Higher property taxes. Major additions or updates, particularly in spaces such as kitchens and baths, can increase your home's assessed value, and that can enlarge your tax bill. Assessors typically get copies of building permit applications, so they'll know about your project and may determine that it warrants upgrading your home's value. Hidden horrors. If demolition reveals a colony of creepy crawlies lurking beneath your drywall, you'll have to call in the pest control folks to evict them before work can proceed. Insects and vermin are just one unpleasant surprise you might discover — you never truly know what's going on behind the walls until a tear-out. Prepare for the possibility of mold, faulty wiring or plumbing, asbestos and other pricey pitfalls.