Budgeting a renovation

How to budget a renovation

Most renovation budgets are not wrong because the prices were wrong. They are wrong because something was left out, or because the quantities were worked out once and never again. This is the method, and the places it usually fails.

The method, in five steps

1. 1Measure the rooms, once. Every quantity in the job descends from floor area, wall area and perimeter. Measure them properly at the start and the rest is arithmetic. Guess them and every number after inherits the guess.
2. 2List by room, not by material. A budget has to survive being cut, and budgets are cut by room — the bathroom waits a year, the kitchen goes ahead. A list organised by material cannot answer what dropping the bathroom saves.
3. 3Put waste in the quantity, not in a note. Buy-quantity and cover-quantity are different numbers, and the gap depends on the pattern and the room. Decide it per line, at the point you work the line out.
4. 4Separate what belongs to the job from what belongs to a room. Skip hire, scaffolding, building control and surveys belong to the project. Spread across rooms they corrupt every room total; left out they corrupt the project total.
5. 5Carry contingency as a percentage, and track actual against estimate. 10% for cosmetic work on a newer house, 15–20% once walls come open. Then fill in what things actually cost as the invoices arrive — a budget nobody updates is a record of what you believed in week one.

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