Here is a tip to help you lower your professional liability costs:
Let’s say you are an architect, and you routinely retain engineering consultants on projects. Let’s say that you pay out about 10% of your $1,000,000 annual fees to such firms.
When you complete your application for professional liability, you have to show these billings, and your firm will be rated including the $100,000 that you only passed through your books. The insurer will insist that if you retained an MEP, for instance, and the client makes a claim arising from the HVAC system design, your insurer will have to get involved, so there will at least be costs to your insurer for the attorney to defend you. Even if you use 100% insured engineering consultants you will still be charged for those fees.
If you feel comfortable doing so, and the owner is willing to, why not have the owner retain the engineers directly? It might not change your behavior on the project, but it should reduce your premiums.