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When planning energy modernisation measures, reciprocal effects between building envelopes and system technology must be taken into account. The better the energy quality of the building envelope, the smaller the systems for heat supply may be dimensioned. Furthermore, the use of renewable energy is often economically more reasonable when the heat demand is lower. Before a modernisation is implemented, one should consider whether measures can be combined usefully or should be carried out in a particular order. For this purposes the following structural and legal preliminary examinations are necessary and useful:

  • Examination of the unchanged building components with regard to carrying capacity and damages (among others, moisture penetration),
  • Determination of the technical feasibility of, e.g., connection details and installation heights,
  • Estimation of the follow-up expenses of individual measures such as adjustment of the roof overhang for façade insulation,
  • Clarification of requirements for construction law, preservation orders, environ-mental protection, and nature conservation and
  • Analysis of possibilities to combine maintenance- or repair-measures and energetic modernisation.

Requirements of the EnEV are linked to many modernisations regarding the thermal building envelope. A catalogue of the relevant measures and the required values for these measures is provided in Annex 3 of the Energy Saving Ordinance. These re-quirements are formulated as maximum values of the heat transmission coefficient of the renovated parts of the surface. They are not compulsory when the partial surface that is subject to the measure does not exceed 10 % of the total surface of the fabric component in question for the specific building. Alternatively, it is also possible to prove that the building after the performed renovation does not exceed 140% of the requirements for a similar new building. This regards the level of requirements “EnEV 2009” (≈level 2014), since the tightening of requirements valid from 2016 for new constructions does not apply to the 140% rule.

For evaluating the cost effectiveness, the following parameters and conditions should be determined based on stock data, preliminary drafts, or concepts:

  • the energy saving potential under realistic assumptions,
  • the construction costs and, separately, the associated EnEV-related additional costs,
  • the expected lifetime of the measure and
  • the existing costs for inspection, maintenance, cleaning (and - if applicable - separately the EnEV-related additional costs).

From the perspective of the building owner or planner, an efficiency evaluation has a broader scope and can/should include the following aspects in addition to the EnEV-related additional costs:

  • expenses for repair, dismantling, and disposal (empirical and comparative values),
  • if applicable, funding opportunities and
  • (additional) planning expenses for energy-efficient concepts.

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