Comparing facade systems

Bryn Williams, quality manager at rainscreen cladding manufacturer Steni UK, discusses the findings of an ecological comparison of facade renovation systems.

Rainscreen cladding systems are something of a modern-day wonder product given their ability not only to transform the aesthetics of a building but also appreciably upgrade its performance, specifically in the area of thermal insulation.

Not only can such systems breath new life into tired, badly-performing buildings such as offices and residential tower blocks, they are also a highly effective method of branding buildings, given theiravailability in a wide range of colours and finishes.

The principles of ventilated rainscreen cladding systems are governed by BS 8200. The cladding is fixed back to the main support structure, forming a relatively lightweight, colourful weatherresistant overcoat. The benefit of this system is that any moisture, either ingress or humidity, is ventilated out of the cavity, ensuring the insulation and the inner leaf of the building are not affected by condensation.

A range of different cladding systems area vailable in the UK, from thin film aluminium or steel cassettes to fibre cement and glass fibre reinforced polyester composite panels. Fixing systems also differ – designers can select from wood, aluminium or steel stud in different thicknesses. But which cladding system to choose?

A study carried out by the Tampere University of Technology (Department of Civil Engineering, Institute of Construction Economics and Management) in Finland considered the environmental performance of the different cladding systems and fixing methods in renovation projects, concentrating on the impact of manufacture and use and maintenance.

Its report, ‘EcologicalComparison of Façade Renovation’helps designers understand the environmental credentials of systems and therefore make better-informed design and specification decisions.

And its conclusion is unequivocal – glass fibre reinforced polyester composite rainscreen panels ecologically outperform competitors in a number of tests, ranging from Global Warming Potential (GWP) to Photochemical Ozone Creation Potential.

The study states: “The comparison shows that of those façade coating products examined, glass fibre reinforced polyester composite has the least impacts on environment, measured by the LCA factors.”

The study was conducted using mainly Life Cycle Analysis developed by the Society of Toxicology and Chemistry (SETAC) - transportation and the effects of the energy required for renovation work were not taken into account.

The investigation considered seven different system materials - glass fibre reinforced polyester, fibre cement, brickwork, concrete panel, plastering, thin film steel cassette and thin film aluminium cassette. Insulations studied were glass wool and expanded polystyrene. Framing systems were aluminium, steel, wood studs and punctual fastenings.

The Global Warming Potential, Acidification Potential (AP), Nutrification Potential (NP), Photochemical Ozone Creation Potential (POCP) and Critical Air Volume (CAV) were compared and in each category glass fibre reinforced polyester panels recorded the lowest – and therefore most advantageous – readings. Indeed, in most cases, its results were less than half of its closest rival.

Take for example the GWP results. Glass fibre reinforced polyester rainscreen cladding panels 8mm thick returned a reading of 2,400g of CO2 per square metre of wall surface. The next closest was 8mm-thick fibre cement boards at 5,800g CO2/m2. An 85mm brick façade was rated a massive 8,000g and a 130mm brick façade even greater at 39,000g CO2/m2. As mentioned previously, these results were mirrored in all but one of the categories studied. Take the POCP results – 8mm glass fibre reinforced polyester composite panels returned a score of 5mg CO2/m2 of wall surface. Its closest rival was again, 8mm fibre cement board with a score of 17mg CO2/m2. Thin film aluminium cassette (1.5mm thick) scored 5,800mg CO2/m² and thin film steel cassette (1.5mm) 7,700mg CO2/m2.

Acidification Potential results also reinforced the sound environmental performance of glass fibre systems, which scored 15g CO2/m² of wall surface. Fibre cement board (8mm thick) was the next closest with a rating of 35g CO2/m2. Other results included 1.5mm-thick thin film aluminium cassette –136g CO2/m2; 85mm thick brick façade – 197g CO2/m2 and 130mm thick brick façade – 274g CO2/m2 of wall surface.

When Nutrification Potential was studied glass fibre reinforced polyester systems were virtually matched in performance by 30mm of plastering [0.6g (phosphate)/m² of wall surface and 0.7g (phosphate)/m² of wall surface respectively]. Fibre cement board scored 1.3g (phosphate)/m2 and 40mm concrete panel returned a reading of 2.5g (phosphate)/m2.Brick façade (130mmthick) topped the NP scale with 10.5g (phosphate)/m2, with thin film aluminium cassette of 1.5mm thickness scoring 9.1g (phosphate)/m2. Glass fibre reinforced polyester systems also performed well in tests measuring the energy contents of façade materials, registering the lowest score of 80MJ/m² of wall surface. The highest was 130mm-thick brick façade, with a reading of 750MJ/m2.

The study also demonstrated that framing materials have an impact on environmental performance. In every category, wood stud was the most ecologically-sound fixing medium. For example in GWP tests, wood stud (30mm) scored 560g CO2/m2 of wall surface, compared with 30mm aluminium stud (8,800g CO2/m2) and 30mm steelstud (7,600g (CO2/m2).

To conclude the report, scientists looked at the ecological impacts of a modernised wall structure during a period of 25 years from renovation. As would be expected, the better insulated the property, the less ecological impact it caused.

The report stated: “The most ecological alternative of those studied proved to be a ventilated structure supported with impregnated long length wood, insulated with 100mm thick glass wool and covered with glass fibre reinforced polyester composite.”

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