Boundary retaining wall failure

[SilverShadow]

Hey all - another day, another quandary that I'd appreciate your guys awesome advice on please 😁

 

We recently moved into a house on a hill, and the boundary wall adjacent to the neighbouring property is also a retaining wall (approx 10m long and up to 1.5m high). Our property is the higher of the 2, so essentially the retaining wall keeps our land from spilling into theirs

 

We introduced ourselves to the neighbours of this boundary (who seem a decent bunch) & they mentioned the wall has 2 big cracks in it.

 

We'd like to ensure this is fixed, but realise it'll be costly (maybe £3k, maybe more???). Fixing it ensures no land slippage our side & keeps them from worrying

 

The neighbours said our old owners built the wall, which suggests it's our responsibility. However, I've checked our deeds & there's no indication its our responsibility to maintain

 

In some ways were happy to pay for fixing it ourselves. But likewise, this might then imply its our responsibility, when it may be shared. Especially when maintaining it in the future 

 

We'd ideally like to share the responsibility/cost with the neighbour, but don't want to suggest it if we're likely liable for it

 

Does anyone have advice on what we could check & go from here please?

 

Many thanks for your time as always 😁

Shadow

[Gus Potter]

12 minutes ago, SilverShadow said:

Hey all - another day, another quandary that I'd appreciate your guys awesome advice on please 😁

 

We recently moved into a house on a hill, and the boundary wall adjacent to the neighbouring property is also a retaining wall (approx 10m long and up to 1.5m high). Our property is the higher of the 2, so essentially the retaining wall keeps our land from spilling into theirs

 

We introduced ourselves to the neighbours of this boundary (who seem a decent bunch) & they mentioned the wall has 2 big cracks in it.

 

We'd like to ensure this is fixed, but realise it'll be costly (maybe £3k, maybe more???). Fixing it ensures no land slippage our side & keeps them from worrying

 

The neighbours said our old owners built the wall, which suggests it's our responsibility. However, I've checked our deeds & there's no indication its our responsibility to maintain

 

In some ways were happy to pay for fixing it ourselves. But likewise, this might then imply its our responsibility, when it may be shared. Especially when maintaining it in the future 

 

We'd ideally like to share the responsibility/cost with the neighbour, but don't want to suggest it if we're likely liable for it

 

Does anyone have advice on what we could check & go from here please?

 

Many thanks for your time as always 😁

Shadow

What a good post and example of approaching things pragmatically.

 

For all. Retaining walls like this often don't have an indefinite life span.

 

A bit of tecky stuff. From time to time the wall gets frosted and this causes the soil behind the wall to swell up a bit right at the top where it can apply a good overturning force, mind you it needs to be a hard prolonged frost. This pushes the wall sideways as the ice crystals grow for example. Then you have settlement of the retained soil and surcharge loading, can be just the wieght of a big tree locally, trees can be heavy! Now you may have heavy rain and this excess water causes the soil to weaken behind the wall so it shoves the wall sideways and then you can add a bit of water pressure. Any trees or big shrubs can push the wall sideways as the roots grow. If you have a timber fence attached to the top or down the side of the wall then the wind loading can push the wall.

 

Now in goetechnical terms (we have many) it's easier for the soil to move than to shove it back into place. We call this active (the soil moving) and passive soil pressure.. shoving the soil back into place. It can often take roughly 2 -3 times the effort to shove the soil back to where it was.

 

Now once the wall moves a bit then cracks tend to develop in the retained soil. These can get filled with muck.. in other words the wall often never can recover it's position... it a slow progessive failure.

 

Odd that there is no mention in the deeds.

 

Anyway. If I was you I would try and figure out what has caused the cracks in the wall. Do what you can to mitigate this if it is on your side. Then have a chat with the neighbours and say.. I've done everything I can on my side to stop it geting worse. Let's see how it goes. Any good will on your side will stand you in good stead later.

 

 

 

 

[SilverShadow]

Many thanks, Gus. That was a very excellent & detailed response, which explains the soil mechanics aspect brilliantly 😁

 

I will have another scan of the deeds, in case it's something I've missed.

 

Looking at the house from the street, the retaining wall is on the right hand side of the property. I'm not sure, but think there's some unspoken rule that left-side boundaries would usually be our responsibility?

 

I could always ask our conveyancer- hopefully they could clarify without it costing much 🤞

 

The wall itself is fairly sturdy, but I noticed it has no drainage outlets, so I imagine the trapped water from excess rain & frosts have caused the swell over time, as you mentioned 

 

As a side note, does anyone recommend a type of wall construction (materials & design)?

 

Additionally, is this something we should ask a structural engineer's advice on, or just trust a builder with retaining wall experience?

 

 

Many thanks again

Shadow

Edited October 17 by SilverShadow

[SilverShadow]

In response to Gus's comments earlier: a double check of the plans/register confirm there is no mention of ownership of the retaining boundary wall.

 

Looking on various legal sites, it seems as though the responsibility lies with the owner who's land it being retained in place. Given that, then i think the onus is on us to maintain this

[TommoUK]

37 minutes ago, SilverShadow said:

In response to Gus's comments earlier: a double check of the plans/register confirm there is no mention of ownership of the retaining boundary wall.

 

Looking on various legal sites, it seems as though the responsibility lies with the owner who's land it being retained in place. Given that, then i think the onus is on us to maintain this

The Land Registry entry and plan is essentially a summary of the ownership details, covenants, charges etc. Tgis entry wont necessarily describe every boundary maintenance obligation. You need to try and get a copy (filed copy) of the original sale agreement (Deed). These are often 'filed' at the land registry and can be obtained for a fee. It's a postal request service unless your solicitor does it via their online account.

[scottishjohn]

2 hours ago, SilverShadow said:

Given that, then i think the onus is on us to maintain this

but is it your wall or theirs  or shared?

depends where the actual boundary is 

and considering it is retaing their land I would suggest it is their problem  not yours 

 

which house was built first ?

 

 i would doubt your land was reduced in height to build your house  ,why would anybody do that ?

 far more likely they wanted to build up some sloping ground to make a flat garden

finding orginal planning drawings if possible of your  house would show that would it not ?

 

Edited October 17 by scottishjohn

[joe90]

Is the wall leaning?.if not then I don’t think it’s a problem . Does it have expansion/movement joints ? If no expansion joints I am not surprised it has cracks at 10m long but  not necessarily unstable. 

[Conor]

Photos please

[Iceverge]

You aren't next door neighbours by any chance?!

 

 

https://forum.buildhub.org.uk/topic/40844-retaining-wall-inspection-by-neighbours-structural-engineer-questions/#comment-579797

[SilverShadow]

On 18/10/2024 at 11:22, joe90 said:

Is the wall leaning?.if not then I don’t think it’s a problem . Does it have expansion/movement joints ? If no expansion joints I am not surprised it has cracks at 10m long but  not necessarily unstable. 

 

 

Hey J90 - at the moment it's only leaning by about 5-10mm max, at the top. Tbh, it may be something we keep an eye on and potentially do later. But it's still good to get advice and impressions from the off

 

There's no expansion joints i can see, or draining holes either. So it would make sense that years of excess water/frosts have eventually taken their toll on it. We'll need to add some sort of drainage on whatever solution we end up with, to ensure no further issues like this. However, the water will drain directly onto the neighbours pathway (unless we add some sort of 'guttering' or drainage on our side of the wall foundations?)

 

I've enclosed pics of the wall in it's current state

 

Wall 1 & 2 pics - cracks up to 1.4m high

wall3 pic - view from our side down, showing retaining boundary wall & neighbours pathway

[SilverShadow]

On 17/10/2024 at 20:26, scottishjohn said:

but is it your wall or theirs  or shared?

depends where the actual boundary is 

and considering it is retaing their land I would suggest it is their problem  not yours 

 

which house was built first ?

 

 i would doubt your land was reduced in height to build your house  ,why would anybody do that ?

 far more likely they wanted to build up some sloping ground to make a flat garden

finding orginal planning drawings if possible of your  house would show that would it not ?

 

 

Hey John - good questions

 

I believe it's (most likely) our wall, as we're on the higher side & so it's retaining our land from encroaching on theirs. Looking at the title plan, it seems to be the boundary wall, and photo above would confirm this i'd imagine. Our land plot does seem to imply the ground was raised to make a level surface, which again suggests it'll be our duty to maintain.

 

Ours is the newer house too (can't be sure, but it seems like it was rebuilt over an old house foundation)

 

 

 

 

[SilverShadow]

Ps guys - we had a builder around the other day (just for advice, for now)

 

His thoughts were:

• This wall was doomed to fail, due to:
  • No drainage in the brickwork to allow water to escape
  • The hollow block (he thinks) probably doesn't have adequate concrete/reinforcement

 

His suggestion would be:

• Rebuild a similar replacement wall (hollow block), from foundations upwards
• Ensure that all hollow blocks are filled with concrete
• Plenty of drainage holes at regular intervals (the water would just drain out onto neightbours pathway - would this have any legal/building regs ramifications?)
• Adequate gravel in backfill, to allow proper drainage (i guess this would probably mitigate much of the above bullet point concerns)
• He mentioned something about Rebar - which i assume is the steel reinforcement our side?
• He also said the concrete & steel our side would be fine, as the weight of the soil above would help anchor everything down & keep it all rigid
• He didn't think the work was big/complex enough to warrant a structural engineers assessment

 

Apologies if some of this is a bit vague - it's not my forte, so something i could only take mental note of at the time

 

 

Cheers

Shadow

 

 

 

[scottishjohn]

your builder is correct 

If it had been filled with concrete first time and had a decent found  it would probably still be  ok 

hollow blocks are not strong and have little weight in them when not filled 

 so get a digger in pull back the soil to below ground level 

put a foundation in twiice as wide ,at least as the blocks  and at least 300mm thick with mesh 

 

whilst down to ground level fit a fench drain or juust fill back 30cm with gravel 

 first row of blocks need drain slots 

then rebuild with concrete filled blocks  or use std blocks on thier backs  this should give the weight required 

 and make sure if anything it is leaning back to you a little .

the only other way i see to repair is to still dig down at yourside and build another wall behind first one with same drainage 

 although looking at it  looks just like it never had enough foundation so it sank a bit and split blocks ,allowing them to move ?

gaps are widder at top so it looks like the bottom has sunk and oppened up the gaps 

 all guessing games at this point 

[joe90]

I tend to agree with your builder but not sure if it’s urgent, you could cut the cracks with a disc cutter and fill with mastic (as an expansion joint) you could always core drill some holes near the bottom, your neighbour has gravel backfill and not a lot of water will emerge. Leave the rebuild till it’s really required. 

[scottishjohn]

1 minute ago, joe90 said:

you could cut the cracks with a disc cutter and fill with mastic (as an expansion joint)

no sthil saw will have big enough cut to do a 9 wall"

even a 16"one will not cut that deep

[joe90]

2 minutes ago, scottishjohn said:

no sthil saw will have big enough cut to do a 9 wall"

even a 16"one will not cut that deep

No but the crack and the cut and mastic will tidy it up (keep the neighbours happy) till it does need rebuilding which could be years away yet 🤷‍♂️ (I did similar on a family members retaining wall, and it’s still there over 10 years after).

[SilverShadow]

34 minutes ago, joe90 said:

I tend to agree with your builder but not sure if it’s urgent, you could cut the cracks with a disc cutter and fill with mastic (as an expansion joint) you could always core drill some holes near the bottom, your neighbour has gravel backfill and not a lot of water will emerge. Leave the rebuild till it’s really required. 

 

 

Thanks J90 - if anything, we thought leaving the cracks there might be slightly useful, as make-do drainage outlets.

 

I guess as we've recently moved in & just seen these whacking-great crack/the amount of soil being propped up, then we panicked a bit. The neighbour said these cracks have been slowly growing the past 20 years (tho accelerated slightly the past few years)

 

It may be something we put off for now. But likewise great to get this feedback & determine the risk/urgency a little better

[scottishjohn]

6 minutes ago, SilverShadow said:

The neighbour said these cracks have been slowly growing the past 20 years (tho accelerated slightly the past few years)

that proves its probably settlement of the founds --so no panic then 

[SilverShadow]

45 minutes ago, scottishjohn said:

your builder is correct 

If it had been filled with concrete first time and had a decent found  it would probably still be  ok 

hollow blocks are not strong and have little weight in them when not filled 

 so get a digger in pull back the soil to below ground level 

put a foundation in twiice as wide ,at least as the blocks  and at least 300mm thick with mesh 

 

whilst down to ground level fit a fench drain or juust fill back 30cm with gravel 

 first row of blocks need drain slots 

then rebuild with concrete filled blocks  or use std blocks on thier backs  this should give the weight required 

 and make sure if anything it is leaning back to you a little .

the only other way i see to repair is to still dig down at yourside and build another wall behind first one with same drainage 

 although looking at it  looks just like it never had enough foundation so it sank a bit and split blocks ,allowing them to move ?

gaps are widder at top so it looks like the bottom has sunk and oppened up the gaps 

 all guessing games at this point 

 

 

Great response again, mate!

 

Yeah, i think gravel in the backfill is what he suggested.

 

I'm not sure, but i don't think the guy can get a mini-digger down there - the neighbours side is down some steps and no more than 1m wide. So if anything he'd probably use one our side for the top section, and then hand-dig the rest out

 

Looking at a few websites - it reckons up to £300/m2 for this type of wall. So it's likely it'll be circa £4k or more for a 10m * 1.3m high - in which case it can definitely wait!

[saveasteading]

It looks quite serious to me. I wouldn't expect a wall to fail by vertical cracking.

As suggested above, it has probably been built wrongly in several ways.

 

I would drill drainage holes as a first step in risk reduction. They should be near the bottom. Best is to insert pipes which will act as spouts.

That will stop it acting as a dam, and the load from the water will disappear.

Because it may not be filled behind with gravel, but with earth,  I would add some higher holes too.

The holes should be fairly wide, to prevent them just blocking up again. 25mm?

It isn't a high wall so any continuing  failure will probably be small movements.

Do the holes, patch the cracks and keep an eye on it.

Otherwise it is best taken down and rebuilt with reinforcement, concrete infill and drainage.

[Blooda]

19 hours ago, SilverShadow said:

The neighbour said these cracks have been slowly growing the past 20 years (tho accelerated slightly the past few years)

 

You can get cheap crack monitors fairly cheaply from amazon.  Fitting these would give you an idea of if and how much the cracks are moving.  Also will give the neighbours the comfort you are taking this seriously.

 

Crack Monitoring Record and Tell-Tale Crack Monitor Kit for The Standard and Corner Tell-Tale Record : Amazon.co.uk: Business, Industry & Science

 

 Randomly found advert ^^^^^^ others are avaialble.  

[ProDave]

Am I having a DeJaVu moment or have I seen that exact wall discussed here before (by previous owner?)

[joe90]

5 hours ago, Blooda said:

You can get cheap crack monitors fairly cheaply from amazon. 

You can glue a small piece of glass across the crack, it will break if the wall moves.

[saveasteading]

2 hours ago, joe90 said:

it will break if the wall moves.

Yes it will. but I think we know it is moving. How much though?

[joe90]

2 hours ago, saveasteading said:

Yes it will. but I think we know it is moving. How much though?

Perhaps I should have said ‘it will break if the wall STILL moves” 🤷‍♂️