Sunand Prasad and Andrew Drury.
Estate redevelopment is just so satisfying and progressive. Residents may have to suffer a decant or two but they get desirable, energy-efficient new homes in place of their tired out and unsuitable old homes. But does the need to count carbon change all that? The question we want to address in this article is not the existence of the redevelopment cycle, but the period of the cycle.
Decay and renewal is part of nature, part of life. Pre-industrial societies in making shelter followed the natural way and in some cultures houses were, and are, rebuilt each year, after the rains, for example. Developing technology may change the length of the re-building cycle. The move from timber to brick lengthened it and stone cottages in the countryside have lasted centuries. In 17th Century London, small timber houses were built, leased for thirty years, then demolished and re-built. The move from timber to brick lengthened the re-building cycle, but the cycle continues, and will always do so. It is difficult to conceive of a technology that will create everlasting buildings and the thought itself is a little disturbing for rebirth and renewal is life affirming.
The associated costs of the cycle come in a number of currencies. The most obvious one is the money cost which will be generally lower if buildings have a longer life. Also evident is the social cost of disrupting those tenuous webs of acquaintance and familiarity, friendship and kinship that add up to a “community”. We have seen many examples (from slum clearance programmes onwards) which result in better quality housing, but poorer quality social cohesion. Again, the longer the development cycle, the lower this cost.
And then there is the carbon cost. There are three complimentary routes to the low carbon future: 1: Changes in lifestyle and business operations; 2: energy efficiencies and 3: decarbonising the energy supply. This last point is a longer tem objective – it won’t happen quickly. So, in the short and medium term it will go on taking a lot of carbon to construct homes. This issue was examined in ”New Tricks from Old Bricks” published by the Empty Homes Agency in March 2008. It looks at the carbon cost of demolition of existing housing and its replacement with new, more energy-efficient dwellings. Clearly, the new buildings will produce less carbon dioxide emissions for each year of use than would have been the case if the old housing had been retained (Point 2, above). But how much carbon dioxide has been generated by building the new dwelling in the first place? How much “embodied carbon” is used in construction?
The answer, of course, varies between different types of construction. According to the Empty Homes Agency report, about 80% of the embodied carbon is to be found in the brickwork and blockwork. This arises from the energy cost of extraction, manufacture and transportation. Timber frame buildings, therefore, will have significantly less embodied carbon – although many timber frame buildings are clad in brick.
So on the one hand we have the new dwelling providing annual carbon “savings”, whilst on the other we have the embodied carbon-cost of demolishing the old and building the new. It is the direct equivalent – in carbon terms – of a cashflow calculation such as Net Present Value. So, how many years need to elapse before a scheme’s carbon NPV moves from being negative (cost greater than benefit) to breakeven, and positive?
“New Tricks from Old Bricks” estimates that given prevailing design and construction practice this may take up to 50 years. The first 50 years of carbon savings of the new dwelling are simply compensating for all the carbon emissions created by rebuilding the old dwelling in the first place. In terms of carbon “cashflow”, we pay the carbon cost of rebuilding right now – in 2008 – but only get back to “breakeven”, and start to reap net benefits by 2058. That is unfortunate, because to get a benefit in 100 years we need to reduce emissions sharply over the next 50 years, not raise them.
How can we address this short-term point? We should be careful to avoid unnecessary demolition, and encourage repair and improvement of existing structures as far as practicable and to the highest possible levels of energy efficiency. How? We need to be able to assess the carbon payback period of a proposed course of action, and only approve demolition when the whole-life carbon cost of the redevelopment is lower than that of retention, and when the carbon payback period is short – maybe 10 years. Such a short period is quite achievable with the best current examples of low carbon design
Planning authorities, despite their Sustainable Development policies, do not consider these questions, not least because demolition of housing comes under the General Permitted Development Order (GPDO). Unless permitted development rights are suspended in an area, demolition can be a fait-accompli before any assessment is possible. We suggest that this position is reviewed, and that Communities and Local Government give serious consideration to removing demolition from the GPDO. This is a necessary first step in addressing this issue.
There is an important longer-term point relating to the length of the redevelopment cycle. If a scheme has to make carbon savings for 50 years before any net gains are realised, but the properties are demolished and redeveloped after – say – 40 years, we really are worse off! We need to ensure a longer redevelopment cycle which means that we must make adaptable buildings that are resilient to “functional obsolescence”. One of the main sources of such obsolescence is sheer lack of space. Cramped buildings, with cramped external areas, are less flexible, adaptable or convertible. They are less able to accommodate the changing needs of users over the decades. Contrast that to many Georgian, Victorian and Edwardian terraced houses used as homes for a few decades, then offices for a number of years, maybe as retail for a few years, perhaps converted into flats, then de-converted back into houses, to accommodate many residents as well as few, to be internally subdivided as well as open-plan.
A relatively small increase in floor area beyond the tightly drawn plans that have become common will give us the ‘long life loose fit’ designs that are the first stepping stones to sustainability. A little generosity of space also helps accessibility. We need to celebrate the 50th anniversary of the publication of the Parker Morris Report in 2011, with another, updated Parker Morris Report for the 21st Century, and local planning authorities should use it. The London Mayor is showing a welcome lead in this regard, and our future carbon load is likely to be lighter if others follow. For the medium term, therefore, we suggest that planning authorities establish and use policies that discourage the building of cramped homes.
Sunand Prasad is President of the Royal Institute of British Architects and founding partner of the architectural practice Penoyre & Prasad LLP
Andrew Drury is Managing Director of housing consultants HATC Ltd and is a member of the HCA’s Design and Sustainability Advisory Panel.