Party wall agreement

[trevorbayliss]

I am doing a single story extension at the back of my house.

It is a semi and we share a small lean to extension out of the back of both houses at the moment. I intend on removing my small lean to extension and so will need to make good the tiled roof here and do some flashings.

I will then be building a new brick and block wall independent from my neighbours lean to extension and his garden wall. I will be sitting my new wall about 200mm away from his boundary.

Do i need to use the party wall notice system. He has mentioned it because i am building near to his foundations.

 

[^woody^]

Only if your foundations will be lower than his

 

[trevorbayliss]

The lean to ext is about 100 yrs old. The garden wall is about 2m high and is 20 yrs old.

If they are lower, do i lay the foundations in 1m stretches ? Similar to underpinning. I think he wants some detail on how this footing will be built because it is near to his house / wall.

 

[^woody^]

You would lay your foundation in one process. If you are underpinning, then that is done in 1m sections. Else you shore up the sides of your trench as necessary.

Garden walls are not party walls, but need protecting under common law duty of care.

 

[wessex101]

The lean to ext is about 100 yrs old. The garden wall is about 2m high and is 20 yrs old.

If they are lower, do i lay the foundations in 1m stretches ? Similar to underpinning. I think he wants some detail on how this footing will be built because it is near to his house / wall.

If you are building adjacent to a shallow foundation then the good practice is to cast the deeper foundation in short 1 metre long bays so that you do not undermine the adjacent foundation and keep the foundation separated with a slip membrane. Underpinning should be avoided unless there is no other option such as digging out a cellar to create more headroom for a basement conversion. Someone posted a newspaper report on here for a side extension, I think it may have been in Birmingham, where the builder dug out the foundation trench in a single operation adjacent to the neighbouring property which then collapsed. I'll try to find the photos.

 

[^woody^]

the good practice is to cast the deeper foundation in short 1 metre long bays

Never heard of this "good practice". Where's the guide?

The OP will then end up with a foundation of uneven parts (with the associated risk of uneven settlement), when he could have a foundation of a single part if he just shores the trench.

 

[wessex101]

Never heard of this "good practice". Where's the guide?

The OP will then end up with a foundation of uneven parts (with the associated risk of uneven settlement), when he could have a foundation of a single part if he just shores the trench.

Shoring the trench for something like a garden wall or small extension would be fine, not sure I'd risk it for anything bigger. Depends how nervous the neighbour or party wall surveyor is I suppose.

For a hit and miss foundation the bays are cast just like underpinning so you incorporate a key between the bays. Just come across a new one on an underpinning job where you fix a large block of polystyrene on the side of the trench. When you excavate the adjacent bay you simply break out the polystyrene block so you get an interlock rather like a mortise and tenon or a giant lego brick, much easier than trying to dig out around steel pins hammered into the side of the excavation.

 

[^woody^]

Shoring the trench for something like a garden wall or small extension would be fine, not sure I'd risk it for anything bigger. Depends how nervous the neighbour or party wall surveyor is I suppose.

For a hit and miss foundation the bays are cast just like underpinning so you incorporate a key between the bays. Just come across a new one on an underpinning job where you fix a large block of polystyrene on the side of the trench. When you excavate the adjacent bay you simply break out the polystyrene block so you get an interlock rather like a mortise and tenon or a giant lego brick, much easier than trying to dig out around steel pins hammered into the side of the excavation.

I know that.

But where is this "good practice" mentioned for trenches for new foundations in bays in the situation as per the OP?

 

[wessex101]

Its my good practice but I'll let you have it for free. Widely used in party wall situations for the last 30 plus years to my knowledge.

Oh and I found that photo, I'm sure the copyright holder wont mind as it is not for commercial use or personal gain.

 

[^woody^]

Its my good practice but I'll let you have it for free

Very kind, but I'll stick with a few million others and follow the more traditional good practice. Thanks all the same

Be sure to check up on all your foundations in a few years time, and see if they are doing a mexican wave.

That image is from a completly different situation, BTW

 

[wessex101]

Really, I seem to recall in the newspaper article they blamed the builder next door. What caused the collapse in the photo then? You can see the excavation running alongside the existing shallow brick footing and you can see where the wall has dropped by about a foot. What on earth could have caused that sort of catastrophic failure, maybe they had a bit of a problem with moles?

 

[^woody^]

Really, I seem to recall in the newspaper article they blamed the builder next door. What caused the collapse in the photo then? You can see the excavation running alongside the existing shallow brick footing and you can see where the wall has dropped by about a foot. What on earth could have caused that sort of catastrophic failure, maybe they had a bit of a problem with moles?

He dug the trench too close and too deep to the neighbours foundations and they slipped sideways into the trench. He should have shored the trench (not done it in 1m bays).

 

[wessex101]

He dug the trench too close and too deep to the neighbours foundations and they slipped sideways into the trench. He should have shored the trench (not done it in 1m bays).

So exactly the same situation then? Where's Freddy when you need him?

 

[^woody^]

Where's Freddy when you need him?

Freddy puts the clot in cream on Fridays.

 

[^woody^]

So exactly the same situation then?

Not quite. It is different in the fact that the "good practice" would be to have shored the trench, not put foundations in in 1m lengths.