Partial refurbishment or full renovation: cost comparison

The classic arithmetic trap: comparing the partial's ratio (on the intervened area) with the full renovation's (on total area) as if they measured the same thing. A 25 m² bathroom-and-kitchen refurbishment at €600/m² looks cheap against a 90 m² full renovation at €800/m²; the correct comparison adds up all the foreseeable partials over the horizon of use.

Repeated fixed costs. Every project pays its own site setup, protection, waste management, travel and start-up curve. Three €20,000 projects carry three times the fixed costs the full renovation carries once.

Overlapping items. Today's partial breaks what tomorrow's partial will redo: suspended ceilings opened twice, duplicated builder's assistance, new finishes damaged by the next project. In old housing, the typical overlap between successive partials sits between 10 and 20 % of each one's amount.

The services frontier. If the general electrical and plumbing systems are at the end of their life, any ambitious partial ends up touching them, and touching them partially means paying for them twice. The condition of the services is the technical criterion that most often decides the question: exhausted services push towards the full renovation regardless of preferences.

The framing rule that holds up well: when the set of foreseeable partials over five years reaches 60-70 % of the full renovation's cost, the full renovation wins, because at that level the overlaps and repeated fixed costs absorb the difference, and the full renovation additionally delivers a homogeneous result, with new services and no recurring works. Below that threshold, and with services in good condition, targeted partials are defensible.

There remains the non-economic factor that often decides in practice: the full renovation requires vacating the dwelling; partials allow living in it. That vacating cost (temporary rent, removals) belongs in the analysis and deserves a figure rather than being treated as an implicit veto.

The partial is cheaper project by project and can be more expensive over the full cycle: repeated fixed costs, 10-20 % overlaps and the services frontier tip the balance towards the full renovation when foreseeable partials exceed 60-70 % of its cost. The serious decision is made with both columns complete: all the partials over the horizon against the full renovation with its vacating cost included.