Differing Site Conditions: Notice, Documentation and Impact Pricing

Rock where the report said soil, a buried foundation, water at four feet, a slab poured over a spring. Every builder has found something nobody expected, and what separates the companies that get paid for it from the ones that absorb it is almost never the merit of the claim — it is whether written notice went out inside the window the contract specifies. This piece covers the two types of differing site condition and how each is argued, what a defensible pre-bid investigation has to include, the six elements of a notice that survives, why impact cost is usually the larger half of the claim, and how to raise it without wrecking the relationship.

The clock starts when the shovel hits it, not when you finish thinking about it

Every builder has opened a wall or a trench and found something nobody expected: rock where the report said soil, a buried foundation, knob-and-tube wiring, water at four feet, asbestos-wrapped duct, a slab poured over a spring. What separates the companies that get paid for that work from the ones that absorb it is almost never the merit of the claim. It is whether written notice went out within the window the contract specifies.

Most construction contracts require notice of a differing or concealed condition promptly and in writing, frequently within a defined number of days, and often before the condition is disturbed. Missing that window can waive an otherwise valid claim entirely — and the most common way builders miss it is by doing the sensible-seeming thing: solving the problem first and paperwork later.

The habit that protects the money. The moment something unexpected is uncovered: stop work in that area, photograph it in place with something for scale and a visible date, and send written notice the same day. The notice does not need a price, a schedule impact or a solution — it needs to say what was found, where, when, and that it appears to differ from the contract documents. Everything else can follow. Sending it is a ten-minute task that decides whether a $28,000 condition is a change order or a donation.

The two kinds of differing site condition

Contracts and case law generally distinguish two categories, and knowing which one you have shapes the argument.

The first is a condition that differs materially from what the contract documents indicated. The soils report showed sand and you found rock; the drawings showed a slab at one elevation and it is eighteen inches lower; the survey showed no utility where one runs. The argument here is documentary: the contract said one thing, the site is another, and the comparison is objective.

The second is an unknown physical condition of an unusual nature, differing materially from what would ordinarily be encountered in work of that character. Nothing in the documents was wrong — the condition simply was not knowable. A buried cistern under a driveway, a previously unrecorded fuel tank, a structural modification made by a previous owner without permits. The argument here is harder and rests on what a reasonable contractor would expect in that kind of work, in that location.

Two things follow. The first type is easier to prove, so the contract documents you relied on need to be preserved with the estimate. The second type is where the pre-bid investigation matters most, because the counterargument is always that you should have anticipated it.

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What the pre-bid investigation actually has to accomplish

Most contracts contain a clause stating that the contractor has visited the site and satisfied itself as to conditions. That clause is used later to defeat claims, and how thoroughly the investigation was performed and documented determines how much weight it carries.

A defensible pre-bid investigation includes a site visit with photographs and notes rather than a drive-by; review of whatever geotechnical, environmental and as-built information the owner has provided, along with a written request for anything referenced but not provided; a check of the available public record for the property, including permit history, which frequently reveals the unpermitted modification before you find it with a saw; and written questions submitted during the bid period about anything genuinely ambiguous, since the response becomes part of the contract and the question itself becomes evidence that you looked.

Just as important is what goes into the bid as a stated assumption. A proposal that says the price assumes no rock above elevation X, no hazardous material, and no structural modification beyond what is shown has converted an unknown into a defined exclusion. That single page of assumptions is worth more in a dispute than any amount of argument afterward.

Writing notice that works

A notice that fails usually fails for one of three reasons: it was verbal, it was late, or it was so vague that the owner could reasonably say they did not understand a claim was being made.

A notice that works is short and contains six things. What was found, described factually and without characterization. Where, precisely enough to be located again. When it was discovered. Why it appears to differ from the contract documents, with a reference to the specific drawing, specification or report. That work in the affected area has stopped pending direction. And a request for direction, with a note that cost and schedule impact will follow once the condition is evaluated.

Two things not to put in it. Do not include a price you have not developed — a number given in the first hours will be treated as a cap and is almost always low. And do not assign blame; the notice is a factual record, and characterizing the designer's error in writing converts a technical conversation into a defensive one.

Send it through the channel the contract specifies, to the person the contract names, and keep proof of delivery. A notice emailed to a project manager when the contract requires written notice to the owner's representative has, in more than one dispute, been treated as no notice at all.

Pricing the work and the impact

Once direction is received, the change has two components, and builders routinely price only the first.

The direct cost is straightforward: labor, materials, equipment and subcontractor cost for the additional work, with markup per the contract. The second component is impact, and it is where the real money in a differing-site-condition claim usually sits — the crew that stood idle while direction was awaited, the resequencing of trades that were scheduled behind the affected area, the equipment on rent during the delay, the extended general conditions if the completion date moves, and the loss of productivity when work is performed out of sequence or in a compressed period afterward.

Impact costs are harder to document, which is exactly why they need to be captured in real time. Daily reports naming the crews idled and for how long, equipment logs, and a marked-up schedule showing what moved are the evidence. Reconstructing them at the end of the project from memory produces a number the owner will not accept and a claim that looks inflated even when it is not.

Ask for direction, do not assume it. A builder who encounters a condition, decides on the reasonable fix and performs it without written direction has done the owner a favor and forfeited most of the leverage. Even when the answer is obvious and the delay is painful, a one-line written instruction to proceed on a time-and-materials basis pending pricing turns the work into a documented change rather than an argument about whether it was authorized.

Handling it without wrecking the relationship

Owners hear "differing site condition" as "the price is going up," and the tone of the first conversation determines whether the rest of the project is collaborative or defensive.

Three things help. Deliver the news in person or by phone before the written notice arrives, so the owner is not surprised by a document. Bring options rather than only a problem — the fix, the alternative fix, and what each does to cost and schedule — because an owner presented with choices participates in the decision instead of resisting it. And be visibly disciplined about scope: a builder who documents a genuine condition, prices it fairly and does not attach unrelated items to it earns credibility that pays on the next one. The builder who treats every discovery as an opportunity gets audited on everything for the rest of the job.

Allocating the risk before the contract is signed

Everything above is about handling a condition after it appears. The cheaper work happens earlier, when the contract is still a draft and the allocation of this risk is still negotiable. Four provisions decide how much exposure the builder carries, and each is worth reading before signing rather than after digging.

Whether a differing site conditions clause exists at all. Some private contracts simply omit it, placing the entire risk of the unknown on the contractor. That is a priceable risk if you know about it, and an uninsurable surprise if you do not. If the clause is absent and cannot be added, the contingency in the number has to reflect that.
The notice period and its form. Seven days is common, some contracts say three, and a few require notice before the condition is disturbed. Know the number before the project starts and make sure the superintendent knows it too, because the person standing in the trench is the one who starts the clock.
Whether the owner's reports are contractually reliable. Many owners furnish a geotechnical report and then disclaim reliance on it in the contract, which removes the documentary basis for the first type of claim. Where that disclaimer exists, the alternatives are to negotiate it out, to conduct your own investigation, or to price the uncertainty.
What relief the clause actually provides. Some clauses grant time but not money, which on a project with liquidated damages is worth something and on a cost-driven job is worth very little. Read what is promised rather than assuming that acknowledgment of the condition implies compensation.

A related point on allowances and contingency. Where a genuine unknown exists and neither party can resolve it before starting — the condition of a slab under existing flooring, the state of framing behind plaster — a defined allowance with a stated scope and a mechanism for reconciliation is better for both sides than a lump sum containing a hidden guess. It puts the uncertainty on the table where the owner can see it, and it converts a future argument into a line item that was agreed before anyone was upset.

Five mistakes with unforeseen conditions

Solving first and documenting later. The notice window is short and the condition is often gone by the time the paperwork starts.
Giving verbal notice. If it is not written and delivered as the contract requires, it frequently counts as nothing.
Naming a price in the first hours. The early number becomes the ceiling, and it is almost always low.
Pricing only direct cost. Idle crews, resequencing, rented equipment and extended general conditions are usually the larger half.
Proceeding without written direction. Performing the reasonable fix unauthorized turns a claim into a request for a favor.

The numbers to track

Five figures make this manageable across a portfolio: hours from discovery to written notice, which should be measured in hours rather than days and is the single strongest predictor of recovery; percentage of conditions that resulted in an approved change order versus absorbed cost; average days from notice to written direction, which is the owner-side metric that justifies impact claims; impact cost as a percentage of direct cost on those changes, which most builders discover is far higher than they assumed; and conditions encountered per project by type, which over time tells you what your pre-bid investigation keeps missing and what belongs in your standard assumptions page.

Get your notice process in place before the next discovery

Send us your standard contract's notice provisions and your last three change orders arising from site conditions. We will show you where your notice window actually is, what your assumptions page should exclude and how much impact cost you left uncollected on those three.

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Frequently asked questions

What should you do the moment you discover an unforeseen condition?

Stop work in that area, photograph the condition in place with something for scale and a visible date, and send written notice the same day. Most construction contracts require notice of a differing or concealed condition promptly and in writing, frequently within a defined number of days and often before the condition is disturbed, and missing that window can waive an otherwise valid claim entirely. The most common way builders miss it is by doing the sensible-seeming thing: solving the problem first and handling paperwork later. The notice does not need a price, a schedule impact or a proposed solution — it needs to state what was found, where, when, and that it appears to differ from the contract documents. Everything else follows. Those ten minutes decide whether a $28,000 condition becomes a change order or a donation.

What are the two types of differing site condition?

The first is a condition that differs materially from what the contract documents indicated: the soils report showed sand and you found rock, the drawings showed a slab at one elevation and it sits eighteen inches lower, the survey showed no utility where one runs. That argument is documentary and objective — the contract said one thing and the site is another — which makes it the easier of the two to prove, provided you preserved the documents you relied on with the estimate. The second is an unknown physical condition of an unusual nature that differs materially from what would ordinarily be encountered in work of that character: a buried cistern, an unrecorded fuel tank, an unpermitted structural modification. Nothing in the documents was wrong; the condition simply was not knowable. That argument is harder and rests on what a reasonable contractor would expect.

What should a pre-bid site investigation include?

Enough to survive the clause stating that the contractor visited the site and satisfied itself as to conditions, which owners use later to defeat claims. A defensible investigation includes a site visit with photographs and notes rather than a drive-by; review of whatever geotechnical, environmental and as-built information the owner provided, plus a written request for anything referenced but not provided; a check of the public record for the property including permit history, which frequently reveals an unpermitted modification before you find it with a saw; and written questions during the bid period about anything genuinely ambiguous, since the response becomes part of the contract and the question is evidence that you looked. Equally important is a stated assumptions page in the proposal — no rock above a given elevation, no hazardous material, no structural modification beyond what is shown — which converts unknowns into defined exclusions.

What should a differing site condition notice contain?

Six things, stated briefly: what was found, described factually and without characterization; where, precisely enough to be located again; when it was discovered; why it appears to differ from the contract documents, referencing the specific drawing, specification or report; that work in the affected area has stopped pending direction; and a request for direction, noting that cost and schedule impact will follow once the condition is evaluated. Two things to leave out. Do not include a price you have not developed, because a number given in the first hours is treated as a cap and is almost always low. And do not assign blame, since characterizing a designer's error in writing turns a technical conversation into a defensive one. Send it through the channel the contract specifies, to the person it names, and keep proof of delivery.

How do you price a change arising from an unforeseen condition?

In two components, and builders routinely price only the first. Direct cost is straightforward — labor, materials, equipment and subcontractor cost for the additional work, with markup per the contract. Impact is where the real money usually sits: the crew idled while direction was awaited, the resequencing of trades scheduled behind the affected area, equipment on rent during the delay, extended general conditions if the completion date moves, and lost productivity from working out of sequence or in a compressed period afterward. Impact costs are harder to document, which is exactly why they must be captured in real time through daily reports naming which crews were idled and for how long, equipment logs and a marked-up schedule showing what moved. Reconstructed from memory at the end of the project, they produce a claim that looks inflated even when it is not.