Full refurbishment: costs by depth of intervention

Figures published in 2026 run from about 600 to 2,500 euros per square metre of habitable area. That range becomes intelligible once ordered by actual strip-out depth.

Individual sources rarely state their strip-out depth. Anyone adopting a figure should therefore first establish which of these three rows it belongs to, and record that allocation in their own estimate.

One further quantity shifts the allocation: the energy target level. A refurbishment aiming at a high efficiency house standard sits systematically above one of the same physical scope without that target, because envelope, windows, airtightness and plant must be coordinated and evidenced.

It is not age itself that drives cost but what a given building era typically used. The year of construction is therefore an indicator and not a cause.

Buildings before 1970 carry the greatest uncertainty. Absent or ineffective damp-proofing, timber joist floors of unknown condition, outdated electrical installations without protective earth, and contamination in certain components are all to be expected. High orders of magnitude are quoted for stock of this era with hidden defects.

Buildings of the 1970s and 1980s are better documented structurally but carry the weakest thermal envelopes and frequently components predating today's restrictions on hazardous materials.

Buildings from the 1990s onwards generally need no full refurbishment in the narrow sense, but targeted individual measures to services and envelope.

For cost estimating, construction period is therefore not a cost factor but an indicator of how much investigation is needed. The older the building, the more effort shifts to before the cost estimate.

A widespread rule holds that a replacement new build becomes worthwhile once refurbishment costs exceed 70 to 80 per cent of new build costs. As orientation it is usable, but in its usual application it is wrong, because the two figures compared cover different things.

The new build figures circulating for this comparison vary considerably, running between roughly 2,500 and 5,500 euros per square metre depending on source. Depending on which is inserted, the rule tips one way or the other without anything about the project having changed.

A sound comparison demands four corrections. They must be applied in that order.

1. The same reference area. Both sides in square metres of habitable area or both in gross floor area, not mixed.
2. The same cost scope. New build adds demolition, disposal, excavation and foundations, which refurbishment avoids. All belong on the new build side.
3. The time factor. A new build after demolition takes longer, generating financing costs and, in let property, loss of rent.
4. The non-monetary quantities. Retention of layout, location and massing on one side; warranty, current standard and an optimised layout on the other.

Only after these corrections is the percentage rule applicable. Before them it compares two figures sharing nothing but their unit. The system of cost scopes is set out in the article on the cost scope of a benchmark.

In new build, a flat contingency signals unfinished design. In existing buildings it is professionally required, because part of the scope demonstrably cannot be known at the time of estimating.

The difference lies in how it is handled. A hidden contingency built into inflated unit rates is worthless: it cannot be explained to the client and dissolves under tender comparison. A stated contingency, by contrast, is a line of its own with a reason and an amount.

Grading it by state of knowledge makes sense. For trades whose extent is settled once elements have been opened up, a small contingency suffices. For trades whose extent only becomes visible during the works, particularly structure, service routing and contamination, it must be set considerably higher.

The second advantage of a stated contingency is that it can be tracked. It falls as the project proceeds and openings are made, and that reduction is a robust progress indicator which a hidden contingency cannot provide.

Published figures describe the construction work. Several items are routinely not included in them.

• ancillary construction costs, meaning design, structural engineering, energy consultancy and site supervision
• disposal of strip-out material and where applicable of hazardous substances
• alternative accommodation during the works, almost always necessary for deep interventions
• storage and removals
• external works, frequently also affected after a full refurbishment

The third point is the most often overlooked. A full refurbishment renders the building uninhabitable for months. At a typical duration of around four to fourteen months, a cost block arises that appears in no construction calculation and that acts twice over in owner-occupied property, since rent and financing run in parallel.

As long as the massing of the building is unchanged, a full refurbishment generally requires no building consent in Germany. Consent becomes necessary as soon as the building is extended or has storeys added, or where the use changes. Listed buildings require the approval of the heritage authority in every case.

That distinction acts directly on cost. A consent-free scheme saves procedural time and fees, but remains subject to the substantive requirements of building and energy law. Freedom from consent does not mean freedom from requirements, and that confusion is among the more expensive ones in existing buildings.

For schemes that change the use, the picture shifts fundamentally. It is covered in the article on conversion and change of use.

In existing buildings, additional costs arise less often from low unit rates than from sequencing problems. Where services must be exposed, walls chased and then made good again, the same area is paid for twice.

Such sequences are the norm in older stock. They cannot be eliminated entirely, but a condition survey before detailed design reduces them considerably. Effort spent on opening up elements, tracing services and assessing the structure before design begins is the single most effective measure for cost certainty in existing buildings.

• Renovation costs per m² by depth of intervention
• Conversion and change of use: cost risks in existing buildings
• What a construction cost benchmark includes
• Ancillary construction costs under KG 700
• Construction costs per m² in Germany