Retrofitting Norwegian residential buildings: an archetype-based dynamic stock model

2.1 ARCHETYPE-BASED RETROFIT MODELLING

Material and space heating intensities of residential buildings (single-family house—SFH, multi-family house—MFH, and apartment blocks—AB) in the 2023 stock were retrieved from Amini et al. (2025b). Based on these baseline archetypes, three retrofitting alternatives were modelled to reach the minimum requirements for energy efficiency, defined by the Norwegian Building Technical Regulations from 2017 (TEK-17) (Direktoratet for byggkvalitet 2017; Standards Norge n.d.):

• Win: replacing windows and external doors with TEK-17-compliant options as well as improving the airtightness of the openings.

• Ren: corresponding to Win plus replacing and increasing insulation for external walls and roof matching TEK-17 criteria as well as improving the airtightness of the whole building envelope.

• Vent: corresponding to Ren plus a balanced ventilation system with 80% heat recovery.

These retrofitted archetypes were built upon the work of Amini et al. (2025a) with the following interventions: while in Amini et al. the original cladding of walls and roofs were assumed to be reused in the Ren strategy, here the material demand for renewal of all external cladding was estimated, i.e. new timber cladding for external walls of wood-based archetypes, new clay tiles for slanted roofs and a new bitumen finish for flat roofs were estimated based on archetype’s net external walls and roof area. Amounts of mineral wool (thermal insulation), bitumen-impregnated cardboard (wind barrier) and polyethylene sheet (vapour barrier) were taken directly from Amini et al.’s supplemental information. In the Vent strategy, Amini et al. only accounted for the materials used in the heat-recovery ventilation units, excluding the distribution ducts; here, the amount of galvanised steel used in circular ducts based on each archetype’s plan dimensions, number of floors, number of rooms, kitchen, toilets and bathrooms, and their required airflow based on TEK-17 was estimated (see Section S1 in the supplemental data online).

To account for the various climate and weather conditions over Norway and their effect on buildings’ space heating demand, six municipalities with the largest residential floor area were identified to use their weather data in energy simulations: Oslo, Bergen, Trondheim, Stavanger, Ringsaker and Tromsø. The weather data in these six municipalities were then used as a proxy for estimating space heating demand in other Norwegian municipalities depending on their geographical location and climate zone (for details, see Section S2.2 in the supplemental data online). Future weather patterns may impact the energy performance of baseline and retrofitted buildings. Therefore, future weather files based on the Intergovernmental Panel on Climate Change’s (IPCC) A1B scenario were developed by using the Meteonorm software (Bernstein et al. 2008; Meteonorm n.d.). The space heating intensities of existing and retrofitted buildings for 2050 were calculated and used to estimate changing intensities in the future.

2.2 DYNAMIC STOCK MODELLING FOR FUTURE MATERIAL, ENERGY AND GHG EMISSIONS

The future residential building stock was modelled using ODYM-RECC-Norway,¹ a minimal version of the Open Dynamic Material Systems Model for Resource Efficiency and Climate Change Mitigation (ODYM-RECC) originally developed by Pauliuk et al. (2021a). In ODYM-RECC, in-use stocks and flows of products (here, residential buildings of different typologies and cohorts) are driven by population and floor area per capita (FApC). Material production, final energy consumption and their associated GHG emissions are then estimated using material, energy and GHG intensities. The framework can also be used to estimate the long-term effects of different retrofitting scenarios on energy consumption and emissions. As an open-source tool, there are variants and branches of ODYM-RECC (Napiontek et al. 2025; Pauliuk et al. 2021a, 2021b, 2024; Rousseau et al. 2025; Vélez-Henao & Pauliuk 2025) as well as a streamlined version established by Akin et al. (2025) excluding the vehicle-related model, and the energy demands associated with demolition and waste treatment. ODYM-RECC-Norway, focusing on building retrofits in Norway, was derived from that streamlined version and introduced features specific to this research, such as modelling retrofit and the adoption of heat pumps (HPs).

The input parameters for ODYM-RECC-Norway model are distributed across numerous spreadsheets and cover each of the 357 Norwegian municipalities. These include demographic trends, FApC, electricity production mix, GHG emission factors for material and energy production, retrofit rates, and material and energy intensities of baseline building archetypes along with their retrofitted versions under different future climate files. Most of these inputs stem from archetype simulations (Amini et al. 2025a, 2025b) and external sources such as population projections (Statistisk Sentralbyrå 2023, 2024a), utility FApC (estimated based on dwellings’ statistics) (Statistisk Sentralbyrå 2024b) or electricity production mix (Ember 2023). Some of the parameters are municipality specific, such as future population, while others are valid for the entire country, such as electricity mix.

At its core, the dynamic stock model builds on building lifespan—an average of 125 years (Bohne et al. 2006) whose variation is partially captured using a normal distribution, with a standard deviation of 37.5 years—FApC and share of building types in new construction (both assumed to stay constant in line with 2023 values) and retrofit rate. The lifetime of retrofitted buildings was extended using the Dynamic Lifetime Model (Krych et al. 2025) (see Section S3 in the supplemental data online) assuming that retrofit extends buildings’ lifetime. The GHG emissions of materials were estimated according to a business-as-usual scenario (Pauliuk 2023), i.e. changes in background systems follow the Shared Socioeconomic Pathway 2 (SSP2) scenario (O’Neill et al. 2014; Riahi et al. 2017). For more details about the input parameters, see Section S1 online; and in the Zenodo repository containing the database.²

2.3 SCENARIOS

Retrofitting consists of measures addressing passive and active components. Measures targeting passive components focus on enhancing building’s thermal resistance by improving insulation, airtightness and glazing. These measures reduce the rate of heat transfer, thereby lowering heating demands (Konstantinou & Hoces 2018). On the other hand, retrofitting active components involves upgrading HVAC systems to optimise energy usage. Examples include installing HPs, energy-efficient appliances and developing district heating-compatible systems (Lund et al. 2014; Tettey et al. 2017). In Norway, electricity is the dominant space heating fuel, with electric heaters and boilers covering 65% of space heating demand in SFH/MFH and 75% in AB, and HPs covering 22.5% in SFH/MFH and 5% in AB (Sartori et al. 2022). Wood stoves cover the rest in SFH/MFH (12.5%) and district heating in AB (20%).

The scenarios analysis encompassed 10 scenarios (Table 2): a baseline scenario without any retrofit (NoRen), scenarios focusing on passive building components only (Win, Ren) and combined with active strategies (Vent) using the retrofitted archetypes described in Section 2.1, a scenario with a widespread adoption of HPs, and scenarios combining Win, Rent and Vent with HPs’ adoption (Win_HP, Ren_HP, Vent_HP). In all the scenarios involving retrofit, 1.89% of the buildings built before 2010 are retrofitted each year (for details about this retrofit rate, see Section S1 in the supplemental data online). In scenarios involving retrofit of the windows (Win, Win_HP), the lifetime of retrofitted buildings is extended by 25 years; and in scenarios involving retrofit of the buildings’ envelope (Ren, Vent, Ren_HP, Vent_HP), the lifetime of retrofitted buildings is extended by 50 years (Egerlid et al. 2025) (for the modelling, see Section S3 online).

In the NoRen and retrofit scenarios, the population projection follows the main projection alternative of the scenarios by Statistics Norway (Statistisk Sentralbyrå 2023, 2024a). The electricity production mix is as of 2023, i.e. 88.5% hydropower, 9.7% wind power, 0.3% other renewables and 1.5% fossil (Ember 2023). A sensitivity analysis was performed to test a high-projection scenario for population (high growth of population as per Statistisk Sentralbyrå 2024a) and the Nordic production mix, i.e. the weighted average of Sweden, Denmark, Finland and Norway for 2023 (37% hydropower, 27% wind power, 18% nuclear, 13% other renewables and 5% fossil) (Ember 2023), as an alternative electricity mix.

3.1 RETROFITTED ARCHETYPES

Replacing windows and doors with TEK-17-compliant components (Win strategy) requires 1.8–10.9 kg/m² glass in new windows and 0.14–0.60 kg/m² aluminium in the external door’s layers (Figure 2a). The variation in glass intensity among archetypes is attributed to the window-to-wall ratio (WWR), which is up to 25% in pre-1955 archetypes, decreasing to 6% on some facades in more recent cohorts (Amini et al. 2025a). The space heating intensity in the Win strategy decreases by 11–65% (Figure 2b), relative to both the WWR and the original thermal conductivity and infiltration value of the openings. These results demonstrate larger potential for space intensity reductions in older archetypes and limited savings by Win in post-2000 ones.

Figure 2

To achieve the Ren strategy, 40–70 kg of material per m² are needed in SFH and MFH, with thermal insulation making at least 40% of materials needed (Figure 2a). Gypsum, used as finish material and a component of the wind barrier layer in walls and ceilings, together with clay tiles, used as roofing finish, are the next predominant materials required in this retrofit strategy. It is worth highlighting that material demand intensity for retrofitting ABs is almost half of SFHs and MFHs, with 20–30 kg/m², due to lower external walls-to-floor area ratios. In ABs, the share of thermal insulation materials is lower, as glass in AB1955 and bitumen in post-1970 ABs take up significant shares of the material intensity due to their much higher densities. In AB1955 and AB5670, as the external walls have a masonry finish, cement is used as the finish over the added insulation layer to provide an architecturally compatible material for the building. The Ren strategy lowers the space heating demand down to a range of 20–40 kWh/m² (Figure 2b). A comparison of the archetypes suggests that Ren is more effective on older archetypes than post-2000 ones. This can be attributed to the architectural features of the more recent archetypes, with taller ceilings and less compact design.

Finally, the material demand intensity in the Vent strategy follows the same trend as in the Ren strategy with less than 1 kg/m² added to the material needed for retrofit due to ventilation unit and its distribution ducts (Figure 2a). Although the added mass is insignificant compared with other materials, they are emission intensive, e.g. steel, copper, aluminium and plastics. This demonstrates the importance of accounting for their share in mass and net emission saving calculations. The space heating demand under the Vent strategy increases slightly in pre-1980 SFHs and MFHs and pre-1970 ABs compared with the Ren strategy, due to the energy consumed by the added ventilation unit to heat the ventilated fresh air and recirculated air to reach the set-point temperature, providing better indoor air quality (Figure 2b). The space heating demand, however, decreases in the more recent cohorts, with the lowest saving in ABs and highest savings in SFHs, followed by MFHs. The savings are attributed to the new ventilation system’s higher heat recovery rates and efficiency factors compared with the existing systems in place (Amini et al. 2025a).

The comparison of the space heating demand using 2023 and 2050 weather conditions shows up to 5 kWh/m² lower demand in base case archetypes, shrinking to less than 2 kWh/m² in the retrofitted archetypes. As the simulated future weather files under the SSP2 scenario show, the average air temperature is expected to increase in the next decades, resulting in slightly lower space heating demand across all archetypes. It is relevant to point out that the space heating demand presented in Figure 2b was estimated under the Oslo conditions in 2023 and 2050, but the trends are relatively similar for the three retrofit strategies when simulated under the other five cities’ weather files (see the supplemental data within the underlying data for Figure 2b).

3.2 FUTURE TRAJECTORIES BY 2050 IN THE BASELINE SCENARIO

The Norwegian residential buildings stock is expected to grow from 329 million m² in 2023 to 363 million m² in 2050 (Figure 3a). Given the assumption of new building constructions following the same typologies’ share as in 2023, the share of AB slightly increases in the stock, from 16% in 2023 to 21%, while the share of SFH slightly decreases, from 65% to 59%. The construction of new residential buildings and the demolition of older less energy-efficient ones will result in a decrease of the yearly final energy consumption for space heating by around 10% (Figure 3b). However, the use of materials for new construction, mostly aggregates (64%), wood (17%), cement (13%) and steel (3%), will increase towards 2050 (Figure 3c). Overall, a reduction of annual GHG emissions by 6% is observed (Figure 3d).

Figure 3

3.3 ENERGY AND MATERIAL USE WITH RETROFIT

Without any retrofit, new residential buildings built from 2024 form 20% of the stock in 2050 (Figure 4a). In the case of only energy systems being retrofitted, the share of new buildings is unchanged (20%), and retrofitted buildings, heated with HPs, represent 36% of the stock (Figure 4b). When retrofit of the envelope is enforced, resulting in lifetime extension of the retrofitted buildings, by 2050, the stock consists of 18% new construction and 37% retrofit (Figure 4c).

Figure 4

Across all scenarios of retrofit and HP adoption, the cumulative final energy consumption (2023–50) is composed of about 70% of electricity, 25% of wood and 3% of district heating (Figure 5a). Electricity production is responsible for nearly 60% of the GHG emissions, wood for over 40% and district heating for 0.2% (Figure 5c). The cumulative final energy consumption is reduced by 6% with the adoption of HPs, 7% with changing windows (Win), and 14% with a full retrofit without or with balanced ventilation (Ren and Vent) compared with the baseline scenario (Figure 5a). If HPs are combined with the retrofit of windows or the envelope, final energy consumption is reduced by another 4–5%. About 0.6 Mt of glass and 2.6 Mt of insulation material are needed to achieve such reductions in energy consumption (Figure 5b). Moreover, gypsum (0.94 Mt), clay tiles (0.9 Mt), wood (0.67 Mt), and other materials (such as bitumen and cement) are also needed for reconstruction of the facade and roof after installation of the new insulation. In addition, 0.08 Mt of stainless steel for HPs are estimated in scenarios comprising their adoption. Insulation material makes more than 50% of the GHG emissions when envelopes are retrofitted, and glass, steel and aluminium are also large contributors to emissions (Figure 5d).

Figure 5

The annual final energy consumption and associated GHG emissions following a full retrofit and HP adoption (Ren_HP and Vent_HP) are reduced by around 8 TWh in 2050 compared with 2023 (Figure 6a) i.e. from 20 TWh in 2023 to 12 TWh in 2050. This results in saving cumulatively up to 101 TWh by 2050, i.e. on average 3.6 TWh/year. Despite the large use of materials in the early years of the analysis, the material use in these two scenarios becomes lower than the one in the baseline and HP scenarios around in the second half of 2030s (Figure 6b). Indeed, the Ren, Vent, Ren_HP and Vent_HP scenarios initially need larger material quantities for retrofit but thanks to the lifetime extension, lower material quantities are needed for new construction. Even if the materials needed are GHG intensive (Figure 6d), the two scenarios Ren_HP and Vent_HP quickly become the best scenarios due the significant reduction in GHG emissions from energy consumption (Figure 6c, e). Cumulatively, up to 13 MtCO₂-eq, i.e. on average 0.5 MtCO₂-eq/year are saved.

Figure 6

At the municipal and per capita level, the reduction in final energy consumption for space heating is not homogenous (Figure 7) as the residential building composition (building types and construction year) differs among municipalities. The lowest energy consumption for space heating per capita is in the region of Oslo and its neighbouring municipalities. Bergen and Trondheim, two populous municipalities, are also in the top 10 of lowest energy consumption for space heating per capita. In 2023, the median energy consumption was around 4600 kWh per capita, while it ranges between 2600 (Vent_HP) and 3900 (baseline) kWh per capita in 2050. With retrofit, the energy consumption per capita becomes more uniform across municipalities toward 2050 with a standard deviation that reduced from 930 kWh per capita in 2023 to 510 (vent_HP)–840 (baseline) kWh per capita.

Figure 7

To achieve the final energy consumption reductions in the individual municipalities presented in Figure 7, the 6 Mt of cumulative material needed for retrofit by 2050 (Figure 5b) would need to be distributed to Oslo (0.42 Mt, i.e. 7%), Bergen (0.26 Mt, i.e. 4.4%), Trondheim (0.18 Mt, i.e. 3%) and the rest of the country.

3.4 SENSITIVITY ANALYSIS

The results of the sensitivity analysis (Table 3) show that with a high growth of population, the residential building stock is projected to surpass 400 million m² in 2050 (+11.6% compared with 2050’s stock following a medium growth of population). However, the cumulative final energy consumption does not increase as much (a 3% increase) as new construction is energy efficient. Regarding the cumulative GHG emissions due to energy consumption for space heating in residential buildings, the choice of electricity mix can significantly affect the results. With a Nordic electricity mix, the cumulative emissions are estimated to be 28% higher than with the Norwegian electricity mix.

4.1 RETROFITTING RESIDENTIAL BUILDINGS AND ENERGY SAVINGS

Residential buildings of all typologies and construction cohorts present a significant potential in reducing space heating demand after retrofit. For most archetypes, changing the windows and doors has the potential to cut around 50% of space heating demand, and for some buildings, a larger reduction is possible. It is important to note that these reductions are only possible if airtightness improvements happen as presumed in the archetype modelling of Amini et al. (2025a). Many building retrofit studies assess window retrofits primarily through thermal conductivity (U-value), solar-gain metrics and visible transmittance, with a fixed or simple infiltration value (Moghaddam et al. 2023). In Amini et al. (2025a), window and door changes are interconnected with air infiltration reduction by improving airtightness. Buildings’ energy demand is highly sensitive to its airtightness, a parameter that is strongly dependent on how the retrofit work is executed. This implies that even if changing windows and doors appears as a simple strategy, it requires professional execution, where guidelines on sealing joints are carefully followed. However, for single-family houses (SFHs) and multi-family houses (MFHs) built after the year 2000, this strategy does not appear to be sufficient to reduce space heating demand. Hence, retrofitting the envelope and improving the ventilation efficiency would be necessary.

In older buildings, where only natural ventilation is in place (pre-1980 SFH/MFHs and pre-1970 apartment buildings—ABs), installing a balanced ventilation system with an 80% heat recovery rate would slightly increase space heating demand, while increasing thermal comfort and improving indoor air quality.

Although retrofit happens at the individual building level, the dynamic stock model in this study aimed to provide an understanding of the potential of various retrofit strategies in saving energy for space heating and reducing greenhouse gas (GHG) emissions at the national scale. Energy savings and GHG emissions reduction are observed in baseline scenarios which are in line with previous research: Pauliuk et al. (2013) observed a reduction in annual energy demand and carbon footprint; Sandberg et al. (2017) estimated that the final energy is reduced by 23% between 2016 and 2050.

The full retrofit and heat pump (HP) adoption scenario in this study has the potential to reduce annual final energy consumption by up to 40% between 2023 and 2050. This reduction is comparable with the 46% reduction in energy demand estimated in the scenario of retrofit with an increasing share of HPs and alternative heating by Pauliuk et al. (2013), and with the 35% reduction in final energy estimated in the scenario of combining advanced and frequent retrofit by Sandberg et al. (2017).

The direct comparison with Pauliuk et al.’s (2013) and Sandberg et al.’s (2017) results reveals the consistency of this study with previous national studies. While assessments at the national scale provide a valuable overview of future material use and energy consumption, generating results for all municipalities individually is an opportunity to inform local decision-makers. Knowing when and how much material is expected to enter or leave the built stock at this finer scale can directly inform local strategies in mitigating GHG emissions. Spatially explicit results may help local decision-makers anticipate construction activity and the amounts of materials required for retrofit. Such information could be used to support retrofit activities through financial incentives or energy auditing programmes.

4.2 ECONOMIC CHALLENGES AND ENERGY POLICY DEBATES

Jowkar et al. (2022) identify economic constraints as the main barrier to building retrofits for homeowners in Trondheim. They find that stronger financial incentives are critical enablers for wider adoption. The government-owned enterprise responsible for energy, Enova, provides advice and financial support for energy upgrades of residential buildings (Enova 2025b). Since autumn 2025, the process requires an application, and once it is approved, the financial support will be provided after the retrofit work is completed and documented through invoices. While this new scheme guarantees financial support for those whose application has been approved, these are based on actual receipts, so the scheme requires homeowners to prepay the entire amount. Moreover, the financial support covers 25% of the costs up to defined maximum amounts.

Even if economic constraints are highlighted as a barrier to energy retrofit, newspapers described Norwegians as champions in home renovation (Mårdalen 2019), with large amounts of money spent on kitchen and bathroom renovations. While such measures might provide immediate functional and aesthetic improvements, passive retrofit strategies’ effects, such as in Win and Ren, are not immediately visible, unless improving the building’s energy rating, providing a documented proof of energy efficiency. The energy rating system is defined by an energy label (A–G) and a heating rating (a colour scale from green to red) (Direktoratet for byggkvalitet 2018). The energy label indicates the range of delivered energy consumption per heated floor area, including heating, ventilation, lighting and equipment’s energy use (Enova 2025c). Therefore, active systems’ energy efficiency rates and the building’s floor area affect the energy label. There is an approximate 10–15 kWh/m² heated floor area gap between the A and B labels, while the individual gaps between the B and C, C and D, D and E, and E and F labels are larger (40–60 kWh/m² heated floor area), suggesting a need for more drastic changes to upgrade the labels of less energy-efficient or older homes and a disregard for the indoor air quality improvements by retrofit. If one considers the standard energy use of lighting systems, equipment and hot water in residential units at around 60 kWh/m² heated floor area (Standards Norge 2023), the space heating energy consumption needs to be less than about 25 kWh/m² heated floor area to achieve the energy label A and less than 35 kWh/m² heated floor area to achieve the energy label B. Among the simulated retrofit strategies, the Ren strategy has the highest potential for reducing space heating by more than 40 kWh/m² heated floor area in pre-2000 archetypes and perhaps give a better energy label to the dwelling. The heating rating, on the other hand, determines the share of space heating and hot water energy that is sourced from non-renewable resources, e.g. gas and electricity. Therefore, no change of rating would be achieved by passive retrofit strategies, and only a change of active heating systems to HPs, district heating systems or biofuels could move the rating on the scale from red towards green.

Electricity prices (in purchasing power standard) in Norway are low compared with other European countries (Eurostat 2025). However, there are large regional disparities and temporal oscillations in electricity prices within the country (Nord Pool 2025), becoming a major political issue in the past years. As a result, the Norwegian government implemented a set of electricity subsidies (Regjeringen 2025). Electricity prices are market dependent, and therefore as soon as the demand rises and outstrips supply, electricity prices shoot up as do the electricity subsidies paid by the government. If instead these funds were used for retrofitting, electricity demand would decrease, alleviating the market and prices and allowing other sectors to use electricity as an alternative energy source. A reduction of nearly 5 TWh in final electricity consumption in 2050 in the Vent_HP scenario compared with final electricity consumption in 2050 in the baseline scenario was estimated. This corresponds to a reduction of 0.7 MtCO₂-eq in GHG emissions in 2050. If the saved electricity were used to produce green ammonia, one of the intended uses of electricity according to Norwegian policy, GHG emissions in 2050 could be reduced by over 2 MtCO₂-eq. If it were to replace fossil process heat in industry, savings could be over 7 MtCO₂-eq (Mayer et al. 2023).

4.3 CONTRIBUTIONS, LIMITATIONS AND FUTURE RESEARCH

Although the two previous sections were focused on discussing the results from a Norwegian context, this study contributes to the literature in a more general way. It is another example of how an open-source software such as Open Dynamic Material Systems Model for Resource Efficiency and Climate Change Mitigation (ODYM-RECC), or here in this study its streamlined version, can be adapted to various geographical scope and research questions. For example, the extended service life of the retrofitted buildings was modelled. The parameters and code were also adapted to include space heating demand under future climate data. Knowledge about buildings from a local perspective is needed to understand how buildings are built and how they consume energy. Physics-based building archetypes enable a greater understanding of energy consumption after retrofit.

Improvements in passive and active systems alone are not sufficient to reliably reduce final energy consumption. Comfort and socio-economic factors must also be accounted for as they are the primary driver of energy consumption (Perez-Bezos et al. 2023; Stazi et al. 2017). Final energy consumption in older buildings, despite their lower technical efficiency (as described by the energy label), may in some cases be similar to the final energy consumption in newer buildings with higher energy efficiency (Mathiesen Gjerde et al. 2025). Such effects known as the rebound and prebound effects were not considered in this study. Sandberg et al. (2017) estimated that accounting for these effects can significantly affect the findings: in the scenario combining advanced and frequent retrofit, the final energy consumption would decrease by only 20% instead of 35%.

The emissions attributed with the energy consumption of the retrofit activities themselves, e.g. equipment used for new facade installation, were neglected. For a complete estimation of the net emissions savings by retrofit measures, as described in the B4 (replacement) stage of the construction life cycle assessment method, the energy consumption by the equipment used for execution of replacement activities should be accounted for (Standards Norge 2023).

Buildings have a long lifetime, and retrofit strategies have a key role to play to reduce energy consumption because increasing demolition for rebuilding increases material use and their GHG emissions (Pauliuk et al. 2013). Based on the findings, changing windows or installing HPs could lead to reducing space heating demand without significant increases in GHG emissions, and this could be rather easily implemented without causing major disturbances in the buildings due to wall or roof retrofitting. Enova also advises the installation of systems to automatically control heating in older buildings (Enova 2025a).

In addition to retrofit, supply- and demand-side-mitigation measures are needed (Creutzig et al. 2018; Hertwich et al. 2019). In this study, GHG intensity factors of materials account for changes in energy mixes used in their production, but besides aluminium, GHG intensity factors are not estimated to decrease significantly as they are for conventional materials. Decarbonisation of material production, especially of materials with high GHG intensities such as insulation material, glass and steel, could contribute to decreasing GHG emissions from material use for retrofit. Additionally, for lower GHG emissions in the entire residential building stock, the size of dwellings and number of inhabitants matter (Pauliuk et al. 2013, 2021b). Smaller dwellings would require less material not only at construction but also during retrofit. If combined with more people per dwelling, i.e. less floor area per capita, it would contribute to lowering the national final energy consumption. These strategies are low hanging fruits for future research.