After the rain: Chipping at the foundations

Many architects will be acquainted with the Crimson Record of constructing supplies. A key a part of the Dwelling Constructing Problem, it’s a record not a lot of supplies however of components and substances, every of which has a poisonous legacy. Most of the nasties are acquainted: asbestos, sure frequent wooden therapies and a slew of risky natural compounds that off-gas because the “new constructing odor” we’re now not so enamoured of. Readers of Structure NZ’s latest article (July/ August 2025) on Claude Dewerse and Mike LeRoy- Dyson’s work serving to to take care of 1200 floodcompromised Auckland homes could have famous the troublesome legacy not of Crimson Record gadgets however of seemingly innocuous constructing parts — they’re problematic not a lot through the lifetime of the constructing however at its finish.

A key set of difficulties deconstruction crews encounter pertains to the elimination of concrete slabs. Concrete flooring slabs, alongside concrete landscaping and driveways, represent an enormous portion of the fabric in a home, each by weight and by quantity. Concrete by itself is comparatively easy to recycle. It may be damaged up on web site earlier than being transported to corporations which obtain the concrete, crush it and provide it again to the trade as a spread of merchandise. A key benefit is that this protects the prices and emissions concerned in extracting and crushing contemporary combination. There are a few sweeteners. When re-used, the latent cement content material of the recycled combination permits a slight discount within the want for costly and energy-intensive new cement. Additional, latest analysis has proven that crushed concrete absorbs CO2 from the ambiance at a fast price; if crushed and left uncovered for a number of months, it could sequester as much as 10 per cent of the concrete’s weight.

Given concrete’s carbon footprint — research recommend it contributes as a lot as eight per cent of worldwide greenhouse emissions — architects will, little question, search to minimise their use of the fabric. For some makes use of, it’s tough to keep away from however we’re doubtless heading in the direction of a time when the ostentatious use of concrete is the architectural equal of carrying fur. A still-developing different is the usage of lowcarbon concrete, which substitutes a portion of the emissions-heavy cement with fly ash or industrial slag. Architects would possibly roll their eyes — it has the texture of claims of ‘low-fat cake’. There are certainly questions however solutions are coming. The altered chemistry signifies that low-carbon concrete takes longer to treatment than does common concrete; that’s, its power is gained extra slowly over time. Nonetheless, cautious building sequencing can normally keep away from or mitigate the necessity for prolonged building instances. Each fly ash and slag are by-products of burning coal so the success of different carbon-reduction efforts is decreasing the accessible provides. Alternate options, although, could also be surprisingly shut at hand; Dr Enrique del Rey Castillo on the College of Auckland is researching the methods through which ‘supplementary cementitious materials’ constructed from pure, domestically sourced supplies resembling pumice, a type of volcanic ash, and kaimoana shells can be utilized as a substitute of fly ash. And, as with nearly each side of our building trade, New Zealand’s small market creates particular wrinkles; the market is dominated by concrete suppliers with shut monetary ties to cement producers, diluting the incentives for concrete suppliers to cut back cement content material.

A wildly complicating issue for Dewerse and LeRoy-Dyson’s work is the presence of polystyrene solid into the concrete slab, normally by way of the quite common follow of utilizing polystyrene pods to create waffle slabs. Designers will little question be acquainted with the problems that polystyrene could cause throughout building: most notably, its susceptibility to blow across the web site however, additionally, that slicing and shaping processes pepper the positioning with microplastics. Harder issues emerge throughout demolition. Dewerse and LeRoy-Dyson have labored with their deconstruction contractors to develop a course of for extracting slabs fashioned with polystyrene. The best is to slice up the slab fastidiously and take away it from the positioning in massive items. It’s taken aside with a digger, in search of to minimise harm to the polystyrene. A member of the deconstruction crew stands prepared with a bag to grab up any crushed items of polystyrene, and with a leaf blower on vacuum setting to gather finer particles. This course of depends on optimum situations; a gust of wind can completely undo these efforts. The place wind points can’t be averted, groups enclose the worksite with fencing coated with scrim, offering each shelter and extra containment. As famous within the earlier article, the prices of disposing of such a slab would possibly rival the prices of setting up it within the first place.

Polystyrene could be collected for recycling on building websites. Offcuts should, nevertheless, stay clear; the inclusion of soil or different building residues will result in rejection by recyclers. For deconstruction crews, the problem is that polystyrene bonds to concrete and is tough to take away in any respect, not to mention cleanly. Because of this, the concrete leaves the positioning entwined with the polystyrene, which recyclers regard as a contaminant, and normally goes to landfill. One native demolition firm does use a crusher outfitted with an air lance that blows mud and different light-weight parts out of the mixture as it’s processed. The ensuing materials is bought for makes use of resembling farm tracks — a win for landfill diversion however, after all, it incorporates entrained microplastics that may inevitably make their manner into the agricultural atmosphere and past.

As may be anticipated, Dewerse and LeRoy-Dyson’s plea to architects is to discover the options: the recycled hole plastic waffle-slab former methods, resembling Cleva Pod, Qpod or Firth’s RibRaft X-Pod. The weather of those methods are simpler to move and, whereas the fabric prices are larger than these for polystyrene, there are compensating financial savings in smaller transport volumes. A key benefit of plastic pod methods comes on the finish of the slab’s life when heavy equipment can simply and cleanly scale back the slab into piles of concrete rubble, polythene and metal, prepared for recycling. Cleva Pod confirmed the effectiveness of its system by demolishing a trial basis slab, demonstrating that it eliminates the necessity for laborious processes or costly contamination management.

Whereas it isn’t true of a era of Christchurch architects who’ve had the grim obligation of witnessing their quake-damaged metropolis being torn down, designers hardly ever see their creations being demolished. That’s, with buildings lasting 50 years or extra, we aren’t uncovered to the affect of our personal design selections as the development course of runs in reverse. Dewerse and LeRoy-Dyson’s work is giving us a window into the legacy that present practices generate, they usually problem us to answer what we see.

Structure NZ and ArchitectureNow will report additional on Dewerse and LeRoy-Dyson’s undertaking in upcoming points, hoping to share the teachings architects would possibly be taught.