A full extra storey on top of a flat roof. The largest floor-area gain of all roof types and maximum increase in residential value. A permit and structural check are always required. We handle everything from drawing to handover-ready.
Adding a storey means placing a complete extra floor on top of a flat roof, across the full footprint of the home or building. A permit-ready drawing starts from €1,595 (excl. VAT) and is delivered within 4 weeks, or 1-2 weeks on an express basis. A building permit is always required.
Adding a storey means building a full additional floor on an existing flat roof, across the entire footprint of the home or complex. This is fundamentally different from a roof extension (extra space on a pitched roof) or a dormer (a projection in the pitched roof surface). Below are the elements that always require attention when adding a storey.
The first check: can the existing load-bearing walls, floor joists and foundation support the additional load? We establish this with a structural calculation. No permit application starts without its approval.
The floor of the new storey rests on the existing walls or on additional steel profiles. Thickness and reinforcement details are determined in consultation with the structural engineer.
Light steel frame or masonry, depending on the load-bearing capacity. Insulation values must meet the current Building Decree requirements (Rc ≥ 4.7 for walls).
The junction between the new facade and the existing exterior wall is a cold bridge risk. We detail this carefully in the drawing.
The top closure of the additional storey, flat or with a shallow pitch. Including roof edge, drainage and roof insulation (Rc ≥ 6.3).
Access to the new floor requires space on the existing storey. We determine the position and width of the staircase early in the design process.
Adding a storey significantly alters height and silhouette. A building permit is always required. Four questions to estimate the complexity.
Adding a storey always requires a building permit with aesthetic review. In addition, a structural calculation is necessary to confirm that the existing structure can handle the additional load. For a flat-roof terraced house with 1 extra storey, this is achievable in most cases. We assess your situation free of charge and prepare a fixed-price quote.
Indicative calculator for design and permit. Construction is carried out separately by a contractor.
* We handle design, building permit and (if desired) structural calculation. Construction is carried out separately by a contractor; build costs are an indication based on approximately €2.200 per m² for adding a storey. Request a quote for exact drawing costs.
From a single extra storey on a terraced house to multiple storeys added to an apartment block. We advise on what is structurally and planning-wise feasible.
The most requested type of adding a storey: a full extra floor on top of a flat-roof terraced house. +30 to +50 m², always including building permit and structural calculation.
Two extra storeys on a flat or gallery-access building. Owners' association approval required, more extensive foundation investigation. Significant area gain for the entire complex.
A combination of adding a storey and a larger footprint on the new level, or merging neighbouring roofs. Maximum floor-area gain, the most complex process.
Adding a storey yields the most m² but places the highest demands on structure and foundations. Here is the full comparison against the alternatives.
The complexity of adding a storey depends greatly on the type of building, the construction period and the local aesthetic review requirements. A few typical scenarios.
Example project · adding a storey 1 floor · post-war home · +45 m²
Challenge: A family in Rotterdam had a post-war flat-roof terraced house (built 1962) and wanted to expand without moving. The property already had a rear extension. Adding a storey was the only option to create a full additional bedroom floor.
Our approach: We started with a structural pre-scan: wall thickness, floor span and an estimate of the foundation. The outcome was positive. We then produced the architectural drawings for the building permit, including the facade connection, roof waterproofing and insulation details. The structural engineer worked out the calculation in parallel.
Result: 45 m² of extra living space on the new floor, existing layout below left untouched. Permit granted in 8 weeks, construction completed in 10 weeks. Property value estimated to have risen by approximately 15%.
Adding a storey is a significant investment with a high return. What you still need to know about financing, homeowners association approval and sustainability requirements.
Adding a storey significantly alters the height and street profile of a building. A building permit with aesthetic review is always required. We handle the application in full, including drawings and supporting documentation.
SOURCE · ENVIRONMENT ACT 2026 / BblAdding a storey significantly increases the property value and can be co-financed through a renovation mortgage (NHG up to 106% of the value after renovation) or a building deposit at your bank.
BRON · NHG.NL 2026For an apartment block, written consent from the owners association (VvE) is required in addition to the building permit. The deed of division determines who becomes the owner of the new storey. We advise on the procedural steps.
ADVICE · CONSULT OWNERS' ASSOCIATION BEFORE STARTYes, always. An additional storey substantially changes the height and profile of the building. A building permit with aesthetic review is always required. We handle the full application, including all required drawings and supporting documentation.
A permit-ready drawing for an extra storey on a terraced house starts from €1,595 (excl. VAT). The price depends on the floor area of the new level, the type of building and the complexity of the connection to the existing structure. We always prepare a no-obligation fixed-price quote.
We establish this through a structural calculation. The existing load-bearing walls, floor beams and foundation must be able to handle the additional load. For most post-war flat-roof terraced houses adding a storey is structurally feasible, but it varies by construction period and soil type. A structural calculation is almost always required when adding a storey.
Adding a storey is a full extra level on top of a flat roof, covering the entire footprint of the home or building. A roof extension is an addition or extra floor on an existing pitched roof. Adding a storey yields the most square metres but places greater demands on the load-bearing structure and the foundations.
We deliver the drawing within 4 weeks (express: 1-2 weeks). The municipality then has 8 weeks to decide on the building permit. Allow a total of 3-4 months for drawing, permit and start of construction.
Yes. We handle storey-addition drawings and permit procedures across the Netherlands. The drawings are done remotely; we submit the permit application to your municipality. Our office is in Amsterdam (Contactweg 131) and our clients come from Groningen to Zeeland.
A fixed-price quote within 1 working day. Free structural pre-scan of your situation. No obligation.