Hi Tigger. The structural survey is normally asked for by the Mortgage Company if something has been found on the Mortgage survey. Maybe he noticed the damp smell under the stairs and reported that, and maybe because of that either the buyer personally, or the Lender, have asked for a more details survey to rule out rising damp or dry rot before a mortgage will be released on the property. A structural survey will take much longer and the surveyor will want to look into the loft space and check any flat roofs etc. It costs between £150 -£300 for a structural survey, so the buyers must still be keen. Hopefully nothing drastic will be found. Expect a revised offer though , to reflect how much work needs to be done, if any. If they do this, you must get yourself an independent estimate from a builder for the work, and not rely on what the buyers say it will cost .