Flat roofs, saddle roofs, and the awkward ones in between

Roofs are rarely one shape. The typical house we configure is a saddle over the main volume, a flat section over an extension, and a small awkward pitch over a porch that nobody thinks about until the ember lands on it.

The trick is to stop thinking about your roof as one object and start listing it as elements. Each distinct plane or saddle becomes its own element with its own measurement: square metres for a flat section, and for a saddle the running metres of its edges. A saddle is protected on its edges only — embers land on edges and gutters, and that is where leaves and debris collect and ignite — so you add each edge as its own element: typically two length edges, two up sides and two down sides, but only as many as your roof actually has. Measuring them separately also lets each edge sit on the circuit that suits it best. You can add as many as you need, and the configurator will work out where the circuit boundaries have to fall.

Those boundaries are not arbitrary. Twenty nozzles is the point at which the last nozzle on a line no longer gets useful pressure, so a circuit stops there. Two circuits and thirty nozzles is what one protection set and one tap can reasonably drive. If your roof needs more, you need another set — and it is far better to know that before you buy than while you are on a ladder.

One more thing to measure while you are up there: the connection runs. From the tap to the first element, then element to element. People consistently underestimate these by a third, because tube follows edges and corners rather than straight lines. Add ten percent to whatever you pace out.