Existing shared flowerbed & new party wall

[toweringtone]

Hi - hopefully someone has dealt with this issue before and can offer some advice... someone must have...

I am planning a rear extension to my semi-detached. Single story, permitted development, just a box across the back of the house, out along the boundary with my "attached" neighbor. At the moment there's a shared flowerbed along the boundary with a fence in the middle. Flowerbed begins about 500mm from the back wall and slopes up to about ~300-400mm deep at about 3m out ,where any extension wall would stop. So build would be up to the boundary with a new external (party) wall, with a flowerbed against it.

This sounds like a recipie for disaster to me, however neighbor is not going to remove flower bed. Building right up to boundary regardless of existing flowerbed has been proposed by several different architects who visited to review (they seem to think "a standard solution" will be put in place - but don't seem to know what that is).

How do I deal with this shared flowerbed ? Can it simply be heaped up against an external wall ? Does it need some special treatment (tanking??) ? As neighbor is very opposed to development, they will not be making life easy.

Grateful for any advice... Thanks, Tony.

 

[freddiemercurystwin]

I don't really understand the problem. If earth is higher than the dpc on the outside wall then appropriate tanking methods need be applied and that is the end of it. When you say build up to the boundary you will need to ensure nothing over sails the boundary eg the eaves or gutter if applicable. But any half decent architect will know all of this.

BTW an architectural technician is adequate for this, you don’t need an architect.

 

[toweringtone]

Hi - The earth would be higher than the dpc on the outside wall. I guess partly my query is about "tanking". The architects we have spoken to did vaguely mention tanking without anything more, the architect we are using has essentially said "don't worry about it right now")... but I have no idea what tanking really means. What would it consist of ? A lead sheet / plastic membrance / a paint ? I want to understand up front so I'm not left with something I'm not happy with later.

My understanding is that any soil above the dcp is not a clever idea, and so was wondering what other people did. Or does anyone in this situation just have "tanking" ?

Many thanks for the response.

 

[freddiemercurystwin]

Tanking is carried out in building all the time and occurs whenever the ground level outside is higher than the floor level inside. It can be achieved in several different ways, with various membrane systems, drained systems or renders etc.

Typically for this situation I would expect a bituminous membrane to be applied to the outside of the outer skin of blockwork and then an additional skin of blockwork or similar protection built up in front of that to protect it. This membrane is sealed with the membrane under the floor slab to create a waterproof barrier. Some thickening of the masonry at low level may be necessary as technically the wall is a retaining wall but again not a big deal if required. All pretty basis stuff and I would add that your architect told you not to worry about it right now and that would pretty much be my response at this stage, really not much of an issue but it does need thinking about and detailing properly when the time’s right. That said you can always post back the detail he does for this for us to comment on!

I would hope whoever you have chosen is going to do you some details which will tell you/the builder exactly how to do this rather than a generic drawing and just a load of generic notes down the side.

 

[Alastairreid]

As freddy said no big deal! concentrate on the build first.

Here's what we use.

http://www.uk.graceconstruction.com/waterproofing/download/Bit2000,3000_14.pdf