distances between all fixing components and edges of concrete shall not be less than recommended by their manufacturers.
• Before commencement of the installation adjust all fixing anchors for line and level, allowing for adequate final adjustment during installation.
• Obtain approval before carrying out corrective fabrication to fixing anchors.

Insulation: Rigid insulation boards shall be installed as a single layer to the thickness specified. All joints between rigid insulation boards shall be tight and no gaps shall exist where the board meets roof lights, edge details and services penetrating the roof structure. End joints shall be staggered.

Ventilators and Louvers: Where required, ventilators and louvers to be incorporated in sheeted roofs and walls shall be manufactured of materials to match the external appearance and color of the surrounding sheeting. The quality of the cladding materials for ventilators and louvers shall not be less than that specified under relevant clauses of specification.