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Climate action: we can put a block on brick

Words:
Rosie Mounsey and Steve Webb

Despite its embodied carbon, masonry is still the default construction method. What are the alternatives?

Ways to reduce embodied carbon: stone, rammed earth, hempcrete and unfired clay and reclaimed masonry bricks.
Ways to reduce embodied carbon: stone, rammed earth, hempcrete and unfired clay and reclaimed masonry bricks.

The UK’s appetite for bricks is growing. With Great British Brick Shortage reports in recent years, increasing annual production and import, and now news that the country’s largest manufacturer will invest across its two sites to ramp up manufacture even further, it seems we can’t specify enough of them. 

While bricks have existed in various forms since Roman times, common use dates back to 350 years ago, when after the Great Fire of London timber framing in the City was banned and replaced with masonry in the London Building Act of 1667. Similar Acts rolled out in cities across the country eventually evolved into the Building Regulations which still define our practice today. From the mid-1900s, cavity wall construction became more commonplace, originally to avoid penetrating water but still used now to incorporate insulation. Dividing the structure into two thinner walls weakens the masonry, but by the end of the century this had become compulsory in new masonry construction.  

So now we have fewer fires and warmer homes. But is there any logic to the way we are building now, and can we do better?  

A three-storey masonry-built house would typically have 50% more embodied carbon than an equivalent timber framed, larch-clad house. And the same house using masonry just as cladding still has 30% more than the timber option.  

Modern brick construction has developed from a straightforward brick, mortar, brick approach to a complex system involving ­numerous accessories: wall ties (to tie back together the wall we have split into two), bed joint reinforcement (to strengthen the inherently weak bending capacity of the thin wall), movement joint ties with fillers and sealants (to allow for the expansion of the brickwork and contrasting shrinkage of the concrete blocks hidden behind), steel angles or boxes (to accommodate long flat openings), steel windposts (again, to strengthen the divided wall), head restraints, column ties… it is difficult to see the modern logic in this heavy, layered construction.  

Yet it remains the prevalent form of construction, with 2.4 billion bricks, producing  2.6 billion kgCO2e, used in the UK each year. This huge amount of energy is of national importance. In our efforts to decarbonise, how can we continue to produce something that, if abolished, would have the decarbonising effect of two medium nuclear power stations? Or 25% of all offshore wind farms?

A three-storey masonry-built house would typically have 50% more embodied carbon than an equivalent timber framed, larch-clad house. And the same house using masonry just as cladding still has 30% more than the timber option

But what are the alternatives? If we, and planning authorities, are ready to step outside our comfort zones, where could we go? 
 
1) Stone presents an easy, abundantly available alternative requiring no firing or processing – a limestone wall saves two thirds of the embodied carbon of a brick wall of equivalent thickness and is two to three times stronger. 
 
2) Rammed earth construction can have an embodied carbon as low as 5-10kgCO2e/m2 if locally sourced and naturally dried. The required ‘hat and boots’ detailing, while less common, is simple to achieve. 
 
3) A 200mm thick hempcrete wall placed in situ into a timber frame with a putty lime render will sequester rather than emit 35kgCO2e/m2, thanks to its quick growing stems. It is also an excellent insulator. 
 
4) Modern unfired clay bricks can be produced to accurate tolerances using commercial pressing or extrusion and have only 14% of the embodied energy of fired bricks. They will typically only achieve around a quarter of the compressive strength of a stock bricks, but this offers a better strength to carbon ­ratio and improved air quality internally. 
 
5) Reclaimed masonry bricks. An estimated 2.5 billion bricks arise as demolition waste each year (almost equal to the number we use new each year!), but only 5% are reclaimed for reuse, with the rest crushed for fill. Challenges involve the removal of hard cement ­mortars and assurance on quality, but many more than 5% should be suitable for reuse.  
 
We have a choice to make: would we ­rather build new timber homes? Or mock Georgian ones next door to the new nuclear power station required to create them? 

Steve Webb and Rosie Mounsey are at Webb Yates Engineers 

Read more of Steve Webb on reducing embodied carbon in structures including on house extensions, towers and design approach. And on using stone

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