Does 'separation of external walls and openings' apply to Class 2/3 SOUs?

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This video describes the application of Volume One C3.3 Separation of external walls and associated openings in different fire compartments.

Transcript

Does separation of external walls and openings apply to Class 2 or 3 Sole Occ Units, or SOUs?

What we're talking about are these windows in the middle here, in the brickwork. On each floor, the window on the left belongs to one unit, and the window to the right of that belongs to another unit that's why there's that privacy screen installed near the downpipes. Do these windows need to be fire separated from one another?

This is what it looks like in plan. We've got SOU 1 on the left, and Sole Occ Unit 2 on the right. Under Specification C1.1 Table 3 the wall between these SOUs needs to have an FRL. So is it necessary to do that thing where we have to protect these external walls and the openings in them to stop fire spreading from Sole Occ 1 to Sole Occ 2?. Well, let's have a look at what the BCA has to say. If you were thinking, "Yes, those walls and windows need protection" you're likely thinking about this table in C3.3. You've remembered this bit, that the walls are intersecting at 90 degrees, so for the first four metres from that intersection we need to have an FRL of 60/60/60, and that those windows need protection. If that's what you're thinking, let me encourage you to look a bit closer at C3.3.

C3.3 is about separation of external walls, and associated openings in different fire compartments which are separated by a fire wall. So this provision only applies to fire compartments separated by a fire wall, nothing else. These are defined terms, so let’s have a look at their meanings: In the Deemed-to-Satisfy Provisions, a fire compartment is that part of a building separated from the rest by a fire wall. And a fire wall is a wall with an appropriate resistance to the spread of fire that does the job of making fire compartments within a storey.

When it talks about having an appropriate resistance to spread of fire, that means that the wall has the minimum FRL, and that usually comes from Table 3, 4 or 5 of Specification C1.1. This wall, highlighted in red, between the two sole occ units, is not a fire wall. It has an FRL, yes. But that doesn't make it a fire wall. The BCA doesn't require each sole occ unit to be a fire compartment, it hasn't asked for the bounding wall to be a fire wall, it simply asks that the internal wall bounding the sole occ units to have an FRL.

As you can see by the highlighted areas in this table, the bounding wall needs to be 90/90/90 if it's loadbearing, or ─/60/60 if it's a non-loadbearing wall and of course that ─/60/60 is less than the FRL 90/90/90 required for a fire wall regardless of being loadbearing or not. The sole occ units aren't fire compartments. So it follows that these windows do not need to be protected from one another at the same storey.

Some of you may be wondering, so when does C3.3. apply? Well, it applies whenever the BCA does require fire compartments and a fire wall. Very commonly you see this in large warehouses. Where you can get some reduction in NCC requirements by introducing a fire wall to reduce your compartment size. Very often this will be done to keep the type of construction at Type C, on account of the maximum fire compartment sizes given in Table C2.2. That red line represents the fire wall providing separation between the fire compartments. And those orange lines along the external walls of the intersection represent the walls and openings that need to be protected in accordance with C3.3.

But in the case of your class two and three sole occ units. These aren't fire compartments and so the external walls and openings on the same storey do not need protection under the Deemed-to-Satisfy Provisions of the BCA.

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