I don’t think you’re nosey at all Chris, here is another photo the property with the conservatory is ours and the building protruding outwards behind the tree branch is the neighbours extension. Sorry, I know it can be confusing.
Thank You for your reply and the additional photo Debra,
All is now clear regarding the orientation of your property and the neighbours extension.
As I am sure that You are aware the reason why there are `minimum clearances` to a Property Boundary is in case someone erects a Building / Structure close to the boundary - as has been done with your Neighbour`s extension.
In theory adhering to the minimum distance to the boundary when there is no Building / Structure present ensures that a property owner is protected in the event that the neighbour does build something adjacent to the boundary.
In your case because of the design / dimensions of the
Neighbour`s extension immediately adjacent to your Boiler Flue there is a slight possibility that Flue gasses / Flue Plume could be blown enter the Extension Roof space / Loft Room via the open Velux window.
There is also the possibility that the slightly acidic water vapour from the Flue Plume could stain the extension Brickwork / guttering facia board or Roof tiles.
The possible staining of parts of the extension is something that would not really have been taken into consideration because any structure immediately adjacent to a Condensing Boiler Flue could get stained by the Plume - but it may cause a complaint in future if it can be seen by your Neighbour ?
The Architect / Designer / Builder of your Neighbour`s extension have not taken into consideration the proximity / existence of your Home`s Boiler Flue when designing the extension regarding the Velux window location.
My advice would be to try again to get a visit from one of your Local Authority Building Control Officers - if you cannot get them involved write to Gas Safe asking for an Inspector to visit your property - if they decline stating that the situation is `not within their remit` contact the HSE and report the fact that neither the LABC or Gas Safe will inspect the situation.
Tell them you have had conflicting opinions from a few Gas Safe registered Gas Engineers / Gas Installers and you cannot afford to keep paying Engineers who you find will not commit their findings in writing which is why you wanted to involve a Gas Safe Inspector.
However now that it seems you simply cannot get a definitive answer in writing you are worried about the Gas Safety aspect of the possibility that under certain wind conditions `Products of Combustion` would be able to enter the Loft Room Velux window.
Unfortunately I am guessing that the HSE would probably refer you back to engaging a Gas Safe registered Gas Engineer / Gas Installer - but it is worth a couple of phone calls / a few Emails.
The problem with that is that an Engineer`s visit obviously costs money and even if you had the imaginary facility to have 3 or 4 Engineers visit free of charge they might NOT all agree a definitive answer.
Even with very experienced / very knowledgeable Engineers `human nature` / `self preservation` dictates that some might prefer to state that the proximity of the Flue terminal to the Velux window is definitely a Safety issue to cover themselves in case of a future problem.
Sorry that I / We cannot be more helpful.
If You do get a written definitive answer please let Us know with an update on here.
Chris