Why do I need to get certifcates of insurance from my subs?

Your workers compensation insurance policy and your general liability insurance policy are rated based on payroll.  This means that any uninsured subcontractors that you use will be included in your total payroll.  If you use uninsured subs, then you should withold from them the amount of additional insurance that you will have to pay on their behalf because they are uninsured.  If they have general liability or workers comp insurance, then you want can avoid having to include what you pay them in your payroll numbers if you obtain a certificate of insurance from them.  Read more about this here.