Requirements for a party wall in a semi-detached house half as a separate building clarified

In the case of semi-detached houses, the classification under building law can be decisive for the obligation to construct a party wall.

The question whether a semi-detached house halfunder building regulationsis to be classified asa separate buildingis one of the core issues of neighbouring fire protection. The classification determines whether the wall on the property boundary is to be constructed only as aparty wall, for example pursuant to § 28 BauO LSA or as abuilding closure wall (party wall)for example pursuant to § 29 BauO LSA. The definition of the term "building" is decisive, as defined for example in § 2 Abs. 2 BauO LSA or comparably in the building regulations (LBauO) of the remaining federal states, and primarily focuses onindependent usability.

This brings functional and use-related criteria to the fore – separate access, spatial enclosure, independent unit of use – more strongly than purely structural aspects such as shared foundation or roof. If a semi-detached house half is classified as a "building", the strict requirements of § 29 BauO LSA apply: the closure wall must becontinuous to the roofand must not be impaired in itsfire resistance. It was precisely at this interface that the central conflict in the present case, which the Higher Regional Court (OVG) Sachsen-Anhalt decided withBeschluss vom 17.11.2025 – 2 L 51/25.Z, lay.

Exactly what was at issue: shared wall vs. party wall

The claimant is the owner of a semi-detached house half within the municipal area of the defendant; the neighbouring semi-detached house half belongs to the interveners. Standing between them on the property boundary is merely ashared wall, without separate structural separation or party wall construction. In 2020, the interveners received a building permit for the heightening of their rear extension by one storey with a roof terrace. The claimant feared a deterioration in fire protection and objected in particular to the fact that the existing shared wall did not meet the requirements of a party wall.

Before the Administrative Court, he challenged the permit and also applied for building supervisory intervention to establish fire protection compliance. The Administrative Court rejected the action for annulment but ordered the authority toreconsiderthe application for intervention, because the rejection order was based on an incorrect legal basis. The building authority applied to admit the appeal – without success.

The legal reasoning of the court

The Higher Regional Court (OVG) first confirms that the building authority adopted aerroneous legal approachby classifying both house halves asa single building. However, for the application of party wall law, it would be decisive whether a house half is to be qualified as aindependently usable building structure. This was clearly the case given the structural and functional circumstances: each house half hasa separate entrance,a separate stairwell,a self-contained residential and functional context, separate land and enclosures. The external appearance – different roof coverings, clear visual separation – also confirmed the classification as two independent building structures. The existence of ashared rooforshared foundationsdid not preclude this; structural self-sufficiency was not required. What was decisive was acomprehensive overall assessmenttaking into account all functional and design-related circumstances.

Consequently, the shared wall was to be treated as abuilding closure wallwhich had to meet the requirements of § 29 BauO LSA. However, according to the Administrative Court's findings, these requirements werenot fulfilled, in particular because the wall after the roof storey extensionno longer ran continuouslyto the roof. In addition, there was a fire protection defect: the newly constructedwooden support structureof the roof construction interfered with the wall and could prematurely fail in the event of fire – a breach of § 29 Abs. 7 Satz 4 BauO LSA. The Higher Regional Court (OVG) makes clear that these considerations do not rely on § 12 Abs. 1 Satz 2 BauO LSA, but directly concern the requirements of § 29 BauO LSA.

However, the authorityfailed to recognisethis material breach of the statute and based its discretion on the assumption that the wall did not need to be configured like a party wall. This therefore constitutes adiscretionary deficiency before it, which would lead to an obligation to make a new decision. The OVG furthermore rejects all grounds for admissibility asserted: no serious doubts as to correctness, no fundamental significance, no divergence and no deficiency in clarification. The submissions of the VG and the fire protection technical assessment are well-founded and comprehensible.

Recommendation

The decision clearly shows that semi-detached houses are often to be qualified as independent buildings – with significant fire protection law consequences. Owners should have planned extensions and conversions reviewed early on to determine whether a fire partition wall requirement exists and whether existing walls meet statutory requirements. Neighbours should also not disregard possible breaches of § 29 BauO LSA or comparable regulations in the other federal states, as building law enforcement can often only be successfully initiated after legal assessment.

The experts for administrative law from AVANTCORE Rechtsanwälte in Stuttgart are happy to advise you on the examination of fire protection law requirements, the design of legally secure building plans as well as the enforcement or defence of neighbouring rights claims.