What the GEG is about
The Building Energy Act (Gebäudeenergiegesetz, GEG) merged the former Energy Saving Ordinance (EnEV), the Energy Saving Act and the Renewable Energies Heat Act in 2020. It governs how much energy a building may consume, what is required of insulation and building services, and what share of heat must come from renewable sources.
For containers this matters for a very practical reason: an uninsulated steel container meets none of these requirements even remotely. If your project falls under the GEG, insulation is no longer a comfort question but a condition of approval – and in a container it costs noticeable interior space. If it does not fall under the act, the verification is dropped, but the heating bills remain real.
The decisive threshold: does the container fall under it at all?
The GEG applies at its core to buildings that are heated or cooled using energy. From this follows the first, often overlooked consequence: an unheated storage container is simply not an energy law topic.
For the second case the act contains a list of exemptions. Buildings excluded from its scope include, among others, those used at a location for no longer than a certain period, operational buildings with low indoor temperatures anyway, greenhouses, air-supported halls and buildings with very small floor areas. The exemption most important for containers is the one for temporary structures and buildings with a limited standing time – classically the site container.
| Constellation | GEG relevance | Practical consequence |
|---|---|---|
| Unheated storage container | not affected | no energy verifications |
| Site container for the duration of works | as a rule exempt | manufacturer’s standard insulation suffices |
| Office container hired for a few months | usually exempt, case by case | document the standing time |
| Office container permanently at the same site | affected | full verification required |
| Residential container, permanent | affected | verification, heating rules, energy certificate |
| Modular building as a regular building | affected | treated like any other building |
The critical variable is therefore the standing time at one location. This is where the most frequent conflict arises in practice: a container is installed as a temporary solution and then stays year after year. That does not retroactively remove the exemption, but at the latest with a change of use or a new application the container will be treated as a permanent building. The link to building law is close; see Building application and change of use.
The exact thresholds and wording are in the statute and are interpreted by the responsible authority. Do not rely on a blanket rule of thumb – clarify the classification before you buy.
What is required when the GEG applies
For a new build – and a permanently installed residential or office container is treated as a new build in energy terms – the GEG works with two key figures: the annual primary energy demand and the specific transmission heat loss through the building envelope. Both are assessed relative to a reference building.
In practice this means: no single insulation value decides the matter, but the balance of the whole building. A weaker wall can be offset by better building services and vice versa. Even so, typical U-values are worth using as orientation, because they show what insulation thicknesses a container actually needs.
| Component | Rough U-value orientation, new build | Required thickness at the container (magnitude) |
|---|---|---|
| External wall | approx. 0.20–0.28 W/(m²·K) | approx. 120–160 mm at λ 0.035 |
| Roof | approx. 0.14–0.20 W/(m²·K) | approx. 160–220 mm |
| Floor over ground or outside air | approx. 0.25–0.35 W/(m²·K) | approx. 100–140 mm |
| Windows | approx. 0.90–1.30 W/(m²·K) | triple glazing usual |
| External door | approx. 1.30–1.80 W/(m²·K) | insulated door instead of container door |
These values are deliberately given as ranges; what counts is always the verification for your specific building.
The right-hand column explains why this hurts so much in a container. A 20-foot container is roughly 2.35 m wide inside. With 140 mm of internal insulation all round plus lining, roughly 2.0 m remains – a good sixth of the floor area gone. That is why external insulation is not only the better solution in building physics terms here, but also the space-saving one. The details are in Insulating a container and Thermal bridges in shipping containers.
A second point hits containers particularly hard: besides insulation, the GEG requires an airtight envelope and limits on thermal bridging. The steel frame of a container is a continuous thermal bridge around the entire structure – something that can only be resolved cleanly in the calculation with an external insulation layer.
Heating: the 65 per cent rule
Since the 2024 amendment, newly installed heating systems must be operated with a share of at least 65 per cent renewable energy. This applies directly to new buildings in new development areas; for existing buildings and new builds outside such areas, staggered deadlines apply that are tied to municipal heat planning.
For a permanently used residential container this means in practice:
| Heating system | GEG classification (orientation) | Note for containers |
|---|---|---|
| Air-to-water or air-to-air heat pump | meets the requirement | often a split or monobloc unit for small areas, well suited |
| Direct electric / infrared heating | permissible only under narrow conditions | conceivable with very good insulation and small area, verification needed |
| District heating | generally meets the requirement | connection rarely available at container sites |
| Pellet stove / biomass | meets the requirement | needs storage space and flue, involve the chimney sweep |
| Gas heating without renewable share | requirement not met | additionally problematic under fire safety law |
| Solar thermal | countable share | container roof area usually sufficient |
An often underestimated advantage: because the floor area is small, the heat load of a well-insulated container is low. That makes small heat pumps viable which would be too weak for a typical detached house, and keeps the investment manageable.
Energy certificate
An energy certificate is required when a building is newly erected, sold or let. Exempt are, among others, the buildings that fall outside the GEG anyway – the site container and the unheated storage container.
For a permanently used residential or office container, however, the duty applies as for any other building. For a new build it must be a demand-based certificate derived from the calculation; a consumption-based certificate only becomes an option later and under conditions. The cost of a demand certificate is roughly in the low hundreds of euros and largely falls out of the verification you need anyway.
Who prepares the verification and what it costs
The GEG verification is normally prepared by an energy consultant, a building physicist or the architectural practice doing the design. For a small project the effort is roughly in the low to mid four-figure range, depending on complexity, number of components and whether a thermal bridge calculation is needed.
In practice the route runs through these steps:
- Clarify classification: does the project fall under the GEG? Settle this with the building authority or energy consultant beforehand, not after the purchase.
- Fix the insulation concept: external or internal, material, thickness. This determines interior dimensions and cost.
- Choose the building services to suit the 65 per cent requirement.
- Have the verification calculated and submit it with the building application.
- Document the execution, particularly airtightness and insulation thicknesses. If these deviate, the verification no longer holds.
- Have the energy certificate issued.
Funding
Because energy requirements cost money, funding programmes exist. The relevant ones are mainly the federal funding for efficient buildings covering heating replacement and individual measures and – depending on the project – loan programmes for efficient new builds. It is almost always a condition that the application is filed before work begins and that a qualified expert is involved.
Whether a container is eligible depends on whether it counts as a building for the purposes of the programme. Permanent modular construction qualifies more readily than a mobile installed container. Clarify this in writing in advance with the funding body or an energy efficiency expert – retrospective applications are regularly rejected.
Important note
This article contains general information and constitutes neither legal, tax nor energy advice. The GEG is amended continuously; scope, exemptions, deadlines for the heating rules and funding conditions can change at short notice and are interpreted by the responsible authorities. All U-values, insulation thicknesses and costs are rough orientation values without guarantee. Binding statements come from the responsible building supervisory authority and a qualified energy consultant.
Conclusion
With containers, the scope of the GEG is the question that decides everything. Unheated storage containers and genuine site containers stay outside it; a permanently used residential or office container, by contrast, is treated in energy terms like a new build – with verification, airtightness, thermal bridge assessment, the 65 per cent heating rule and an energy certificate. Clarify that classification before you buy, plan the insulation on the outside, and you will avoid discovering that only two metres of width remain inside.
Further reading: Insulating a container, Thermal bridges in shipping containers and Container ventilation.