How does JCT clause 4.20 work?

To do so, it must follow the route in clause 4.21. The clause numbers here are from SBC/Q 2016, the JCT Standard Building Contract With Quantities. There, the Contractor is your main contractor and the Employer is the client. Clause 4.20 covers progress already affected and progress likely to be affected. It is the money clause. The extension of time clauses deal with time, and the two run separately. Clause 4.21 sets out the route. First, the Contractor notifies the Architect/Contract Administrator and names the Relevant Matter. It must do this as soon as the actual or likely effect on regular progress is, or should reasonably be, apparent. Next, with the notice or as soon as reasonably practicable afterwards, it gives its initial assessment. That covers the loss and expense already incurred and likely to be incurred. It comes with the information reasonably needed for the amount to be ascertained. Ascertained is the contract's word for worked out and fixed. The Contractor then updates the assessment every month, until it has supplied all the information needed for the final figure. The Architect/Contract Administrator, or the Quantity Surveyor on its instruction, ascertains the amount within the periods the clause sets. It does this first for the initial assessment and then for each update. The amount ascertained is added to the Contract Sum and included in the next Interim Certificate. Direct loss and expense means the cost the Relevant Matter actually caused. Examples are the extra preliminaries of a longer job and disruption to labour and plant. It is built from records, not a percentage. Clause 5.10 keeps this money out of Variation valuations, so it is not paid twice. As a subcontractor, you do not claim under clause 4.20 itself. Your claim runs under the loss and expense clause of your subcontract. But your main contractor needs your notices and records in time to give its own clause 4.21 notice and assessments. So the same discipline applies to you, one tier down. Four mistakes come up again and again. The notice goes in when the cost is counted, not when the effect became apparent. The initial assessment is a round sum with nothing behind it. The monthly updates stop. And the ascertainment is left to be argued at the final account. The clause wants each update ascertained as it comes, while the records are fresh.