Bbl rules for living spaces: checklist

Daylight: sufficient window area in proportion to the floor

A habitable room must receive sufficient daylight. The Bbl sets requirements for the so-called equivalent daylight area: the amount of daylight that enters the space through windows, skylights, or light domes, expressed as a ratio to the floor area of the room.

The exact ratio that applies differs per situation and type of renovation. For new construction the strictest standards apply; for renovation and change of use the legally acquired level may be lower. Because the threshold values depend on the actual situation, we do not cite hard percentages as established fact here. Have the assessment carried out by a drawing firm or structural engineer who prepares the calculation for your specific space.

Daylighting checklist:

• Is there a window, roof window or roof light present in the room?
• Does the glass surface area have a sufficient ratio to the floor area?
• Is the daylight area at the correct height and orientation for effective light penetration?
• Is the view to the outside not completely blocked by a neighbouring building or obstacles?

On a construction drawing for the permit the positioning of windows and the glazed area are always indicated on the facade drawing and the floor plan. Tekenpunt states the relevant dimensions so that the municipality can carry out the Bbl assessment.

Ventilation: fresh air and extraction of moisture

A habitable room must be provided with adequate ventilation. The Bbl distinguishes two functions for this: the supply of fresh air (purge ventilation or mechanical supply) and the extraction of moist or contaminated air. Both are required.

For the supply of fresh air, an opening to the outside must be present with a certain minimum capacity relative to the floor area. This can be via an openable window, a tilt position, a grille in the window frame, or a mechanical ventilation system. Similar requirements apply for the exhaust.

Ventilation checklist:

• Is there an openable window or other ventilation provision present?
• Does the ventilation capacity (in volume per hour or in free flow area) meet the Bbl requirements for habitable rooms?
• Is there an extract for humid air, particularly in rooms with high moisture levels such as a bedroom?
• Is the ventilation system connected to a mechanical system, or is there natural ventilation?

In a renovation ventilation is a common sticking point, especially in attic spaces without a roof window or in garages without windows. The construction drawing indicates the position and type of ventilation provision; a calculation of the ventilation capacity is sometimes a separately submitted document with the permit application.

Ceiling height and clear height: room to stand

The Bbl sets requirements for the clear height in a habitable room: the height you actually experience as a user, measured from floor to ceiling or to the lowest obstacle (such as a beam or roof structure). That clear height must be achieved over a sufficiently large part of the floor area.

This point is one of the most common bottlenecks in loft conversions. With a pitched roof, the clear height along the sides is lower than in the centre. The Bbl sets requirements for how much floor area falls above a minimum clear height. Here too: for renovation, the legally acquired level may be lower than the new-construction standard.

Ceiling height checklist:

• Is the clear height in the centre and over most of the room sufficient?
• Is the required minimum height achieved over a sufficiently large share of the floor area?
• Are beams, roof structures or pipework not so low that they overly restrict the usability of the space?
• Is the height clearly readable on the section of the construction drawing?

On the cross-section of the construction drawing, the clear height is always dimensioned. Tekenpunt checks whether the stated heights are realistic relative to the existing roof structure, so you are not faced with surprises during the permit application or during execution.

Fire safety: smoke detectors, resistance and compartmentation

Fire safety is one of the most heavily weighted topics in the Bbl. For habitable rooms, requirements apply on multiple fronts.

Smoke detectors

In every habitable room and on every floor a smoke detector must be present. When renovating in a way that creates a new habitable room, you must also extend the smoke detector installation. This sounds straightforward but is assessed as part of the permit application.

Fire resistance of partition walls and floors

Between habitable rooms and between habitable rooms and other fire compartments (such as a garage or storage room) requirements apply to the fire resistance of walls and floors, expressed in minutes (WBDBO: resistance to fire penetration and fire spread). When converting a garage into a living space, the fire resistance of the partition between the garage and the dwelling is a standard point of attention.

Fire safety checklist:

• Is a smoke alarm provided in every habitable room and on every storey?
• Does the separation between the new habitable room and adjacent spaces (garage, storage, utility room) meet the fire resistance requirement?
• Do doors in fire-separating walls have the correct fire rating?
• Are there no unprotected penetrations (for pipework or installations) in fire-separating walls?

The drawings for the permit application indicate the wall and floor composition with material indications. In a garage conversion the partition between the garage and the dwelling is always a point that the municipality assesses.

Escape route: being able to get safely outside

Every habitable room must be accessible to the occupant via a safe escape route and must be able to be exited in the event of fire. The Bbl sets requirements for the length and composition of the escape route and for the presence of a second escape route on higher floors.

In an attic conversion, the escape route is a frequently discussed topic. If the attic is only accessible via a loft ladder or a hatch, that generally does not suffice. The escape route must consist of a fixed staircase and a hallway or landing that leads to the outside.

Escape route checklist:

• Is there a fixed staircase present connecting the new habitable room to the rest of the house?
• Does the staircase meet the Bbl requirements for pitch, width and handrail (see also the section on the staircase below)?
• Is the escape route free of obstacles and does it lead to an exit outside?
• Is a second escape route possible on a higher storey (via a window or roof window at escape-route height)?

The escape route is always drawn on the floor plan and cross-section of the construction drawing. Tekenpunt checks whether the route is logical and complete before the drawing is submitted.

The staircase: safety and dimensions

A fixed staircase is a prerequisite for a full habitable room on a higher building level. The Bbl sets requirements for the pitch, the tread (the depth of each step), the riser (the height of each step), the clear headroom above the staircase and the presence of a handrail or balustrade.

In a loft conversion, the staircase is one of the most complex components. The staircase must fit in the existing floor plan, comply with the Bbl requirements for pitch and tread, and at the same time leave sufficient clear height at the landing. In older homes with low ceiling heights this is not always straightforward.

Staircase checklist:

• Is there a fixed staircase (not a loft ladder or ladder-type structure)?
• Is the pitch of the stairs not too steep for a habitable room?
• Are the going and riser height of each step equal and within the Bbl standards?
• Is there a railing or handrail present on the open side?
• Is the clear headroom above the stairs sufficient?

The staircase is drawn on the floor plan and in the cross-section with dimensions. For a renovation, Tekenpunt shows the existing and the new situation so the municipality can immediately see what is changing.

How Tekenpunt makes your drawing Bbl-proof

A drawing that does not meet the Bbl requirements leads to a correction request or a refused permit. Tekenpunt elaborates the floor plans, elevations and sections so that all relevant dimensions are visible: the clear height in the habitable room, the glazing area of the windows, the position of smoke detectors and the layout of the escape route. For structural interventions such as adding a dormer window or removing a load-bearing wall, Tekenpunt works together with a KIWA-certified structural engineer for the calculation. This way you have all documents complete in one go. More than 800 projects have been submitted through Tekenpunt; 90% passes the aesthetics committee in one go. Construction drawings are available from 595 euros.

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