What is the difference between a structural calculation and a strength calculation?

In everyday usage, the terms are often used interchangeably. Formally, a structural calculation is the broader term: it covers the complete analysis of a building structure including loads, material choices, and the dimensioning of load-bearing parts. A strength calculation can be a part of this, specifically aimed at the capacity of an individual structural element such as a lintel beam or a column.

Do I always need a qualified structural engineer?

For building activities subject to a permit that affect load-bearing parts, the Building Decree requires that the structural calculation be drawn up by a qualified building engineer. Our structural engineers all have an HBO building-engineering diploma or an MTS building-engineering diploma with additional certification. For structurally simple adjustments, we can carry out the calculations internally; for more complex projects, we bring in our registered structural engineers.

What if the municipality requests additional structural calculations?

Sometimes a municipality requests additional calculations for specific components, for example a wind-load analysis for high-rise or an earthquake-resistance assessment for projects in Groningen. This falls outside the standard structural calculation. If the municipality requests an additional calculation on a component we delivered, we carry it out free of charge. We cannot guarantee acceptance.

Do I get the calculations on paper or digitally?

As standard, we deliver the structural calculation report as a digital PDF document. For the permit application this is sufficient; we submit it via the Environment Desk (Omgevingsloket). On request, we also deliver a paper version for administrative purposes or for the contractor who wants to be able to read along on the building site.

How long is a structural calculation valid?

A structural calculation is technically valid for an unlimited period as long as the building and the original starting points remain unchanged. In the case of changes in material choice, design, or Building Decree standards, the calculation must be revised. In practice, permits last 26 weeks from issue; within that period, construction must have begun, otherwise the permit lapses and the application (including an up-to-date calculation) must be resubmitted.

Do you also work with external structural engineers?

For very specialised projects (home splitting with several apartments, monument renovation, load-bearing-structure renewal), we work together with external structural engineers from our partner network. The price remains transparent and the final invoice runs via us. The advantage: you have a single point of contact and we coordinate the alignment between the drawing work, the structural engineer, and the municipality.

What if the contractor builds something different from what is in the calculation?

The structural calculation is leading for the execution. A contractor may not simply deviate from the report. Should a contractor propose using a different material or dimension, this must be coordinated with the structural engineer. In such cases, we deliver an update calculation at a reduced hourly rate because the main work has already been done.

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Calculations

Structural calculation costs in 2026: when needed and what you pay

Snel Kwaliteit Tekenwerk5 May 202610 min read

3D illustration of an engineer in a hard hat making a structural calculation beside a steel beam.

A structural calculation costs an average of €395 to €1.250 in 2026. For regular renovations (a dormer with a load-bearing structure, an extension with a large glass surface), the price lies between €395 and €600. For a roof addition, ridge raise, or home split, count on €750 to €1.250. A structural calculation is mandatory as soon as the building activity affects load-bearing parts, and is submitted together with the permit application.

When is a structural calculation mandatory?

The Building Decree (replaced since 2024 by the Dutch Building Decree under the Environment and Planning Act) requires a structural calculation for every building activity that affects the load-bearing structure of a building. In practice, this means that a structural calculation is mandatory for almost all roof additions and ridge raises, because these interventions place an extra load on the foundation and load-bearing walls. The structural engineer must demonstrate that the existing foundation can bear this extra load, or propose reinforcement via an additional foundation, columns, or load-bearing walls.

For extensions, a structural calculation is usually required as soon as the surface area exceeds 6m² or it has a new roof shape. A simple extension with a platform roof and standard timber-frame construction can do without a calculation as long as the spans stay within the standards. As soon as a sliding door wider than 5 metres is installed, a lintel-beam calculation is mandatory because the overlying load must be distributed across the window opening via a load-bearing beam. For rear extensions the same applies: most rear extensions require a calculation because they set up their own load-bearing structure alongside the existing home.

For dormers, a structural calculation is rarely requested, with the exception of very wide dormers (over 60% of the roof surface) or dormers that project deep into the existing roof surface. For a garage addition, sheds under 30m³, and simple carports, no structural calculation is mandatory. The permit check (Vergunningcheck) of the Environment Desk (Omgevingsloket) indicates in advance whether a structural calculation is needed on the basis of the project characteristics you enter.

What is in a structural calculation?

A professional structural calculation report has a fixed structure according to the NEN standards in force in the Netherlands. The report begins with a starting-points section in which the structural engineer describes which assumptions are used: building location (wind zone, snow zone, earthquake zone), building class (residential, office, industrial), use class, and any special loads. For projects in the Randstad, wind zone 2 or 3 applies, for the northern coastal strip wind zone 3 or 4, and for hilly terrain special rules.

Next, the loads are defined. Self-weight is the load of the structure itself (floor, roof, walls) and is calculated on the basis of material choices and dimensions. Variable loads include use loads (people, furniture, equipment) and climate loads such as snow load and wind load. Special loads can arise from explosions, earthquakes, or fire. The combination of these loads according to NEN-EN 1990 results in governing load cases for which the structure must be dimensioned.

The heart of the report is the dimensioning phase. Here, for each load-bearing element (beam, column, foundation, lintel beam, roof slab), it is calculated which dimensions and materials are needed to transfer the loads safely. Timber calculations follow NEN-EN 1995, steel calculations NEN-EN 1993, concrete calculations NEN-EN 1992. The report ends with a conclusion in which the structural engineer declares that the design is structurally safe according to the applicable standards, followed by technical drawings that visually substantiate the dimensioning.

Prices per project type

For a simple dormer or extension with load-bearing elements, we charge from €395. This covers a calculation of 1 to 2 governing elements, usually a lintel beam or roof beam. For extensions with large glass surfaces or flat roof structures, the price rises to €495 to €595 because the roof-slab dimensioning and the connection to the existing roof structure must then also be calculated. A rear extension with its own roof shape and foundation costs €650 to €850, depending on complexity.

For a roof addition or ridge raise, we charge €850 to €1.250. Here all aspects must be calculated: the extra load on the existing foundation, the revised load-bearing structure of the roof shape, insulation and roofing details, and the connection to the existing floor of the storey. For a home split in which one dwelling unit is divided into two or more units, we charge €1.099 to €1.499 because, in addition to the structural aspects, fire compartmentation, sound insulation, and any load-bearing-structure reinforcement for the dividing walls must also be dimensioned.

We do not handle a complete new-build home, but refer you to specialised structural engineering firms from our partner network. For such projects, you can count on structural calculation costs of €4.500 to €12.000 depending on the size and complexity of the home. For monument renovations that preserve the existing load-bearing structure, a specialised monument structural engineer is needed whose rates are 30-50% higher than regular rates because of the expertise required in historical building methods.

How does a structural engineer make the calculation?

A structural engineer always begins by studying the construction drawing and the starting points of the project. On the basis of the floor plans and cross sections, the structural scheme is extracted: which walls are load-bearing, how the beam layers run, where the columns are, what the spans are. For a renovation of an existing home, research into the existing situation is always needed: which materials have been used (brick, concrete, timber), what the foundation is, and how much load the existing load-bearing structure can still bear before reinforcement is needed.

Next, the structural model is built up. For simple projects, this is done on paper or in a spreadsheet. For more complex projects, structural engineers work with software such as Scia Engineer, Autodesk Robot, or special modules in AutoCAD. The model contains all load-bearing elements with their material choices, dimensions, and connections. The structural engineer enters the relevant load combinations according to NEN standards, and the software calculates for each element whether it can bear the load safely.

When an element proves to be overloaded, the structural engineer opts for a larger profile or a stronger material. For a lintel beam over a sliding door, this may mean that a timber beam is replaced by a steel profile HEA 200, or that a concrete lintel beam is specified instead of a timber one. For a roof addition, it may emerge that the existing foundation needs reinforcement via additional pile foundations or a thickened floor slab. The iterative process between design and calculation typically takes 2-5 days for a regular renovation.

How do we work together with the structural engineer?

In our internal work process, we first deliver the construction drawing to the structural engineer. On the basis of the drawing and the starting points (location, desired material choices, use), the structural engineer makes the calculation. Should structural adjustments prove necessary, the structural engineer feeds this back to our draughtsman so that the construction drawing is updated. The final package contains an updated construction drawing and a structural calculation report that are mutually consistent.

For projects with dependent specialists (for example an acoustics adviser for home splitting or a fire-safety adviser for mixed-use), we coordinate the alignment between all disciplines. The end customer has a single point of contact and does not have to liaise with several firms themselves. Our fixed price remains transparent: before the start you know what you pay, and the final invoice follows that agreement.

What if existing drawings are missing?

A common problem with older homes is that the original construction drawings are missing. The current owner does not know which walls are load-bearing, how the foundation is constructed, or how many storey floors there are. In such cases, we carry out an on-site survey: a structural engineer and a draughtsman visit the home, take measurements, assess the use of materials, and draw up a reconstruction of the existing load-bearing structure. The costs for this vary from €495 to €895 depending on the size and complexity of the home.

In some cases, destructive investigation is needed: temporarily removing plasterwork, floor covering, or ceiling panelling in order to inspect the underlying structure. This always happens in consultation with the owner and is professionally restored after inspection. Destructive investigation is invoiced separately and generally amounts to €350 to €750. For projects where the renovation plans are still early in development, we recommend first carrying out a quick scan in which a structural engineer assesses, free of charge, whether the desired renovation is structurally feasible before we start a formal drawing phase.

Common mistakes and how to avoid them

A common mistake is that customers have a contractor make a quotation without a formal structural calculation in advance. The contractor then estimates dimensions on the basis of experience, but at the permit application it subsequently emerges that the municipality requests an official calculation and the contractor's estimate does not suffice. This costs extra time and money because a structural engineer then has to be brought in halfway through the process after all, often with adjustments to the original quotation.

A second mistake is choosing the cheapest structural engineer without checking qualifications. Not every "structural engineer" is a qualified building engineer. Some companies use the term loosely for anything to do with building calculations. For projects subject to a permit, the municipality requires a calculation by a qualified HBO or university graduate. A calculation by an unqualified person is refused and costs you valuable time again. With us, all structural engineers work with the proper certification and all calculations are delivered permit-ready.