If you have purchased the property with a mortgage your lender will usually have a surveyor carry out a valuation, and this should indicate a rebuilding sum insured. If you do not have a mortgage valuation you can seek guidance from the Royal Institution of Chartered Surveyors by visiting www.bcis.co.uk, however the only way to obtain an accurate rebuilding valuation is to enlist the services of a qualified surveyor. This may cost a little more now but could save you money if you overestimate your sum insured or save you a considerable sum if you under insure.