OK. So I need a plumbing expert to answer this one please (would that be PigletJohn?). We have a soil vent pipe that ends just below a flat roof near DS's bedroom. Although it conforms to building regs., in summer and especially when the wind blows, there's the most disgusting smell in the back garden from the toilet through the vent pipe.
We've had numerous investigations done to see what's going on and there are no blockages in the drain/ sewage pipe. It seems that it's because the soil vent pipe from the toilet ends too low down and is also in a natural 'wind tunnel' between a large garden shed and an enormous fir tree in the neighbour's back garden. When the wind blows along this channel, the sewage smell blows directly down and across into the garden.
So I've done some online research and discovered this thing called an Air Admittance Valve. Although these are usually used internally, instead of an external vent pipe, from what I can see, you can get an external type to cap the vent pipe and prevent smells.
However, the plumber is sure that these are against building regs to use externally. Is he right? Has anyone used one? Did it work and is it a valid way of preventing smells?