What type of insurance do you need for your small business to subcontract on commercial jobs?

To start with you would definitely need liability. And if you have employees workmans comp.

You don't state what type of business you're in and I don't know if there would be any specialized insurance involved.

Do your research and start calling ins. brokers.

A 2:

Sounds lke you might need Public liability insurance (covers the cost of compensation from anybody injured). You still need to check with your insurance broker before making any decision on the type of insurance you require

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subcontractors normally are required to carry and be able to verify their workers comp and state unemployment insurance. There is sometimes a performance bond required for the amount of the work. If vehicles are involved at least basic liability coverage which covers business use of the vehicles. You will most likely be required to sign an agreement indemnifying the owner or general contractor from liability for you workmanship, procedures etc. As above a public liability policy is a good idea to protect yourself.