Site Instruction

Definition

A Site Instruction — often written SI, and known in some contract forms as an Engineer's Instruction or Architect's Instruction — is a formal written direction issued by the contract administrator to the contractor. It tells the contractor to do something, stop something, change something, or clarify something. It is the mechanism by which decisions made in meetings and site walks become contractually binding.

What an SI Is (and Is Not)

An SI is an instruction, not a variation. It tells the contractor to act; it may or may not have cost or time implications. A variation, or change order, is the commercial consequence of an instruction that alters the scope, cost or time. Every variation begins with an SI; not every SI becomes a variation. The distinction matters because contractors sometimes claim variation costs against SIs that were merely clarifications, and administrators sometimes issue instructions that clearly change the scope but decline to acknowledge the commercial consequences.

What Should Be on the SI

• Unique SI number, date, project name.
• Issued by (name and role) and issued to (contractor or subcontractor).
• Clear description of the instruction — what is to be done, where, and by when.
• Reference to the contract clause that gives the administrator the authority to instruct.
• Attached sketch, drawing or specification amendment where relevant.
• A note stating whether the instruction is considered to have cost and/or time implications, and if so the process by which those will be evaluated.
• Signature and distribution list.

Real-World Example

On a hotel refurbishment in Riyadh, the contract administrator held a site walk with the interior designer and the client. During the walk the client asked for the reception desk to be moved 800 mm to open the sight-line to the lift lobby. The site engineer sketched it on a print, everyone nodded, and work continued. Two months later, when the desk was already installed, the contractor submitted a variation for AED 42,000 covering the extra electrical routing and the modified stone panel. The administrator refused it — there was no SI, no written record, and no evidence that the client's verbal request had been agreed with the necessary commercial process. The dispute took six months to resolve and cost more in fees than the variation itself. The habit the contractor adopted afterwards: no work off a verbal instruction, ever. If the administrator would not issue an SI, the work did not start.

Why Written Instructions Matter

Construction contracts are unusual in the volume of decisions that get made informally in the middle of the works. Every one of those decisions has cost, time, quality and safety consequences. The SI process converts an informal conversation into a document that both parties have to stand behind. It protects the contractor from being told, six months later, that a piece of work was unauthorised. It protects the administrator from being told, six months later, that a verbal instruction is worth ten times what it seemed at the time.

SI vs RFI vs Variation

• RFI — the contractor asks a question, the administrator answers. If the answer requires new work, the answer is often issued as an SI.
• SI — the administrator instructs the contractor to act.
• Variation / Change Order — the commercial evaluation of the cost and time impact of an SI that has changed the scope.

The three form a chain. Skipping any link — usually the SI — creates the disputes that consume the project's last six months.

Practical Lessons Learned

• The contractor's rule: no SI, no work. Every crew has been told once too often to "just get on with it" and then not paid for the change.
• The administrator's rule: every SI acknowledges the commercial consequence up front, even if the answer is "no cost, no time." Silence on the commercial side is what causes the arguments.
• Verbal instructions on site do happen. The professional habit is to follow up with an email within 24 hours summarising what was agreed, and treat that email as an interim SI pending the formal one.
• Track SIs in a live register with status, associated RFI, associated variation, and closeout date. The register is the single source of truth for what has been instructed on the project.
• Never accept SIs from anyone outside the authorised signatory list. Client representatives who are not authorised to instruct create the worst disputes.

Expert Tips

• Number SIs sequentially across the project, not by discipline. A single sequence makes closeout tracking straightforward.
• Publish the authorised signatory list at kickoff and refresh it on every organisational change on either side.
• Attach the sketch or amended drawing to the SI itself, not to a follow-up email. The SI becomes self-contained and defensible.
• Distribute the SI to the same recipients as the RFI so the QS, the planner and the site team all see it simultaneously.
• Close SIs formally. An SI still marked "open" six months after the work was completed pollutes the register and makes real open items harder to see.

Common Mistakes

• Verbal instructions accepted without follow-up.
• SIs issued by people not on the authorised signatory list.
• Commercial silence — the SI is issued, the work is done, and neither party addresses the cost until much later.
• No register, so nobody knows the current SI count or status.
• Attaching amended drawings by email rather than to the SI, so the document is not self-contained.
• Confusing SIs and RFIs — the administrator answering an RFI in a way that clearly instructs new work, without recognising that an SI is now required.

Key Takeaways

• An SI is the contractual instrument that turns a decision into an enforceable action.
• No SI, no work — and no work, no dispute six months later.
• Every SI addresses the commercial consequence up front, even if the consequence is nil.
• Only authorised signatories issue SIs; the list is published and current.
• SIs live in a numbered register alongside RFIs and variations and are formally closed.

Related Concepts

Interlocks with RFI Management, Change Order Management, Change Control and Daily Site Diary. SI templates and register formats at PMMilestone.org.