Unexpected problems usually occur during or after demolition. They are usually problems that could not be seen during pre-construction inspections because they were inside walls or in other places that were inaccessible at the time. These can include outdated or faulty electrical wiring, outdated or damaged pipes, or construction deficiencies that should be corrected before work continues. For example, the structure of the house might not have been intended to support two rooms and a bathroom in the attic area. The structure might need reinforcement before construction can continue.