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  • Writer's picturePaul Sobota

Illegal buildings: All you need to know

How do you recognise illegal buildings? What impact do they have on the value of a property? Is obtaining a building permit in retrospect possible? We have summarised the most frequently asked questions for you!

What are illegal buildings?

Illegal buildings are buildings without a building permit.

When do I need a building permit?

The rule of thumb is: "At the latest when the building possesses a foundation", e.g. a concrete plate. However, the rules vary from municipality to municipality and ultimately only the local building authority can provide information on this.

Is a grandfather policy with applicable for illegal constructions?

Contrary to popular belief, grandfathering of illegal buildings is not permitted in general.

How do I recognise illegal buildings?

Whether it is a new conservatory, a new extension or an additional storey: unauthorised buildings in the outdoor area are easily recognised. The TIM-online map service of the state of North Rhine-Westphalia usually provides good indications. The cadastral map there shows building outlines and the number of full storeys. If the existing development deviates from the buildings noted there, you should become suspicious. Precise information can ultimately only be obtained from the building file, which can be inspected at the responsible building authority, but the entries on the cadastral map are usually based on the data deposited there. If the relevant building permit cannot be found at the building authority, it is most likely an illegal building. In the case of pre-war buildings, it is necessary to check whether a building permit existed and may have been lost during the war.

Another common problem, which is not so easy to spot, is unauthorised interior work: the attic is easily converted or a cellar is turned into a souterrain flat, but the corresponding change of use is not indicated to the authorities. In this case, a glance at the building plans is usually enough to discover the unauthorised conversions. Also be vigilant and critical during an inspection: If the estate agent shows the attic and then nimbly mentions it was not included in the calculation of the living space, this should set alarm bells ringing. Also question critically if you are shown the kitchen in the annex but it was not mentioned anywhere in the property description. It has also happened that the garage, which was badly retouched on Immoscout, was converted into living space.

Is a subsequent approval possible?

An approval of illegal buildings in retrospect is generally possible. However, some steps have to be taken into account: As a rule, it must be proven that the building corresponds to the state of the art at the time of application (!). This can lead to high modernisation costs, especially in the case of older buildings, if retrofitting is necessary with regard to escape routes, fire protection, sound insulation, heat insulation or window areas. If necessary, property rights to neighbouring properties must also be acquired at horrendous prices, e.g. for parking spaces, rights of way or non-compliance with clearance areas. In the worst case, approval is ruled out because the illegal building in question is not compatible with the development plan. In this case, "deconstruction" (demolition) of the building structures is required.

The requirements of the current state of the art may mean that a building that was approvable in the past is no longer approvable according to today's standards. However, if it can be proven that the building was approvable at an earlier time, passive grandfathering can be obtained. Experience shows, however, that this proof is difficult to provide, since in the rarest cases it was simply "forgotten" to submit a building application. If this fails due to a detail, no matter how small, the only remaining option is to provide proof according to current standards.

Effects on insurance cover:

As a rule, insurance companies do not inquire about the legality of building structures when concluding a contract. However, since extensions and additions increase the value of the building, this results in underinsurance, due to which building insurers will reduce the payout in the event of a claim.

Effects on purchase/sale:

Concealing the lack of a building permit is equivalent to a material deficiency, so that the seller may be liable for damages. If you recognise illegal buildings during a potential purchase, it is advisable to contractually regulate how they are to be dealt with. A common agreement stipulates that the seller has to provide the permission afterwards; if this does not happen, the purchase price has to be reduced according to the price per square metre, whereby possibly incurred deconstruction costs have to be considered additionally. In extreme cases, the value can thus be reduced to the land value minus the "clearance costs".

Effect on lettings:

Compared to the liability risks in case of personal injury, the financial risk of a justified termination without notice by the tenant seems rather mild. If, for example, you rent out an unauthorised attic and someone is injured in a fire, you can be prosecuted according to criminal law.


Do you have any further questions?

Contact us and we will be happy to advise you.

Dr Paul Sobota | Expert for Real Estate Valuation

Johannes-Hesse-Straße 44

40597 Düsseldorf-Benrath

+49 176 55 66 2343

Mitglied im Bundesverstand öffentlich bestellter und vereidigter sowie qualifizierter Sachverständiger e.V. | Gastmitglied

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