The contractor you appoint should have some level of new build insurance cover, however they may only have cover for Public Liability. This will only provide cover if they cause damage to your property or neighbouring property because of the contract works. It will not provide cover for the actual works. Their insurance is not likely to provide cover for any tools or materials you have purchased either.Also, if you are using a number of different contractors, it would be hard to prove who was at fault in the event of a claim in order to claim off their Public Liability insurance.