Building standards for flat units in a tenement: what are the minimum requirements

What does it really mean to 'comply with standards' for a flat in a tenement building?

The owner often asks one simple question: what is the minimum size a flat must be? The legal and technical reality is more complex. Requirements for buildings are set out in the Building Act No. 283/2021 Coll. and its implementing regulations on technical requirements for buildings. These are supplemented by Czech technical standards, which reference the regulations and clarify solutions.

It is important to distinguish two things:

• legal definition of the unit – according to the Civil Code No. 89/2012 Coll. (§ 1159 et seq.), a unit is a flat or non-residential space defined by an owner's declaration (prohlášení vlastníka) (§ 1166 et seq.),
• technical suitability of the flat – that is, whether the space actually meets the requirements for living and can be used as a separate flat.

An owner's declaration can only be made for a space that is technically and functionally defined. If the flat does not meet technical requirements, problems may arise when obtaining building permits, when registering in the Czech Land Registry (katastr nemovitostí), and when securing buyer financing.

The difference between a new building and an existing building

A tenement building is typically an older building constructed according to earlier regulations. This does not mean it must fully meet all parameters of a new building. The scope of requirements depends on what work you plan to carry out:

• Without building work – existing flats are only defined legally. Even so, you must verify that the flats are genuinely separate and their current condition is not contrary to regulations.
• Building work or modification of a completed building – affected parts are assessed against current requirements, with possible exemptions for elements not affected by the work. The scope is determined by the design professional and the Building Authority.
• Change of use – for example, from non-residential spaces, a loft or studio to a flat. Here, full compliance with living requirements is expected.

The actual permit process is a separate matter. Here we focus on what must be technically satisfied.

Dimensions and layout: what regulations actually require

The implementing regulations and standards do not set a single 'minimum flat size' for all cases. Rather, they ensure a flat functions as a complete unit. When dividing a tenement building, the main areas of concern are:

• Living rooms – must have sufficient floor area and clear ceiling height for human occupancy. Specific values vary depending on the type of room and are set out in the current regulation; in older buildings with high ceilings, height is usually an advantage.
• Flat facilities – every flat must have its own toilet, washing and bathing facilities, space for cooking, and its own entrance from a corridor or staircase, which does not pass through another flat.
• Circulation spaces – widths of corridors, doors and staircases must allow safe movement and evacuation.
• Basement and ancillary spaces – are not a mandatory requirement for a flat, but buyers expect them and their allocation must be resolved in the owner's declaration.

When designing the layout, it is therefore more practical to start with the specific measurements of the building and its structural analysis than with general tables. Partitions can often only be moved to a limited extent because of load-bearing walls and roof structures.

Lighting, ventilation, and heating

Natural lighting and sunshine

Living rooms must have adequate natural lighting, which means windows of appropriate size and orientation. The division of large city flats with deep floor plans can result in rooms without direct light from a courtyard or the street. It is precisely such rooms that most often present a problem in preparation and cannot be classified as living rooms.

Ventilation

Rooms with cooking, bathrooms and toilets require secured ventilation, either natural or mechanical. When dividing flats, you must check the condition of existing chimney and ventilation ducts and their connections. New draught-proof windows may change the ventilation method for the entire flat, which must be taken into account.

Heating and thermal protection

Each flat must have heating secured that corresponds to the way it is used. In tenement buildings, this often means transitioning from a shared heat source or stoves to separate metering and regulation. If the building envelope is altered, thermal protection requirements for buildings also apply. Always verify the scope of these requirements with the designer of the energy solution.

Fire safety, sound insulation, and building services

These are precisely the areas that are usually most expensive and least visible in older buildings.

• Fire separation – flats must be separated from each other and from common areas by structures with appropriate fire resistance. Also important are escape routes and securing the staircase. The solution typically requires a fire safety assessment.
• Sound insulation – wooden ceilings and thin partitions in old buildings often fail to meet noise protection requirements between separate flats. Subsequent modifications may affect floor and ceiling heights.
• Water supply, drainage, gas and electrical distribution – each unit needs separate metering and inspection. Common risers and switchboards must be arranged so that one flat is not dependent on access to another.
• Chimneys and flue gas outlets – when changing the heating method, inspection is required and possibly a new assessment from the relevant qualified person.

These items have a direct impact on the renovation budget and therefore on whether dividing the building is economically worthwhile.

Accessibility and common parts of the building

Accessibility requirements apply depending on the type and scope of building work. In residential buildings they typically affect entrances, common circulation areas and possibly lifts, not each flat individually. For an existing building with limited work, exemptions may be acceptable, but their approval must always be documented in the project documentation.

In relation to selling units, it is also important that common parts of the building (staircases, roof, building services, foundations) remain in co-ownership of the unit owners. The technical condition of common parts is therefore examined by buyers with the same care as the flat itself. Neglected common parts can reduce price and buyer interest.

How to proceed and why to start with an audit

Before an owner decides on subdivision, it is reasonable to obtain professional assessment that summarises the technical obstacles, estimated scope of work and impact on returns. The typical price difference between selling the building as a whole and selling individual units ranges from 20–40 %, but the exact figure is determined only by the feasibility of the specific building, including the cost of meeting technical requirements.

The Audit and Plan service is a paid feasibility study with output within 6 weeks. The entire process of transformation, including three gates (legal, permit, sales gate), is described on the How it works page. Further steps are undertaken only with confirmed figures. If you want preparation, construction and sales under one contract, use the End-to-end delivery service.

Always verify binding values in the current regulations and with a qualified design professional. This article is intended to help the owner understand the issues; it does not replace the project or a Building Authority decision.