Structural class 3 (KK3): control requirements and documentation under DS1140

Under BR18 § 489, KK3 covers:

• Structures in consequence class CC2 that are unconventional or complex (and are not detached, terraced, semi-detached or holiday homes covered by KK1).
• All structures in consequence class CC3.

For alterations, simple, traditional alterations to existing CC3+ structures can be placed in KK3 (§ 489(2)).

What do “complex” and “unconventional” mean?

A structure is complex when its load paths are hard to follow, when equilibrium requires special assumptions or tools, or when changed assumptions could significantly affect how it behaves (§ 487). It is unconventional when the industry lacks broad, long experience with the type of structure, or when new technologies or methods are used (§ 488). If in doubt, the structure must be treated as complex or unconventional.

BR18 Annex 3, table 1 requires self-inspection and independent control in KK3. Unlike KK2, there are no special relaxations or small-building exception: independent control must be carried out. Independent control is carried out by someone who took no part in the design or execution of that specific work (§§ 526 and 526 a). See Independent control under DS1140.

The documentation is checked at the level BR18 Annex 3, table 2a sets for KK3.

BR18 Annex 3, table 2b sets a minimum sample of 25% for special control of the executed structure in KK3. Special control is additional control of particularly critical items, which are set out in the structural control plan for execution (B2). General control of the execution follows the control level in DS1140. So sampling isn’t wrong in itself in KK3. The scope just has to meet the requirements and be justified.

In KK3, the certified structural engineer prepares the start and final declarations (§§ 496–499). Since 1 January 2025, the final declaration covers the control of the design and the special control of the execution. General control of the execution is instead documented in a separate declaration at completion, stating that the control has been carried out and deviations dealt with (§ 41(3)).

The structural documentation (§ 496): the relevant parts of A1–A5 and B1–B3 (§§ 500–502), including the basis for the classification (§ 503). For the contractor: the Control plan under DS1140, B2 control plan, B3 control report and A5 as-built documentation. Because more items typically need independent control, traceability from plan to record is especially important in KK3.

• Settle the class and the special control points early. Start with the design engineer’s B2 and the start declaration, so you know which items need special control.
• Name the independent inspector. They must not have taken part in the work and must be able to be on site when the check is due.
• Plan control of work that gets covered up. Reinforcement, connections and cast-in items must be checked and photographed before they disappear.
• Justify the samples. For each control item, state what share is checked, so the scope can be followed from plan to record.
• Keep deviations in one place. Record who decided the fix and document that each deviation is closed.

• Complexity is underestimated. The building is planned as KK2 even though the solution is complex or unconventional.
• The KK2 exception is used. KK3 has no exception for smaller buildings.
• “25%” is read as the scope of all control. It only applies to the sample for special control.
• Independent control is planned too late. The inspector must be in place before the work is covered up.

We help main contractors, trade contractors and developers set up control that matches the structural class: from the control plan and self-inspection to independent control and the final handover package. We can take on the whole job or just the part you’re missing, anywhere in Denmark, and we explain the Danish requirements in English.

We can’t promise approval on anyone else’s behalf, and the formal classification and the certified roles sit with the responsible parties under BR18. But we make sure your control and documentation are structured, traceable and complete, based on the project material that exists.