Differing Site Conditions: How to Protect Your Right to a Change Order When the Ground Doesn't Match the Plans

Not every problem that shows up mid-project is bad luck the contractor has to absorb. Some of it is a specific, contractually protected event: the ground, or what's under it, turning out to be something other than what the contract documents said — or something no reasonable bidder could have anticipated for that type of work and location. Contractors lose real money on these situations less often because the condition wasn't real, and more often because nobody handled the notice and documentation the way the contract required. Here is how a differing site condition actually works, and what separates a claim that gets paid from one that gets denied.

What a Differing Site Condition Actually Is

A differing site condition — sometimes called a changed condition or a concealed condition — is a physical condition encountered at the site that is materially different from what the contract documents represented, or materially different from what an experienced contractor could reasonably have anticipated for that type of work in that location. It has to be tied to the physical site itself: soil, rock, groundwater, existing structure, buried utilities, hazardous material, or something comparable. “The job turned out to be harder than we priced it” is not, by itself, a differing site condition.

The concept exists because bidders cannot excavate the entire site before submitting a price. Contracts allocate that risk deliberately: the owner represents certain conditions — through borings, geotechnical reports, or drawings of existing construction — and, in exchange for a competitively priced bid instead of one loaded with contingency for the unknown, agrees to adjust price and time when the physical reality diverges meaningfully from what was represented.

Type I and Type II Conditions

Most differing site conditions clauses, public and private, are built around a two-category framework that traces back to standard federal contracting language and has since been adopted broadly across public and private contract forms.

Type I conditions are subsurface or latent physical conditions that differ materially from those indicated in the contract documents — for example, the geotechnical report showed sand and the contractor encountered rock, buried fill, or groundwater instead.

Type II conditions are unknown physical conditions of an unusual nature that differ materially from conditions ordinarily encountered in work of that character in that area — an undocumented underground tank, contaminated soil, or an unrecorded utility line, even where the contract documents made no representation one way or the other.

The distinction matters because it changes what the contractor has to prove. A Type I claim is measured against what the contract documents said. A Type II claim is measured against what is ordinarily encountered in similar work — a higher and more subjective bar, and one that owners and construction managers contest far more aggressively.

Why the Clause Exists — and Why It Gets Scrutinized

Without a differing site conditions clause, every bidder would have to price in a large contingency for the unknown, contract prices would rise across the board, and owners would end up paying for risk that never materializes on most projects. With the clause, pricing stays competitive — but only because owners, construction managers, and their insurers scrutinize every differing site conditions claim closely, to separate a genuine unforeseen condition from an ordinary cost overrun dressed up as one. That scrutiny is the reason process discipline matters as much as the merits of the claim itself.

The Condition That Kills More Claims Than the Condition Itself: No Notice

Virtually every differing site conditions clause requires prompt written notice — often before the condition is disturbed further, and typically within a short window measured in days, not weeks. Continuing to work through the condition, backfilling or covering it, or waiting to raise it until a pricing dispute develops later in the project is often fatal to the claim, regardless of how genuinely unforeseen the condition was.

Notice is not a courtesy. In many contracts it is a condition precedent to entitlement — meaning a contractor can have a completely legitimate differing site condition and still recover nothing, because the clause's own notice requirement was never satisfied.

What Proper Notice and Documentation Look Like

• Stop or isolate the affected area before disturbing the condition further, to the extent safety and the work sequence allow.
• Give written notice the same day, or within the window your contract specifies — a phone call or a mention at the next coordination meeting is rarely treated as adequate notice on its own.
• Photograph and video the condition before it is altered, removed, or covered, from multiple angles and at a scale that shows context.
• Record the exact location — grid line, station, elevation, or GPS coordinate — so the condition can be verified and correlated to the contract documents later.
• Identify the specific document it contradicts — which boring log, drawing, specification, or existing-conditions document the condition contradicts, or why it falls outside what is ordinarily encountered for the area.
• Log every subsequent site visit, test, sample, and conversation connected to the condition, with dates and names.
• Track cost and schedule impact contemporaneously, as it is incurred — not reconstructed from memory once the claim is assembled.

Document Before You Disturb the Condition Further

Once a condition is removed, backfilled, or poured over, it is gone as physical evidence. Owners and construction managers often want their own representative, or an independent testing lab, to inspect or sample the condition before it changes further. Proceeding unilaterally — even for legitimate schedule reasons — can hand the owner a straightforward basis to dispute the claim later: if no one else ever saw the condition, the contractor is asking to be taken at its word.

A Differing Site Condition Is Not the Same as Ordinary Contractor Risk

Contractors are generally expected to have anticipated: conditions typical for the region that were disclosed anywhere in the contract documents or incorporated public records; conditions that were visible on a reasonable pre-bid site visit; and the ordinary variability inherent in the type of work being bid. A condition being more difficult, more expensive, or more time-consuming than hoped is not the same as a condition being materially different from what was represented or ordinarily expected. Contracts draw that line deliberately, and the burden is on the contractor to show which side of it a given condition falls on.

From Notice, to RFI, to Change Order

In practice, a differing site condition rarely travels alone. The written notice is often accompanied by, or quickly followed by, a Request for Information asking the design team how to proceed once the condition is found — see our guide to writing an RFI that actually protects you. Once direction is given and the condition is resolved, the cost and time impact of a validated differing site condition moves through the same change order process as any other change in the work — see our guide to how extra work actually gets approved and paid. Treating notice, RFI, and change order as one continuous paper trail, rather than three separate conversations, is what keeps a differing site condition claim coherent months later.

What Owners and Construction Managers Actually Look For

Reviewers evaluating a differing site conditions claim are typically looking for four things: notice that was contemporaneous, not reconstructed after the fact; photographic or testing evidence of the condition before it was disturbed; a cost and schedule impact that is isolated to the specific differing condition rather than bundled with unrelated inefficiency; and a clear, specific statement of what the contract documents represented or what is ordinarily expected, matched against what was actually found. Claims that satisfy all four move quickly. Claims that are missing even one tend to get returned for more support, or denied outright.

Common Mistakes That Turn a Valid Claim Into a Denied One

The condition itself is rarely the reason a differing site conditions claim fails. The more common causes: waiting to see whether the condition becomes a real problem before giving notice; continuing production through the condition without documenting it first; treating a verbal heads-up as sufficient notice; disturbing or removing the condition before anyone else can inspect it; folding the cost into a general end-of-project claim instead of processing it in real time; and describing a condition as obviously different without ever tying it to the specific document or standard it contradicts.

A differing site condition claim is not a story told at closeout. It is built the day the condition is found — with a notice letter, a photograph, and a paper trail that starts before the condition is disturbed and doesn't stop until it is resolved.

This article is for general informational purposes only and does not constitute legal, contractual, or claims advice. Differing site conditions clauses vary significantly by contract, by owner, and by jurisdiction — including whether the clause exists at all, what notice period applies, and what documentation is required. Always read your actual contract's differing site conditions or changed conditions clause in full, and consult your contract documents and qualified counsel before relying on any specific notice period, procedure, or entitlement described here.