Study: Life cycle cost comparison of decarbonisation and renovation measures using the example of a detached house and a multi-family house

Project description

The two studies present a cost-effectiveness comparison of various renovation measures (building envelope and building services) for two fictitious yet typical buildings.

A multi-family house (approx. 1,000 m² of living space) built between 1981 and 1990 in its original condition with decentralised gas heating systems and a location-specific heating energy requirement (HEB) of 128 kWh/m²a was examined.

In addition, a single-family house built between 1961 and 1980 was defined as an example building. Assuming that individual renovation measures have already been implemented, the heating energy requirement (HEB) calculated under standard conditions for gas as an energy source for the St. Pölten location climate and a room temperature of 22°C is 259.3 kWh/m²a.

The methodological approach for the analysis of the buildings was carried out in three steps. First, the energy demand was determined in accordance with OIB RL6 (2023), followed by a calculation of the operating and investment costs and a 30-year life cycle cost assessment, taking into account residual values and reinvestments. The economic comparison was carried out with and without taking into account federal and state subsidies (one-off grants as of January 2026).

Several variants were compared, differing in the degree of thermal renovation and the type of heat supply. In terms of thermal renovation, the existing building was compared with a partial renovation and a comprehensive renovation. In terms of heat supply, the existing decentralised gas boiler systems were compared with district heating, brine-water heat pumps and air-water heat pumps, as well as pellet boilers for the detached house.

Results of the study on multi-family house

• The basic analysis without subsidies shows that comprehensive renovations incur high initial costs, but these are offset by reduced energy costs. Despite varying initial investments, almost all renovation options converge after 30 years within a narrow range between approximately €1.1 million and €1.2 million in cumulative present value.
• To test resilience, three sensitivity analyses were calculated, with a higher price increase for gas in the coming years, a 20% increase in investment costs and an increase in the calculation interest rate to 5%.
• The inclusion of subsidies significantly changes the economic ranking. The subsidy acts as an incentive system that brings forward the payback period by up to 10 years. The amount of subsidies for renovation varies greatly between the individual federal states, and there is also a clear difference between multi-family and single-family homes in terms of the proportion of the subsidy.
• The study shows that comprehensive renovations often only just achieve a payback period of 30 years. However, when considering the combination of technical efficiency (low energy costs), long-term value retention (high residual values) and subsidies for the measures (investment grants), energy-efficient modernisation, including decarbonisation, proves to be the more economically advantageous option compared to maintaining the status quo, and is also significantly more resilient to energy price fluctuations.

Results of the study on a detached house

• It is clear that, in all sensitivity analyses, the basic variant (no thermal renovation measures, gas boiler) performs worst over the period under consideration.
• In general, it should also be noted that those variants in which gas continues to be used for heating (existing, renovated and partially renovated) do not offer any financial advantage over 30 years. In addition, there is a continuing dependence on fossil fuels and the associated potential price fluctuations.
• Although comprehensive renovation measures involve significantly higher investment costs, they can be amortised in the same or a shorter period of time than those variants that are only partially renovated.
• Comprehensive refurbishments are associated with significantly lower energy requirements and are therefore less susceptible to fluctuating energy prices.
• Comprehensive refurbishments also reduce the costs of new heat supply, as this can be smaller in scale. This also has a reducing effect on reinvestments.
• Considering the sensitivities that assume higher price increases for electricity and pellets, the variants with a heat pump or a biomass boiler are still variants that do not lose ground over the period under consideration. On the one hand, this can be attributed to the low specific costs of pellets and the low electricity consumption of heat pumps (due to their high efficiency). The comprehensively renovated variants in particular show low susceptibility to these price increases.
• When considering the different subsidies, different approaches and funding priorities can be identified. The amounts of the subsidies (one-off grants) also vary greatly, leading to significant differences in the amortisation period between the federal states.