A differing site conditions (DSC) clause shifts the risk of hidden conditions to the owner, so bidders don’t have to pad prices for the unknown. The federal clause (FAR 52.236-2), and similar language in AIA A201’s concealed conditions provision, recognizes two types:
- Type I: conditions that differ materially from what the contract documents indicate. Example: borings show clay, and the excavator hits rock.
- Type II: unusual conditions that differ materially from what’s ordinarily encountered in that kind of work, even if the documents say nothing. Example: an abandoned underground tank or unexpected contamination.
The contractor must give prompt written notice, generally before disturbing the condition, so the owner can investigate. Then the parties price the change in cost and time through a change order.
Why it matters
Renovation and site work are full of surprises: buried utilities, unexpected rock, rotted framing behind finishes. Without a DSC clause, or if notice is late, the contractor eats the cost. A DSC event also often affects the schedule, so it should be logged as a potential delay at the same time.
Common mistakes
- Excavating through the condition before notifying the owner.
- No photos or daily log entries to prove what was found.
- Contract language that disclaims the owner’s soils data, weakening a Type I claim.
- Treating a DSC as a cost problem only and missing the time impact.
How os.construction handles it
We’re building field capture so a super can log a hidden condition with photos, open an RFI, and start a change event from the same record, the way RFI-212 leads to CO #14 in our sample Riverside story. It’s in development.