What pays for itself and what does not

Four components, and the third is the most uncertain. It concerns the path of energy prices.

Component	Note
The size of the investment after support	the starting point
The annual reduction in energy cost	the income side
The expected development of energy prices	it determines the result more than the size of the investment
The life of the investment	longer for insulation than for equipment

The third must not be presented as a single figure, which is why a payback calculation should be given as a range together with its assumptions. Scenarios show how sensitive the calculation is.

Four things are real but absent from the calculation, and the fourth changes the result most. It concerns the value of the property.

The improvement in the indoor climate, which is not measured in money but is often the main thing for residents. The extension of the building's life, which defers future costs. Property value, which depends on the area. And the avoidance of unavoidable works, that is what would have had to be done anyway.

If the roof has to be replaced in five years anyway, its cost is not an additional cost of the renovation. The right comparison is therefore not renovation versus doing nothing but renovation versus carrying out the unavoidable works one at a time without support.

One principle is set out in the national plan. It is cost optimality.

According to professional sources, the renovation of buildings proceeds from cost optimality, and according to the same source full renovation is preferred for residential buildings while minimum standards apply to non-residential ones. The principle ties cost to result.

Cost optimality means the minimum total cost over the life cycle rather than the lowest investment, which explains why the support conditions favour the full route, as covered by the article on the two routes. The logic of the state and that of an individual association are therefore not identical, but they point the same way.

Three situations, and the first is common in apartment buildings. It concerns unavoidable works.

Situation	Why
The building is in poor technical condition	the choice is not whether, but when and how
The indoor climate is poor	health is not a concept in a payback calculation
Not acting creates a growing cost	for instance moisture damage worsening

The first is not always acknowledged, because acknowledging it means expenditure. In these three cases the right question is not "does it pay" but "what does not acting cost".

Three rules, and the third is the most persuasive. Present a range rather than a single figure. Show the assumptions, above all the energy price forecast. And present two scenarios side by side, the renovation and carrying out the unavoidable works separately, since that shows the real choice rather than an artificial one.

A figure whose assumptions are not shown is not an argument but a promise, and it is remembered when it is not met. The assumptions have to be set out.

A payback calculation has four components, of which the development of energy prices is the most uncertain and determines the result more than the size of the investment. The calculation leaves out the indoor climate, the building's life, property value and the avoidance of unavoidable works, the last of which changes the result most, since the right comparison is renovation versus carrying out the unavoidable works one at a time without support. The national plan proceeds from cost optimality, meaning the minimum total cost over the life cycle, and prefers full renovation for residential buildings.

Four rules: compare renovation with carrying out the unavoidable works, not with doing nothing. Present payback as a range with its assumptions. Do not use payback as the only argument where the building's condition does not allow it. Name the indoor climate and the building's life separately, since they do not fit into the calculation.