7 – Construction and Demolition Waste

This is Part 7 of the input into the Department of Communications, Climate Action and Environment’s Waste Advisory Group consultation process on the circular economy by Feasta member Féidhlim Harty.

Rather than sticking with the typical Q&A process I approached this issue as an article from the outset, and contributed the following as a response to the Department:

As with all waste streams, the place to look first is not at the full skip outside a typical construction site and wonder where to dump it, or how best to recover the few recyclables that are present and downgrade the concrete blocks into low grade aggregates… The place to start is with the design; with what goes onto the shopping list for the builder in the first instance.


First let’s look at the materials that go into a standard construction project. Concrete, steel, glass, roofing materials, tiles and floor coverings, timber and a host of associated chemical preservatives, glues, admixtures, fillers and resins. Then there are insulation materials, plumbing fittings and piping, electrical wiring, devices and fittings, paints and finishes.

All this before ever we consider furnishing or other material choices associated with the occupancy of the building. In the Living Building Challenge the house is assessed for qualification as a living building only after 12 months of occupancy, so that the overall impact of the dwelling as a used building is considered, and not simply the design and construction methodology.

Following the basic Reduce, Reuse, Recycle model, it becomes quickly apparent that our building design and material selection processes can be amended to provide large contributions to the creation of a circular economy. There are many materials substitutions that can be incorporated for house construction instead of the conventional waste- or energy-intensive options.

Concrete block construction can be replaced with structural timber. This is perhaps the most straightforward substitution, but other materials also have distinct advantages. Straw bale construction, for example, has excellent fire prevention characteristics when lime rendered; provides its own insulation; and produces a perfectly strong, comfortable and durable home. This ticks the Reduce option. For Reuse and Recycle, Timber can be reused after removal from old buildings, and if broken or too small for reuse, untreated timber can safely be used as a fuel wood for home heating. Straw bale can be composted after demolition, thus feeding the soil in which the cereal crop was first grown in a perfect cycle.

Cement plasters can be replaced with lime, hemp or clay renders, often with pigments included to eliminate the need for painting. Glass may not have many suitable substitutions, but is endlessly recyclable directly back into new glass rather than downcycling into a lower grade product, which is the norm for many materials, loosing energy and resources along the way.

There are many more examples for substitution of building materials that Reduce the toxic or non-recyclable wastes; maximise the Reusability of reclaimed materials at the point of demolition/dismantling of the building and make Recycling of materials safer and more effective. In any circular economy model it is essential that materials that do not make this grade of being easily reused, recycled or otherwise safely reused are systematically phased out of the supply chain.

A wider look at C&D Waste

The waste associated with construction and demolition is not simply the handful of material we call C&D waste – contradictory as that may sound. There are three main elements we need to look at:

First is the materials, what we call C&D waste; as explored already above.

The second is the embedded energy used in the manufacture and transport of those materials; all wasted energy if there are suitable low-energy or zero-energy alternatives.

The third are the utilities used and/or the the wider infrastructure that supports the construction project; specifically electricity supply, water supply, sewage treatment, transport networks and the availability of services and community.


We cannot build a circular economy where fossil fuels are used. It’s a misnomer to think that we can extract these from the Earth, use them briefly for heat, electricity and manufacturing, and still have any sort of circularity of energy and material flows within our economy and society. That’s the very definition of greenwash; putting a circular label on a model built entirely on a linear foundation.

Step one in creating a visible connection between fossil energy and our economic choices; and thus creating the conditions whereby a true circular economy becomes possible, is to cap global carbon extraction. The cost of fossil fuels will inevitably rise with such a measure, and as a consequence, lower-energy-input products such as timber and hemp will drop in comparative price compared to the high-energy process of cement production, for example.

As a further measure, Cap and Share[1] is a proposed policy instrument whereby the benefits that our society has already enjoyed from abundant use of fossil energy may be shared with a majority-world country which has not yet developed extensive infrastructure. By putting a price on our carbon use and transferring the generated revenue to another country or to specific carbon drawdown projects we can offset the imbalance generated by both historic and current northern-latitude use of stored fossil carbon; a stored carbon reserve which may reasonably be seen as a global commons, as are the air and climatic systems that our excessive carbon use harms.

Utilities and networks

While building construction has specific requirements for certain standards of safety, thermal insulation and sanitation, it is planning policy rather than house design that usually considers the wider issue of networks and interconnectivity. However when considering the circularity of energy and material flows within the construction sector, we cannot ignore the implications of the utilities and networks that are an inevitable part of any building.

There are some very specific measures in this area that can be adopted at government policy level that would greatly facilitate the creation of a more circular society, as follows:

Domestic electricity supply: Permit feed-in tariffs to show a tangible return on investment in micro-solar installations. In our own household we installed a 4000kW PV array; and reached close to net zero usage over the year. Thus the potential exists for Irish housing to supply its own electricity when distributed across the grid as a central buffer/battery. However current policy places obstacles to offsetting electricity exports to the grid against purchases, meaning that excess electricity either gets placed on the grid at no savings to the homeowner (which disincentives uptake), or is dumped into the main hot water cylinder as heat, often at times when such heat is not necessary, and thus essentially wasting that energy which could be contributing to our national grid.

Water supply: Actively encourage rainwater reuse in buildings. Water extraction, treatment and distribution uses as much as 1% of global energy, c.80% of which is used in pumping. A lot of domestic tap water is used for washing cars and yards, garden watering, clothes washing or for flushing toilets. None of this water needs to be potable quality. Thus, instead of being extracted from the local aquifer or river, pumped to the local treatment system, treated using energy and chemicals, medicated with fluoride and further pumped to a storage tower for gravity feed to the local houses and businesses, we could redesign our houses to permit the substitution of rainwater for these non-potable uses. Ideally this could be done utilising gravity rather than including any pumps within the system, but micro-solar arrays could also be used for delivery of stored rainwater to on-site header tanks for delivery as needed. This could offer substantial savings on national energy consumption.

Sewage treatment and sanitation: Actively encourage the use of systems that are zero or low energy, or offer active carbon sequestration benefits and/or nutrient cycling. Low energy sewage treatment is an area that I have been working on since 1996, offering a design and planting service for constructed wetland, reed bed systems and willows. It is eminently possible to replace mechanical treatment systems, and their inherent electricity consumption, with zero energy input systems such as these.

One of the wastes inherent in our current sanitation infrastructure model is the biomass and inherent nutrients that we flush down our toilets every day. As land mammals we should reconsider the wisdom of remaining with a linear movement of nutrients, energy and biomass from our farms to our tables to our local watercourses. There are Scandinavian sanitation technologies such as urine diverters and faecal separators which recoup the biomass and nutrients as early in the flush toilet infrastructure as possible. These need to be included in Irish building and sanitation codes to maximise their uptake. For source separation technologies and compost toilets, government policy needs to be strengthened to provide clear guidance to local authorities who are faced with such planning applications and do not currently have the expertise to respond appropriately, even though composting units are mentioned in the EPA Code of Practice[2]. Composting humanure from dry toilet systems can sequester about twice as much carbon as the composting of sewage sludge[3] – an important consideration as we explore a low carbon future.

While facilitating the uptake of source separation on new projects, willow systems are an easy way to recoup nutrients from existing infrastructure. They can be used to actively sequester carbon into the growing willow biomass, using the nutrients in the sewage to fuel their high growth rates. The potential for extensive roll-out of domestic and municipal willow systems could provide considerable carbon sequestration or biomass fuel wood generation to offset fossil carbon heat sources or electricity generation.

Transport networks and the availability of services and community: Implement Cap and Share or Cap Global Carbon to make embedded energy visible financially rather than hiding it as an externalised cost of high-energy transport; hand in hand with the provision of an excellent public transport network. Currently our road networks are given the vast majority of our transport budget, actively subsidising energy intensive car travel and truck haulage. By contrast our rail network is underfunded and expensive at the point of use. One way to overcome some of this discrepancy is to charge car tax and insurance on the price of petrol rather than up front, making enabling greater savings for use of public transport than are currently the case if a car is sitting unused but fully taxed and insured.

Similarly, cycleways and pedestrian infrastructure is hugely underfunded in Ireland. With careful design and some decent investment, we could have a wonderful network of safe, beautiful off-road cycle paths around every school in the country, with secure covered storage areas at the point of arrival – and in a stroke, remove much of the morning traffic (and carbon emissions) in our urban areas around schools.

These points all relate to the circular economy of the construction sector insofar as our designs for our built environments need to extend beyond each individual building and look at networks and connections. Perhaps if we focus on building an extensive network of village hubs with child care, care for the elderly, shops and services, work spaces etc. with commuter train or bus links between hubs, then we may find that leaving the car at home isn’t just cheaper, but also more sociable, pleasant and healthy.

One of the central policy measures that would help to create the conditions for such a restructuring of all of the above subject areas is to cap global carbon and/or introduce cap and share within Ireland and/or the EU. This would remove the inherent leakages of the linear model of extract-use-dispose which we apply to fossil energy and resources at present.

In the absence of such a policy, we can still make a lot of changes in each subject area, as touched on very briefly above – but the real gold is to be mined in the more ambitious policy changes that can be introduced only at wider government and inter-governmental level. If we want to make Ireland a leader in the area of circular economy, pushing Cap Global Carbon at the international level is one of the very visible ways to jump onto world stage. We have done it in a smaller way with plastic bag taxes and smoking bans. Perhaps we can do it for black carbon limits as well.

1. Johnson M, M Harfoot, C Musser, T Wiley, H Pollitt, U Chewpreecha and J Tarafdar. (2008) A Study in Personal Carbon Allocation: Cap and Share. Comhar – Sustainable Development Council, Dublin.
2. EPA (2009) Code of Practice – Wastewater Treatment and Disposal Systems serving Single Houses (pe≤10), EPA, Wexford.
3. Harty F (2016) Closed Loop Agricultural for Environmental Enhancement – Returning Biomass and Nutrients from Humanure and Urine to Agriculture. FEASTA (Foundation for the Economics of Sustainability), Dublin.

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