Tridentfirepl

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FSI Ltd do a shallow neck collar that is only 25mm deep for this very application.

You should be trained and competent to undertake fire stopping works. You do not have to be 3rd party accredited. The fire stopping materials manufacturer will have all of the correct installation information if you request it or visit the website. It is not a simple job and there are many different approved details for each application required. Many times when I inspect fire stopping carried out by untrained installers it is non-compliant and has to be rectified.

It depends a lot in the construction of the ceiling, provision of compartment walls and cavity barrier's. In a roof void cavity barrier's should be installed directly in line with any compartment walls below, but if the ceiling is fire rated the cavity barrier's are not required to be inline with the walls below and are used to reduce the roof space to maximum 20m in length. The issue is that a fire rated ceiling is normally only tested from below for fire resistance and not from above, so a fire in a roof void could compromise the ceiling in less than the required time of fire resistance and if the dividing walls in the roof space do not align with the walls below 2 or more flats may be compromised by the fire. This would render a stay out policy ineffective. I would expect to see solid block or brick compartment walls separating each flat in the roof space fire stopped to the head as per ADB with an intermediate cavity barrier installed if the distance exceeds 20m between both compartment walls.