Last summer we had a wooden outbuilding made at the end of our garden. It is made of oak, with a flat roof - low enough to not need planning permission. Shorty after, the neighbours behind us had a swimming pool & I think a pool room built, at the end of their garden, sort of backing onto our building. Over recent months we have noticed the roof and back wall is mouldy and bowing - no leak anywhere. We have just realised they actually have some sort of heater / boiler pumping out steam directly at our building, about 1 foot away, 24/7.
I want to speak to them about it - but I'm unsure what to say - we are not friendly with them at all, but I don't want to cause any bad feeling.
Any advice?