CPD 07 2023: Specifying steel standing seam systems for residential projects

This Catnic-sponsored CPD module looks at the use of steel standing seam systems, exploring their design features, advantages and limitations in residential applications, as well as relevant guidelines considerations during installation

Modern standing seam roofs were first developed in the 1960s, using metal instead of asphalt, tile or slate. Known for their durability and resistance to weather damage, standing seam roofs have been used for decades across a wide range of buildings, from large prestigious landmarks to smaller residential applications.

Learning objectives:

  • Understand standing seam roof and cladding systems – their designs, features, advantages and limitations in residential applications.
  • Awareness of the key product performance and installation considerations.
  • Knowledge of relevant regulations and guidance when specifying standing seam systems.

Standing seam technology

Standing seam technology refers to continuous metal panels, used for either roofs or cladding, that have raised seams above the level of the panel itself – hence the term “standing seam”.

The system consists of wide, relatively flat metal panels that have vertical legs (or ribs) on each end. The metal panels are designed to lock together, and are mounted to the roof by being fastened to the sheathing underneath through a series of hidden clips. All fasteners are hidden and there are minimal through fixings.

Metals that have traditionally been used for standing seam roofs include:

  • Zinc – chosen for its longevity due to it being resistant to corrosion and to UV damage.
  • Aluminium – chosen for its excellent strength-to-weight ratio.
  • Lead – chosen for durability, corrosion resistance and malleability, but with a downside of weight.
  • Copper – chosen for its ability to provide excellent corrosion resistance as its surface forms tough, oxide-sulphate patina coatings that protect underlying copper surfaces. Copper’s low thermal expansion properties, 40% less than zinc and lead, help to prevent deterioration and failure.

Some standing seam systems can be site rolled or formed, but traditionally the panels are crimped together on site by hand or by a mechanical seaming tool to secure the joint along the length of the panel and create a watertight envelope. Installation time and manual workloads can differ by system – it is important to be aware of this and consider the best installation method for each individual project.

The rising costs of these metals, coupled with a skilled labour-intensive installation method, means that new solutions have been developed to meet modern housing needs.

Standing seam technology consists of wide, relatively flat metal panels that have vertical legs (or ribs) on each end

Pre-finished

Pre-finished steel solutions are now available as a cost-effective alternative to traditional metals. They are manufactured from galvanised steel, which is then either coated or painted to further enhance its aesthetics and durability.

Pre-finished solutions deliver installation speed advantages as they are connected with click or snaplock technology, which is further secured using hidden fastenings. They are typically seven times lighter than traditional clay or slate tiles and provide a good solution for all types of residential new-builds.

The process involves fastening the starter panel in position using the specified nails in the nailing strip slots. Once the starter panel is secured, all intermediate panels can be installed. It is then a matter of positioning the folded notch to the eave plate and aligning the female profile over the male of the previously installed panel, using a rubber mallet to hammer it into place.

The solution can also be used for renovation or extension projects, with the ability to be installed with a minimum pitch of 5o, and it supports the modern methods of construction approach due to being compatible with structural insulated panels (SIPS).

Holton Lodge in Halesworth in Suffolk, England

A closer look: Catnic Holton Lodge

An extension to a 16th-century cottage, Holton Lodge in Halesworth, has used a steel standing seam roof as a cost-effective alternative to zinc. The roof and cladding met the desired aesthetics – with the quick-fit system offering a fast and problem-free installation.

Hilary and Robert Garner wanted to open up their existing kitchen with a build that used full-height glazing to flood the area with light and give them an unobstructed view of their garden. In response, architect Tim Hannon, from Brooks Architects in Leiston, designed a contemporary extension that provides a strong new focal point.

The vaulted roof was designed to bring drama to the space, with a ridge that was purposefully set higher than the roof of the main house so that visitors get a glimpse of the striking design as they approach the house. An overhang provides a covered outside eating area and works to reduce solar gain, with the sleek lines of the standing seam continued down the side of the extension, which is wrapped in matching cladding. Typical of the area, the design also includes a lean-to roof on an area that houses the utility room and cloakroom.

Holton Lodge has used a steel standing seam roof as a cost-effective alternative to zinc

Sustainability

Pre-finished steel standing seam systems support an eco-design philosophy by minimising the environmental impact of a building’s construction.

The systems are 100% recyclable (with zero degradation of the material’s properties) and typically contain between 10% and 30% recycled content. Pre-finished steel standing seam roofs can support rainwater harvesting, which can be used in such applications as toilet-flushing, laundry, car-washing and garden irrigation.

Rated A+ within the BRE green guide, some pre-finished steel standing seam systems have even achieved BES 6001, which is the framework standard for responsible sourcing of construction products by assessing a product from the point at which component materials are mined or harvested, through to manufacture and processing.

Some manufacturers of pre-finished steel standing seam systems have achieved environmental standard ISO 14001 certification, demonstrating the product is manufactured in a factory with an environmental management system.

Some systems hold independent EPDs (environmental product declarations). Pre-finished steel can have relatively low CO2 creation in the making and transportation of the finished product, depending on the factory location. Along with low maintenance and long life, independently verified EPDs can provide maximum credits within BREEAM and LEED.

Pre-finished standing seam systems support an eco-design philosophy by minimising the environmental impact of a building’s construction

Performance considerations

There are a number of key performance considerations that specifiers need to evaluate when selecting the right pre-finished steel standing seam solution for their project.

Corrosion resistance

Pre-finished steel is manufactured as a multi-layered system, and the use of zinc-based formulations offers increased corrosion resistance. The principle behind this is oxidisation, which occurs on all metals. Steel on its own has open oxidisation, allowing water through onto the metal below and resulting in rust. Zinc, however, is closed but very soft and will wash away, wearing down the metal relatively quickly. By mixing zinc and aluminium, which is a very hard-wearing material, a galvanic protective coating is created. This slows the rate of corrosion to a 10th of that of standard galvanised steel.

EN 10169:2022 lays out the requirements for continuously organic coated (coil coated) steel flat products and classifies the corrosive nature of the environments. This classification is dependent on the weight loss of various metal coupons measured throughout the year. Depending on the recorded weight loss of carbon steel in grams, the natural weathering site is assigned a classification between C1 and C5.

The chart below shows the different corrosion resistance categories (RC1 –RC5), the typical product types that fall into each category, and the environments where they are suitable for use.

To ensure long-term performance, it is essential to specify a pre-finished steel product that satisfies the highest EU standards for corrosion resistance (RC5) and can be used in all the listed environments.

To achieve an RC classification, a material sample needs to be tested for two years at an accredited real-world natural weathering site. Additionally, it must undergo accelerated corrosion tests including salt spray, prohesion, water soak, humidity and Kesternich.

UV resistance

Coil coating standard EN 10169:2022 defines the test method and classification of a painted steel product’s resistance to UV radiation.

Similarly to achieving an RV classification, to achieve a Ruv classification a material sample needs to be tested for two years at an accredited real-world natural weathering site. Additionally, it must undergo 2,000 hours of UVA accelerated laboratory testing.

Gloss and colour retention are key requirements for painted steel as they are early indicators of the paint starting to break down. Gloss loss occurs as UV light begins to break down the paint resin, which creates a slight roughening of the surface.

Further degradation of the surface will expose fillers, which causes the surface to discolour and is often referred to as chalking. Continued exposure to radiation will cause the polymer resin molecules to break down, resulting in embrittlement and cracking of the coating, which exposes the metallic substrate.

EN 10169:2022 classifies the UV resistance of the pre-finished steel from Ruv2 to Ruv4 – with Ruv4 being the best. To ensure long-term performance, it is essential to specify a pre-finished steel product that satisfies the highest EU standards for UV.

Impact resistance

Impact resistance is another measure of durability. Roof and cladding must be able to withstand everyday impacts to which it may be reasonably subjected.

All buildings and building components are exposed to impact in service, the type and frequency of which varies according to location and occupancy. The majority of impacts occur under normal conditions of service, others are accidental and some are caused maliciously or through vandalism.

The variety of possible impacts is virtually endless, and impacts are extremely variable in regard to the mass, shape, hardness of impact bodies and the value of the impact energy. In addition, the effect of an impact also depends on the properties of the building component being subjected to impact, which differ greatly.

MOAT 43:1987 is the UEAtc Directive for impact testing on opaque vertical building components. This document is established in order to standardise and simplify impact tests and testing methods to be used for British Board of Agrément certification by member institutes, in assessing the behaviour of opaque vertical building components under impact.

The strength of a prefabricated standing seam system is determined by its material thickness. It is required to meet the hard and large soft body impact requirements of Moat 43:UEAtc when installed in combination with a standard wood board build-up.

Part 2.2.1: Impact from large soft bodies – represents the impact of the human shoulder. Part 2.2.2: Hard body impacts – reference the impact of other items striking the roof or cladding, for example, tree branches and stones.

The document does not deal with the technology of impact testing nor with the resistance to impact of materials, products and components during transport, handling and installation. It does not deal with impacts which may be regarded as special cases, such as accidental impact from cradles and their suspension cables, used in the repair and maintenance of claddings on high-rise buildings, for which assessment criteria will have to be established on an ad hoc basis.

Acoustics

A key concern for residential roofs is impact noise from rainfall. The perception is usually that the noise increases with the specification of a metal roof, but a well-designed and installed standing seam roof can offer the same acoustic performance as other traditional roofs.

Steps to delivering this include direct fixing of the standing seam to a boarded structure with a membrane that reduces the ability of the roof sheet to vibrate. Oriented strand board (OSB) or similar boarding provides effective absorption of vibration. The dense plasterboard on the inside is usually fixed to battens or adhesive dabs, providing a degree of acoustic isolation.

The main consideration when looking at the acoustic performance of walls is sound reduction and sound absorption. Sound reduction is a measure of the reduction in sound level of noise escaping from or entering a building from an external noise source such as traffic.

In traditional construction, the sound reduction is proportional to the mass, but in metal cladding systems it is also improved by the use of airtight skins combined with soft acoustically absorbent insulation and air spaces.

Sound absorption is the damping of echoes or reverberant sound that would normally reflect back off internal surfaces. Different internal lying will affect the sound absorption of a room.

Where special considerations are essential, designers will need to address the internal acoustics or reverberation of a building with input from an acoustic engineer.

A well-designed and installed standing seam roof can offer the same acoustic performance as other traditional roofs

Compliance

Approved Document L is concerned with the conservation of fuel and power in dwellings. An SAP rating is required for all new dwellings to produce a predicted energy assessment and an on-construction energy performance certificate.

Building Regulations require that a SAP calculation and a predicted EPC be submitted for new dwellings prior to the commencement of work.

To measure energy consumption there is also a requirement that the fabric energy efficiency (kWh/m2/year), expressed as a dwelling fabric energy efficiency (DFEE), is lower than the target fabric energy efficiency (TFEE). Fabric energy efficiency is a measure of the efficiency of the building fabric, which looks at U-values, airtightness and thermal bridging – the parts of the building that lose heat.

As a general rule, an EPC is required when a home is put up for sale or for rent (whether new-build or existing stock). This gives the prospective buyer or tenant an indication of its energy efficiency and running costs. These are calculated from the SAP calculation and are valid for 10 years.

Standing seam roofs and cladding can meet the Part L requirements through fully supported build-up systems.

The government’s Future Homes Standard (FHS) – set to become mandatory in 2025 – will also require new-build homes to be future-proofed with low-carbon heating and high levels of energy efficiency.

New homes built from 2025 will produce 75%-80% less carbon emissions than homes built under the Building Regulations from 2019, which was when consultation on the standard began. As a precursor to the specifications set out in the 2025 FHS, the government uplifted Parts F and L of the current Building Regulations at the end of 2021.

Part F introduces new standards for ventilation, while Part L sets out minimum energy efficiency performance targets for buildings, airtightness requirements and improved minimum insulation standards. These more rigorous requirements have applied to UK homes since June 2022 – with more stringent regulations due to follow in 2025.

The uplift means new homes are now expected to produce around 31% less CO2 emissions. Although solar panels are not currently mandated, the government predicts most developers will use them to meet the new energy efficiency standards. Where new homes do not include solar panels, designers and developers are likely to specify other low-carbon heating technologies, such as heat pumps.

Solar solutions

Various lobbying groups for the solar panel industry (including in Scotland) are trying to push for the government to include mandating solar panel use in the FHS. At the moment there is no indication that it will. However, we still expect to see a greater uptake in the technology, as it has been proven to vastly help meet net zero targets, as well as being a solution that utilises existing roof space while remaining out of sight.

There are a number of options for incorporating solar solutions into standing seam roofs. Pre-finished steel standing seam systems are ideal for fixing renewable PV or solar panels, and most manufacturers offer a clamp-based system which does not penetrate the roof. However, clamps specified must be suitable for the standing seam system to avoid marking and damage to the material. Designers should refer to the manufacturer’s guidelines, taking into consideration material choice and guarantees.

Standing seam systems can integrate PV modules bonded directly to the roof, which offers a more subtle aesthetic than the clamp systems. The PV can be supplied to site pre-bonded, saving time and expense – with a single install for a “plug and play” solution.

Some of the advantages of incorporating solar solutions directly onto the roof, as opposed to clamping, are:

  • Panels are laminated directly onto the standing seam profile and there is no requirement for any secondary structure, which saves materials cost.
  • Being pre-fixed offsite in factory-controlled conditions produces a guaranteed quality and cost reduction, with the roof provided as a complete kit of parts.
  • Reduced on-site installation cost, as the single roof installation is ready for the MCS-certified contractor to connect up the system.
  • Reduced maintenance costs, as there is no protruding frame that debris or bird nests could get stuck under. Panels have a textured, Teflon-type top layer providing self-cleaning and minimising glare to enhance the light capture and energy performance.
  • Embodied energy reductions – there is around a 50% lower carbon footprint than for multi-crystalline silicon-based PV panels.
  • Increased durability – wind can not get under the panel so wind loading is unaffected. They are also difficult to remove so there is reduced likelihood of theft.
  • Maximisation of energy output through the life of the solar panels, as the solar panel is made up of multiple diodes and cell interconnections. This means that if any cells of the panel are shaded then the unshaded cells will still work.

Possible challenges to incorporating solar panels include the availability of products and suitably qualified installers. There is also a backlog of connection of the panels to the grid by utility companies, all of which need to be considered when selecting solar technology for any given project.

Expect to see a greater uptake in solar technology, as it helps to meet net zero targets while utilising existing roof space and remaining out of sight

Fire characteristics

Fire characteristics can be split into reaction to fire and fire resistance. Reaction to fire describes how the material itself reacts in the case of fire, and tests are used to evaluate the contribution a material makes to fire growth.

BS EN 13501-1: Fire classification of construction products and building elements – classifies products into seven main categories based on their reaction to fire performance, as shown in the table below. The performance ranges from class A1 (best) to class F (worst).

Building regulations restrict the use of combustible materials under two main areas:

  • Building height and use
  • Distance from a relevant boundary.

The fire resistance of a product is quoted in minutes and is a measure of one or more of the following:

  • Integrity (E) – resistance to fire penetration
  • Insulation (I) – resistance to the transfer of excessive heat.

The extent of the fire-resisting construction and the standard of the fire resistance required will be set out in the relevant building regulations. A number of factors such as building use, building size and proximity to a boundary will determine the required level of fire resistance required.

Design and detailing

Fully supported roof systems

Fully supported systems are generally used on residential buildings and are covered by EN 14783:2013. A fully supported standing seam roof system is installed onto a fully boarded timber deck, with a breather membrane interlayer. The breather membrane protects the substrate from any moisture trapped during the installation of the panels and prevents any chemical reactions between the wood and metal. It also acts as a barrier, should any moisture travel beyond the sheeting once installed.

The roof is squared off using fabrications at the eve, verge and ridge (for monopitch roofs). The cold roof system contains all the details of a warm roof system but has been specifically designed for use on pitched roofs and is suitable for use within most timber-framed constructions. Boarding is usually 18mm plywood or OSB board. Some SIPS boards can be 15mm, but boarding can also be made with timbers.

Wall construction

For wall construction applications, seams can run vertically or horizontally. It is vital to ensure the seam is installed to prevent water from being trapped in the joint. For limited combustible constructions, the support structure can be altered to a steel and cement particle board construction.

Chapter 6.2 of the National House Building Council’s Building Standards states that in areas of exposure to wind-driven rain, wall construction should include a 50mm cavity between the sheathing and the cladding, installed with a high-performance breather membrane. Cavities should be ventilated to allow some limited but not necessarily through movement of air. All build-ups should be checked for British Board of Agrément (BBA) approval.

Measurements

Standing seam pre-finished steel roof systems are available for a wide range of popular roof designs, with the particular design impacting the type of ancillaries required. Designers should consider the sheet lengths and profile widths of the manufacturer’s product – as this helps with the placement of windows, rooflights, chimneys and so on.

Oil canning

Oil canning is a cosmetic surface-level occurrence where the metal seems wavy, especially in the broad, flat areas of a roof or wall system. The good news is that oil canning is cosmetic and does not affect the structural or performance aspects of a roof or wall system. The National Roofing Contractor Association (NRCA) does not consider oil canning to be a cause for rejection, as there is no adverse effect on the property’s structural integrity or waterproofing capability.

Oil canning is a natural occurrence, and part of the aesthetic appeal of standing seam solutions, which is thought to originate in the processes the material undergoes. If it is an effect not to your liking, then consider the following to reduce its appearance and frequency:

  • Lighter colours
  • Matt finish
  • Shorter panel lengths
  • Narrower panel widths.
Oil canning is a cosmetic surface-level occurrence where the metal seems wavy, especially in the broad, flat areas of a roof or wall system

Wind

The wind loadings on a roof are dependent on the building location, building height and number of storeys, roof pitch and topography. The fixing specification of a standing seam system must take into account these factors. A wind uplift calculation should be completed by an independent structural engineer. It is worth checking with system manufacturers, as panel widths and fixing specifics vary.

Specification

Specifying a system includes the panels along with their recommended fixings, which form the manufacturers’ materials and performance guarantee. The switching-out of fixings risks creating a point of failure – due to material and strength reductions. It can reduce the lifespan of the roof or cladding and invalidate the warranty that comes with the system. If the contractor changes any part, then they become the manufacturer of that part of the system – and are responsible for testing.

It is also vital that systems are installed by competent and experienced installers; some system manufacturers can recommend trained installers. Inspection and maintenance requirements will be dependent on each manufacturer’s guidelines.

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