 Does separation of external walls and openings apply to class 2 or 3 Solok 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. These windows need to be far separated from one another. This is what it looks like in plan. We've got SOU 1 on the left and Solok 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 Solok 1 to Solok 2? Well, let's have a look at what the BCA has to say. If you're 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 and 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 firewall. So this provision only applies to fire compartments separated by a firewall, nothing else. These are defined terms, so let's have a look at their meanings. In the Dean to Satisfy provisions, a fire compartment is that part of a building separated from the rest by a firewall and a firewall is a wall with an appropriate resistance to the spread of fire that does the job of making fire compartments within a story. Now 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 tables 3, 4 or 5 of specifications C1.1. This wall highlighted in red between the two solar units is not a firewall. It has an FRL, yes, but that doesn't make it a firewall. The BCA doesn't require each solar unit to be a fire compartment. It hasn't asked for the bounding wall to be a firewall. It simply asks that the internal wall bounding the solar units to have an FRL. And as you can see by the highlighted areas in this table, the bounding wall needs to be 1990, if it's load bearing, or dash 6060 if it's a non-load bearing wall. And of course that dash 6060 is less than the FRL of 1990-90 required for a firewall regardless of being load bearing or not. The solar unit sound fire compartment, so it follows that these windows do not need to be protected from one another at the same story. Some of you may be wondering, so when does C3.3 apply? Well, it applies whenever the BCA does require fire compartments in a firewall. Very commonly you see this in large warehouses where you can get some reduction in the NCC requirements by introducing a firewall 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 size as given in table C2.2. That red line represents the firewall providing separation between the fire compartments and those orange lines along the external walls at the intersection represent the walls and openings that need to be protected in accordance with C3.3. But in the case of your class 2 and 3 solar units, these aren't fire compartments and so the external walls and openings on the same story do not need protection under deemed to satisfy provisions of the BCA.