Why written requirements matter
You cannot check a certificate against a requirement that only lives in someone's head. A written schedule, attached to every subcontract, turns certificate review from a judgment call into a comparison. It also gives the sub's agent exactly what they need to issue a correct certificate the first time.
Standard schedule for most trades
Commercial general liability on an occurrence form: $1,000,000 each occurrence, $2,000,000 general aggregate applying per project, $2,000,000 products/completed operations aggregate. The certificate holder, its officers, employees and the project owner named as additional insured for ongoing and completed operations (ISO CG 20 10 and CG 20 37 or equivalent), on a primary and non-contributory basis, with waiver of subrogation.
Automobile liability covering any auto, or hired and non-owned autos if the sub owns no vehicles: $1,000,000 combined single limit, additional insured and waiver of subrogation.
Workers' compensation per statute with employer's liability of $1,000,000 each accident, each employee and policy limit, with waiver of subrogation. No owner or officer exclusions for anyone who will be on site.
Umbrella or excess liability of $1,000,000 following form over GL, auto and employer's liability.
High-hazard trades
For roofing, structural steel, demolition, excavation, crane and rigging, scaffolding, electrical and fire protection, raise the umbrella to $5,000,000 and require the same additional-insured and completed-operations endorsements on the umbrella. Ask for a copy of the endorsement pages, not just the certificate. Where the sub uses lifts or hoists, confirm no height or residential exclusions. For any trade generating fumes, dust or runoff, add contractors' pollution liability of $1,000,000 per occurrence.
Design-build and consultants
Engineers, architects, surveyors and anyone giving professional advice need professional liability of at least $1,000,000 per claim. Professional policies are claims-made, so require a retroactive date before the start of their work and tail coverage for two to three years after completion.
Certificate wording to require
Specify that the certificate must show the project name and address, the certificate holder's exact legal name and address, the additional-insured, waiver and primary/non-contributory language in the description of operations, and the endorsement form numbers. State that certificates are due before mobilisation and that renewal certificates are due before any policy expires, and that work may be stopped without a current certificate on file.
Keep it enforceable
Attach the schedule to the subcontract as an exhibit and reference it in the insurance clause. Then hold every certificate to it: a written requirement that is not checked is worse than none, because it creates a paper trail showing you knew what to look for and did not.
None of this is legal advice — have your broker and attorney review limits for your state, your owners' contracts and your risk appetite.