Variations influence every construction project. What is less widely recognised is how an excessive flow of change increases the site-based, 
non–task-related overheads required to run the job. These additional overheads are often referred to as “thickening of preliminaries,” but in practical terms the issue is simpler: the cost of running the site increases because the method and sequence of executing the works has changed.
This impact can be substantial, and on many projects it remains unrecovered.
What It Actually Means
Preliminaries cover the site-based resources required to operate the project: supervision, site management, HSE, logistics, planning, project controls, temporary facilities, and similar project support resources. These costs are priced on the assumption that work will follow a stable programme with predictable sequencing.
When variations disrupt that programme, the original preliminaries allowance may become insufficient. Additional site management effort is required, not because more work was added, but because the working environment has changed. This is what “thickening” refers to.
Typical drivers include:
- Increased supervision due to congested work fronts
- Additional HSE coverage as manpower densities rise
- Higher project controls workload to manage multiple change streams
- Extended facilities or temporary works occupancy
- More logistical coordination
- Management hours increasing because planned sequences no longer hold
These costs are not task-related. They exist because the project’s operating conditions shift away from the baseline plan.
When It Arises
Contractors often see this impact develop under conditions such as:
- A high number of variations issued deep into execution
- Out-of-sequence work caused by late information or design slippage
- Compressed procurement or short-notice design releases
- Loss of productivity before any formal extension of time is granted
- Actual prolongation
It often only becomes visible later in the project, when preliminaries budgets have already been exceeded.
Addressing the “You Already Recovered This in Your Overhead and Profit (OH&P)” Argument
Employers commonly argue that the contractor has already been compensated for these overheads through the OH&P uplift applied to individual variation valuations. The distinction needs to be made clearly.
OH&P compensates the contractor for overhead and profit on the varied work itself.
It does not compensate the contractor for site-based overheads that increase because the variation disrupts the wider project environment.
OH&P is tied to the additional work item. Thickening arises because of how the changed work affects everything around it.
If OH&P were intended to cover site-wide disruption, no contractor would ever need to claim for loss of productivity, re-sequencing or change-driven overheads. Employers know this is not the case. Once the distinction is stated plainly, the argument often falls away.
How to Prove It
A successful ‘thickening’ claim requires four elements:
- Liability: identify the change events and contractual triggers.
- Cause and effect: show how those events changed execution environment.
- Impact: quantify the additional site-based, non–task-related overheads incurred.
- No double recovery: prove that these costs were not already paid through variation OH&P or prolongation.
The strongest analyses / assessments rely on project-specific records. Approaches include:
- Measured mile comparison between unimpacted and impacted periods (where feasible);
- Analysis of supervision levels, management hours, HSE coverage, logistics effort and project controls workload;
- Evidence of temporary facilities operating longer than planned; and
- Records showing additional site-based staff, plant, or services brought in to stabilise re-sequenced work
Industry-based ‘norms’ may be used where project records are limited, but they carry less weight.
Chances of Success
These claims succeed when the contractor demonstrates a clear pattern of change, no allowance for these overheads within variation pricing, and measurable increases in site-based overheads. Programme evidence showing re-sequencing or congestion strengthens the causal link.
They fail when contemporaneous records are poor, when the causal explanation relies on generalisations, or when costs overlap with prolongation or variation valuations.
Summary
An increase in site-based, non–task-related overheads arising from variations is a real and recoverable impact. It is often misunderstood, sometimes mislabelled, and frequently left unclaimed. With clear reasoning, solid records and a clean separation from OH&P on varied work, contractors can recover costs that would otherwise be silently absorbed into overruns.
Disclaimer
This article is provided for general information and discussion only. It does not constitute legal advice, expert advice, or professional opinion on any specific matter. Views expressed are those of the author and not necessarily those of DisputeIQ or its experts. Readers should seek appropriate professional advice before acting on any issue discussed.
