Demolition takeoff

The first decision is whether the work is a whole structure demolition or a selective removal, because the unit of measure flips on that answer. Every formal standard prices a whole structure as a single enumerated item or a lump sum, not a measured volume. NRM2 Work Section 3 measures demolitions as an item, classified as all structures, individual structures, or parts of structures. NZS 4202 allows one item only for a complete structure, with its dimensions, number of storeys, and construction described. United States highway practice pays removal of structures and obstructions, and building demolition, as a lump sum, stating that no measurement will be made. So the whole building task is to describe and bound the structure, not to chase a net cubic metre.

Selective or partial demolition measures each existing element in the unit native to that element, exactly as the equivalent new work would be, and NRM2 Work Section 4 on alterations, repairs and conservation lets the surveyor choose the most suitable unit. The element drives the unit: foundations and thick concrete over 150 millimetres by volume; slabs and pavings up to 150 millimetres, plus masonry, finishes, and roofs, by area; pipe, kerb, and trim by length; and fixtures, doors, windows, and trusses by number. In imperial regions the same dimensions carry imperial units, with surfacing in square yards, structural concrete in cubic yards, pipe and curb in linear feet, and fixtures each. CESMM4 Class D covers civil work, with site clearance, buildings, pipelines, and trees each in their native unit, computed net from the drawings with no allowance for bulking, shrinkage, or waste.

When you demolish an element you remove the whole existing element, its full length, thickness, and height, regardless of what smaller new work replaces it. Removal is therefore measured to the outer extent of the existing element, not to the reduced footprint of the replacement, a principle supported by NRM2 Work Section 4 and by NZS 4202, which states the sectional sizes and lengths of the existing element. A remove and replace item is two separate quantities: a gross removing line to the existing extent, and a net new work line to the new geometry. Cutting or forming a new opening in existing fabric is its own item, never netted out of the wall removal, because saw cutting, propping, lintels, and making good are distinct labour. NRM2 measures cutting openings, recesses, cutting back, and filling in as separate items, by item, area, length, or number, with the type and thickness of the existing structure stated, and making good after removal is measured separately too.

For selective work measured by area or volume, openings and voids follow the same threshold as the parent trade, since it is the existing finish or structure being measured. The NRM2 general rule always deducts openings at the boundaries of a measured area irrespective of size, but within that area it leaves voids of 1.00 square metre or less, and 0.05 cubic metre or less for some volumes, undeducted. Whole building demolition carries no void deduction, so the gross enclosed volume or the lump sum stands. The United States has no codified demolition void threshold, so the deduction is the estimator's judgement.

Once an element is broken loose it occupies more volume, because of the voids between fragments. The swell, or bulking, factor converts the measured in place bank volume to the loose volume that is loaded, hauled, and tipped, and haul cost is driven by that loose volume or by weight. The formula is loose equals bank multiplied by one plus the swell percentage. A 67 percent swell means 100 cubic metres of slab becomes about 167 cubic metres of debris in the truck, and sizing the haul on the original 100 is the most common under bid in the trade.

The factors come from neutral data, chiefly the FHWA earthwork tables, the US Forest Service FLH 1996 figures, the Caterpillar Performance Handbook, and the Church Excavation Handbook of 1981. As approximate planning values, broken pavement concrete bulks about 67 percent, with cinder and stone concrete nearer 72 percent; brick and masonry rubble about 67 percent; broken asphalt about 50 percent; broken rock roughly 50 to 65 percent; mixed spoil and common earth or loam about 25 percent, up to about 35 percent for dry loam; and clay about 40 percent.

The measured bill of quantities stays net. CESMM4 and NRM2 both measure with no bulking allowance, and the estimator applies the swell afterward to derive the haul or skip quantity. Disposal is often re quoted by weight at the tip, since loose broken concrete and asphalt are heavier per loose volume than their solid is per bank volume, so both a volume swell path and a unit weight path are worth carrying. Disposal is procured in whole containers or truck loads, or by weight at the tip, so the swelled loose volume is rounded up to the next whole container or load. That rounding is a procurement step, separate from the measured bank quantity, which is never rounded.

Demolition contracts pin a lowest level of demolition, which is mandatory information under NRM2 and changes the quantity materially, since superstructure only, slab removed, and foundations out are three different volumes. The work may run to the superstructure above the ground floor slab, down to the underside of that slab when it is removed, to foundations taken to a stated depth below grade such as 600 millimetres below finished subgrade, or full removal including basements. The cut off elevation has to be read from the demolition notes before any volume is computed.

Even when demolition is a single lump sum item, the estimator bounds it with a descriptive volume in order to price labour, plant, and haul. The defensible basis is the gross enclosed building volume, the footprint to the outer faces multiplied by the overall height, including internal partitions and openings, with no void deduction. This is the same gross enclosed volume, known in German practice as umbauter Raum, that DIN 277 defines as the building volume to the outer boundary surfaces. Net interior volume understates the demolition effort.

Salvage is a cost credit, measured separately, never a deduction from the demolition quantity. Salvageable items designated in the contract, described in NRM2 as material to be retained for reuse or to remain the property of the employer, are removed carefully, counted or weighed in their own unit, fixtures and fittings by number and scrap metals by weight, then credited against cost. The demolition quantity stays intact because the whole building is still demolished. Recycling and diversion are reported by stream, such as concrete, metals, wood, and masonry, and may be calculated by weight or by volume as long as the unit is consistent throughout, with soil and land clearing debris excluded. The thresholds are version specific: LEED v4 credit MRc5 Option 1 awards one point for 50 percent diversion across three streams and two points for 75 percent across four streams, while LEED v4.1 restructured the two point path to 50 percent diversion together with less than 10 pounds per square foot, about 50 kilograms per square metre, of new construction waste. The European Union Waste Framework Directive sets a 70 percent recovery target by weight for non hazardous construction and demolition waste.

Hazardous material is a regulated adjacent scope, measured separately from the demolition quantity. Asbestos containing material abatement is quantified by the type of material: surfacing, insulation, flooring, and finishes by area, pipe and duct lagging by length, and regulated waste disposal billed by manifested weight. The notification and work practice limits are regulatory, not estimating conventions. The United States EPA NESHAP rule, at 40 CFR 61 Subpart M, sets notification at 260 linear feet, 160 square feet, or 35 cubic feet of regulated asbestos material, and OSHA 1926.1101 governs work practices. NRM2 treats decontamination as its own item, so the asbestos is carved out of the demolition quantity and priced under the abatement scope.

Partial demolition next to a structure that is to remain requires temporary support to the retained fabric, including shoring, propping, needling, and raking shores. This is measured as a described item under temporary works, with the supported element, the support type, and the duration described, and priced separately under NRM2 Work Sections 3 and 4 and CESMM4, never netted into the demolition quantity. Demolition zones are also protected and screened with perimeter hoarding, debris netting, dust screens, and scaffold mounted sheeting, measured by area for screening and sheeting, by length for the hoarding run, or as an item, under NRM2 preliminaries and protection provisions.

Demolition uniquely uncovers conditions not shown on the drawings, such as extra structure behind finishes, buried foundations, or asbestos. Estimators commonly add a contingency for these unknowns, often around 10 percent and up to about 15 percent on heavy renovation work, but no neutral standard fixes the percentage, so it is pure judgement. United States highway specifications take the opposite stance and explicitly exclude unknown buried features from the lump sum, pricing them as extra work when encountered.

The United Kingdom is the most codified. NRM2 Work Section 3 measures demolitions as an item with the lowest level stated, Work Section 4 measures removing and cutting in the surveyor's chosen unit, and civil work follows CESMM4 Class D, measured net with no bulking in the bill of quantities. It also carries the clearest deduction rule, the 1.00 square metre minimum void. In Australia and New Zealand, NZS 4202 and the Australia and New Zealand method treat a complete structure as one item and measure detailed demolition by element, with foundations by volume, slabs and masonry by area, kerbs by length, and doors and trusses by number, salvage conditions stated.

Across Europe, VOB Part C with DIN 18459 on demolition and deconstruction bills by the actual measured quantity, the Aufmass, of the dismantled element, with national methods otherwise. The United States has no legal method of measurement: whole structure removal is a lump sum, while selective surfacing is taken by the square yard, pipe and curb by the linear foot, items each, and structural concrete by the cubic yard, with swell from the published earthwork tables. Canada is a hybrid of the Canadian quantity surveying method and United States lump sum site practice, often pairing metric drawings with imperial disposal units. International work uses element native, metric units with no harmonised void or bulking clause, so convention governs the swell.