SIPS Structural Performance

SIPCO SIPs are engineered engineered for exceptional structural performance, racking resistance, and wind loading capabilities, in strict accordance with the test results specified within the SIPCO BBA certification.

SIPs are comprised of two high-density facings, typically Oriented Strand Board (OSB), which are auto-adhesively bonded to a low-density cellular foam core. This core includes rigid foam polyurethane (PUR) insulation, creating a robust structural bond between the layers. This bond is crucial for SIPs’ load-bearing capacity, allowing them to efficiently transmit high loads while reducing the need for internal studding.

SIP walls effectively bear both vertical and horizontal loads, with load transfer to the ground facilitated by the OSB skins secured in place by the insulation core.

Manufactured under tightly controlled factory conditions, SIPs can be custom-designed for a wide range of applications, resulting in a building system celebrated for its strength, energy efficiency, and cost-effectiveness. SIPCO upholds strict quality control procedures during production to ensure the consistent performance and quality of these panels.

Why Us
  • BS 5534 : 2003+A1: 2010 Code of practice for slating and tiling (including shingles)
  • BS 5628-3 : 2005 Code of practice for BS EN 338 : 2009 Structural timber — Strength classes
  • BS EN 594 : 1996 Timber structures – Test methods. Racking strength and stiffness of timber frame wall panels
  • BS EN 846-6 : 2000 Methods of test for ancillary components for masonry — Determination of tensile and compressive load capacity and load displacement characteristics of wall ties (single end test)
  • BS EN 1995-1-1 : 2004+A1: 2008 Eurocode 5 — Design of timber structures — General — Common rules and rules for buildings
  • BS EN 1995-1-2 : 2004 Eurocode 5 — Design of timber structures — General — Structural fire design
  • BS EN 1996-2 : 2006 Eurocode 6 — Design of masonry structures — Design considerations, selection of materials and execution of masonry the use of masonry — Materials and components, design and workmanship

Applications and Compliance with Standards:

SIPs serve two fundamental applications: full structural use and infill walling for concrete, steel, or engineered timber frames. In all cases, SIPs are meticulously engineered to meet rigorous load-bearing requirements, racking resistance, and wind loading standards, as stipulated within the SIPCO BBA certification.

Structural Strength and Testing

SIPCO panels are subjected to rigorous testing procedures to guarantee their exceptional performance. These tests include loading panels with a uniformly distributed load (UDL) to measure strength and deflection between two supports, axial loads placed centrally and eccentrically, racking loads, and shear and bending loads on the panel joints. The robustness of the joints between individual panels allows for potential spans over openings, supported by adjacent panels.

Tests have consistently demonstrated that SIPCO panels possess an exceptionally high ultimate bending strength. Deflection, as calculated according to our Design Guide, serves as the governing criterion in design, providing confidence that safe working loads comfortably exceed standard deflection limits.

The localised concentration of loading is achievable by incorporating additional timber at the panel joints. However, with careful detailing, much of this is avoidable. Tests have shown that the panels have a very high ultimate bending strength. Deflection, calculated as per our Design Guide, is the governing criterion in design. This increases user confidence that safe working loads are well over standard deflection limits.

Axial loading tests on panels, measuring 100mm in thickness, 2.4m in height, and 2.4m in width, have revealed impressive results. With a factor of safety of 2.0, panels comfortably support a vertical load of 90 kN/m, significantly surpassing the average foundation loading of a typical two-storey house constructed using traditional methods.


Additional information about SIPs structural performance can be found within the Structural Timber Association SIPs Technical Bulletin 1.

Domestic and Commercial Applications

SIPs are recognised for their exceptional structural performance in both domestic and commercial constructions. For domestic properties like complete houses and extensions, SIPs provide robust vertical and lateral load-bearing capacities. Connections to existing structures are enhanced through methods like using timber wall plates or steel angles, which anchor the SIPs effectively to existing walls. The vertical and lateral loads above three stories require strategic stiffening of SIPs using internal timber stud walls that may be sheathed for added racking resistance, optimising structural integrity while minimising material costs.

Modular Units and Schools

In the context of modular units and schools, where precise load handling and quick assembly are crucial, SIPs demonstrate superior performance. The dynamic loads during modular unit installation are meticulously calculated to ensure safety and structural integrity. Schools built with SIPs benefit from the system’s ability to efficiently handle both racking and axial loads, with design considerations that include additional stiffening to accommodate the specific educational infrastructure needs.

Typical SIPs Assembly and Joints

The assembly process uses 1.2m wide OSB strips, with panels typically extending up to 6.5m for advanced applications. This length is particularly beneficial in roof constructions, enhancing structural continuity and reducing joints. The use of spline joints is crucial for maintaining the structural integrity of connections between panels. These joints are reinforced with a bonding agent and mechanically fastened to ensure a strong shear interface, enabling the entire assembly to act as a continuous diaphragm that significantly enhances the panel’s overall racking strength and rigidity.

Panel Design in Bending Structural Insights

The bending strength of SIP panels is a critical aspect of their structural performance, analysed based on sandwich panel theory. The panels are designed to resist flexural stresses through axial tension and compression effectively. Shear strength at support points is a critical factor, especially under uniformly distributed loads (UDL). Enhanced shear strength is achieved with timber splines, which provide additional resistance compared to unreinforced panels, ensuring that the panels can withstand significant shear forces without failure.

SIPs Panels as Structural Cladding

When SIPs are used as cladding infill or support, they not only provide insulation and waterproofing but also contribute significantly to the structural stability of the building. Attached to primary structural frames using methods like vertical timber plates bolted to steel columns, these SIPs handle both dead and wind loads efficiently. The design and engineering of these panels take into consideration the necessary safety and performance standards, including those enhanced following the Grenfell fire, ensuring that they meet stringent structural and fire safety requirements.

This content has been enriched with information derived from additional sources to provide a more comprehensive understanding of SIPCO’s structural performance capabilities. For further details, please refer to