Use of pre-finished steel compared with aluminium for standing seam roofing

 

Standing seam roof cladding is often specified where low pitch or curved roofing is required. The construction generally offers a more aesthetic, less industrial profile, with no through fixings, which could be vulnerable in low pitch applications.

 

Standing seam profiles are mainly specified in aluminium, however pre-finished steel can offer a number of significant benefits.

Where would you use pre-finished steel in preference to aluminium?

Pre-finished steel can provide enhanced durability and aesthetic performance in certain environments. Generally mill finish aluminium is tolerant of pH values between 4.0 and 8.5 at room temperatures, forming a film of hydrated aluminium oxide on the surface.

A coastal environment can cause pitting to the aluminium surface with the severity of the pitting being dependant on the aggressiveness of the surrounding environment. Therefore it is often recommended that painted aluminium be specified. The most common paint employed to coat aluminium is PVDF, which typically has a guarantee of 15 years.

Colorcoat HPS200 Ultra® pre-finished steel has a 200 microns coating thickness providing a more effective barrier against the permeation of salt polluted moisture than thinner coatings such as PVDF (27 microns thick). The excellent corrosion resistance and robustness of Colorcoat HPS200 Ultra® is of particular advantage where a potentially aggressive atmosphere can readily attack steel substrate exposed at cut edges or due to physical damage.

Where a coloured roof is required Colorcoat HPS200 Ultra® provides a Confidex® guarantee of up to 30 years on roof cladding in coastal environments and 40 years in inland environments

How do the material physical properties affect the roof performance and construction considerations

Pre-finished steel generally has a higher yield strength than aluminium, with increased resistance to point loading and damage from pedestrian activities on the roof and also offers better resistance to deflection under load. To compensate for the reduced mechanical properties, a thicker aluminium gauge must be used.

The coefficient of thermal expansion for aluminium is approximately twice that of steel. Careful design is required to ensure that aluminium cladding can expand and contract freely with changes in ambient temperatures, without affecting the weather-tightness of the building.

The thermal conductivity of aluminium is approximately 5 times that of steel. When designing building details particular care must be taken to minimise cold bridging through the building envelope, which will cause increased heat loss and potential condensation risk.

Colorcoat Prisma® Relaunch at Jaguar Land Rover, Halewood

What a day! All our supply chain partners, distributors and a room full of contractors all come to hear about the new attributes of Colorcoat Prisma®. Combined with a tour of the Land Rover manufacturing plant, a subsidiary of our parent company Tata Group, and some off-road fun it really was a day not to be missed!

I knew that it was going to be a busy day as the event had already been over subscribed so much that I had to split the day into two groups with one group arriving at 8.30 am and the other at 10.30 am.

The format of the day involved a presentation to relaunch Colorcoat Prisma® with it’s new attributes, a session on the gauge of pre-finished steel and a factory tour and Land Rover off-road experience.

Peter Wilks, General Manager of Corus Colors, welcomed the audience reminding them of our continuous drive for the improvement of the Colorcoat® products that we supply into the market.

Peter Barker - Product Development Manager, then introduced the audience to the new attributes of Colorcoat Prisma®:

With his main points being:-

• An increased Confidex® Guarantee for solid and metallic colours for up to 30 years, and matt colours for up to 25 years – the longest on the market.
• A new colour range which includes 3 new matt colours, chosen to replicate more traditional building materials such as terracotta and slate tiles and weathered copper.
• The comprehensive testing proving outstanding colour retention & corrosion resistance.
• The approvals by both WRAS for cold water use and TUV for PV laminates.
• A double sided capability for buildings with demanding internal environments, rainscreens and rainwater goods where double sided protection is required.
• Standard sizes available on short production lead times.
• Reverse side branding for easy traceability.
• Plus of course all the benefits of our previous offer, including the Galvalloy® metallic substrate for corrosion resistance, and Confidex Sustain® for CarbonNeutral building envelopes.

All of this comprehensively backed up by test evidence and physical results and samples for everyone to see.

Next Joanne Ingham, Marketing Manager UK & Ireland, showed us the new Colorcoat Prisma® colourcard, technical paper, samples, website and an iPhone app. If you have an iPhone you can use the app to view sample colours and specifications, order samples and view existing buildings already using the Colorcoat Prisma® colours. It’s a quick and easy reference tool. Extremely useful for all those attending sat with their iPhone’s on the table!

It seemed that few people were sure exactly what they should be measuring when Ian Clarke, Applications Development Manager, asked the audience to measure the gauge of some samples of pre-finished steel. He demonstrated how some where within the tollerances of EN 10143:2006, how some of the material was under gauge and how the paint coating should always be removed before measurement.

It seems that buying under gauge coil because it is cheaper can have a big impact on the structural performance of a roof and wall cladding system, the video and drop test images certainly demonstrated that.

Feedback on the presentations was excellent and everyone seemed thankful for the tip off on the use of under gauge material and the accident waiting to happen.

After lunch and fully up to date on Colorcoat Prisma® the guests then had a tour of the Land Rover manufacturing site and saw the birth of a Freelander before putting their lives at risk on the off road assault course of ramps, hills, rivers and rocks. An afternoon that everyone enjoyed.

All in all the day itself was a huge success in updating the actual users of Colorcoat Prisma®, such as distributors and cladding contractors and manufacturers, raising awareness of the structural and health and safety implications of the use of under gauge pre-finished steel versus any cost saving and providing a great opportunity for all to network whilst having a bit of fun!

Who’s afraid of refurbishment?

We all know that improving energy efficiency of buildings and reducing our demand for energy is a priority if we are to cut carbon emissions, but whilst environmental concerns are clearly important, they are simply not enough on their own to secure genuine buy-in from the wider industry and building owners alike.

The real motivating factor is, as often the case, economic.

Energy efficiency measures in refurbishment projects

Escalating energy costs makes reducing energy consumption good for the pocket as well as the planet. This is of course obvious, but the main barrier to action seems to reside in the misconception that incorporating energy efficiency measures into a refurbishment project  is fraught with difficulty and expense.

In some instances, particularly older buildings, this can obviously be the case – especially where this would involve work to the building’s structure. However, for more recent buildings, particularly in the industrial and commercial shed sector, significant improvements can be made that are highly cost effective, and will add value to the property itself. For example, by achieving high-levels of air-tightness and thermal efficiency in the building envelope, significant energy and CO2 savings can be made. Achieving this on a refurbishment project is often simply a case of attention to detail and specifying the right products.

Energy efficient buildings command a higher rental and wholesale value

It is not just through improved energy efficiency and reduced consumption where economic benefits can be derived. We are now starting to see tangible evidence that energy efficient buildings command a higher rental and wholesale value.

A recent McGraw-Hill study revealed that thermally efficient buildings command 3 per cent higher rental rates and an average increase of 7.5 per cent in building value. Alongside this, the study found that they can deliver a 3.5 per cent higher occupancy rate and ultimately improve return on investment by an average of 6.6 per cent. Even though the study is US based, given the strength of the statistics, the UK is sure to follow.

Whilst there has been concern that the current economic climate may impact negatively on sustainable building practices, what I believe we are actually seeing, somewhat ironically, is a change of focus on how we perceive these practices, as well as a realisation that improvements to our existing building stock are as much about saving money and adding value, as they are about saving the planet.

By Dave Taylor, Business Development Manager at Corus Colors

Colorcoat Prisma® re-launch your questions answered

 

 Q1: You have re-launched Colorcoat Prisma®, does this mean changes to the guarantee?

Extended and comprehensive testing involving both natural and artificial exposure has given us the ability to extend the Confidex® Guarantee period for Colorcoat® Prisma to up to 30 years.

In certain applications like coastal roofs in the UK, the Confidex® Guarantee period has been extended by as much as 15 years. But there are no changes to the terms and conditions, there is still no requirement to maintain or inspect to validate the guarantee and cut edges are still covered for the life of the guarantee.

As independent verification, Colorcoat Prisma® is BBA certified for durability in excess of 40 years.

 

Q2: Have you added to the choice of colours available?

Following a series of workshops with architects and colour specialists, Corus has extended the Colorcoat Prisma® range to include 12 solid colours, 12 metallic colours and 3 matt colours. The new colour range reflects current architectural colour trends and ensures the demands of contemporary and architecturally challenging projects can be met.

Q3: My client has asked for a cost effective alternative to traditional roofing materials such as terracotta, or slate tile, or copper. Is this reflected in the new offering?

Colorcoat Prisma® now includes 3 matt colours. By utilising the very latest paint and paint application technology, we have introduced three new matt colours: Terracotta, Anthracite and Copprium. These matt colours have been chosen to replicate more traditional building materials such as terracotta and slate tiles and in the case of Copprium, weathered copper.

The Colorcoat Prisma® matt colours have been designed to achieve individual styles for a variety of applications from churches and domestic roofs to rainscreens and flat panels.

All Colorcoat Prisma® matt colours achieve Ruv4 status proving outstanding colour retention and come with Confidex® Guarantee periods of up to 25 years, the longest guarantee on the market for matt colours.

Q4: Just how durable is the product?

In addition to all colours achieving Ruv4, all solid and metallic colours are certified as RC5. The coil coating standard EN 10169:2009 classifies the corrosive nature of different environments between C1 and C5. Pre-finished steels are then assessed under natural weathering exposure and assigned a corrosion resistance category between RC1 to RC5 (RC5 being the highest corrosion resistance classification).

Samples of Colorcoat Prisma® were exposed for >2 years at the European classified C5 site at Brest on the West coast of France. Analysis of the samples showed had no significant edge peel, blistering or any other signs of coating degradation during this period.

The relevant certification has now been issued by the French Corrosion Institute and confirms that solid and metallic colours of Colorcoat Prisma® are classified as RC5.

Thermally efficient building envelope using pre-finished steel cladding

Pre-finished steel cladding systems can be used to form the basis of a highly thermally efficient building envelope, with low fabric U-values and excellent levels of air-tightness.

Work carried out by Corus and Oxford Brookes University (OBU) has demonstrated that air leakage rates through correctly installed pre-finished steel cladding side and end lap joints account for less than 2% of the allowable air infiltration rates.

U-value requirements of Part L 2006 and the 2010 revisions

Modern pre-finished steel cladding systems can be specified to easily meet the U-value requirements of Part L 2006 and the 2010 revisions due for implementation in October.

This places the emphasis on the performance of building details and junctions and how they have been designed and installed.

How do I ensure air-tightness of the building envelope is maintained at the cladding interfaces and junctions?

There are 2 main types of interface to consider.

1) Pre-finished steel to pre-finished steel
2) Pre-finished steel to an alternative material such as brickwork or concrete.

Pre-finished steel to pre-finished steel cladding joints have been assessed as part of a comprehensive test programme with OBU.

The key issue is to firstly identify the liner sheet of the cladding system as the air-tightness layer.  If the correct compressible foam filler blocks and sealant are used and the detail has been correctly installed, test data indicates that the leakage rates from these joints will not be a significant factor in the overall building performance.

Pre-finished steel to alternative materials need to be treated on a case-by-case basis. The key points are to firstly ensure that the different cladding materials have been installed to the specified tolerances, to ensure good alignment at the interface and minimise excessive gaps. The interface detail which is used should have been designed for the application, using the appropriate sealant and filler blocks.

How do I ensure that the building details have been correctly designed and installed to minimise heat losses?

Pre-finished steel has a very high thermal conductivity, details must be carefully designed to ensure that they do not penetrate through the insulation cavity, creating a thermal bridge through the cladding system. Poorly designed details will lead to excessive heat losses and may result in condensation forming within the detail. This could lead to corrosion and premature failure of the cladding.

Corus work with a number of supply chain partners, who provide building specific details and calculations of the associated thermal heat loss and condensation factor. Details have been designed by the cladding system manufacturer to ensure that they can be practically installed on site and then assessed using a thermal modelling package. 

Use of a reputable cladding installation contractor with good site practices and inspection procedures will ensure that the cladding and details are installed as designed.