We have two insurers. With one of them our policy is structured so we pay one amount, under a sort of umbrella policy, for the liability coverage for the group of our properties that they insure. The total value of those properties is just under 3 million and the cost of the 2 million dollar liability coverage is around $1,000 per year. I think this is a less costly method to purchase liability coverage.
Our coverage for single family homes runs from about $500 to $750 per year, dependant on value. The average, including the liability coverage is $705 per year. The most expensive is a triplex in Edmonton worth about $550,000 where the premium is $900 per year, including the liability portion.
It doesn`t seem logical to me that liability would differ with the age of a property.
Hope that helps,