Avoiding single-use plastic in daily life has gone mainstream but do you know how much oil-based material is used in your building? The list of plastic products in construction is endless, ranging from toilet seats to windows. In the UK construction industry, oil-based phenolic insulation is the norm and once installed is difficult to change. Below is the logical behind why we are eradicating phenolic insulation from our projects.
Buildings are insulated in the temperate climate of the UK to keep the heat in during the cold months and reduce overheating in the summer. The UK Building Regulations (1) specifies a minimum standard for the levels of insulation in the roof, wall and floor to comply with legal requirements. The current code was issued in 2016 and is about to change in 2021 as part of the HM Government’s development of the Future Homes Standard (2) for new homes. At least 75mm of phenolic insulation (3) will be required in walls under the new regulations to meet the new minimum u-value (4) standard of 0.18W/m2k. That is not going to achieve the zero target of 2050, especially as we are working to standards that are already out of step with the problem they are trying to regulate.
The UK building industry relies on phenolic insulations as they are relatively thin at about 100mm for a typical brick cavity wall. To build the same wall to the minimum standard using plastic-free insulations at least 160mm for mineral wool (5) and approximately double that for natural materials including wool, cork and cellulose fibre would be required. In our experience insulation needs to be at least 20% thicker in the real world to achieve the minimum standard to allow for workmanship, air leakage and the UK’s obsession with huge windows. It is easy to see why phenolic insulation dominates the UK construction industry due to the impact on the internal building area that has a much greater financial value than the wall at the point of investment in the building works.
However, there is an alternative solution. Firstly, walls are much better at reducing heat loss and overheating in buildings than windows that at best at best have a u-value of between 1.0 and 1.2W/m2k. Reducing the size of windows will help to reduce the demand on the wall to compensate. Working with a good architect will demonstrate that using smaller windows will not compromise daylight or views as much as you would think and arrive at a good balance of window area and wall thickness.
Secondly, the UK must adopt timber-framed walls as the standard construction as is the case in many countries including the United States. Brickwork has 4 times the amount of embodied carbon (the amount of CO2emitted in producing the material) than timber (6). Timber framed walls allow high levels of insulation within their depth, whether mineral or cellulose, and this allows for a wall as thin as 380mm (7) compared to 345mm for a masonry wall to achieve the same performance, a differential that is narrower than the phone that you may be reading this on.
Thirdly, using an architect, or other building professional trained in low energy design, will help to improve the quality control and workmanship during construction. The benefit of this is reduced heat loss due to even the tiniest gap in the wall that will cause draughts and making sure that the insulation is well installed and continuous.
Finally, eradicating phenolic insulations from our buildings will reduce non-recyclable waste. Did you know that mineral wool can be recycled? (8) Surplus or waste or material from construction can be diverted from landfill if you work with a good contractor and demolition/waste management provider.
The cost impact of avoiding phenolic insulations is small. For a typical rear extension on a London terraced house (9) approximately 0.3sqm of floor area is lost with mineral wool insulation in a timber frame, or the equivalent of 5 sheets of A4 paper. The project cost uplift with mineral wool is a total of approximately £215 (10), slightly less than the cost of a Tom Dixon 250ø Copper pendant light. Neither of these would render a typical domestic extension unfeasible.
At Mulroy we have taken the step to eradicate phenolic insulation from our buildings to reduce the reliance on oil-based industries and climate changing processes. For the sake of a couple of inches in wall depth it is relatively easy to improve the performance of buildings.
Andrew Mulroy, March 2021
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Notes:
1 – The current Approved Documents that show how to comply with current UK Building Regulations may be found at https://www.planningportal.co.uk/info/200135/approved_documents
2 – HM Government’s announcement of the Future Homes Standard may be found at - https://www.gov.uk/government/news/rigorous-new-targets-for-green-building-revolution
3 – Celotex u-value calculator, March 2021, based on a brick/block cavity wall that is the mainstay of the UK volume housing sector.
4 – The rate of heat loss of the wall is measured by its u-value. A low number is good. By comparison, a Victorian solid brick wall with no insulation has a u-value of approximately 2W/m2k.
5 – Rockwool Calculator, March 2021, based on a brick outer skin, cavity, partial fill and insulation between timber stud structure, to give a u-value of 0.18W/m2k.
6 – LETI Embodied Carbon Primer, LETI, January 2020.
7 – Rockwool Calculator, March 2021
8 – Rockwool has a recycling programme - https://www.rockwool.com/uk/about-us/sustainability/recycling/
9 – Assumes a 3m deep x 6m wide full-width rear extension to a 1920s home with cavity party walls and full-width patio doors.
10 – Figures and specification correct at 07 March 2021, insulationexpress.co.uk amongst others based on 18sqm of wall, Rockwool Flexi + HP partial fill = £27.50; Celotex CW400 = £15.70/sqm.
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