11.3.3 Structural design
Volumetric systems shall be designed to support and transfer loads to foundations and supporting construction safely and without undue movement and shall have adequate resistance to loads imposed during manufacture, transportation, and installation. Issues to be taken into account include:
- overall stability
- unit connections
- temporary loads
- durability.
The structural design of the building should ensure adequate resistance to loadings in accordance with either the relevant Eurocode parts and their corresponding National Annexes relevant to the materials used to form the structural frame of the volumetric unit.
Where necessary, supplementary industry guidance should be followed where permitted by the relevant Eurocode and corresponding National Annex.
The design data may be supplemented with appropriate values derived from structural tests, acceptable to NHBC, where permitted by the relevant Eurocode and corresponding National Annex.
11.3.3.1 Overall stability
The building comprising volumetric units should be capable of supporting the specified loadings with adequate safety against structural collapse, inadmissible deformations, vibration, and disproportionate collapse.
Each unit should be framed in order to support itself fully and safely, by either:
- being designed as a rigid frame, or
- additional bracing or sheathing.
Overall stability of the building should be provided by either:
- the fully braced volumetric units, or
- connection to an independent bracing system such as a building core, shear walls and/or stability frame/s.
Design of a completed building should account for the effect of discontinuities in any system providing overall stability, eg the interruption of diaphragms or shear walls between modules.
Where differential movement between the volumetric units and any supporting structure such as a building core is expected, this should be considered as part of the design.
11.3.3.2 Unit connections
Connections between volumetric units should be designed by a Structural Engineer in accordance with Technical Requirement R5.
The design of connections between units or between units and surrounding construction, typically in-situ, should be compatible and have sufficient strength to transfer the necessary design loads and stiffness to enable the connected units to behave as a complete structure.
Connections should be designed and installed to achieve the required structural performance, and:
- accommodate movement where required
- allow for tolerance and adjustment
- be designed to avoid the risk of damaging or compromising the functional performance of factory installed elements such as breather membranes, AVCLs and lining boards.
The design, System Manual, and Installation Manual should include details of:
- specification and limits for shimming or adjustment of connections
- design and specification of fixings
- sequencing of installation.
Volumetric units should be mechanically fastened to supporting slab or foundations and not rely wholly on frictional resistance to resist sliding.
11.3.3.3 Temporary loads
Structural design of the units should consider the loads imposed during manufacture, storage, lifting and transportation and provide sufficient stiffness or protection against inadmissible deformation or deflection. See also Clause 11.1.8.
Where required, the design should specify temporary bracing and/or additional support arrangements for large openings or weak points in the structure and clearly identify the conditions under which such works can be removed.
11.3.3.4 Durability
The durability of materials and components should be specified in accordance with Technical Requirement R3. Structural elements and components that cannot easily be repaired or replaced should be suitably durable for the environment to which they will be exposed.
Metal fasteners, connectors and other structural steel parts in the element should either be:
- inherently corrosion resistant, or
- protected against corrosion to provide the required design life for the expected exposure condition.
Reinforced concrete should be in accordance with Chapter 3.1 Concrete and its reinforcement.
Timber should have adequate natural durability or be preservative treated in accordance with Chapter 3.3 Timber preservation (natural solid timber).
Steelwork should have protective coating in accordance with Chapter 6.5 Steelwork.
Light steel frame should have corrosion protection in accordance with Chapter 6.10 Light steel framed walls and floors.
Last updated: 2nd January 2025