Water is a miracle elixir for our total bodily function, so if you do not have pristine clean water to drink you cannot effectively flush your liver or kidneys you cannot properly move your bowels, this would cause your body to retain unhealthy toxins which would reabsorb into your bloodstream and circulate these harmful chemicals to every organ in your body.
So you would not drink water from a toxic city swamp, would you?
City swamps are toxic and poisonous with all types of chemical wastes, blue-green algae a literally stagnant disgusting solution, so of course you would not drink it.
However, to filter this water for the possibility for drinking would need a filtering system costing in the hundreds of thousands of dollars.
So why would you consider the use of stale toxic air from your roof space to be ducted back into your home for you and your family to breathe. What you would find in your roof space and real possibilities – insulation fibres, dusts from breaking down of roofing materials, shower steam, kitchen exhaust, condensation, moisture, mould, mildew, fungus, bacteria, dead rats, mice, you name it it’s up there.
To filter the stale air from the roof space into a home safely enough for fresh air to breathe into your body it would be the same situation as water, you would need a filtering system costing in the tens of thousands of dollars.
Your health is priceless - so when it comes to the safe ventilation of the roof space there is no substitute to a proper roof ventilation system, within the roof covering allowing ambient air temperature to flow through the roof space and back out again.