Can partition plasterboard be installed vertically or horizontally?

Identifying the correct board orientation for internal systems

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Plasterboard within internal partitions can be installed both vertically and horizontally in principle. However, where a partition is designed to achieve a fire‑resistance classification, the orientation of the boards must follow the tested and classified Siniat partition system.
 
If the board orientation differs from that used in the tested partition construction, the installation may fall outside the scope of the classification unless this variation is specifically permitted by the relevant system evidence.

For fire-resistant systems 

Where a Siniat system is required to achieve a fire‑resistance classification, the plasterboard must be installed exactly as defined within the classified system.

  • Individual components alone, such as plasterboards, do not provide fire resistance; performance is achieved by the complete Siniat system build‑up.
  • Siniat fire‑resistant partition systems are classified based on vertical board orientation as set out in system documentation, classification reports and associated EXAP evidence. 
  • The field of application is governed by EN 15254‑3 (EXAP) for metal stud partitions. Changing board orientation is not permitted within the EXAP rules and therefore falls outside the classified field of application.
  • Any change, including board orientation, must be supported by appropriate test evidence or assessment (e.g. EXAP). Any untested change would no longer represent the classified system and the fire‑resistance classification cannot be assumed.

Key point:
Vertical board orientation forms part of the tested configuration of the partition therefore, horizontal installation invalidates the fire classification for fire‑resistant wall systems. Board orientation within fire‑resistant partitions is not a site preference - it is part of the validated system design.

 
 

For non-fire-resistant systems

Where a system does not require fire resistance, there is greater flexibility in plasterboard orientation.

  • Plasterboard in partitions may be installed vertically or horizontally, provided boards are adequately supported and fixed in accordance with Siniat installation guidance.
  • Orientation may be selected to suit board layout efficiency, joint positioning, or installation sequence.

Finishing consideration:
Horizontal installation may introduce square‑edge joints, which are more likely to be visible through a tape‑and‑joint finish. Vertical installation is often preferred for aesthetic reasons, but this is a finishing consideration rather than a performance requirement.

 
 

Quick Summary

System Requirement Can boards be installed horizontally? Why?
Fire‑resistant internal system NO
Orientation forms part of the classified system. Changing it falls outside EN 15254‑3 (EXAP) and invalidates the fire classification.
Non‑fire‑resistant system YES

No classification applies; standard mechanical installation guidance can be followed.

 

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