Sum insured is when you choose the maximum amount of cover you want for your home. For example, if you think your home will cost $1,500,000 to rebuild from scratch, this is the sum insured you'd select. On the other hand, total replacement insurance covers the market value of rebuilding your home.
Sum insured is riskier (and usually cheaper) because there's a chance you won't value the home properly. For example, if your sum insured is $1,500,000 but your home ends up costing $1,800,000 to rebuild, you'll have to pay the $300,000 yourself. Find out more about total replacement cover in our full guide.