The Southern Tonar Block consisted of five houses plus a set of 2-storey multi-units - one having four dwellings and three comprising two dwellings. All houses had been built in the 1960s and were part of the Housing New Zealand estate. Thanks to their solid construction, they lent themselves well to refurbishment or recycling. They were being replaced with 44 modern style 2 to 6-bedroom flats.
Demolition 1 had the objective to divert 90% of potential waste from landfills through salvaging, recycling and reuse of what was estimated to be 40% of all materials
| Building name | Tonar Block |
|---|---|
| Developer | Housing New Zealand |
| Main contractor | Demolition 1 |
| Location | Northcote, North Shore |
| Project start date | 2008 |
| Project completion date | 2008 |
| Waste diverted from landfill | 94% |
| Total waste generated | 58.2 m³ |
Planning
Key to the success of the project was careful planning, training of staff and subcontractors and detailed monitoring of progress. While this was administratively heavy and took persistence as well as persuasion of all involved, the results proved the value of this approach.
Execution
Demolition 1 was responsible for preparing the houses for removal, demolition of the bottom storeys and clearance of the site. Their objective was to divert 90% of potential waste from landfill through salvaging, recycling and reuse. The five houses and top storeys of all multi-units (comprising the remaining 60%) were taken off site for reuse by Whangarei House Movers.
Reusable houses taken off site accounted for 60% of materials contained in the development. Removal was done under separate contract, by Whanganui Housemovers Ltd.
A hands-on supervisor was contracted to deliver the project and the paperwork and to assist staff who "came to knock down buildings and load them into bins" and who were less inclined to fill in forms, yet it was the comprehensive paperwork that showed up any weaknesses quickly so these could be dealt with effectively.
Key waste reduction outputs
| Waste material type | Destination | Approximate volume (m³) |
|---|---|---|
| Timber | Export/mulching | 377.1 |
| Plasterboard | Composted | 20 |
| Ferrous metal | Recycled | 1 |
| Non-ferrous metal | Recycled | 2.05 |
| Concrete | Recycled | 447.5 |
| Glass | Recycled | 0.75 |
| Reusable building components | Reused | 6.9 |
| Landfill | To landfill | 58.2 |
Lessons learned/recommendations
Contamination of top soil was another potential problem. If this contains concrete or timber, it is only suitable for landfill. Careful planning minimised contamination with builder's rubble where that was excavated and processed.
Demolition 1 has been separating and recycling materials for a while and has been receiving financial benefits accordingly, but better coordination with the company that collected the materials led to even better sorting practices and reduced landfill waste, so further cost savings were made.
There was a higher administrative cost for keeping track of all the waste and reporting it. However, including waste minimisation plans in tenders for new jobs is expected to increase their success rate, so there is also a competitive advantage that is hard to quantify.