Inspection and test plans

The requirements register from lesson 2 tells the team what must be inspected and tested. An inspection and test plan (ITP) says how, when and by whom, step by step, for one activity. It is the working document of quality control: the foreman uses it to know what will be checked, the field engineer uses it to arrange inspections, the consultants use it to know when to come, and at the end of the job the signed ITPs and their records are part of the evidence that the building was built as designed.

This lesson explains the structure of an ITP, the meaning of hold, witness and review points, how ITPs connect to the look-ahead, and how inspection records are kept. The examples are the firestopping plan that Mei wrote after the coverage check in lesson 2 and the plan for the post-tensioned transfer slab at level 3.

The structure of an ITP

An ITP lists the steps of an activity in the order they happen, and for each step the check to be made, the standard it is checked against, how often, who does it and what record proves it was done. Most ITPs fit on one or two pages. They are written from the specifications, the drawings, the manufacturer's installation instructions and any code requirements, and they are reviewed by the subcontractor who will do the work, because the subcontractor's crew carries out most of the checks.

Acceptance criteria deserve care. 'Install properly' is not a criterion. A criterion is something two people would judge the same way: a dimension with a tolerance, a test value, a listed system number, a product name, or a visual standard set by an approved mock-up. When the specification is vague, the ITP should point to the document that defines acceptance, such as the manufacturer's instructions or the approved shop drawing, or the field engineer should ask the consultant for a clear criterion before the work starts rather than argue about it afterwards.

Hold, witness, review and surveillance points

The point types tell everyone how much control a step carries. Terms vary slightly between companies and owners, but the meanings below are widely used.

Hold points are powerful and expensive, because every hold point can stop a crew. They belong where the consequence of an error is high and the work will be hidden or costly to change once the next step is done: before concrete is placed over reinforcing and tendons, before tendons are cut after stressing, before fire separations are closed, before windows are covered by cladding. Witness points suit steps where the owner's consultant wants the option to see the work but does not need to stop it, such as the start of a membrane installation. Too many hold points slow the job and train everyone to treat them as formalities; too few let critical work be covered unseen.

The release of a hold point must be clear. On Larkspur Commons, a hold point is released only in writing, by a signature on the ITP or a recorded approval in the inspection app, by the party named in the ITP. A verbal 'looks fine' from a consultant walking past does not release a hold point, because six weeks later nobody will remember who said it about which area.

Example: the firestopping ITP

Firestopping in a wood-frame building is a good example of an activity that needs a strong ITP. Every pipe, duct, cable and conduit that passes through a fire-rated wall or floor needs a tested firestop system matched to the penetrating item, the size of the opening and the type of assembly. On a single residential floor of Larkspur Commons there are more than 600 penetrations through fire separations, installed by several trades over several weeks, and almost all of them will be hidden by drywall.

The first-work hold point in step 2 matters most. If the first zone is right, the installers have shown they understand the systems and the remaining zones mostly follow. If it is wrong, the error is caught in one zone instead of eight. Lesson 5 returns to first-work inspections. Step 6 handles a classic weakness: penetrations made after the walls are closed, for example when a late change adds a cable, are easy to forget because the zone has already passed its inspection.

Example: the transfer slab ITP

The level 3 transfer slab, introduced in CON-315, is a post-tensioned concrete slab that carries the four wood-frame storeys above and transfers their loads to the podium columns. It is the most critical single pour on the project. Its ITP has more hold points than any other on the job.

Before the first pour, the ITP requires: approved formwork and shoring design (CON-325), surveyed soffit elevations, inspection of mild reinforcing for size, spacing and cover, inspection of tendon profiles against the shop drawings with chair heights checked at marked points, inspection of anchorages and pocket formers, the structural engineer's field review, and the building official's inspection where required. During the pour, the testing agency samples the concrete and the contractor records placement times and temperatures. After the pour, the ITP requires concrete strength results reaching the specified stressing strength, typically about 20 MPa for this slab, before stressing, the stressing records with measured elongations within tolerance of the calculated values, and the engineer's review of those records before the tendon tails are cut and the pockets grouted.

The pre-pour hold point is where Mei's checklists earn their keep. On the second transfer slab pour, her pre-pour check found three tendon chairs crushed by foot traffic, which would have lowered the tendons by about the height of a chair and reduced the slab's capacity. They were replaced before the engineer's review, and nobody outside the field team ever saw the problem. That is what a good hold point is for: finding problems while they are still cheap.

Notification and the look-ahead

Hold and witness points only work if the right people know when to come. Each ITP states how much notice each party needs: on Larkspur Commons, the structural engineer asks for 48 hours before pre-pour reviews, the envelope consultant 72 hours before mock-up tests, and the building official's inspections are booked through the City's system the day before. CON-335 showed how inspections are placed in the look-ahead as constraints. The ITPs supply the list: every hold point in the next three weeks becomes a line in the look-ahead with its notice period and the person who will book it.

The script below checks the coming week's activities against the ITP hold points and flags any that have not been booked with enough notice.

# Check that hold points in the coming week are booked with enough notice (illustrative)
from datetime import date, timedelta
today = date(2026, 3, 9)  # Monday
holds = [  # (activity, hold point, party, notice in working days, planned date, booked on)
    ("L3 transfer slab pour 2", "pre-pour review", "structural engineer", 2, date(2026, 3, 12), date(2026, 3, 9)),
    ("L3 transfer slab pour 1", "stressing records", "structural engineer", 1, date(2026, 3, 10), date(2026, 3, 6)),
    ("L4 west framing", "shear wall nailing", "structural engineer", 2, date(2026, 3, 13), None),
    ("Podium north wall", "waterproofing before backfill", "envelope consultant", 3, date(2026, 3, 11), date(2026, 3, 9)),
]
def working_days(a, b):
    n, d = 0, a
    while d < b:
        d += timedelta(days=1)
        if d.weekday() < 5:
            n += 1
    return n
for act, hp, party, need, planned, booked in holds:
    if booked is None:
        print(f"NOT BOOKED  {act}: {hp} ({party}), needed {need} working days before {planned}")
        continue
    given = working_days(booked, planned)
    flag = "ok" if given >= need else "SHORT NOTICE"
    print(f"{flag:13s}{act}: {hp}, notice {given} of {need} working days")

ok           L3 transfer slab pour 2: pre-pour review, notice 3 of 2 working days
ok           L3 transfer slab pour 1: stressing records, notice 2 of 1 working days
NOT BOOKED  L4 west framing: shear wall nailing (structural engineer), needed 2 working days before 2026-03-13
SHORT NOTICE Podium north wall: waterproofing before backfill, notice 2 of 3 working days

Two problems show up. The shear wall nailing review on level 4 west has not been booked at all, and the envelope consultant was given two working days' notice for a review that needs three. Omar calls the consultant that morning to ask whether the review can still happen on Wednesday; if not, the backfill moves, because backfilling over unreviewed waterproofing would hide it. Finding these conflicts on Monday morning is much cheaper than finding them on Wednesday when the excavator is waiting.

Inspection records

An inspection that is not recorded did not happen, as far as anyone can prove later. Records serve three purposes: they show the work was checked, they allow trends to be analysed (lesson 12) and they protect the contractor if questions arise years later. Good records are specific: the location by gridline, level and suite; the item checked; the result; the name of the inspector; the date; and photographs with enough context to identify where they were taken.

Most contractors now keep inspection records in a construction management application on tablets, with checklists built from the ITPs, photos attached automatically and records linked to drawing locations. The software does not make the inspection better by itself, but it makes records easier to complete, harder to lose and possible to analyse. Thornbury's procedure requires that every hold point release be recorded in the application before the next step starts, so the field engineer can see at a glance which zones are released.

Sampling or inspecting everything

Some items must be checked one by one: every hold point release, every anchor bolt group under a steel column, every firestop before the building official's inspection if the official requires it. For repetitive items, inspecting every unit by the contractor may be neither practical nor necessary if the installer checks every unit and the contractor samples. The question is how big the sample should be.

A simple way to think about it is the probability that a sample catches a problem if one exists. If a zone has a certain share of defective items and the inspector checks a random sample, the chance of finding at least one defect rises quickly with the sample size. The script below shows this for firestopping in one zone of 304 penetrations.

# Probability that a random sample finds at least one defect in a zone of 304 penetrations
from math import comb
N = 304
for defect_rate in (0.01, 0.03, 0.05):
    D = round(N * defect_rate)
    row = []
    for n in (10, 30, 61, 100):
        p_none = comb(N - D, n) / comb(N, n)
        row.append(f"n={n:3d}: {1 - p_none:5.1%}")
    print(f"{D:2d} defective ({defect_rate:.0%}):  " + "   ".join(row))

 3 defective (1%):  n= 10:  9.6%   n= 30: 26.9%   n= 61: 49.1%   n=100: 69.9%
 9 defective (3%):  n= 10: 26.3%   n= 30: 61.3%   n= 61: 87.1%   n=100: 97.4%
15 defective (5%):  n= 10: 40.2%   n= 30: 79.8%   n= 61: 96.8%   n=100: 99.8%

With a 20 percent sample of 61 penetrations, the chance of finding at least one defect is about 87 percent if 3 percent of penetrations are defective, and about 97 percent at 5 percent, but only about 49 percent if just three penetrations are bad. That is why Mei's ITP does more than sample. It requires the installer to label and photograph every penetration, it tightens the sample to 100 percent for any penetration type that failed earlier, and it keeps the building official's inspection as a final hold point. Sampling is a tool for finding systemic problems, not a guarantee that every unit is right. Lesson 12 returns to sampling plans.

ITPs and subcontractors

Most of the checks in an ITP are done by the subcontractor's own people. Thornbury's subcontracts on Larkspur Commons require each subcontractor to review the ITP for its scope, to name a person responsible for its quality control, to perform and record its own inspections before calling for the contractor's inspection, and to correct nonconforming work at its own cost. Before each new scope starts, the subcontractor's foreman walks through the ITP with Mei at the preinstallation meeting (lesson 4).

The principle is that each trade inspects its own work first. A contractor's inspector who finds dozens of obvious defects is doing the subcontractor's job, and the contractor's time would be better spent on sampling, hold points and the interfaces between trades, where defects most often hide.