Adding a storey on a flat roof
Adding a storey means building a complete extra residential floor on top of an existing flat roof. This can be done on a stairwell flat, a commercial building, or a terraced house with a flat roof. In virtually all cases you need an environmental permit and must have a structural calculation drawn up. Tekenpunt takes care of the construction drawings, the structural calculation, and the environmental permit application so you are ready to build.
Adding a full extra storey on a flat roof (known as 'optoppen') is almost never permit-free. You usually need a permit for the technical building activity (Bbl) and for the zoning plan activity, because the extra storey nearly always exceeds the maximum building height in the municipal plan. A structural calculation is legally required; the foundation is the most critical element. A construction drawing from Tekenpunt starts at €595, the permit application costs €500 and the structural calculation €700.
What is adding a storey and what distinguishes it from a roof extension?
When adding a storey you add a complete, self-contained residential floor on top of an existing flat roof. The new floor has its own floor, walls, windows, and a new roof. The living area of the building thereby increases by a full storey without the footprint at ground level becoming larger.
The term 'roof extension' is used more broadly in practice: it can be a partial extension that covers only part of the roof, or a smaller structure on a pitched roof. Adding a storey refers specifically to shifting the full building height upward by an entire floor. That scale has direct consequences for the structure, the foundation, and the permit procedure.
Adding a storey is popular with stairwell apartment blocks from the 1950s and 1960s, with premises above shops in city centres and with terraced houses with a flat roof. Municipalities and housing associations also use adding a storey as a tool to increase housing supply without using new land. That policy context can have a positive influence on the permit procedure in your municipality.
Adding a storey is very much in the spotlight as a way to create extra living space. Central government and five provinces published a national guidance document on adding a storey (Handreiking optoppen); you can find it on the official knowledge platform volkshuisvestingnederland.nl/optoppen.
Environmental permit: almost always required
Adding a storey is almost never permit-free. A full additional building floor does not fall under the permit-free regulation for outbuildings in the rear garden area; that applies exclusively to low, small structures at the back of the plot. A newly added storey sits on the main mass of the building and is therefore always subject to a permit.
In most cases you need to arrange two separate activities:
The technical building activity (Bbl): the new storey must comply with the building technical requirements of the Bbl. Think of structural safety, energy efficiency, fire and sound insulation. For buildings with a residential function above a certain size, an environmental permit is required for this. Carry out the permit check via the Omgevingsloket for the exact threshold value at your address.
The environment plan activity (spatial component): the municipality's environment plan determines the maximum building height on your plot. Adding a storey almost always exceeds that limit. If your plan deviates from the environment plan, you need a separate permit for the environment plan activity, or even an environment plan amendment. This process takes longer than the standard 8 weeks.
As a first step, submit a principle request to the municipality if you are not sure whether the desired height is achievable. The municipality then responds informally to your plan before you submit the full application.
Aesthetic review and visual quality
When adding a storey, the aesthetic review committee assesses whether the new storey fits the streetscape and the surroundings. Because adding a storey fundamentally changes the silhouette of a building, the committee looks closely at architectural quality.
The committee pays attention to, among other things:
- Height and volume: does the extra storey suit the scale of the street and adjacent buildings?
- Setback: many municipalities require the new storey to be set back behind the front building line so that the added storey is less visible from the street. The required setback differs per municipality and per street and is set out in the aesthetic policy document.
- Materials and facade detailing: steel, glass, timber or zinc are valued differently depending on the neighbourhood. Adding a storey in a different material can confuse the aesthetic review committee from the outset if it isn't properly explained.
- Roof form: a flat roof with a recessed balustrade or a lightweight steel structure is often approved more easily than a tall, solid facade that connects directly to the existing facade opening.
What can you do yourself? Consult your municipality's aesthetic review policy and the applicable environment plan before having a design drawn up. Tekenpunt takes common aesthetic review requirements into account when producing drawings and has achieved first-round approval in more than 90% of projects. It starts with clear drawings: correct dimensions, material indications and a realistic street-facing elevation.
In protected townscapes or village scenes and for monuments, additional and often stricter aesthetic review requirements apply. In those cases also consult the municipality before having a design prepared.
Structural calculation: extra critical when adding a storey
A full additional building floor places considerably more load on the existing structure and foundation than a partial roof extension. The floor, walls, new roof and occupants together add a significant weight that is transferred to the foundation via the existing walls, columns or floor beams.
The structural calculation for adding a storey has three points of attention:
The new structure: how are the floor, walls and new roof of the added storey constructed? Which steel profiles, CLT panels or other structural elements are needed? How is the wind load on the new facade transferred?
The existing structure: can the existing walls, floor beams and columns absorb the extra load? In older buildings the walls are sometimes not designed for an additional floor. Reinforcement or the addition of steel structures may then be necessary.
The foundation: the foundation is the most critical component when adding a storey. Homes and buildings from the first half of the twentieth century are often founded on wooden piles that were not designed for additional weight. Foundation research and any necessary foundation reinforcement can claim a significant portion of the construction budget. This is one of the reasons to have the structural calculation carried out early in the process, so you are not caught off guard once the contractor has already started.
The structural calculation is legally required as part of the environmental permit application for the technical construction activity. Tekenpunt works with a KIWA-certified structural engineer who prepares the calculations and also assesses the existing foundation.
Neighbours, sunlight and the surroundings
Adding a storey has more impact on the surroundings than a small dormer window or a limited extension. Neighbours have no formal right of consent but can lodge an objection after the environmental permit has been made available for inspection. A careful design that takes the interests of residents into account reduces the likelihood of objections.
Sunlight: a higher facade casts more shadow on the garden and facade of neighbours. Some municipalities request a sunlight study as part of the permit application when adding a storey. Tekenpunt can include a sunlight indication in the drawings if the municipality requires it.
Fire-resistant separation: if the building directly adjoins a neighbouring property, requirements apply for the fire resistance of the new outer facade and the roof. For terraced houses or continuous built-up areas this is a standard point of attention in the drawings and the structural calculation.
Maximum building height in the environment plan: the environment plan determines the highest permitted building height on your plot. Adding a storey almost always exceeds that limit, which requires an additional permit procedure for the environment plan activity. In some cases a deviation is not possible due to the spatial planning in the neighbourhood. Check the building height via the Omgevingsloket or submit a preliminary consultation request to the municipality.
Apartment buildings: for an apartment building or a property with a homeowners association (VvE) you need consent from the Vereniging van Eigenaren in addition to the municipal permit. The VvE may have its own decision-making procedure requiring a specific majority of votes. Make sure that consent is in place before you submit the permit application.
The drawing process at Tekenpunt
Tekenpunt is a drawing office; we elaborate your plan into construction drawings that are ready for the environmental permit application and the contractor. We do not design new builds from scratch but translate your wishes and the existing situation into concrete, verifiable drawings.
1. Intake and measurements: you send us the existing floor plans of the building or we work from your sketch. We ask targeted questions about the desired layout of the new floor, the desired roof form, and the choice of materials.
2. Preparation of the construction drawings: we create an existing situation and a new situation: floor plans of the new storey, facade elevations (front, side, rear) and a cross-section of the building including the added storey. The drawings show dimensions, material indications and the new building height that the municipality and aesthetic review committee require.
3. Structural calculation (add-on): our KIWA-certified structural engineer prepares the calculations for the new structure and assesses the existing structure and foundation for suitability.
4. Environmental permit application (add-on): we submit the complete application on your behalf via the Omgevingsloket, including all required attachments.
5. Delivery: you receive the final drawings in PDF and DXF/DWG format, ready for the contractor and the municipality.
The standard delivery time is 4 weeks after approval of the intake. In a hurry? With the express option we deliver within 1 to 2 weeks. We have been working since 2016 and have completed more than 800 projects.
Costs of adding-a-storey drawings at Tekenpunt
Adding a storey is a substantial project. The exact price of the construction drawings depends on the size of the building, the number of facade openings on the new floor and the complexity of the existing situation. A construction drawing at Tekenpunt starts from € 595; adding a storey typically comes in higher due to the scale and number of elements to be drawn. You always receive a fixed quote after the intake.
Add-ons (available separately):
- Submitting the environmental permit: € 500
- Structural calculation (KIWA-certified): € 700
- 3D visualisation: € 400
- Express delivery (1-2 weeks instead of 4 weeks): € 495
In addition to the drawing fees you pay municipal levies for processing the environmental permit application. The amount of the levies differs per municipality and is based on the construction costs or a fixed rate. Check the levy table of your municipality or enquire with the Permits department. Tekenpunt does not charge a margin on the municipal levies; you pay these directly to the municipality.
When adding a storey, the construction costs for the contractor are substantial and highly dependent on the structural solution, the materials used and any foundation reinforcements. Request quotes from at least two contractors based on the Tekenpunt drawings and the structural calculation.
Frequently asked questions
Q01What is the difference between adding a storey and a roof extension?
When adding a storey, you add a full additional residential floor to an existing building with a flat roof: a new floor, new walls, new windows and a new roof over the entire footprint. A roof extension is a broader term and also covers smaller or partial structures on the roof. Adding a storey is therefore the most drastic variant and places higher demands on the structure, the foundation and the permit procedure.
Q02Is adding a storey always subject to a permit requirement?
Yes, almost always. A full additional building floor does not fall under the permit-free regulation for outbuildings. You generally need both a permit for the technical building activity (Bbl) and a permit for the environment plan activity. Carry out the permit check via the Omgevingsloket for the exact situation at your address.
Q03Can I add a storey if the environment plan has a maximum building height?
In most cases adding a storey exceeds the maximum building height in the environment plan. You then need a deviation permit for the environment plan activity in addition to the technical building permit. Whether that deviation is allowed depends on the municipality and the policy in your neighbourhood. Submit a principle request to the municipality to get clarity on this early in the process.
Q04Is a structural calculation mandatory when adding a storey?
Yes. The structural calculation is legally required as part of the environmental permit application for the technical building activity. For adding a storey, the structural engineer assesses three things: the new structure of the additional floor, the load-bearing capacity of the existing walls and floors, and the suitability of the foundation for the extra weight. Tekenpunt works with a KIWA-certified structural engineer who takes care of this for you.
Q05Can my foundation be too weak for an extra floor?
That is a real risk. Older buildings are often founded on wooden piles or a limited concrete foundation that was not calculated for an additional storey. The structural engineer assesses this as part of the structural calculation. If the foundation is insufficient, foundation reinforcement or additional piles are required. This is one of the biggest unknowns when adding a storey; have the structural and foundation assessment carried out as early as possible in the process.
Q06Do I need permission from the neighbours for adding a storey?
Formally you do not need to ask the neighbours for permission. However, they can submit objections during the inspection period of the environmental permit application. A design that takes into account sunlight, overlooking and the streetscape reduces the chance of objections. If you live in an apartment building or have a homeowners association (VvE), you also need the approval of the Owners Association in addition to the municipal permit.
Q07How long does the permit procedure take when adding a storey?
The standard procedure for an environmental permit takes 8 weeks, with a possible extension of 6 weeks. If adding a storey deviates from the environment plan and you need an environment plan activity permit, the extended procedure of 26 weeks may apply. For adding a storey, allow for a total lead time of 4 to 9 months for permit plus construction, depending on the municipality and complexity.
Q08What does it cost to have an added storey drawn at Tekenpunt?
A construction drawing at Tekenpunt starts from € 595. Because adding a storey is a substantial project, the price for a complete set of drawings is higher; you receive a fixed quote after the intake. The environmental permit application can be added for € 500 and the structural calculation costs € 700. If you are in a hurry, expedited delivery is available: +30% for delivery in 2 weeks (minimum €295) or +50% for delivery in 1 week (minimum €495), on top of the regular drawing work. Municipal fees come on top of this and vary by municipality.
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