When only one home is being built, the same kind of efficient scheduling is rarely possible. Labor normally accounts for the largest share of home-building costs. When new houses are under construction, there is usually no landscaping, allowing easy access to the site. Materials can be driven directly up to any side of each structure as needed. When a house is being rebuilt among existing homes, there are trees, shrubs, lawns, flowerbeds, fences and other obstructions limiting access.
Materials often have to be off-loaded further away and hand carried to where they re needed.
This factor is compounded if the building site is on sloping ground. The impact on labor costs can be significant. Older homes and homes that have been extensively remodeled often have customized features or include materials not commonly found in homes being built today. These features and materials can be very expensive, if not impossible, to duplicate. Most older homes, and many newer homes, were built during times when building codes were less strict than they are today.