Structural calculation: when needed?
A structural calculation is a mathematical proof that the load-bearing structure of your building is safe. The municipality can make it mandatory as part of your environmental permit, but even without a permit requirement it is legally required for certain works under the Building Works in the Living Environment Decree. This article explains when you need one, what it contains, who is authorised to draw one up and what it costs at Tekenpunt.
A structural calculation is mandatory as soon as you touch the load-bearing structure: removing a load-bearing wall, a roof extension or additional storey, an extension with a new foundation, a large span, a modified roof structure, and always for new builds. The calculation proves, in accordance with the Bbl and the Eurocode, that the structure can safely carry the loads. At Tekenpunt a structural calculation costs from €395 as an add-on, prepared by a KIWA-certified structural engineer; combined with a construction drawing it costs from €990.
When is a structural calculation mandatory?
The Bbl requires every builder to comply with the structural safety requirements in section 4.1. This also applies when building permit-free: you do not have to submit the calculation in that case, but the structure must still be safe. For a structure requiring a permit, the municipality typically requests the calculation as an appendix to the application.
In practice, you almost always need a structural calculation in the following situations:
Removing a load-bearing wall A load-bearing wall carries a floor or roof load. If you remove that wall, you must transfer that load via a steel or timber beam to the support points on either side. Which beam you need, which profile and which bearing arrangement, all follow from the calculation. Without a calculation you cannot know whether the support points can handle the point load.
Roof addition or extra storey A roof extension adds weight to the existing structure: roofing, insulation, possibly a new floor and the walls of the extension itself. The current foundation and the load-bearing walls beneath it were designed for the original load. A structural engineer assesses whether that extra load is safe without modifications or whether the foundation needs to be reinforced.
Extension larger than permit-free In an extension a new roof structure rests on walls that are connected to the existing facade. The foundation of the extension must accommodate the floor and roof loads. Depending on the soil type this may require a concrete strip foundation, piles or a raft foundation. The structural engineer determines this on the basis of a soil investigation or the existing foundation drawings.
Large span or open space If you want to create an open living-dining room without intermediate columns, that span calls for a heavy beam or a steel structure. The larger the span, the heavier the profile. The calculation verifies deflection and bending stress in accordance with the Eurocode.
New construction and foundation For new construction a structural calculation is always required, including a foundation calculation. The latter is based on a geotechnical report (soil investigation). The structural engineer dimensions foundation beams, piles or a crawl-space-free ground floor slab on the basis of the load-bearing capacity of the ground.
Change of roof or roof structure If you replace a pitched roof with a flat roof or make significant alterations to the roof structure, the load distribution also changes. Roof and wind loads are transferred differently. A calculation ensures that the modified structure can handle this.
For small permit-free works, such as a garden shed up to 10 m², a pergola or a standard dormer to scale, a structural calculation is generally not required. As the building owner you remain responsible for structural safety at all times.
What does a structural calculation contain?
A structural calculation is not a free-form document: its content is determined by the Bbl and the Dutch application of the Eurocode (NEN-EN 1990 through NEN-EN 1999). A complete calculation contains at least the following sections.
Load diagrams The structural engineer draws up a load diagram for all forces acting on the structure. These include permanent loads (self-weight of floors, roof and walls), variable loads (occupancy, snow, wind) and accidental loads (seismic loading in specific regions). The load values are derived from NEN-EN 1991 (Eurocode 1: actions on structures). The loads are combined into design values using the partial factors from NEN-EN 1990.
Sizing of beams and joists The structural engineer calculates the required profile for every load-bearing beam or joist. For steel these are HEA, HEB or IPE profiles in accordance with NEN-EN 1993 (Eurocode 3). For timber the strength classes and dimensions from NEN-EN 1995 (Eurocode 5) apply. The calculation verifies whether the selected profile meets the requirements for strength (bending moment, shear force) and stiffness (deflection). For steel, the bearing detail (weld or bolt) is also included.
Floor structure Whether it is a timber joist floor, a hollow-core slab or a cast-in-situ concrete floor: the structural engineer calculates the span, the centre-to-centre spacing of beams or ribs and the thickness of the floor slab. They also check the vibration requirement: a floor that deflects may be structurally safe, but an excessively flexible floor produces uncomfortable vibrations during normal use.
Foundation The foundation calculation links the superimposed load (everything the building weighs) to the bearing capacity of the soil. Based on a cone penetration test report (CPT), the structural engineer determines whether a shallow foundation (strip or raft) or a pile foundation is required. In the Netherlands, with its soft peat and clay soils, a pile foundation quickly becomes necessary for extensions or roof additions. The regulations for this are set out in NEN-EN 1997 (Eurocode 7: geotechnical design).
Verification against the Bbl and the Eurocode Every result is checked against the limit values in the Bbl (minimum structural requirements) and the design values of the applicable Eurocode standards. The structural engineer signs the calculation and is therefore responsible for its accuracy. Municipalities that request a structural calculation as part of the environmental permit application assess whether the calculation was prepared by a qualified structural engineer and whether the outcomes are plausible. They do not carry out their own recalculation.
Drawings as an attachment A structural calculation is always accompanied by structural drawings: sketches or DWG drawings that show where the calculated beams are located, how the bearing points are constructed and how the structure connects to the existing situation. Those structural drawings are the basis for the contractor to carry out the work correctly.
The role of the KIWA-certified structural engineer
Not everyone may draw up a structural calculation that will be accepted in a permit application. The Bbl sets quality requirements for the person responsible for structural safety. In Dutch construction practice, KIWA certification (or equivalent BRL 5019 certificate) is the recognised way to demonstrate that a structural engineer is sufficiently qualified.
A KIWA-certified structural engineer has demonstrated:
- Correctly apply the relevant Eurocode standards
- Working with quality assurance (four-eyes principle for high-risk calculations)
- Being up to date with changes to the Bbl and the NEN standards
Tekenpunt works with a KIWA-certified structural engineer who draws up and signs the calculation. This means the calculation can be used directly in the permit application: you do not need to find and brief a structural engineer yourself. The structural engineer works closely with the drawing office so that the structural drawings and construction drawings align with each other.
Municipalities sometimes also accept calculations from structural engineers without KIWA certification, but experience shows that certified calculations result in significantly fewer requests for corrections. For larger municipalities or construction projects above a certain complexity threshold, the municipality may explicitly require a certified structural engineer under the Quality Assurance for Construction Act (Wkb). The Wkb has been in force since 1 January 2024 for structures in consequence class 1 (most homes and small utility buildings).
How does a structural calculation relate to the environmental permit?
An environmental permit for a technical building activity is applied for via the Omgevingsloket. The Omgevingsregeling (article 7.17 et seq.) describes which documents you must submit. For structural interventions, the municipality requests the structural calculation as an appendix in addition to the construction drawings.
The municipality's assessment consists of two tracks:
- Environment plan activity: does the building plan fit within the municipality's zoning plan (designations, maximum building heights, building lines)?
- Technical building activity: does the structure meet the technical requirements of the Bbl, including structural safety?
The structural calculation is only relevant in the second track. If the structural engineer establishes that the existing foundation is insufficient for the planned extension, the construction drawing must be amended: the foundation is strengthened or the building plan is scaled back. Drawing and calculation must therefore always be consistent with each other before you submit.
The municipality has 8 weeks to decide on an application for a technical building activity (simple cases) or up to 12 weeks for more complex structures. An incomplete application pauses this period. If you submit a calculation that is incomplete or that gives results inconsistent with the drawings, a request for correction will follow and you will lose weeks.
From 2024 onwards a large proportion of private construction works (consequence class 1) fall under the Wkb. For Wkb projects it is not the municipality but an independent quality assurance inspector who assesses the technical execution. The structural calculation plays a central role in this: the quality assurance inspector verifies whether the calculation is correct and whether the contractor is building in accordance with it. A well-documented calculation from a certified structural engineer makes that process smoother.
Tekenpunt handles the complete application Tekenpunt prepares the construction drawings and coordinates the structural calculation. You provide us with your building plan; we ensure the drawings and the calculation align and submit everything as one application package. That way you only need to deal with one point of contact.
And the Building Quality Assurance Act (Wkb)? For new construction in consequence class 1 an independent quality assurance officer has been checking the structure during construction since 1 January 2024. For renovations the Wkb does not yet apply: there the municipality assesses the structural calculation as described above and a quality assurance officer is not required.
The process: from commission to approved permit
Below you can see what the process looks like when you request a construction drawing plus structural calculation from Tekenpunt.
Step 1: intake and sketch design After you complete the quote form, a draughtsman will contact you. We discuss the building plan, the desired layout and the structural starting points. Based on your wishes, the existing situation and the available drawings (cadastral map, any existing construction drawings) we produce a sketch design. This forms the basis for the structural engineer to prepare the calculation.
Step 2: develop the construction drawings The draughtsperson develops the sketch design into a complete set of permit drawings: site plan, floor plans (existing and new), elevation drawings and sections, at a scale of 1:100. Standard delivery time is 4 weeks; express delivery is 1 to 2 weeks.
Step 3: structural calculation In parallel with or directly after the drawings, the KIWA-certified structural engineer draws up the calculation. He bases it on the worked-out drawings and on the load assumptions (occupancy, snow, wind, self-weight). If there is any doubt about the foundation, he recommends a soil investigation report. The calculation is checked internally before delivery.
Step 4: coordination and corrections The drawing and the calculation are reviewed side by side. If the calculation shows that a beam must be larger than shown on the drawing, we update the drawing accordingly. This mutual alignment is why it is more efficient to place both drawings and calculation with a single party: no miscommunication between a separate draughting firm and a separate structural engineering firm.
Step 5: submission to the municipality Tekenpunt submits the application package via the Omgevingsloket, including all required appendices. You will receive a confirmation with the case number.
Step 6: assessment and any questions The municipality assesses the application. If they request additional information, we handle that for you. Tekenpunt gets 90% of applications through the aesthetic review in one go: no extra rounds, no delay. After approval you receive the permit and can start with the contractor.
What does a structural calculation cost at Tekenpunt?
A structural calculation is an add-on to the construction drawing. You can order it separately if you already have drawings, or combine it with the full draughting assignment.
Rates:
- Construction drawing (standard permit drawing set): from €595
- Structural calculation (add-on): from €395
- Combination of construction drawing + structural calculation: from €990
The final price depends on the complexity of the structure, the number of elements to be calculated (removing one load-bearing wall is simpler than a roof extension with a foundation check) and the availability of existing drawings. When you submit a request via the quote form we always provide a fixed price for the entire process, no hourly rates.
What is included in the structural calculation?
- Load schedule in accordance with the Eurocode
- Sizing of all relevant structural elements (beams, floors, columns)
- Foundation assessment if applicable
- Structural drawings as an appendix to the calculation
- Signed off by the KIWA-certified structural engineer
- Coordination with the construction drawings so everything is consistent upon submission
What is not included? A geotechnical report (soil investigation report) is not included as standard. If the structural engineer determines that a soil investigation is required for the foundation calculation, you will receive a separate quote. In practice this is only necessary for larger extensions or on soft ground where the foundation depth is uncertain.
At Tekenpunt we have been working on more than 800 building projects since 2016, ranging from roof extensions and house extensions to complete new-build homes. That experience means we can quickly assess what your building plan does and does not need, so you do not pay for a calculation that is more extensive than a straightforward intervention warrants.
Structural calculation versus construction drawing: what is the difference?
Many people use the terms interchangeably, but they are two fundamentally different documents that serve different purposes.
Construction drawing A construction drawing is a scaled graphical representation of the structure: how it looks (elevations), how it is laid out (floor plans) and how it relates to its surroundings (site plan). The construction drawing communicates form, dimensions and layout. The municipality uses it for the aesthetic review and to check the spatial fit within the environment plan. The contractor uses it as a reference for execution.
Structural calculation A structural calculation is a mathematical document that demonstrates that the structure can safely bear the loads applied to it. It does not contain drawings of what it looks like, but formulas, load diagrams, material properties and verifications against the Eurocode. The municipality uses it for the technical building assessment; the structural engineer signs it and stands behind it personally with their professional certificate.
When do you need both? For every permit-required structural intervention you need both: the construction drawing for the spatial assessment and the structural calculation for the technical assessment. They cannot exist without each other: an approved drawing without a calculation does not give you a building permit if the municipality requires the calculation. And a calculation without the accompanying drawings is useless for the contractor.
In summary:
- Construction drawing = WHAT is being built and what it looks like
- Structural calculation = WHY it is safe and which profiles that requires
Related: see also What is a construction drawing for a detailed explanation of all drawing types and when you need which one.
Frequently asked questions
Q01Can I submit a structural calculation to the municipality myself?
Technically there is no law requiring you to hire a certified structural engineer, but the municipality assesses the calculation on its merits. If it is incomplete, lacks sufficient substantiation, or does not match the submitted drawings, a request for corrections will follow and the decision period will be paused. In addition, for structures in consequence class 1 (most homes), the technical assessment falls under the Quality Assurance for Construction Act (Wkb), whereby a quality assurance inspector requires that the calculation has been prepared by a qualified structural engineer. In practice, a certified structural engineer is therefore almost always necessary.
Q02How long does it take to prepare a structural calculation?
At Tekenpunt the structural engineer works in parallel with the construction drawings. On average the complete set, drawings plus calculation, is ready within 4 weeks. For rush orders that is 1 to 2 weeks. The exact turnaround time depends on the complexity of the structure and the availability of existing data such as foundation drawings or soil investigation reports.
Q03Do I also need a structural calculation if I do not need an environmental permit?
The Bbl requires you to guarantee structural safety, even when you build permit-free. In that case you do not need to submit the calculation, but you must be able to demonstrate that it is safe if the municipality requests it. For larger permit-free works, such as a large detached outbuilding or a roof that you substantially alter, it is wise to have a calculation carried out anyway to avoid liability.
Q04When is a soil investigation (cone penetration test) required in addition to the structural calculation?
A soil investigation report is required when there is uncertainty about the load-bearing capacity of the ground, for example with a new foundation for an extension or roof extension, with weak subsoil (peat, clay) or when no data is available on the existing foundation. The structural engineer will indicate whether a soil investigation is needed after the initial intake. A soil investigation is not included in the standard rate and is quoted separately.
Q05What is the Eurocode and why is it relevant to my renovation?
The Eurocode is a series of European standards (NEN-EN 1990 through 1999) for the calculation of structures. In the Netherlands they are mandatory under the Bbl. Every load (self-weight, occupancy, wind, snow) and every structural element (steel, timber, concrete, foundations) has its own Eurocode standard. A structural engineer who calculates in accordance with the Eurocode automatically meets the Dutch statutory requirements for structural safety. For you as a client this means: you can be certain that the calculation is legally sound with the municipality.
Q06Can I add the structural calculation later if I only have drawings made now?
That is possible, but it is less efficient. The calculation may produce deviations from the drawing (a beam that needs to be larger, an adjustment to the opening), requiring the drawings to be revised. If you have the drawings and calculation prepared simultaneously, they are coordinated with each other before submission. That saves you an extra round of corrections and therefore time.
Q07What is the difference between a KIWA-certified structural engineer and an ordinary structural engineer?
A KIWA-certified structural engineer has an accredited quality system that demonstrates they apply the Eurocodes correctly and that their calculations are subject to a four-eyes check. Municipalities and quality assurance bodies (Wkb) accept their calculations without additional questions about qualifications. A non-certified structural engineer may deliver high-quality work, but the municipality can ask for additional substantiation. Tekenpunt works exclusively with a KIWA-certified structural engineer.
Q08Do I need to have a contractor before Tekenpunt can draw up the structural calculation?
No, you do not need to have a contractor. The structural calculation is drawn up on the basis of the building plan and the drawings. The contractor receives the calculation and the structural drawings later as part of the execution file. It is actually useful to have the calculation before you request quotes from contractors: that way they know exactly which steel profiles, beam dimensions or foundation elements they need to price in.
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