Incorrect Installation of an Open-State Cavity Barrier
The intumescent open-state cavity barrier was installed too far forward and finished flush with the vertical cavity barrier. Once the façade panels were installed, the barrier would press tightly against the rear of the cladding, leaving no open air gap for normal cavity ventilation and drainage. An open-state barrier must maintain the manufacturer’s specified gap during normal service and expand to close that gap only when exposed to fire. Installing it in direct contact with the cladding could restrict ventilation, trap moisture and mean the barrier arrangement no longer matches the tested and approved fire-stopping system.
- NCQLE reference
- NCQLE-2026-00015
- Quality topic
- Defects and corrective action
- Lesson type
- Failure
- Evidence rating
- Experience
- Published
- 1 August 2026
- Last reviewed
- 1 August 2026
Evidence basis: Supported by relevant professional experience. This learning is provided for professional consideration and does not replace project-specific competent advice, statutory duties or contractual requirements.
Context
The issue was identified during inspection of a ventilated rainscreen façade before the cavity was fully concealed by the external cladding panels. The observation concerned the junction between a horizontal intumescent open-state cavity barrier and a vertical full-fill cavity barrier. The horizontal barrier projected too far into the cavity and would contact the rear of the cladding, preventing the designed ventilation gap from being maintained. During inspection, the horizontal intumescent open-state cavity barrier was found to project forward and finish flush with the vertical cavity barrier. This meant it would press directly against the rear of the cladding panels, leaving no clear ventilation gap. The installation did not maintain the manufacturer’s specified open-state cavity dimension and therefore differed from the approved and tested system arrangement.
The transferable lesson
Open-state cavity barriers must be positioned to maintain the manufacturer’s specified ventilation gap between the barrier and the rear of the cladding. They should not automatically be installed flush with adjacent vertical barriers. The complete façade build-up, including cavity depth and cladding position, must be checked before installation so the barrier remains open during normal service and closes correctly when activated by fire.
Recommended action
Confirm the required cavity depth, barrier position and open-state gap against the approved façade drawings, tested system and manufacturer’s instructions before installation. Establish an approved benchmark and use a suitable gauge to check and record the ventilation gap. Coordinate horizontal barriers with vertical barriers, rails, brackets and cladding panels, and inspect the installation before it is concealed. Any incorrectly positioned barriers must be referred to the designer and manufacturer and corrected before the cladding is completed.
Limitations and application
The required open-state gap varies according to the specific product, tested system, cavity depth and cladding arrangement; a generic dimension must not be assumed. Visual inspection alone cannot confirm compliance or fire performance. The as-built gap, fixings and barrier orientation must be checked against the manufacturer’s instructions, fire-test evidence and approved design. Any deviation or remedial proposal requires approval from the façade designer and cavity-barrier manufacturer.