Not all sprays are equal and they won’t fix every ember problem.
What do you know about spray type, location, and what to spray?
You really should be trying to project water onto your house. It should impact the house, it should impact all the elements that you're trying to wet out and protect. So, it might only be a deck, so, wet the entire deck. It might be a combustible fascia on your house and eaves, well, wet the fascias and eaves. It doesn't have to be constantly wetted, but an impact sprinkler that keeps coming around and intermittently passing is certainly fine for that.
Water spray is going to be very useful to address where embers land and build up on the external features of a structure.
But what they're not going to be able to be effective in is preventing embers getting through gaps and getting into the cavities of the house which typically stay dry during a deluge, or being sprayed with water externally.
For wetting down windows or wetting the areas around the house and addressing the places where the debris might build up, like the fine embers might land, is to put these types of chopper sprinklers or impact sprinklers in around the periphery of your house and actually spray them back onto the house and the broader surroundings.
Water doesn't actually seal the typical gaps and entry points that embers can reach into the building cavities.
On a tile roof the water simply doesn't seal the gaps. It flows over the tiles, but the embers can blow up to and through those gaps even if the roof tiles are wet, or water is dribbling over those gaps. The roof tiles themselves aren't combustible, so making them wet doesn't help.
The thing that water on a roof does do is flow into the gutters, and the debris that has built up in those gutters will obviously then be wet. So, it does address some aspects of the debris around your gutters.
The spray systems that are mounted along the ridge lines of the roofs are spraying, but there's water only going into the downwind side gutters, and virtually none get into the upwind side gutters.
Roof mounted sprinklers are very good at wetting a roof. Roofs in Australia are non-combustible, so a wet non-combustible roof and a dry non-combustible roof are as effective as each other.
Water sprays on a roof can put water into gutters. And the question is what's the most effective way to get that water into gutters if you're trying to solve a gutter ignition risk. And probably the most effective way is to directly deliver the water to the gutter, rather than try to pass it through the air, have it wind affected and maybe not get to all the gutters under very windy conditions.
I would question the efficacy of actually having roof mounted sprinklers at all.
I find that the perimeter sprinklers, ones out in the broader area of the garden projecting back towards the house, are potentially far more effective because they get in under the eaves, they get on the wall surfaces, and they deliver water to all those ground and surface fuels.
I’ve never seen a spray system design that's particularly effective at solving all aspects of bushfire risk that an otherwise vulnerable house could face.
What has been learned about pipes, hoses, knapsacks and mops?
Once you get around 10 centimetres below the ground, the temperatures are not adequate to melt poly in the ground except in the event that you put a significant fuel load on the ground itself. Watch out for old dead tree roots, timber posts and garden ending which can burn down into the ground adjacent to poly pipe well below 10 centimetres.
Anything – pipes or sprays above ground, I would say metal is the way to go.
The old knapsack and mops are an extremely effective way to put out a lot of ignitions with very little water.
Plastic hoses invariably are burnt out and useless if they were out during the fire event itself.