Short answer
Selective dismantling means taking a building apart by material group, in reverse of the order it was built, rather than bringing it down in one go. The aim is twofold: separating recoverable material cleanly, and keeping hazardous or contaminating material out of the rubble. The plan is built by producing a material inventory, not by walking the building; which material comes out at which stage and with which attachment is decided in advance. Once the order is broken there is no going back, because mixed rubble cannot be separated again.
Why reverse order?
A building is constructed in layers: structural frame, infill walls, services, finishes, final coatings. Selective dismantling runs that order backwards, because each layer covers the one after it.
You cannot reach the services beneath a finish until the finish is removed; if a wall comes down before the services are out, copper, aluminium and plastic end up mixed into the rubble. Mixed material both loses its recovery value and raises the cost of separating it.
So selective dismantling is less a demolition technique than a sequencing discipline. The attachments used are the same as in demolition; the difference is when each one comes into play.
How the plan is built
- Produce a material inventory: roughly how much of each material is in the building? Concrete, steel, timber, glass, service metals and insulation are listed separately.
- Mark hazardous material: asbestos, paint, fuel tanks, chemical residues. These are removed by a specialist before demolition begins; no attachment decision comes before this.
- Set the recovery target: which material will be sold, which reused on site, which disposed of?
- Assign an attachment and machine to each stage; plan how many machines will be on site at once and how they will be positioned.
- Decide the material exit route and storage area at the outset. If separated material has nowhere to go, the separation breaks down one stage later.
The attachment sequence
Grapples and shears are used for stripping services and light metal; this stage usually runs alongside manual stripping.
The shear comes into play for cutting steel structure and rebar. To protect the blade, it must be kept out of concrete mass.
The pulveriser crushes concrete off the rebar. This stage decides how clean the scrap is and therefore what it is worth.
The breaker is used for bulk demolition and reducing mass; the structural frame comes down at this stage.
In the final stage a crusher bucket reduces the separated concrete to a size reusable on site.
The stage most often skipped
Separating concrete from rebar with a pulveriser is the stage most often skipped under time pressure. Skip it and rebar stays inside the concrete, the scrap comes out dirty and loses value; on top of that, reinforced material entering a crusher bucket wraps around the jaws and the work stops. Skipping this stage breaks the two stages that follow.
Extra constraints in a city
- Vibration and noise: where neighbouring structures exist, measurement and limit checks are needed. We explain, with sources, how the regulation places different obligations on breakers and hand-held tools on our noise page.
- Dust: in enclosed and confined spaces dust suppression becomes mandatory; water or dust channel tools come into play.
- Falling material control: in tall structures, where material will fall and how the area below is closed off has to be planned.
- Working hours: municipal restrictions shape the programme directly and can clash with the longer duration of selective dismantling.
- Haulage: if load numbers and times are permit-controlled, on-site separation and size reduction become even more valuable.