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Settlement - House extension pulling away from the existing house

Gus Potter

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For BH folk that have "movement"


Today I was installing tell tales to monitor movement or not. Have a Client that wants to refurbish and expand an existing rear extension.




But the existing extension we want to upgrade has parted company with the existing house. You can see the "partin some 1.0 m to the right of the light bulb.


I need to know if the movement has stopped or is relatively benign before I go ahead and design the upgrade. The extension is on CLAY soil so expect some seasonal movement.


The photo below shows a smallish crack at low level and at the top there is some 14mm of separation. Now the Client wants to install a kitchen along this wall so if I don't get a handle on this then.. well.. trouble ahead!


The house is semi detached... the neighbours have just introduced some kind of steel box frame next door as they have knocked out the back of their house.. I think they have added load to the party wall foundation. I want to make sure that my Client is protected as if later if something goes wrong.. my Client will get the blame to start with... best to be prudent as "last man on the job gets the blame" . I'm monitoring partly to see if the folk next door have caused an extra problem.


You can get tell tales that do corners but they don't give you much room to get a drill in to fix them. Here I have cut brackets from offcuts of metal framing so have much more room to play with.


The whole lot is screwed and fixed with construction adhesive.. so I can be sure the screws don't slip.


The tell tales are actually quite fragile so you need to be gentle with them.. again the adhesive cuts you a bit of slack here and allows you to adjust the tell tale alignment.


I installed six tell tales and it took me about six hours.. you need to take your time as the surfaces you are fixing to are rough and the tell tales need to align.


But there was a bit before today. I spent time looking at the job and identified about six possible causes for the movement, there may be more, I need to sleep on it further. The main thing is to think of everything that could cause movement, be logical, look at probablilty and narrow the field down.. I think there may be more than just one cause here.


The nity gritty of the tell tales. They have a cross hair that sits over a paper grid. They come with pins that lock the cross hairs over the zero point of the grid. While you screw them to the wall the screws can't be too tight as they crack the plastic tell tales. It's the adhesive that does the real work holding them in postition.


I'll leave them for a couple of days for the adhesive to set and then take out the pins. Hopefully the wall is not moving that much that the pins shear or the tell tales fracture over the next  couple of days..!


When I take out the pins the cross hairs may shift, hopefully not, then I'll record what happens over the next few months while we get the planning permission in place and detailed drawings / structural calcs for the BC permissions. My gut feeling is that things will pan out ok.. but I need to do some monitoring to mitigate risk and be responsible.


In posted this as I hope it helps BH folk see how we go about this and how you could do this for yourself as an excercise. If you go about it the right way, photograph and take records then who can doubt you?










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That is a fair old crack. I have got some under the windows of my old bungalow. they are about 5 to 6mm wide. I have owned it for 6 years, and they have never got any worse. to be honest i don't know if they close and open during the seasons. I do know that it is only about 1 meter from a Poplar tree. The soil test just fell into the low shrinkabiliy band, (just) The footings are 9 inches deep. When i pull it down it will be interesting to see if the footings are cracked. My friends old place about 500 yards away, has got similar cracks to yours. Narrow at the bottom, and wider to the top. His have got wider, and wider over the 5 years he has owned it. it will be interesting to hear what the problem is with the place you are monitoring. 

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Reminds me of the near identical  crack in my lounge wall. turns out it was the rainwater down pipe on the external of the wall not fully connected into the underground pipework washing away everything around it, thankfully the Victorians built this house not to badly so after the repair it’s not moved in 18years.



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10 minutes ago, Big Jimbo said:

That is a fair old crack.

Yes once you can put your finger in it.. it is a structural crack!


11 minutes ago, Big Jimbo said:

Narrow at the bottom, and wider to the top.

One thing that I have in mind is that the side walls of the extension are resting on the ledge (scarecement ) of the original house founds and the front of the extension has settled... hence the widening gap as you go up. But it may not be that obvious so I need to rule out all other reasonable causes as best I can.


There are some trees lurcking about, different ages and varying depths of founds, leaking drains and Network Rail have been messing (piling for electrification) about near the site apparently.. will investigate next week but will put on a shirt etc and some head gear on so I "look official" before I go for a wonder around the public part of Network Rail property. I will go look at as many possibilties I can think of but want to check that they have been doing next door... very important.


I'll keep posting when I can so folk can follow the process and how I reach a reasoned and evidence based conclusion.






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17 minutes ago, TonyT said:

Reminds me of the near identical  crack in my lounge wall. turns out it was the rainwater down pipe on the external of the wall not fully connected into the underground pipework washing away everything around it, thankfully the Victorians built this house not to badly so after the repair it’s not moved in 18years.

Yes sometimes it can be that simple.. no need to panic... easily fixed.

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This retaining wall at Porthleven has had some 'tell tales' on it for years.

You can just seem them.  One just to the left of the telegraph post and the other a few metres to the right.



The harbour wall usually takes the brunt of the storm waves, but there will be a lot of water that filters down the higher wall.

The storm below took out a number of the stone blocks on the harbour wall and then moved them down the road about 20 metres.



Edited by SteamyTea
A better video.
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On 31/08/2023 at 14:49, George said:

What did you charge for the day?

Good question @George


There is a bit more to this story.


It started with the Client asking me round to have a look at upgrading a rear extension built say 30 years ago, badly, so it is done now... leaking heat, windows and doors beyond repair... flat roof .. no / negligable insulation. On the end of the rear extension there is a conseravtory that is done but has what look like a good found.


Putting my Architectural design hat on I was thinking of knocking down the conservatory down to dwarf wall level and incorporating that into the upgraded extension. For me there is the structural design, calcs etc and the Architectural side. I wear two hats so that allows me to provide a one stop shop.


When I went round to first meeting the Client I spotted these big cracks. After talking about the Architectural opportunities I started to discuss how with my SE hat on I would make it all work. At that point I said.. I won't do the job unless we can understand more about the cracking. They told me that the neighbours (semi detached house) had just slapped out their rear elevation and put in a "goal post frame".. I'm thinking I bet their SE has not thought this through and not provided enough detailed drawings for the builder to follow.  Maybe I will be pleasantly surprised.. but from experience I know that SE's under the Scotland SER scheme are cutting corners... and I don't want their bad work putting my Client at risk... and me also.


The Client mentioned that Network rail have been working near their property.. but I know the location, nipped round to have a look at what they have been up to and concluded that none of their retaining walls have shifted such that they could have impacted on my Client's property to any significant degree.. I had a look at possible ground vibration.. again.. was happy with that.


Now given that I'm doing all the design work for the project I itemised the tell tale installation and crack monitoring out at £600.00, I don't charge vat as below the threshold.  The tell tales cost about £100.00 ( bits and bobs and me driving about), I allowed £300.00 for my day to install and I'll tie in the monitoring with my visits to do the dimensional survey and when I meet with the Client as part of the usual design process. It will take about six months to do the design / planning and building permissions.. nothing happens fast with the council... but six months is enough time for me to get a feel for any significant movement.. before the big bucks get spent.


I have explained all this to the Client so they are fully on board with the approach. They know that it is not perfect but we are doing the best we can in time we have to a avoid a catastrophic outcome...


This job is a little different as normally I would often monitor settlements over a longer period of time. But here my gut feeling is that the cracks are long standing and pretty much stopped moving.. but I have my doubts about what their SE / Builder has been doing next door. If they have made a mistake then I should be able to clock this pretty quickly before my Client starts their work.. as soon as they start the neighbours could blame them and me and they are off the hook... as last man on the job gets the blame... or has to prove they are not.. very costly potentially.


If I find things are moving then I would dig deeper.. maybe phone up the SE for next door and say.. I'm finding this.. do you want to have a chat?


I can't expose my Client to this risk.


The rates would be different if it was isolated settlement monitoring.. much will depend on the risk element etc. For me as I'm in at the start of the job and designing it I can make sure I stay away from things like big point loads in vulnerable spots..close to party walls etc so reduce risk that way.













Edited by Gus Potter
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Update on Guses tell tales.


Week past Monday I went back to take the locking pins out the tell tales, now they are free to move and the adhesive has set.


On two of them the locking pins were binding fractionally. Probably does not mean much as the fixings were probably settling in.


I'll wait and see what things look like in another couple of weeks. Have asked the Client to keep an eye on them too and if they see movement to give me a call. That said I warned them not to look at them every day as they will start to live in your head.











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