Ecological comparison of facade systems

The results of an ecological comparison of facade renovation systems are revealed by Ian Anderson, managing director at rainscreen cladding manufacturer Steni UK.

The growing popularity in the UK of dry-trade construction methods has led to a plethora of rainscreen cladding systems, ranging from thin-film aluminium or steel cassettes to fibre cement and glass fibre reinforced polyester composite panels.

Along with the actual panels themselves, the fixing systems also differ, with specifiers and designers able to choose between wood, aluminium or steel stud in different thicknesses as well as glue. So where on earth do they start when choosing which cladding system to use?

Given their capability not only of transforming a building’s visual appeal but also its performance, particularly in terms of thermal insulation, rainscreen cladding systems have become something of a modern-day wonder product although they in fact date back decades.

Not only are they capable of breathing new life into ugly, tired and poorly-performing commercial, education, healthcare, leisure and residential buildings, including high-rise tower blocks, they are also a highly efficient way of branding buildings, with a wide range of colours and finishes enabling them to adopt corporate colours.

The principles of ventilated rainscreen cladding allow for thermal movement and moisture dispersion through panel joints and a ventilated cavity. Basically the cladding is fixed back to the main support structure with one of the aforementioned methods, to form a weather, impact and rot-resistant, colourful and relatively lightweight jacket.

The benefit of the rainscreen system is that any moisture, either ingress or humidity, is ventilated out of the cavity at the rear of the panels, ensuring the insulation and inner leaf of the building are not affected by interstitial condensation.

The environmental performance of different cladding systems and fixing methods in renovation projects was the subject of a study by the Tampere University of Technology (Department of Civil Engineering, Institute of Construction Economics and Management) in Finland. This focused on the impact of manufacture and use and maintenance.

The Ecological Comparison of Facade Renovation report helps specifiers better understand the environmental credentials of the various rainscreen systems and make better-informed design and specification decisions.

It concluded that glass fibre reinforced polyester composite rainscreen panels ecologically outperform competitors in numerous tests, ranging from Global Warming Potential (GWP) to Photochemical Ozone Creation Potential (POCP). The study states:

“The comparison shows that of those facade coating products examined, glass fibre reinforced poly- ester 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 poly- ester 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 sq m of wall surface. The next closest was 8mm-thick fibre cement boards at 5,800g CO2/m². An 85mm brick facade was rated a massive 28,000g and a 130mm brick facade even greater at 39,000g CO2/m².

As mentioned previously, these results were mirrored in all ‘The benefit of the rainscreen system is that any moisture, either ingress or humidity, is ventilated out of the cavity at the rear of the panels’ Ian Anderson, managing director at Steni UK 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 envi- ronmental 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 facade – 197g CO2/m² and 130mm thick brick facade – 274g CO2/m² of wall surface.

When Nutrification Potential was studied, glass fibre reinforced polyester systems were virtually matched in perform- ance by 30mm of plastering . Fibre cement board scored 1.3g (phosphate)/m2 and 40mm concrete panel returned a reading of 2.5g (phosphate)/m². Brick facade (130mm thick) 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 facade materials, reg- istering the lowest score of 80MJ/m2 of wall surface. The highest was 130mm-thick brick facade, 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 steel stud (7,600g ( CO2/m²).

Concluding 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.”