Neighbour wants to externally insulate the party wall

Our 2-storey 1980s house shares a party wall with the adjoining neighbour’s 2-storey house.
This party wall then extends beyond the length of my house - the houses are offset by about 4 metres - and the neighbouring house essentially has a partial “gable end” as a boundary wall to my property for about 4 metres along the garden, then continues as a boundary wall. It’s not ideal, but not a practical issue until now.

We’ve had no problems at all with the neighbour… but an issue has come up around insulation.

The neighbour wants to insulate that exposed wall. It will be expensive and intrusive, but not impossible, for him to internally insulate the 2-storeys (bathroom/staircase are all that side of the house).
Naturally the easiest option - for him - is to externally insulate the gable.

To be fair to him, he has mentioned to me that he’d like to get quotes for this work, and could he have access to my back garden to have a look for quoting purposes. He hasn’t just started into it. He would need access to my garden to do the work.
I’ve said he can have a look, but not agreed to any works.

The issue I have is that technically he’ll be insulating a few inches into our site boundary: so his insulation will be “overhanging” a part of our roof, and will extend into our site along his house wall on my side of the boundary.

Apart from being concerned about a shoddy job that may not seal properly over our roof if not done correctly, I’m concerned that if we want to extend that side of our house along the boundary wall then:

  • it’ll be a few inches lost due to his insulation (not overly concerned with that tbh).
  • more importantly: can I build right up against his insulation in the future or are there issues/regulations here to address?
  • Does it set a precedent for where exactly the boundary is in the future?

I’d much prefer that he internally insulates to avoid all these issues but, given the instrusiveness and potential cost for him, I think he’ll push for external insulation.

Any advice here, or things I need to consider?
Or any contacts/surveyors etc that I should hire for a position on this?

You can register a mutual wayleave,yours to his front garden and his to your back garden for purposes of applying external insulation and maintaining same, and only that much of a wayleave. It is marked in the land registry permanently then. You need to know how many cm thick it is.

You will have to be careful in future and so will he. This stuff is not robust.

This means you can do the same in future. I’d reckon you might have to within 10 years or so anyway and insulation in Dublin houses is a total joke, even the ones built 10 years ago.

Look at this

Would it make sense to add something to agree that if you extend you are within your rights to have it removed?

Thanks 2Pack, AWAAF.

I was thinking a formalised agreement is the way to go alright. I feel that the neighbour just thinks it’s a simple job - but as you said: I’m thinking ahead 3-5 years when his insulation is leaking water behind and running down on to my roof etc.
And if I want to extend - I’d like to be able to remove his insulation etc.