Self-performed trades in depth

CON-200 showed how to take off concrete, formwork, reinforcing, masonry, framing and structural steel and how to apply unit prices to the quantities. That is enough to price a small foundation package. On a complete bid for a building, the general contractor's self-performed work is usually the largest single source of risk in the estimate, and pricing it well depends less on the quantities than on the method: how many form sets, how the concrete gets from the truck to the forms, how the work is sequenced around the crane, what happens in winter and how much the firm's own crews actually produce. This lesson works through method-based pricing for the trades general contractors most often self-perform: cast-in-place concrete, structural steel erection and rough carpentry, with notes on miscellaneous installation work.

Method before price

A method statement is a short description of how the work will be done: the sequence, the equipment, the crews, the form systems and the duration. Writing one before pricing forces the estimator to think the work through and makes the estimate reviewable, because a reviewer can challenge the method rather than guessing what a unit price assumed. It also connects the estimate to the schedule. If the method assumes two wall form sets cycling every three days, the schedule must allow the corresponding duration, and the general conditions must carry the crane and supervision for that duration.

Formwork: the biggest lever

Formwork often costs as much as the concrete it shapes, and most of that cost is labour. Two quantities control it: the contact area (the area of form in contact with concrete, measured in CON-200) and the number of times each form can be reused. Job-built plywood forms might be used three to six times before they are too damaged to give an acceptable finish; engineered aluminium or steel panel systems can be used hundreds of times and are usually rented. The cost per use falls as reuse increases, but the contractor must have enough sets to keep the crews and the schedule moving.

# Cost per square metre of contact area for different numbers of form sets (illustrative)
contact_total = 2_400        # m2 of wall contact area on the project
set_area = 200               # m2 of forms in one set
material = 95                # $ per m2 to build or buy job-built forms
labour = 48                  # $ per m2 per use to erect, align and strip
repair = 4                   # $ per m2 per use
crane_week = 14_000          # $ per week of crane time tied to the walls
for sets in (1, 2, 3):
    uses = contact_total / (set_area * sets)        # uses of each set
    weeks = contact_total / (set_area * sets) * 0.6 # 3 working days per cycle per set (assumed)
    weeks = max(weeks, contact_total / 800)         # crew can form at most 800 m2 per week
    cost = (material * set_area * sets + (labour + repair) * contact_total
            + crane_week * weeks)
    print(f"{sets} set(s): {uses:4.1f} uses each, {weeks:4.1f} weeks, "
          f"${cost:,.0f} total, ${cost / contact_total:,.2f} per m2")

1 set(s): 12.0 uses each,  7.2 weeks, $244,600 total, $101.92 per m2
2 set(s):  6.0 uses each,  3.6 weeks, $213,200 total, $88.83 per m2
3 set(s):  4.0 uses each,  3.0 weeks, $223,800 total, $93.25 per m2

With one set, each form is reused twelve times and material cost per use is low, but the walls take more than seven weeks and the crane is tied up the whole time. With two sets the walls finish in under four weeks; the extra material is more than repaid by the crane time saved. A third set saves less than a week of crane time, because the crew, not the forms, now limits progress, and its material costs more than it saves. The general lesson is that formwork must be priced with the schedule and the crane, not as a unit rate in isolation. (The crew's own cost is the same in each case because its total hours depend on the contact area, which is why it does not appear in the comparison.)

Placing and finishing concrete

Placing concrete looks simple: trucks arrive, concrete goes into the forms, finishers do their work. The cost depends on how fast concrete can be delivered and placed, which determines the crew hours and equipment time. The placing rate is limited by the slowest link: the ready-mix plant's ability to supply trucks, the travel time, the pump or crane's output, and the finishers' ability to keep up. A slab pour that is too large for the finishing crew leads to cold joints or poor finishes; one that is too small wastes the fixed costs of mobilizing the pump and crew.

Concrete material itself is priced from supplier quotes per unit volume, with extras for high strength, air entrainment, special cements, fibres, accelerators or retarders, hot water or chilled water, short loads (loads below a minimum size), waiting time beyond the free unloading period, and weekend or night delivery. CON-200 covered the main items; on a complete bid the estimator also checks the specified testing regime, because the cost of cylinders, slump and air tests and any third-party inspection usually falls to the contractor or must be coordinated with an owner-paid testing firm.

Winter concreting

In most of Canada, a building with concrete work between November and March will need cold-weather protection. CSA A23.1 requires that freshly placed concrete be protected from freezing and kept above specified temperatures for a curing period, and that concrete not be placed against frozen ground. The costs include hoarding (tarpaulin or poly enclosures on scaffold or frames), indirect-fired heaters and fuel, ground-thawing equipment, insulated blankets, heated aggregates and hot water from the ready-mix supplier, accelerating admixtures, temperature monitoring, and the lower productivity of crews working in heavy clothing in short days.

Structural steel erection

Many general contractors subcontract structural steel as a supply-and-erect package, but some self-perform erection or erect pre-engineered buildings. Erection is priced on pieces and connections rather than on tonnage alone, because a crew's daily output is limited by the number of lifts and bolted or welded connections. Light, numerous members can cost more per tonne to erect than heavy members.

Rough carpentry and the general contractor's own work

The general contractor's carpenters and labourers often carry a long list of small items that no subcontractor wants: wood blocking and backing in walls, rough hardware, temporary stairs and guardrails, hoarding and covered walkways, floor and finish protection, installation of owner-supplied items, doors, frames and hardware installation, washroom accessories and other specialties, and miscellaneous patching. Each is small, but together they can be a significant cost and a common source of scope gaps between trades.

Good practice is to keep a checklist of these items, assign each to a package or to the general contractor explicitly, and price the general contractor's share with crew-days and materials. Doors, frames and hardware installation, for example, is priced per opening, with adjustments for frame type (knock-down or welded), hardware complexity (simple passage sets versus electrified hardware with access control) and fire-rated assemblies.