Homeowner field guide
Setting an Addition Budget Around Scope
The budget should account for more than the new room’s visible finishes.
List the full work
Include design, review, permits, foundations, structural changes, utilities, exterior envelope, interior finishes, and restoration of disturbed areas.
Name the unknowns
Existing foundation condition, buried utilities, and system capacity may require investigation. Ask which assumptions are provisional.
Keep choices comparable
When options are priced, compare the same size, finish level, and affected existing rooms. A smaller addition can still involve complex connections.
Bring this into the planning conversation
Ask for a budget organized by work category, including design and municipal review, site work, foundations, structure, envelope, systems, finishes, and repair to the existing house. Mark unknowns and allowances separately. This reveals whether a promising number omits the work needed to make the old and new parts function together. Include restoration of landscaping and paths disturbed by construction access.