Specifying the correct material for your roofing and cladding installation is important to ensure its success. The following section provides the necessary information to help assist in the specification process. The Atmospheric Chart (left) and Roofing Zone Usage Charts (below-left) provide specification guidelines of both ColorCote and Calder Stewart profile options respectively. Additionally, complete descriptions of the material options available are listed below. For certain applications and settings, consultation with Calder Stewart Roofing's support team is recommended.
Galvanised steel is the oldest steel roofing product in New Zealand and is manufactured by ‘hot dipping’ the steel coil into a bath of molten zinc. The material is manufactured to AS 1397 with a pure zinc coating weight of 450 g/m2. Galvanised steel protects itself by ‘galvanic’ or ‘anodic’ action meaning that the coating is consumed by the action of protecting the steel.
Use & Limitations
The coating does however allow the material to be soldered, brazed and spot welded. Note that localised damage to the zinc coating must be repaired using a zinc rich primer for all applications.
The material has been largely replaced by aluminium/ zinc (Zincalume®) coated steel except for the following applications:
Galvanised steel (even when painted or powder coated) may exhibit ‘white rust’ which is zinc hydroxide and the product is therefore not recommended for unwashed areas.
The material carries no specific warranty cover and is only recommended where Zincalume® is not appropriate and is therefore NOT RECOMMENDED for residential or commercial applications.
Galvanised steel finish is denoted by a bright silvery spangle and high reflectivity, over a number of years in an external environment this dulls off to a matt metallic grey.
Galvanised material is readily paintable using a propriety primer and acrylic top coat in accordance with the paint manufacturer’s instructions.
Aluminium / zinc coated steel (also known as Zincalume ) is a development of galvanised steel. The material is the most common plain and pre-painted material for roofing in New Zealand. Note: Never shorten the name Zincalume® down.
The coating is ‘hot dipped’ and the alloy comprises of 55% aluminium, 43.5% zinc and 1.5% silicon with the percentages derived to provide a more stable compound and a reduced oxidising rate of the zinc by virtue of the aluminium providing a protective barrier layer.
Typical designation for roofing is AZ150 or 150 g/m2 coating weight.
Use & Limitations
Zincalume® is not suitable for the following:
Zincalume® is not weldable and should not be exposed to any thermal processes, as this will invalidate the warranty and may cause premature failure of the product. In addition, graphite pencils should not be used to mark the surface as the carbon may react with the coating.
The appearance of Zincalume® is a semi-matt fine spangle metallic silver which dulls off to a matt silver over a number of years in an external environment.
Zincalume® is readily paintable using a propriety primer and acrylic top coat in accordance with the paint manufacturer’s instructions. Painting would normally invalidate the substrate warranty so it is advised that where a paint finish is required, that pre-painted material (i.e. ZinaCore™) is used with a full warranty cover.
An aluminium/ zinc alloy coated steel substrate (or Galvanised for GR8) based material, which is factory painted to ensure that consistent high quality paint finish is achieved.
The paint system comprises of a polyester primer and baked on polyester or acrylic top coat applied to the coloured side (with a Shadow Grey wash coat on other) or the top coat maybe applied to both sides (when specified).
Use & Limitations
For general exterior architectural uses, suitable for roofing, cladding, fascia and rainwater goods in accordance with the correct zone selection using the Atmospheric Chart (right sidebar - this page).
In addition, when specifying ZinaCore ensure that the restrictions on the use of Zincalume® based material (i.e. use as formwork) are observed.
GR8 is a galvanised steel based pre-painted equivalent for use where ZinaCore material is not appropriate (i.e. fertiliser stores) or where existing galvanised product has already been installed. This product is non-standard and must be ordered in on a job to job basis.
A wide range of colours are available (see Colour Chart section of this website). In addition, non-standard colours, specially matched colours and metallic and low gloss options are available. Contact Calder Stewart Roofing Support for details.
ZinaCore X is a pre-painted aluminium/ zinc coated steel based material. The paint system is comprised of a high build primer on both sides and PVF2 top coat on either one side (with Shadow Grey wash coat on other) or top coat both sides (when specified). For general exterior architectural uses, suitable for roofing, cladding, fascia and rainwater goods in all but Zone 5 (Very Severe area’s), Care also required when used in Zone 4 refer to the Atmospheric Chart (left sidebar - this page).
In Zone 4 (Severe Marine Environments) the material requires edge sealant applied to all cut edges and this should be applied at the time of installation following all cutting. The use of PVF2 coating increases the resistance to chemical attack and the principle grade used for airports and area’s likely to be exposed to vehicle fumes.
A wide range of colours are available (see Colour Chart section of this website) in addition non-standard and even specially matched colours are available including metallic and low gloss options.
MagnaFlow™ (previously known as ZM8™), is a pre-painted aluminium, zinc and magnesium alloy coated steel based material and is a highly durable product with improved cut edge performance design to give excellent colour retention and high formability at a moderate cost.
MagnaFlow™X (previously known as ZMX™) uses exactly the same substrate as MagnaFlow™, but comes with a more protective paint system and offers a slightly better installation zone range than MagnaFlow™ for use in chemical or industrial environments.
Aluminium is generally reserved for specific applications where outstanding corrosion resistance or specific resistance to chemical attack is required zones 4 & 5. The 5000 series grades are chosen for general exterior architectural uses, suitable for roofing, cladding, and rainwater goods in all zones including industrial and severe marine areas.
Aluminium Alloys for Roofing
|5005||H34||1/2 hard||135||105||2.5t||General Sheet Metal
|5052||H34||1/2 hard||235||180||3t||General Sheet Metal
Note: In Zone 5 (Severe Marine Environments) 5052 should be requested.
Plain aluminium has a high reflectance and should be specified as painted (ARX™) where this may be an issue. Aluminium is paintable, however etch primers and specific top coats are required to achieve a satisfactory bond. Where painted, using the correct systems painting will not affect the warranty.
Oil canning, flatness or waviness may occur on wider panned profiles during the roll forming process of this type of material due to its softness.
AlumiGard™ (previously known as AR8), is made from marine grade 5005 or 5052 aluminium alloy with a H34 or H36 temper. That’s why we can confidently recommend this substrate to give superior protection in the most extreme environments.
AlumiGard™X (previously known as ARX), uses exactly the same aluminium substrate as AlumiGard™ but comes with a more protective paint system designed for use in chemical, industrial or geothermal environments.
The material is significantly more expensive than other steel based products and care should be taken when specifying with other building materials:
All pre-painted material (ZR8™, GR8™, ZRX™, ZMX™ and ARX™) will weather and new and old material should not be mixed if possible.
Copper alloy is normally supplied in a ½ hard condition for flashings or ¾ hard condition for roofing. The material is selected for a higher tensile strength than pure copper and is capable of being brazed or soldered where necessary.
Copper has a high thermal conductivity relative to its tensile strength and oil canning, flatness or waviness may be visible on trays, flashings or roofing applications.
In addition, copper is protected from corrosion by a patina or surface oxide film. This the tarnishing of the copper from shiny to brown, black or green (depending upon the environment) it is impossible to stop and staining may occur due to contact with other materials or substances which will normally fade as the thickness of patina increases.
Copper has excellent durability in coastal or other marine environments; however copper must not be allowed to be in contact with or be allowed to run off onto steel or steel based products (see Fixing Material Selection Chart - in the Compatability & Fixings section of this website).
Stainless steel has a high tensile strength which further increases due to work hardening in manufacture. Due to the higher strength, available profiles are limited and reference should be made to the Roofing Zone Usage Table (right sidebar - this page).
Unless specified otherwise stainless steel supplied by Calder Stewart is grade 304. This is normally supplied in a 2b finish.
Stainless steel has good corrosion resistance, however, it is capable of being stained by other materials and particularly airborne ferrous dust from grinding and other construction activities which manifest as ‘tea staining’ which although is not structural can cause severe visible damage to the surface.
Where tea staining is likely to occur or in severe/ very severe marine environments, grade 316 must be specified, this material is unable to be roll-formed, but can be folded and this is due to the high tensile strength of the material. An equivalent type of material call ‘445M2’ is available and this can be roll-formed for areas other than very severe marine environments subject to prior approval by Calder Stewart Roofing.
Note: - Only 316 grade fixings can be used with this material.
One of the oldest roofing materials used, pure zinc (alloyed with titanium to increase strength) is a malleable grey material which is normally supplied in a pre-weathered condition and is available with a back side material protection cover (known as Plus) for improved performance in severe environments.
Zinc has excellent weathering abilities and although less susceptible to staining and marking compared with copper, it should be noted that a white zinc oxide powder is produced on the surface under extreme conditions.
Zinc is also very soft and easily damaged and is usually laid over or on top of a solid substrate for support and should not be used in areas which are subject to heavy use.
Zinc is a homogenous material, rather than galvanised or zinc/ aluminium coated steel and is therefore significantly more expensive and should not be specified where initial cost is the main element. Zinc is mainly used for hand seamed trays and panels, where the unique looks and longevity are required.
Oil canning, flatness or waviness, this condition may occur during the roll forming, with thermal expansion of the material or possibly during the installation process and may be more noticeable when using wide panned profiles.
NOTE: Do not order Zinc as an abbreviation for Zincalume® or galvanised iron
Developed for residential roofing the product is a polycarbonate (PVC / Acrylic composite) manufactured into roofing profiles and coated with UV or heat stabilising films. It is a semi opaque material allowing light transmission but preventing up to 99% of UV rays.
Polycarbonate sheeting is available in a number of colours and with heat reflective foils with light transmission levels of 93% to 12% dependent upon colour and foil type.
Polycarbonate has excellent chemical resistance and is suitable for any zone classification.
Polycarbonate sheeting has a co-efficient of expansion of 0.7mm per metre per 10°C or approximately 10 times steel roofing. It must therefore be fixed with pre-drilled holes and is limited in length of sheet.
Polycarbonate also has a low rigidity and can be curved relatively easily compared with metallic roofing materials and must therefore be fixed at relatively small purlin spacings.
Glass Reinforced Polyester (GRP) provides a light and heat trans-missive material option with addition options of protective surface film option that offer the highest level of protection in aggressive environments and is capable of being used in:
GRP sheeting can be supplied in a solid colour option where matching to roofing materials is required, such as unwashed areas and as a fire retardant sheet.
The sheeting also has an improved rigidity compared with polycarbonate although is still significantly less than commercial profile metallic roofing and attention to correct purlin spacing is vital for performance.
Adobe Acrobat PDF file, 2.6 MB
9 February 2016
The Atmospheric Chart provides pertinent information regarding the use of ColorCote™ materials in various conditions and climates, pdf, 2.6MDownload
Adobe Acrobat PDF file, 2.6 MB
9 February 2016
The Roofing Zone Usage Chart provides information regarding the full range of materials options available, their suitability as applied to a given Calder Stewart Roofing profile and their appropriateness based on general roofing zone usage guidelines., pdf, 2.6MDownload
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