Where can the outside hose of my air conditioner run?

Questioner

I live in Utrecht in the city and we have an extra floor on our house compared to the neighbor. Since we bought the house in 2016, the flue gas exhaust has been on the side of the house, above her house. This has never been objected to by us and this was not discussed during the purchase process (also think of building inspections, valuation, etc.). Now we have had an air conditioning unit installed, the outside unit of which is on our roof. The noise of the outside unit does not exceed the legally permitted limits for installing an air conditioner within a built-up area. The contractor indicated that the hose can simply run outside via the side of our house to the roof without permission from the neighbor (I also received confirmation in an email). According to him, we only need permission from the neighbor if, for example, we discharge condensation water onto her roof, but this is not the case (it goes through the internal drain). So we just continued with that, and during all the arranging I forgot to discuss this with the neighbor (according to the contractor it was not necessary either). Now the neighbor objected to this yesterday via a WhatsApp message and she indicated that the air conditioning had to be moved - and even the flue gas exhaust, because this should never have been done like this in the first place. I suggested to the neighbor to meet up and discuss it further, because it was of course not the intention to cause problems, I indicated that we discussed this with the contractor and I apologized for forgetting to let her know in advance. We have a reasonable relationship - there are often some minor irritations about e.g. the trees in her garden that grow bigger every year and take away a lot of our sun (and are less than 2m from the property boundary) and conversely she was a bit irritated about the stone partition that we placed under the fence to prevent cats in the garden and to support a new terrace. But we usually manage to work this out. However, I am now very curious about what I can do about the air conditioning situation - and on the one hand towards the neighbor (is that hose actually allowed to run outside above her house or not?) and if this is not allowed, can I recover this from the contractor and ensure that he adjusts the design? Thank you in advance,

Lawyer

Is there no provision in your deeds of sale that easements of pipes may be placed on either side? Sometimes that is the case. If not, then you are not formally allowed to let the drain hose run on or over your neighbor's roof. However, I do not think that your neighbor will be right if she demands in court that you remove it if it will be difficult or involve high costs to let it run elsewhere.