2.II.i. Progress and current status of existing buildings (regulation overall performance) – OVERVIEW

The OIB Guideline 6 includes requirements for heating, cooling and final energy demand for existing buildings undergoing major renovations.

Residential buildings

Tables 9 and 10 show the minimum requirements for the energy efficiency of residential buildings, either as a combination of the requirements of space heating demand, heating energy demand and final energy demand (Table 9), or, alternatively, as a combination of space heating demand and final energy efficiency factor (Table 10).

Table 9. Maximum value requirements for the energy performance of major renovations of existing residential buildings by heating energy demand.

Table 10. Maximum value requirements for the energy performance of major renovations of existing residential buildings by total energy efficiency factor.

Non-residential buildings

Respectively, Tables 11 and 12 show the minimum requirements for the energy efficiency of non-residential buildings in the case of major renovations, either as the combination of space heating demand, heating and cooling energy demand and final energy demand (Table 11), or, as the combination of space heating and cooling demand and final energy efficiency factor (Table 12):

Ref: Reference space heating demand for reference climate RC: Reference climate NRB: Non-residential building fGEE: Total energy efficiency factor lc: Building shape factor

Table 11. Maximum value requirements for the energy performance of major renovations of existing non-residential buildings by heating energy demand.

Table 12. Maximum value requirements for the energy performance of major renovations of existing non-residential buildings by total energy efficiency factor.

The national plan (February 2018) also defines minimum requirements for residential and non‐residential buildings undergoing major renovations valid from 1 January 2021. Deviations to these requirements may be undertaken if necessary measures are not feasible⁴.

All types of building units (residential, commercial and public buildings) undergoing renovations are required to obtain a building permit and have to comply with the same U-value requirement level as a new building unit. They also need to comply with a minimum requirement of ventilation rate. In addition, a building undergoing renovation of more than 75% of its surface is subject to the requirements of primary energy consumption (PEC) (considered as new units⁷).

Since 2006, the U-value requirements have been strengthened systematically. A number of new requirements were introduced in 2015: minimal requirements for technical building systems, maximal U-values for existing, insulated structures and a maximum E90 for deep renovations. A 'deep renovation' is defined as a renovation where more than 75% of the surfaces in contact with the outdoor environment are insulated and all technical building systems are replaced. The calculation method of the E-level is the same as for new buildings, but values to calculate the transmission of existing building components are also added. The set of requirements and related cost-optimal levels were thoroughly evaluated in 2015. Based on the Long-Term Renovation Strategy and the cost optimal level, the required E-level is strengthened in 2020 to E70 and will evolve to E60 (the long-term goal for the building stock) in the near future.

The performance of existing residential buildings is assessed by the building certification process. According to the database gathering all the certificates (approximately 600,000 by June 2020), the average energy performance of the Walloon residential units in 2019 corresponds to the EPC energy class F, i.e., a theoretical consumption of 459 kWh/m².year (Figure 3).

Figure 3. The distribution of Walloon residential buildings by energy performance (EPC database); housing (left) and apartments (right).

The majority of houses show a poor energy performance: 37% at level G, 17% at level F and 17% at level E (Figure 3). The Walloon housing stock is old; almost 25% of the houses were built before 1921 and about 80% date from before 1991. These old buildings consume the most energy (Figure 4).

Figure 4. Repartitioning of EPC energy classes by age of building (by end 2019).
1^st graph: existing residential buildings units. 2^nd graph: existing + new residential buildings units.

In addition, the existing housing stock has a low rate of renovation; every year, applications for planning permission for refurbishments are submitted for just 1% of the houses.

The total residential energy consumption in 2013 is only 5% higher than its 1990 level, although the housing stock has grown by 16%, and the annual degree-days have increased by 24% during that period. Figure 5 shows the evolution of this consumption.

Figure 5. Evolution of the residential sector consumption by energy vector (“Bilans wallons” 2013).

The Energy Efficiency Act, the Law on Spatial Planning and the relevant executive orders based on these laws set out the legislative and technical measures that must, by law, be applied to existing buildings. The “Energy Performance Certificate of New Building” is valid for 6 years from the date of commissioning of the building (see section 2.I.i.). The owners of all these buildings are required to obtain an “Energy Performance Certificate of Existing Building” within a three-year period. This period begins three years after the date of commissioning. The energy performance of existing buildings is established by an energy audit, which is completed with the issuing of an EPC of the building. The “Energy Performance Certificate of Existing Building” shall be updated following any change in the energy performance of the building, for example after a change of use, deep renovation, or major renovation.

Minimum energy performance requirements for existing buildings have been gradually tightened since the EPBD was first implemented. At present, these requirements are set with the goal of achieving cost-optimal levels and have been defined for ten categories of buildings, depending on their assigned use. Existing buildings meet the requirement for energy efficiency when the value of their integrated energy efficiency indicator ("specific annual expenditure of primary energy" in kWh/m²) corresponds, at least, to energy efficiency class “B”, for buildings commissioned after 1 February 2010, or to class “C”, for buildings commissioned before 1 February 2010.

The National Plan for Nearly Zero-Energy Buildings, adopted in December 2015, provides the national definition and the technical parameters of NZEB and the national targets for transforming refurbished state-owned and municipality-owned public buildings into NZEB by 2020.

For all types of buildings, in the case where only certain building envelope elements of a heated part of the building covering an area over 25% are renovated, the U-value of the entire building element shall fulfil the prescribed requirements.

In the case where reconstruction covers an area over 75% of the surface of the heated building envelope, requirements are set as U-values for the building elements, Q"_H,nd, E"_prim (including energy for heating, cooling, ventilation, hot water, and lighting for non-residential buildings).

Existing buildings undergoing major reconstruction meet the requirements for the use of RES if at least 10% of the energy needs are covered by RES, which may include remote or block heating, which is fully or partially based on energy from RES, unless the achievement of these conditions is not economically, technically and functionally feasible. The application of highly efficient alternative systems should also be considered and taken into account in so far as they are technically, economically and functionally feasible.

The minimum energy performance requirements include requirements for existing buildings. The first minimum energy performance requirements issued in 2007 mandated that buildings over 1,000 m² that undergo major renovation shall be insulated at the same level as a new building². From January 2010, the minimum category B on the EPC was added to requirements for buildings over 1,000 m² that undergo major renovation³. In December 2013, maximum U-values have been reduced by 15% and have also been implemented for building elements that are replaced or retrofitted⁴. In order to reach cost-optimal levels, as of 1 January 2017 all buildings that undergo major renovation should reach at least energy class B as far as it is technically and financially feasible⁵. Additionally, all building elements that are replaced or retrofitted have to reach the same U-value requirements as new buildings.

The new minimum energy efficiency requirements that will take effect in 2020, will require all residential buildings undergoing major renovation to reach energy class A, and all other buildings at least energy class B+.

Existing buildings have to meet strict energy performance requirements in case of major or other renovations. In this case, the builder, owner or association of unit owners must fulfil the requirements given by the applicable legislation, Decree No. 264/2020 Coll., which sets the minimum parameters and energy performance indicators. The EPC must demonstrate that the cost-optimal levels are met for the changed building envelope and/or technical building systems, and that the assessment of the alternative energy delivery system as well as recommendations for improving the energy performance have been provided. The EPC must be part of the building permit application.

Table 5: Number of non-residential existing buildings of the public sector.

As an alternative to the component requirements, two voluntary renovation classes have been introduced:

• A residential building may be classified as 'Renovation Class 2' when the total demand for energy supply for heating, ventilation, cooling and domestic hot water per square meter of heated floor area does not exceed 70.0 kWh/m² per year plus 2,200 kWh per year divided by the heated floor area.
• A residential building may be classified as 'Renovation Class 1' when the total demand for energy supply for heating, ventilation, cooling and domestic hot water per square meter of heated floor area does not exceed 52.5 kWh/m² per year plus 1,650 kWh per year divided by the heated floor area.

Requirements for non-residential buildings are presented below. Verification must be on the basis of 'Energy demands of buildings (SBi Direction 213 Bygningers energibehov)'² where the energy demand for the whole building must be calculated.

To comply with the renovation classes, the requirement for supplied energy must be improved by at least 30 kWh/m² per year. To obtain 'Renovation Class 1', the requirements for the indoor climate for new buildings must be observed as well.

Renovation classes for both residential and non-residential buildings are defined as:

The minimum energy performance requirements are expressed as a primary energy performance indicator calculated for the building according to its standardised use and applied to the building as a whole. The maximum primary energy values are listed in Table 2, see column ‘Renovation of existing building (class C)’.

Estonia has not set minimum requirements for U-values. The building has to meet the minimum energy performance requirements as a whole.

Minimum energy performance requirements have also been developed for existing buildings undergoing renovation and/or retrofitting that is subject to a building permit, for changing the use of a building, or repairing its technical systems.

The approach to improving energy efficiency is chosen in the planning phase of the renovation or retrofitting project, and it dictates the calculation methods as well as minimum energy requirements to be fulfilled. The three approach options are depicted in Figure 2.

Figure 2: Three approaches to improving energy efficiency in existing buildings.

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There are two thermal regulations for existing buildings. The first one, called ‘RT par élément’ (Regulation by Building Component), was published in late 2007 and the second one, called ‘RT globale’ (Global Thermal Regulation), in April 2008. Figure 1 shows how to determine the necessary regulation, depending on the renovation type (major or minor). Both regulations were reviewed in 2016 and the new requirements were set to come into force in 2018, followed by supplementary requirements in 2023 for envelope components.

The Global Thermal Regulation is based on the overall consumption with minimum requirements for each component of the building (envelope and technical systems). Energy performance is assessed using a complex hourly methodology, called TH-CE ex⁶, based on the new buildings’ methodology. The TH-CE-ex methodology is currently under review, the main purpose being to make it consistent with the Th-BCE methodology for new buildings.

Figure 1. Thermal Regulations for existing buildings.

Lately, the ELAN law (which stands for ‘Housing, spatial planning and digital evolution’) also introduced a new article in the Housing and Construction Code making it mandatory for tertiary buildings to reduce their final energy consumption by at least 40% until 2030, 50% until 2040 and 60% until 2050 compared to 2010. This regulation is called ‘Eco-Energy Tertiaire’. Published in July 2019, the decree determines all the application modalities, such as:

• scope;
• objectives of energy consumption reduction calculation method;
• modalities in case of activity change;
• modalities for the establishment of an online platform displaying the energy consumption data for every building;
• possible sanctions.

The objective of energy consumption reduction can be reached by two methods. First, the building can reach the relative reduction included in the law (-40% by 2030). Second, objectives in terms of an absolute value are defined for each type of activity. This means that for each tertiary building type, an energy consumption threshold will be defined by an upcoming order. The government works with professionals to define the thresholds that are to be achieved by 2030, 2040 and 2050. Those thresholds will vary with different indicators, e.g., temperature level, economic activity level, presence or absence of certain types of activities.

Therefore, this regulation gives a long-term vision of what can be expected of any tertiary building in the coming decades in terms of energy performance. It is not a classical regulation with sanctions and control. It also helps owners and tenants understand what is expected from them in this energy transition, allowing them to compare their building against other buildings used for similar activities and providing them with a rating based on the building’s performance. The regulation is thus intended to lead them into action.

Germany does not have a database describing the energy efficiency features of the building stock as a whole. For residential buildings – mainly for apartment buildings – the consumption and the development of the normalised average are known from several studies performed with data derived from individual heating-cost billing. The current average consumption of existing buildings was reduced from 230 kWh/(m².year) in the 1990s to 155 kWh/(m².year). Details about the German stock of residential buildings can be found in a study from 2016¹⁸. A total of 16,982 datasets of residential buildings give details of their current condition and implemented refurbishment measures: e.g., 50.4% of the external walls of these buildings had already been equipped with thermal insulation. The reduction of average consumption is not only due to refurbishment, but is also partly a result of rising awareness and actions resulting from mandatory individual heat billing and increased energy prices. In a current project called 'ENOB:dataNWG' a consortium is establishing a scientific database with actual data of the German non-residential building stock. This data has been collected with a specific method during the project.

Requirements to upgrade the building stock comprise conditional requirements in case of relevant refurbishments, mandatory update requirements to be met without any triggering measures (e.g., insulation of the highest floor slap) and requirements in case of extensions (Figure 2).

Heaters running on fossil fuels that have been installed before 1 October 1978 cannot be used any more. Heaters running on fossil fuels that have been installed before 1 January 1985 are not allowed since 2015. Effectively, heaters older than 30 years are not allowed anymore.

Furthermore, building owners have to make sure that the insulation of the highest floor slap or roof does not exceed a certain U-value. As of 31 December 2015, building owners need to ensure that these building parts do not exceed 0.24W/m²K. There are some exceptions to this rule. Particularly, these rules do not have to be followed if the building owner himself has lived in the building before 1 February 2002 or if the measures would not be economically feasible.

After a change of ownership, the deadline to fulfil the above obligations is two years.

Figure 2. Requirements in case of extensions of existing buildings.

Regarding existing buildings, the definition of major renovation is set in Law 4122/2013 which was then amended by Law 4409/2016, Article 49 (A’ 136). A renovation is considered as major when the total cost relating to the renovation of the building envelope or the technical building system is higher than 25% of the value of the building, excluding the value of the land upon which the building is situated.

A ministerial decision was issued in February 2019 (M.D YPEN/DEPEA/6949/72, GoG B’408/14.02.2019) defining the calculation methodology for characterising a renovation as major renovation.

Law 4342/2015 (A’ 143), which transposed the EED into national legislation, sets the obligation that, from 1 January 2014, 3% of the total floor area of heated and/or cooled buildings owned and occupied by the central government must be renovated each year so as to meet the minimum energy performance requirements. In 2017, the list of the central government buildings included 82 buildings with a total area of 309,712 m², but in recent years there have been re-evaluations of what is considered a central government building, leading to a decrease of the number of registered buildings. The refurbishment of these buildings is included in the national structural funds programmes. The YPEN had initiated an official communication with all central government organisations, in order to update the list with buildings with a floor area greater than 250 m², and to acquire all necessary information. By the end of 2019, this list included 21 buildings with a total area of approximately 200,000 m².

In July 2017, with Ministerial Decision (M.D. DEPEA/oik. 178581, GoG B’ 2367/12.07.2017) the KENAK was amended according to the results of the cost-optimal study. This cost-optimal study determined the minimum energy performance requirements for existing buildings or building units that undergo a major renovation, so that the maximum energy savings are achieved with the lower cost impact. The results of the cost-optimal study were also incorporated in the new technical guidelines of the TOTEE, approved in November 2017 with the issue of Ministerial Decree (M.D. DEPEA/oik.182365, GoG B’ 4003/17.11.2017).

The energy performance of an existing building that undergoes major renovation should be energy class B or better, unless it can be proved, through a technical report, that this is technically, functionally and economically not feasible.

Since 2006, requirements for major renovations are the same as for new buildings. Other renovations are regulated since 2013 and only requirements for individual elements (both envelope and technical building elements) have to be fulfilled. From 2016, major building extensions are considered as new buildings and all requirements are relevant, but in case of minor extensions only requirements for individual elements are defined. After 2018, cost-optimal requirements shall be obligatory for both renovations and extensions. NZEB requirements are not planned to become mandatory for retrofits.

In general, Building Regulations apply to the construction of new buildings and to extensions and material alterations to existing buildings. In addition, certain parts of the Regulations, including Part L, apply to existing buildings where a material change of use takes place. Guidance is given on insulation levels to be achieved by the plane fabric elements, thermal bridging and limitation of air permeability. The major renovation requirement was added to the Building Regulations for residential buildings in 2019. The cost-optimal works activated by major renovation for dwellings (residential) is shown in Table 9.

Table 9: Cost-optimal works activated by a major renovation for residential buildings, 2019.

For buildings undergoing major renovation, the 2017 Building Regulations for non-residential buildings require that the building is upgraded to the cost-optimal level of energy performance in so far as this is technically, functionally and economically feasible. Upgrading the heating, cooling, ventilation and lighting systems are normally considered to be cost-optimal and will typically be economically feasible when more than 25% of the surface area of a building is being upgraded. As an alternative, the whole building performance achieves the performance levels specified in Table 10 where technically, functionally and economically feasible this can be considered the cost-optimal level of performance.

Table 10: Whole building cost-optimal level of performance for major renovations for non-residential buildings, 2017.

The building sector is responsible for 45% of the final energy consumption and for 17.5% of CO₂ direct emissions in Italy, due to the use of fossil fuels in building premises and the related emission of any greenhouse gases into the atmosphere.

The Italian National Energy and Climate Plan (PNIEC) for residential building stock requires in 2030 a final energy saving of 0.332 Mtoe/year. To achieve such goal an annual rate of deep energy renovation of existing residential buildings is estimated to be nearly 0.85%.

Energy performance requirements for existing buildings are identical regardless of whether they concern residential or non-residential buildings. Minimum requirements are differentiated according to the extent of the renovation intervention:

• First-level major renovations are defined as 'refurbishment of at least 50% of the envelope and renovation of the heating and/or cooling plant of the entire building'. Requirements for new buildings apply to the whole building, limited to the considered energy service(s). For building extensions (new volume >15% of the existing volume or >500 m³), these requirements apply only to the new volume.
• Second-level major renovations are defined as 'refurbishment of at least 25% of the external surfaces of the building with or without renovation of the heating and/or cooling plant'. The U-value of the concerned surfaces is lower than the limit values (Table 6). The mean transmission heat transfer coefficient H’_T of refurbished building elements is lower that the limit value (Table 4, row 4). The mean efficiencies of renovated technical building systems are higher than the reference values.
• Minor renovations are defined as 'refurbishment of less than 25% of the external surfaces of the building and/or modification of the heating and/or cooling plants)'. The performance of single components and of technical building systems has to comply with mandatory limit values.

Table 6. U-value limits for second level major renovation and minor renovation.

As determined in Cabinet Regulation No. 907 of 28 September 2010, 'Regulations Regarding the Survey, Technical Servicing, Current Repairs and Minimal Requirements for Energy Efficiency of the Residential House'⁹, if the minimum energy performance requirements for existing residential buildings are exceeded, the building owner is obligated to undertake measures for the improvement of the energy performance. Regulation No. 907 states that the administrator of a multi-family residential building shall plan measures for improving the energy efficiency, including the renovation of the building, if the average thermal energy consumption (heating and domestic hot water) within the last three calendar years has exceeded 200 kWh/m² per year, or 150 kWh/m² per year if the heat is used for space heating only.

As described in the requirements for new residential buildings, the same requirements apply also to existing residential buildings (with the ability to partly take into account photovoltaic production: aligning real energy consumption in the EPC with the calculated theoretical energy need and introducing an interface in the EPC calculating tool for measured airtightness values).

Subsidy schemes for the refurbishment (PRIMe-House⁷) of existing residential buildings are frequently updated. These schemes have been reviewed and a top-up was introduced in mid-2020 as part of the Covid-19 recovery programme (Neistart Lëtzebuerg). The priority is on deep renovations reaching a very good energy class after refurbishment⁸. The extent of the grant is related to the degree of insulation, expressed by the level of performance (U-value) that is reached after insulation. More sustainable insulation materials are also promoted by a bonus system.

The updated minimum requirements, which came into force in 2016, address minor renovations, staged renovations and the replacement of building components. When a building component is replaced in an existing building, the requirements for the replaced component are the same as for a new building.

Regulations for buildings undergoing major renovations have also been updated, while requirements were introduced for the first time for minor renovations. Together with the requirements for individual building elements already in place, an overall energy performance requirement was introduced for buildings undergoing major renovations so that the maximum energy demand of the newly renovated building has been limited. A common methodology applies for the calculation of the overall energy balance required for minimum energy performance and the calculation of the energy performance indicator for EPCs. This simplifies calculation, as well as comparison between buildings and enforcement of the requirements. When assessors issue EPCs, they are required to report the date of any renovations carried out. This simplifies the enforcement of energy performance requirements for both minor and major renovations.

To support the assessment of opportunities for the renovation of existing buildings, cost-optimal studies were carried out on both new and renovated buildings and for both residential and non-residential buildings. The studies gave valuable insight into the most cost-effective methods to reap the benefits of investment in energy efficiency for existing buildings beyond the cost-optimal level, with a view to reaching NZEB levels. These studies are being used to further develop the provisions regulating buildings undergoing all levels of renovation.

The Dutch strategy for the renovation of buildings is based on the Energy Agreement signed in 2013, endorsed by around 40 parties, public and private, with strong ambitions, goals, intentions and agreements regarding energy saving in many areas in the Netherlands. By the end of 2016, the Cabinet presented the Energy Agenda. Herein, the requirements for the long term are set to 2050.

Building on the Energy Agreement and the Energy Agenda, on 28 June 2019 the Climate Agreement⁷ was signed by the Government and over 100 public and private parties, representing all relevant sectors. On 2 July 2019 the Climate Law⁸ was adopted by the Parliament. The Climate Law aims to reduce the emission of greenhouse gasses in all sectors by 49% in 2030 and by 95% in 2050. The Climate Agreement describes the measures that public and private parties agreed upon to reach the goals set in the Climate Law. The mentioned parties are responsible for the execution of the measures agreed upon under supervision of the relevant Ministers and sectoral implementation councils that have been established to this end. The sectors addressed are the built environment, mobility, industry, agriculture and electricity. On top of that, cross sectoral integration includes measures that apply to all five sectors, e.g., financing, biomass, Regional Energy Strategies⁹, public support, labour market, training of employees, etc.

As of 1 January 2023, all (existing) office buildings in the Netherlands should have an energy label C or better. If an office building does not meet this requirement, as of this date, it may no longer be rented out. This requirement is part of the Building Decree 2012. Some buildings are exempted from the ‘minimum-label-C-requirement’, e.g., buildings where the useful floor area of the offices is less than 50% of the total floor area of the building, offices < 100 m², monuments, temporary buildings and buildings for which the measures to reach label C have a payback time of more than 10 years.

Figure 3 shows that building-related energy consumption of households has decreased over the years until 2015, mainly due to the decreasing demand for natural gas. Since then, building-related consumption has more or less stabilised. Building-related electricity consumption remains virtually unchanged, but self-generation of electricity is increasing. The increase in non-building-related consumption is striking. Two causes of this are domestic ICT use and the increasing use of electrical appliances.

Figure 3. Energy consumption of households (source: RVO (2019) Monitor Energiebesparing Gebouwde Omgeving)

Legend: Aardgas = natural gas, Warmte = Heat,

Gebouwgebonden elektriciteit = building-related electricity, PV = PV,

Niet gebouwgebonden verbruik = energy consumption that is not building-related.

The share of homes with a favourable energy label (A or B) is highest among owner-occupied homes (36%); it is 29% for housing associations and 27% for private rental housing. Household energy consumption consists of approximately 70% natural gas. Government policy aimed at energy savings differs per type of owner.

Figure 4 shows that also building-related energy consumption in the services sector decreased until 2016 and more or less stabilised thereafter. Natural gas consumption for space heating has decreased. The decline has leveled off in recent years. The increase of the building stock could be a plausible explanation for this. Electricity consumption in the services sector has been almost constant over the years. Non-building-related consumption has slightly grown. This may have been caused by the increase in economic activities.

Figure 4. Energy consumption of the services sector (source: RVO (2019) Monitor Energiebesparing Gebouwde Omgeving)

Legend: Aardgas = natural gas, Warmte = Heat,

Gebouwgebonden elektriciteit = building-related electricity, PV = PV,

Niet gebouwgebonden verbruik = energy consumption that is not building-related.

A very large part of non-residential construction (82%) does not yet have a registered energy label. The number of properties with a favourable energy label (A+ or better, A or B) is highest among shops (69%). This is followed by healthcare buildings (64%), offices (52%) and finally education facilities (44%). About half of the energy consumption of services consists of natural gas. Government policy aimed at saving energy in non-residential construction differs per sector.

In general, the measures applicable to the renovation of existing buildings are the same as the requirements for new buildings if the measures are covered by the building regulations. The local authorities can give exemptions from the requirements under certain conditions. This applies to necessary remodelling, renovation and change of use, and in cases when, for example, the requirements will be unreasonable compared to the energy savings the measures will provide. For extensions, additions, underpinning and change of use, the requirements only apply to the new part of the building.

	Heating	5.9 kWh/m2 year
	Hot water	1.4 kWh/m2 year
	Ventilation	2.3 kWh/m2 year
	Cooling	1.3 kWh/m2 year
	Lighting	7.7 kWh/m2 year
	Others	0.8 kWh/m2 year
	Total	19.4 kWh/m2 year

Figure 2. ‘Powerhouse Kjørbo’ with the specified calculated energy need during operation.

The renovated office building 'Powerhouse Kjørbo' demonstrates the benefits of transforming a typical 1980s office building into a plus-energy building, as it will now generate more energy during its lifetime since renovation than the total energy used for materials production, construction and operation, and demolition. The project was completed in 2014 and was awarded the BREEAM-NOR 'Outstanding' classification, the highest classification in BREEAM-NOR (http://ngbc.no/breeam-nor/). The project also fulfils all requirements in the Norwegian passive house standard for non-residential buildings, NS 3701. The building produces energy using tilted solar panels on its flat roofs.

From research carried out as part of the research work 'Developing a methodology and conducting a survey on the scale of thermal modernisation activities of multi-apartment residential buildings in order to improve their energy consumption, and assessing the needs and planned activities in this direction' by the Central Statistical Office, in which respondents (owners or building managers) participated, owning or managing 189,289 buildings, it appears that:

• 60.7% of buildings do not require thermal modernisation: 29.7% due to thermal modernisation works carried out prior to 2016, and 31.0% having no thermal modernisation needs (e.g., construction already using energy-saving technologies);
• 39.3% of buildings require thermal modernisation to meet current energy performance standards: for 9.4% of those, thermal modernisation is implemented or planned between 2017 and 2020, and for 29.9% it is not planned.

For 2020, it is estimated that:

• for 14% of residential and public buildings, energy performance is in the 340-450 kWh/m² range;
• for 24% of residential and public buildings, energy performance is in the 230-390 kWh/m² range;
• for 31% of residential and public buildings, energy performance is in the 150-200 kWh/m² range;
• for 24% of residential and public buildings, energy performance is in the 90-150 kWh/m² range;
• for 4% of residential and public buildings, energy performance is in the 50-90 kWh/m² range;
• for 1% of residential and public buildings, energy performance is below 50 kWh/m².

Assuming that the obtained test results are also representative of the 64.6% of unexamined buildings, by extrapolating the above results to the entire stock of multi-family buildings in Poland, it can be assumed that approximately 210,000 multi-family buildings still require thermo-modernisation works.

Existing buildings are the main target for improving the energy performance of the building stock. They comprise the vast majority of buildings with the poorest performance, and therefore they are the ones with the largest potential for improvement.

For many decades, Portugal was lacking in terms of energy performance regulations. It was not until 1990 that the first energy efficiency regulation was introduced, but with limited impact on building performance. At that time, preventing building pathologies such as mould growth was one of the most important aspects. Nevertheless, requirements relating to insulation and double-glazing were also introduced.

With the transposition of the EPBD, attention was given to technical building systems and RES, but also on reinforcing the building envelope. When comparing the heating and cooling energy needs of existing residential buildings over the last 100 years, it is possible to discern a clear evolution, especially regarding heating needs (Figure 2).

Figure 2: Energy needs by construction period - Residential [kWh/m².year].

Currently, when a specific building component (building envelope or technical building system) is renovated, minimum requirements apply. In these cases, the energy efficiency is improved 'part-by-part', meaning that each new component of the building performs as well as it would in a new building. If a building is to undergo major renovations, then an overall assessment has to be made, and a minimum performance for the whole building has to be achieved; in these cases, it might be necessary to replace or improve certain additional elements in order to reach that minimum threshold.

Independently of being renovated, existing non-residential buildings that have an energy consumption of over 2.5 GWh, or at an energy label C or worse, are obliged to present and put into action an Energy Rationalisation Plan (PRE). This plan refers to a set of measures to be implemented in the building, in order to make it more efficient (resulting in label C or better). For buildings consuming more than 2.5 GWh of energy, this means reducing the final energy consumption by 2.5%, and for those consuming more than 5 GWh, it means reducing the final energy consumption by 5%. The measures and reduction in final energy consumption are to be completed during the time set for implementing the PRE, which is six (6) years. Further information about the PRE can be found in the relevant legislation⁸.

The building code states that all construction works must fulfil essential requirements. The gradual tightening of requirements for energy performance started in 2013. From 2016, major renovations had to meet the requirements for ultra-low energy construction, namely energy class A1, if technically, functionally and economically feasible. To meet the requirements for the global indicator for primary energy, a major renovation of technical building systems is also needed. Deep renovation also includes changes to the technical building systems, including changes connected to the heat and hot water generation and distribution. In case it is not possible to change the efficiency of the device (e.g., the owner of the renovated building is not able to influence the primary energy factor), the renovated building must meet energy class A for the total energy use of the building. The energy rating is focused on technical building systems for heating and domestic hot water preparation when residential buildings are renovated, as well as for cooling, ventilation and lighting when non-residential buildings are renovated. From 2021 (2019 for public buildings), major renovations have to meet the requirements for NZEB construction, namely energy class A0, if technically, functionally and economically feasible. To meet the requirements for the global indicator for primary energy, deep renovation is needed, including heat recovery and the use of RES. Measures implemented should be cost-effective where possible. The payback time of the measures proposed in the EPC should be less than 15 years.

Minimum requirements for existing buildings have been part of the Slovenian building codes since 2002. Renovation works for which a building permit is required must be done according to the building codes and following the requirements valid for new buildings.

PURES 2010 also transposed the EPBD as regards major renovations. Thus, the minimum requirements apply to all new buildings as well as major renovations, i.e., if at least 25% of the area of the building envelope is subject to renovation. In case of maintenance works on building envelopes, if a renovation (when a building permit is needed) is less than 25% of the thermal envelope area, or if buildings have a floor area smaller than 50 m², only the minimum requirements for the U-values of the envelope must be considered (i.e., only an additional insulation layer will be mandatory). For major renovations of the heating system, and in case of maintenance and replacement works, minimum requirements for the systems, subsystems and elements are at the same level as those required for new buildings.

The 2013 revision of the CTE was in line with the requirements established in the previous document of 2007, though effectively tightening them up, mainly because the requirements for deep renovations were set to be the same as for new buildings. This section will analyse the requirements for the partial renovation of buildings.

In general, it can be considered that the maximum and minimum limit values of the 2013 CTE for partial renovations of buildings are similar to the limit values that newly constructed buildings had in the CTE of 2007. These values have been obtained based on the cost-optimal calculations made by the Spanish administration.

This change implies a tightening of requirements, which is also reflected into the actual construction trends identified in recent years. The building sector has been able to incorporate new components into buildings, taking advantage of the progress that had to be made for the construction of new buildings, and applying it now to the renovation of existing buildings.

In 2017, the building stock (referred to as the housing and service sector in the national statistics), accounted for 39% of the final energy consumption in Sweden. Temperature-corrected statistics divided by the building surface in the period 1995-2017 show a trend where energy use decreased by 33% for single-family houses, 22% for residential apartment buildings and 21% for non-residential buildings.

In Sweden, different definitions of area are used; BOA refers to the residential floor area in single- and multi-family houses, not including cellars and A_temp refers to the temperature-controlled areas intended to be heated to more than 10 ºC, including cellars, in all type of buildings.

In Sweden, 43% of the dwellings (or 93% of residential buildings) are single-family houses, and in 2017 this part of the building stock used 32 TWh energy for heating and hot water. In 2016, the heated area amounted to 302 million m² (BOA, residential area in accordance with Swedish Standard SS 02 10 53, not the same as the area definition A_temp) and the average energy consumption for heating and hot water was 106 kWh/m² (excluding auxiliary energy). As of July 2019, 22% of single-family houses had an EPC (existing single-family houses are only required to be declared on sale, which explains the low proportion – new single-family houses are required to have an EPC but the proportion of new buildings is low). The declared single-family houses have an average energy performance expressed in a primary energy number of 144 kWh/m²_Atemp, year. Fifteen per cent (15%) of the declared single-family houses meet the requirement for NZEB, i.e., energy class A-C.

The residential apartment buildings in Sweden comprise 51% of the dwellings (but only 5% of the buildings), and in 2017 this part of the building stock used 27 TWh of energy for heating and hot water. In 2016, the heated area amounted to 196 million m² (BOA) and the average energy consumption for heating and hot water was 136 kWh/m² (excluding auxiliary energy). Sixty-three per cent (63%) of apartment buildings had an EPC as of July 2019 (sometimes property owners do not declare the EPC even though they are subject to EPC-regulation). The declared apartment buildings have an average energy performance expressed in a primary energy number of 149 kWh/m²_Atemp, year. Five per cent (5%) of the buildings meet the requirement for NZEB, i.e., energy class A-C.

The non-residential buildings that are included in the sector for residential and service (i.e., not industrial buildings) used 23 TWh of energy for heating and hot water in 2017. In 2016, the average energy consumption for heating and hot water was 124 kWh/m² (excluding auxiliary energy). In July 2019, there were 55,675 non-residential buildings with an EPC. The declared buildings have an average energy performance expressed in a primary energy number of 186 kWh/m²_Atemp, year. Fourteen per cent (14%) of the buildings meet the requirement for NZEB, i.e., energy class A-C.

Energy requirements apply to existing buildings only in the event of a change. A modification of a building shall not impair energy efficiency, unless there are exceptional reasons, or if the building nevertheless meets the energy requirements applicable to new buildings.

The main principle is that requirements are the same for both existing buildings undergoing change and new buildings. Accordingly, NZEB requirements also include existing buildings. Each time the regulation for new buildings is tightened, a tightening of the regulation for existing buildings follows.

Building Regulations are supported by AD L1B and AD L2B for existing residential and existing non‐residential buildings respectively⁷, which set out an elemental approach for existing buildings, and Domestic and Non‐domestic Building Services Compliance Guides^{25, 26} which include minimum energy efficiency standards for new and replacement of existing building systems.

Under certain circumstances (typically where the liveable building area is extended or where the capacity of building services is increased), additional energy efficiency measures (named “consequential improvements”) must be undertaken. These requirements only apply to large, existing residential and non‐residential buildings (greater than 1,000 m²) and can include improvements to the performance of the building fabric and/ or services, where technically, functionally or economically feasible.

The Government plans to consult further in due course, proposing improvements to the energy efficiency standards, set through Part L (conservation of fuel and power) and Part F (ventilation) of the Building Regulations, for building works to existing homes and non-domestic buildings.

Similarly to England, an elemental approach has been adopted for existing buildings. See England report for details. The 2014 revision of the Building Regulations introduced consequential energy performance improvements to all existing buildings that are extended.

Similarly to England, an elemental approach has been adopted for existing buildings. Alternatively, and at the discretion of the building designer, a comparative whole building performance model (as used for new buildings) may be used. These methods are set out in Section 3 of the relevant Technical Booklet^7 8. Under certain circumstances (i.e. buildings >1,000 m², where the habitable area is extended, or where fixed building services are installed for the first time, or their capacity is increased) additional energy efficiency measures (i.e. “consequential improvements”) must be undertaken.

Similarly to England, an elemental approach has been adopted for existing buildings. See England report for details. In non‐domestic buildings, under certain circumstances (e.g. where work to an existing building includes the provision of new fixed building services or extends the capacity of existing services), the existing services must be improved to meet the current performance recommendations in the Scottish Technical Handbooks^2 3. This approach is referred to as “consequential improvements”.