Boundary solution help required

[Comedydave]

Hi all,
As my diagram tries to show, we have a rear extension the wall of which is set back from the boundary with my neighbour by 100mm. This was because the neighbour didn't want to have founds on his land - which was absolutely fine, no issue.
The level of the gardens rises as you move away from the house - ours has been dug down so the extension floor is level - but the neighbour's still rises.
The issue is that at the back edge of our extension, their garden is higher than the DPM on our extension wall. Initially this wasn't an issue but the flowerbed on his side has been filled in up against the wall.
I was considering putting a low, narrow fence along the outside of my wall, just inside the boundary (like a 2 foot high one) to prevent buildup against my wall. But this isn't ideal as it too would have mud up against it, and rot over time.
So I'm looking for any hints or tips on how to prevent the level of the neighbour's garden encroach above my DPM.
We get along, so I'm sure he's amenable to things...
Thank you!

 

[Old Salt]

How much room do you have before the boundary? How about a low brick wall or concrete / wooden gravel boards? Possibly with a dpm between.

 

[freddiemercurystwin]

If he's amenable then you can politely ask him to sort it out then surely?

 

[Murdochcat]

You need to get the level of the flower bed reduced ASAP or you will have damp issues.

 

[Comedydave]

How much room do you have before the boundary? How about a low brick wall or concrete / wooden gravel boards? Possibly with a dpm between.

It's 100mm. So a low brick wall would be right up against the house and might be too tight - I can't see how to insert a DPM into that, joining with the DPM in the house wall... And it feels that if there were a tiny gap it's just asking for trouble with buildup of crud over the years. A low fence with concrete gravel boards could be the solution. It would be narrower and easier to clean out between the wall and fence to avoid build up.

 

[Comedydave]

If he's amenable then you can politely ask him to sort it out then surely?

Ideally yes, and I'm sure he'd give it a go, but at the end of the day, damp in my kitchen is a me problem, not a him problem, and reliance on others' goodwill is something I'd rather avoid. He might be fine and diligent but I think a solid solution is probably best...

 

[Comedydave]

You need to get the level of the flower bed reduced ASAP or you will have damp issues.

Thanks. Fully agreed. Any suggestions on getting it reduced and keeping it reduced?

 

[Old Salt]

It's 100mm. So a low brick wall would be right up against the house and might be too tight - I can't see how to insert a DPM into that, joining with the DPM in the house wall... And it feels that if there were a tiny gap it's just asking for trouble with buildup of crud over the years. A low fence with concrete gravel boards could be the solution. It would be narrower and easier to clean out between the wall and fence to avoid build up.

The dpm would go vertically between the house wall and boundary wall or gravel boards. Whatever!

 

[Murdochcat]

Thanks. Fully agreed. Any suggestions on getting it reduced and keeping it reduced?

The 100mm from your wall is yours so your neighbour shouldn’t be doing anything there.

Speak to them

 

[Diver Fred]

Do the foundations go to the edge of your property or does the wall stand on the edge of the foundations?
I hope the former. Is your neighbours garden planted? Is it mature?

If you can build on the foundation edge - the answers to the questions regarding the neighbours garden will affect my suggestion.

If you can gain access to build a stub wall alongside your extension wall then that is what I suggest you get completed. Plastic DPC membrane is available in various widths up to (and maybe wider) 900mm wide.
Get a stub wall built hard alongside the boundary with a DPC vertically up against your extension wall. Use 'engineering bricks' as high as you can afford or like. the top edge of the DPC should be above the top of the stub wall and if possible pointed into a joint on the extension wall.