Requirements for new Residential Buildings
Besides the general requirements for new buildings, for residential buildings the following requirements apply:
- limitation of the yearly primary energy demand by a maximum value determined individually ("overall energy performance")
- limitation of the specific transmission heat loss per square meter of building shell ("requirement on thermal insulation")
- limitation of either solar irradiation indicators or over-temperature degree hours according to DIN 4108-2 ("summer heat protection")
For all three requirements, the way to proof as well as the boundary conditions are fixed via reference to certain technical regulations in order to ensure that the requirements are clear without ambiguity.
Reference Building Approach
The requirements pay respect to the individual building task. The size of the building, its shape and orientation (often determined by the building site) as well as the relative share of the shell components may limit the possibility to reduce the primary energy demand and the transmission heat loss. That’s why the maximum values in Germany are determined using the reference building approach.
Concerning its overall geometry, its orientation and its use pattern the reference building is identical to the real building. The reference building’s energetic features of the shell (outer walls, roof, windows, doors, ground plate, thermal bridges, tightness) as well as the features of the building services (heating-, domestic hot water- and AC-/ventilation systems), however, are pre-determined for the purpose of calculating the maximum values.
For proof of compliance, the same calculation method and identical boundary conditions have to be applied on both versions of the building (reference- and real building). Modern software-solutions calculate the reference building simultaneously; in case that the planer changes e. g. the geometry of the real building, the reference building will be adapted automatically.
For residential buildings, two alternative calculation methods are allowed for proof of compliance:
- DIN V 18599: 2011-12 or
- DIN V 4198-6: 2003-06 in connection with DIN V 4701-10: 2003-08 (including amendment A1: 2012-07)
The calculation of the transmission heat loss is an intermediate step in both procedures.
According to the current state of legislation (in force since 1st January 2016), the determination of reference building for the determination of the maximum primary energy demand includes an additional reduction factor (0,75), by which the result of calculation using the reference features (basically in force since 2009) has to be reduced for new buildings.
In current state of legislation, the heat transmission loss of the reference building is the maximum value for the real building. In addition it is required that the former maximum values – given by a table – may not be exceeded (which is possible for small detached buildings with higher share of windows).
Irrespective of the above mentioned calculation methods, the proof of sufficient summer heat protection is due to be done according to DIN 4108-2: 2013-02. The maximum values are also part of this standard. In addition, the standard sets up some conditions that allow skipping the calculation. For residential buildings this is the case if
- the surface of windows in relation to floor space does not exceed 35 % for the critical room (room with maximum solar irradiation)
- all windows facing from east via south to west (if applicable, including glazed conservatories adjacent to the building) are equipped with solar shading devices with a reduction factor for solar shading FC ≤ 0,30.
Model Building Approach ("EnEV-easy")
The model building approach (abridged "EnEV easy" with respect to its origin from a research project initiated by the regional government of Baden-Württemberg) is based on § 3 section 5 EnEV 2013. By this provision the responsible federal ministries are enabled to issue an official bulletin with determined variants of building designs accompanied by limitations for their applications. These published designs should be selected in a way that ensures compliance with the energy performance requirements without any calculation.
With the model building approach a method could be developed, which ensures compliance for a new residential building by simply looking up in tables the relevant features for construction as well as the indicators for the energy certificate. The method is applicable for most of the currently typical residential buildings.
The user first only has to check
- whether the building is within the allowed size range and has a standard ceiling height,
- whether ground plan and floor sequence result in a sufficiently compact form of the building and
- whether the percentage of windows and other areas with higher heat transfer is sufficiently limited.
If the building is heated by one of the listed variants of technical building systems and has no active cooling, the necessary maximum U-values of the various components for each variant of technical building systems can be found in the applicable table. The same applies to the indicators to be shown in the energy certificate.
Thus, the method is not only suitable as "quick approach" but also as a "first approach" in order to later optimise the design using detailed calculation. Since the values of the model building approach are kept on the so called "save side", the application of the reference building approach with its broad possibilities to optimise the design provides significant advantages in relation to the model building approach.