In short and in plain language
This article is for firms that offer houses and flats on their own website.
It explains which energy details belong on this page. An energy certificate shows how much energy a building uses.
A template with fixed fields can help. It lets a listing go live only when all fields are filled in.
When you move to a new site, details often get lost. The article shows what to watch for. It does not replace a check by a lawyer.
We build property templates with fixed fields. If you wish, we also move your current listings.
A property page looks like self-presentation: a few photos, location, floor area, asking price, a contact form underneath. Legally it is something else. As soon as a property advertisement is placed in commercial media ahead of a sale, a letting, a lease or a leasing arrangement, and an energy performance certificate exists at that moment, Section 87 of the German building energy act — the official text now carries it as Gebäudemodernisierungsgesetz, the building modernisation act — requires five fixed details in that advertisement. The statute does not list media. It attaches to the advertisement and to the person responsible for publishing it. Your own website is therefore not a special case but the ordinary case with house rules: whoever runs it also answers for what appears on it. In practice the gap still shows up on the company's own pages first and not in a portal. The portal has mandatory fields; the in-house property template often has a free-text box and the hope that somebody remembers. This article therefore treats the mandatory details not as a legal text to read up on but as a data model: which five fields belong in every property form, which sixth one joins them for commercial buildings, what a guard looks like that refuses to publish an incomplete record, and what regularly gets lost when an existing portfolio moves to a new site. It places the legal position in the context of website work and does not replace legal advice in an individual case — it makes sure that such advice finds complete fields to look at in the first place.
Key points at a glance
- Where an energy performance certificate exists, five details (Section 87(1) GModG) belong in every property advertisement: type of certificate, final energy value, main energy sources, plus year of construction and energy efficiency class for residential buildings.
- For a non-residential building the single figure becomes a pair: final energy for heat and for electricity must be stated separately (Section 87(2) GModG).
- Missing details are an administrative offence under number 21 of the catalogue, with a range of up to ten thousand euros (Section 108 GModG).
- An energy performance certificate is issued for a validity period of ten years (Section 79(3) GModG). The expiry date belongs in a date field in the property form, not in a note.
- The energy efficiency class is not free input: Annex 10 of the act sorts residential buildings into nine classes from A+ to H.
- Mandatory fields only work with a guard in front of them. A record without the details must not go online at all, rather than being corrected later.
When a property page becomes a property advertisement
The trigger sits in Section 87(1) and consists of two conditions that have to coincide. First, a property advertisement is placed in commercial media ahead of a sale, a letting, a lease or a leasing arrangement. Second, an energy performance certificate exists at that point in time. Where both apply, the person responsible for publication — seller, landlord, lessor, leasing provider or estate agent — has to ensure that the advertisement contains the five mandatory details. What is remarkable is what the provision does not say: it contains no list of permitted channels. The wording does not distinguish between a portal, a newspaper advertisement, a window display and the property page on your own site. Anyone showing a portfolio on a website for real estate is running a commercial medium in-house, responsibility included. The converse holds as well: where no certificate exists yet, the mandatory details do not apply. The duty to present the certificate at the viewing at the latest (Section 80(4) GModG) is untouched by that.
This allocation is where website operators regularly get it wrong. The duty attaches neither to the technical service provider nor to the portal a property additionally runs through, but to whoever is responsible for the publication. If the same property appears complete in the portal and incomplete on the company's own page, the company's own page is the advertisement with the gap. That makes your own site not the sheltered space many take it for, but the place with the weakest controls: the portal enforces the fields through its input mask, the in-house property template often does not. Anyone who has sorted out the provider details on their site before will recognise the pattern from the legal notice requirements for 2026: a statutory duty is only met reliably once it has a field, not just good intentions.
The statute names no medium, it names a responsibility
The five details and the fields behind them
The five details are numbered in the statute and translate one to one into fields. First, the type of energy performance certificate: demand-based or consumption-based, so a select field with exactly two values and no free text. Second, the value for final energy demand or final energy consumption for the building as stated in the certificate, a number with a fixed unit. Third, the main energy sources used for heating, usually a multiple choice. Fourth, only for a residential building, the year of construction as stated in the certificate. Fifth, again only for a residential building, the energy efficiency class. All five share something that implementations like to overlook: they come from the energy performance certificate and not from the property file. The building's year of construction and the year stated in the certificate can diverge; the certificate governs. That is precisely why the form should also hold the certificate's registration number, even though it has no place in the advertisement: it is the thread back to the document.
In the form, a split has proved itself that follows the statute rather than the layout: a dedicated section for the energy performance certificate with the five mandatory fields, plus two fields the statute does not ask for but the editorial work needs — date of issue and expiry date. Only then can you answer whether a property is still being advertised today on the basis of a valid certificate. The arrangement inside the listing is free, completeness is not. Anyone who has implemented mandatory details for products knows the mechanics from the shop: with mandatory product information in an online shop too, what decides is not goodwill but whether a record can be saved without them at all. The same tidiness pays twice over, because separate fields are also the basis for structured data.
Select lists, not free text
Certificate type and energy sources are closed value lists. As free text a portfolio ends up with five spellings for the same heating system — and none of them can be filtered or checked.
Unit on the field, not in the text
The final energy value is a number with a unit attached to the field. Put the unit in the typed text and sooner or later it reaches the page twice, not at all, or in a spelling of its own.
Two date fields
The advertisement does not require date of issue and expiry date; day-to-day maintenance does. Without them you cannot answer which property is being advertised on an expired certificate.
- Type of energy performance certificate as a select: demand-based or consumption-based
- Final energy demand or consumption as a numeric field with a fixed unit
- Main energy sources for heating as a multiple choice from a list
- Year of construction per the certificate, kept apart from the year in the property file
- Energy efficiency class as a select from A+ to H, residential buildings only
- Date of issue, expiry date and registration number as internal maintenance fields
Non-residential buildings: one figure becomes two
For commercial properties exactly one point changes, and it is the most forgotten part of the whole rule. For a non-residential building, final energy demand or consumption must be stated separately for heat and for electricity (Section 87(2) GModG). One numeric field therefore becomes two. This is not legislative fine print, it follows the certificate itself: a demand-based certificate for a non-residential building contains final energy demand for heat and final energy demand for electricity as two entries (Section 85(2) GModG). So anyone advertising an office building, a warehouse or a practice unit while publishing only one figure has not met the requirement under number 2, they have halved it. That year of construction and efficiency class drop away here does not make things simpler: the template has to be able to distinguish two building types rather than show one field more or less.
In practice this almost always fails at the same spot: the property template knows only one building type. It was built for flats, then the first commercial property arrived, and the electricity figure had no field. It ended up in the description text or not on the page at all. The clean solution is a mandatory building-type field right at the start of the form that steers the fields below it: residential shows year of construction and efficiency class and requires one figure, non-residential hides both and requires two. That also makes the most common spot check answerable, the one that gets run when a complaint arrives: show me every commercial property where only one figure is set.
| Aspect | Residential building | Non-residential building |
|---|---|---|
| Type of certificate | Demand-based or consumption-based | Demand-based or consumption-based |
| Final energy | One value for the building | Heat and electricity separately (Section 87(2) GModG) |
| Main energy sources | Mandatory | Mandatory |
| Year of construction per certificate | Mandatory | Not required |
| Energy efficiency class | Mandatory | Not required |
| Mandatory fields in the form | Five | Four, two of them figures |
| Reference area in the certificate | Usable building floor area | Net floor area |
| Typical gap | Efficiency class sits in running text only | Electricity figure missing entirely |
The property template as a required-field form
A rule that lives only in a working instruction gets broken on the day things have to move fast. So the duty belongs in the technology. Three layers have proved themselves. The input form enforces the fields according to building type. A guard ahead of publication checks the record once more and refuses the status change to published as long as something is missing. And the template itself outputs the details at a fixed place in the listing, so they do not depend on whether somebody typed them into the description. How the property pages then hang into the rest of the site — search result, category, detail page — is a question of website structure and should be settled before the first property, not after the hundredth.
On a phone the order matters as well. The mandatory details must not disappear behind a collapsed section that only appears after three swipes, and they must not sit in a table that overflows sideways. A plain definition list with label and value stacked survives any screen width; the field may wrap, the pairing may not. That is the same thought as in a mobile-first build: what stays visible on the smallest device stays visible everywhere. One more note on the block itself: the text around it may advertise, the block may not. A line such as particularly economical consumption turns a mandatory detail into a claim that wants evidence.
The guard is the actual measure
- Is a building type set? Without it none of the following rules can be applied.
- Does an energy performance certificate exist? If not, the mandatory details fall away — and the reason is recorded on the property.
- Are certificate type, figure and energy sources set? For residential buildings also year of construction and efficiency class.
- For non-residential buildings: are both figures set, for heat and for electricity?
- Is the expiry date in the future? An expired certificate no longer carries an advertisement.
Existing portfolios: old certificates, old records
Properties age more slowly than certificates. Because an energy performance certificate is issued for a validity period of ten years (Section 79(3) GModG), every portfolio that has grown over time eventually carries an advertisement resting on a document that no longer holds. On top of that comes a transitional rule that affects exactly those certificates most likely to run out today: for certificates issued after 30 September 2007 and before 1 May 2014, the duties apply subject to a special provision (Section 87(3) GModG). In practice that includes the rule that for a consumption-based certificate without a hot-water share the figure is to be increased by a flat 20 kilowatt hours per year and square metre (Section 112(3) GModG). Anyone who once copied such values incorrectly carries them through every migration — a reason to treat a portfolio like a content audit rather than a database table to be copied.
A second point concerns small older residential buildings. Where a residential building with fewer than five flats is to be let or sold and the building application was filed before 1 November 1977, a demand-based certificate is generally required (Section 80(3) GModG) — a consumption-based certificate does not automatically suffice there. For the property form that yields an unremarkable but useful field: the number of flats. It does not decide the mandatory details, but it does decide whether the certificate at hand is the right one at all. If you are capturing it anyway, you can extend the guard with a warning instead of asking the question afresh every time.
Count the portfolio once
How many properties are online, how many of them with a certificate, how many with the mandatory fields set? Three numbers, one query — and the basis for every decision that follows.
Backfill expiry dates
Without an expiry date validity cannot be checked. Backfilling is manual work, but it happens once; after that the portfolio reports for itself before a certificate runs out.
A rule before the import
When taking records from an older source the same check applies as when creating one by hand. An import that bypasses the guard is the fastest way to render a clean form useless.
Mandatory details rarely come alone
What a relaunch does to the fields
When a site moves, the text is rarely what gets lost — the fields are. Five separate details become a paragraph, because the new system had no matching field and the migration ran under time pressure. Afterwards the efficiency class is still on the page, but no longer in a place that can be queried, checked or output. A website relaunch with a property portfolio therefore needs a field map before the first line of code: which field of the old source lands in which field of the new form, which field is new, and which one deliberately stays empty. It sounds like bookkeeping and it is the difference between a migration and a fresh start with old text.
Then there is the address question. Property pages disappear once a property is sold, and that is exactly what makes them a source of dead links. If you do not archive properties permanently, at least decide where a retired address leads: to the overview of available properties, not to an error page. The remaining steps are collected in the article on a relaunch without losing rankings. For the mandatory details a simple order applies: fields first, design second. A listing can be laid out again at any time; a portfolio whose fields turned into running text during the move can only be rebuilt by hand.
- Draw up a field map: every field of the old source gets a target or a documented deletion
- Set the building type per property before the figures are taken over
- Provide two figure fields for non-residential buildings, even if today the portfolio holds flats only
- Carry expiry dates across or backfill them, otherwise maintenance starts again from zero
- Decide on redirects for retired property addresses instead of letting error pages appear
- After the move, run the guard across the whole portfolio once and write down the number
When a complaint arrives
The statute lists the omission as an offence of its own: an administrative offence is committed by anyone who, contrary to Section 87(1), fails to ensure that the property advertisement contains the mandatory details named there — that is number 21 in the list in Section 108(1) GModG. The range for it goes up to ten thousand euros (Section 108(2) GModG). That is a range and not an expectation; what is imposed in an individual case is for the competent authority to decide. For practitioners the wording is more interesting than the number: the accusation is not an incorrect detail, it is the failure to ensure. What is penalised is the missing precaution — and a precaution is exactly what a form and a guard can evidence.
Alongside that stands a second route, one that occurs more often in practice than a fine. An act of unfair competition is committed by anyone who infringes a statutory provision that is also intended to regulate market conduct, where the infringement is liable to appreciably harm the interests of consumers or competitors (Section 3a UWG). Mandatory details in property advertisements are widely classed as such a market conduct rule, which is why complaints tend to come from competitors or associations rather than from an authority. For the website operator that changes the order of work: what drives implementation is not how high a fine might be, but how quickly a portfolio can be shown to be complete when somebody asks.
What counts if it happens
How to set up the property page
The path is short if it is walked in the right order. First the building type as a steering mandatory field, then the five details as fields of their own, then the two date fields and the registration number, then the guard ahead of publication, and last the output in the listing at a fixed place. Only after that is it worth looking at visibility: property pages are pages in their own right with their own address, title and description, and they benefit from the same fundamentals as any other subpage — the points for that are in the technical SEO checklist. The order matters, because an easily found page with an incomplete advertisement is worse than one nobody finds.
For an existing site the work starts with a count, not a rebuild: how many properties are online, how many of them have a certificate, how many have all mandatory fields set? Those three numbers say whether manual follow-up is enough or whether the template has to change. What such a form looks like alongside search, filters and detail pages is shown on the page for a website for real estate; if you would like an existing portfolio taken over, the quickest way in is a short message through the contact form with the number of properties and the system you use today.
Sources and legal references
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