Natural subsidence and pluvial (surface water) flooding

justpassingthrough24

Hi all, I'm a first time buyer and am currently quite far into the buying process. My level 3 survey report came up with a few issues and I have already negotiated some minor repair work with the sellers. However I've just received a lengthy email from my solicitor with multiple documents and a number of points that they want me to look into and action, and I really have no idea where to start. The main reason I've come here for advice is because of two specific points:

1. The property is within an area of moderate to high risk of natural subsidence.
2. The property is within an area with significant risk of pluvial (surface water) flooding.

I am just not sure what to make of this, because my survey report said the property is not at risk of flooding from rivers but did not mention anything about surface water flooding. They also said there was no evidence that the property itself has been affected by subsidence, so I'm not sure what to make of this in the solicitor's report. The property is in London and I know from a brief bit of research that it's not unusual for London properties to have natural subsidence. But this coupled with the significant risk of pluvial flooding is giving me massive cold feet. I don't plan on staying in this property for more than 5-7 years, and the onward selling is what puts me off the most rather than the actual flood/subsidence risk.

They have advised that I obtain insurance quotes to ensure I can be covered for both the above. What I don't get is that they have also sent some quotes directly to me but these specifically say that flooding risk is not included. I don't really understand why they send quotes that don't include this but advise that I need to get quotes that ensure the above risks are covered? What am I missing?

Would be very grateful for any advice. If it's not obvious from my waffle of a post, I'm feeling a bit overwhelmed with all this information and really have no idea where to start!

And just before anyone says it, I do fully intend on getting some clarification from my solicitor ASAP. Just quite hard to juggle speaking to them in working hours while also working a patient facing job, and so here I am posting on MSE at 10.30pm.

Thanks in advance

MysteryMe

Some degree of settlement is common on clay soil, which is what you will find under most if not all of London. That does not mean the settlement / subsidence will continue or worsen.

As to your purchase, did the surveyor observe any signs of subsidence in the property, or signs of water damage?

Have you asked neighbours if there has been surface water flooding affecting property or if they know of examples of subsidence? Obtain your own insurance quotes, ring up established insurance companies where you can explain you are in the process of buying a property and want to know if it insurable.  Ask the vendors who insures their property and are there any exclusions.

Insurance companies have access to the same databases as your solicitor's searches, except the insurance companies also have the benefit of real life data dealing with claims for subsistence and flooding. 

If you are able to obtain insurance without exclusions then you have to exercise best judgement and deal with the what is rather than what might. 

justpassingthrough24

MysteryMe said:

Some degree of settlement is common on clay soil, which is what you will find under most if not all of London. That does not mean the settlement / subsidence will continue or worsen.

As to your purchase, did the surveyor observe any signs of subsidence in the property, or signs of water damage?

Have you asked neighbours if there has been surface water flooding affecting property or if they know of examples of subsidence? Obtain your own insurance quotes, ring up established insurance companies where you can explain you are in the process of buying a property and want to know if it insurable.  Ask the vendors who insures their property and are there any exclusions.

Insurance companies have access to the same databases as your solicitor's searches, except the insurance companies also have the benefit of real life data dealing with claims for subsistence and flooding. 

If you are able to obtain insurance without exclusions then you have to exercise best judgement and deal with the what is rather than what might. 

Thanks for the reply.

The surveyor mentioned "Some minor evidence of cracking was noted throughout the property and these have been detailed below. However, no evidence was seen of any cracking which might indicate that the property is

subject to subsidence or unusual settlement". I am assuming that would give the property the clear for now, even though it is supposedly at risk of subsidence?

Getting some information from neighbours is a good idea. I'll get some quotes from insurers and ask my solicitors to see what the sellers had been doing also.

The subsidence sounds like it is generally expected and quite common. But how common is the risk of surface water flooding across London/the UK? The information online seems to say it's a huge risk to property and life... but it also seems the risk is present in most nearby places from my brief click around on the flooding map. It would be good to know if this is actually quite common across London and not just the area I am buying as I just feel massively put off this place from what I'm seeing so far.

MysteryMe

The opinion of your surveyor is far more relevant and contextual to this property you are interested in.

The surveyor is telling you that are signs of historic minor settle (which I mentioned was common on clay) but nothing to suggest that it has continued. That would only tend to occur if for example roots from a large tree nearby started encroaching or there was something to cause significant groundwork disturbance like collapsed pipework.

As for surface flooding, are you familiar with the area of London you are looking to buy in? You could research local newspapers to see if there are any articles about flooding, households who have had their homes flooded tend to be the sort of human interest story that will get in the local papers. Look at facebook groups that cover that area, ask them.  If you see refuse collectors about, speak to them. They are on the roads every day and will know if they flood. Local lived experience is invaluable. These will be people with no skin in the game so will be upfront if their are issues whereas your vendor may not be quite as candid.

My gut feeling is that this property is going to be fine, and it's just your solicitor pointing out every eventuality under the sun to cover their backs. 

justpassingthrough24

MysteryMe said:

The opinion of your surveyor is far more relevant and contextual to this property you are interested in.

The surveyor is telling you that are signs of historic minor settle (which I mentioned was common on clay) but nothing to suggest that it has continued. That would only tend to occur if for example roots from a large tree nearby started encroaching or there was something to cause significant groundwork disturbance like collapsed pipework.

As for surface flooding, are you familiar with the area of London you are looking to buy in? You could research local newspapers to see if there are any articles about flooding, households who have had their homes flooded tend to be the sort of human interest story that will get in the local papers. Look at facebook groups that cover that area, ask them.  If you see refuse collectors about, speak to them. They are on the roads every day and will know if they flood. Local lived experience is invaluable. These will be people with no skin in the game so will be upfront if their are issues whereas your vendor may not be quite as candid.

My gut feeling is that this property is going to be fine, and it's just your solicitor pointing out every eventuality under the sun to cover their backs. 

Interestingly, there is actually a felled tree near the property survey did mention this could risk structural damage, but my thoughts were that it has stood for 100 years without being pierced by these roots.. am I right to somewhat ignore this?

The main worry I've got now is climate change and how quickly this appears to be affecting the subsidence risk. I spoke to a few friends who purchased properties in a similar area within the last few years and the risk came up mostly as "moderate". Whereas this property is flagging a very high risk of shrink-swell subsidence and scored 9s and 10s pretty much across the board. All the houses in the nearby area seem to either be moderate or high risk according to the environmental search. Again, I have convinced myself this is to be expected in London and any property I end up with will likely have a similar risk..? I wouldn't be so concerned if I wasn't planning to sell on in 5-7 years.

Funnily enough it turns out the mention of pluvial flooding risk was an error on the solicitor's part. I only realised after speaking to the locals who were baffled, then re-scouring the search report and flood risk websites which confirmed the same... probably a copy and paste job from the solicitor but doesn't really fill me with confidence.

Really do appreciate your replies and reassurance. The FTB world for someone who hasn't got the first clue about property is extremely daunting without this place to come to for advice 

Annemos

Just to say, that tree roots do not "pierce" foundations.

(I also thought that... before my place actually subsided and I found out I had always had completely the wrong idea. Subsidence is NOT caused by tree roots pushing into a foundation or piercing it.)

What actually happens with Subsidence on Clay Soil is the following: 

1    If Tree is same age as home or was planted after home was built.   So soil under the foundation when the home was built had its normal moisture content.   

The Tree then grows and grows over say 30 years and if the tree is close enough and the foundations not deep enough, then the many FIBROUS roots will suck out the water in the clay beneath the foundations, in the summer seasons. And if a serious drought, then the the home may subside and crack. (That happened to mine. Zigzag cracking outside.) The foundation has moved downwards.

One then gets oscillations in the cracks between the Winter wet seasons and the Summer dry seasons. As the clay rehydrates and then dries out again. 

One cure for this is to remove the Tree and that is not normally a problem. The ground then hopefully rehabilitates and the ground and foundation then remain stable. 

Note that the root action can take place in an area that has a radius the same height as the tree! 


2    If Tree is older than the home. So foundation was built on clay soil that was already dried out by Tree root action

If one removes the Tree, then it stops taking up any water.  The rain goes back into the clay over subsequent rainy winters and the soil can then swell and one gets heave. This is the opposite of Subsidence and the foundation moves UPwards.   Apparently this can last for some years and may cause worse damage than Subsidence.   So before any tree is removed, a Heave survey should be done by Structural Engineers, taking into account the make-up of the Soil and the age of the Tree.  If there is a Heave risk, then alternative methods must be used instead of removing a Tree, 


Hope that explains it a bit for you. Oak trees can be very old, for example. 

justpassingthrough24

Annemos said:

Just to say, that tree roots do not "pierce" foundations.

(I also thought that... before my place actually subsided and I found out I had always had completely the wrong idea. Subsidence is NOT caused by tree roots pushing into a foundation or piercing it.)

What actually happens with Subsidence on Clay Soil is the following: 

1    If Tree is same age as home or was planted after home was built.   So soil under the foundation when the home was built had its normal moisture content.   

The Tree then grows and grows over say 30 years and if the tree is close enough and the foundations not deep enough, then the many FIBROUS roots will suck out the water in the clay beneath the foundations, in the summer seasons. And if a serious drought, then the the home may subside and crack. (That happened to mine. Zigzag cracking outside.) The foundation has moved downwards.

One then gets oscillations in the cracks between the Winter wet seasons and the Summer dry seasons. As the clay rehydrates and then dries out again. 

One cure for this is to remove the Tree and that is not normally a problem. The ground then hopefully rehabilitates and the ground and foundation then remain stable. 

Note that the root action can take place in an area that has a radius the same height as the tree! 


2    If Tree is older than the home. So foundation was built on clay soil that was already dried out by Tree root action

If one removes the Tree, then it stops taking up any water.  The rain goes back into the clay over subsequent rainy winters and the soil can then swell and one gets heave. This is the opposite of Subsidence and the foundation moves UPwards.   Apparently this can last for some years and may cause worse damage than Subsidence.   So before any tree is removed, a Heave survey should be done by Structural Engineers, taking into account the make-up of the Soil and the age of the Tree.  If there is a Heave risk, then alternative methods must be used instead of removing a Tree, 


Hope that explains it a bit for you. Oak trees can be very old, for example. 

Thank you, that is incredibly helpful. My naivety knows no bounds
Is there some way of finding out when the tree was planted? I don't even know what kind of tree it is/was to be honest.

Out of interest, how exactly does felling the tree change this risk vs removing the tree? I can't seem to find much online other than one of the solutions to prevent subsidence is to fell the tree.

Annemos

My naivety was like that too. As a regular homeowner, one only really gets to learn about this if one either knows someone who had Subsidence.... or it strikes ones own home. 

We can see on our original house deeds that one old Cherry Plum Tree was shown on the corner as our new Estate was being built. And there were several others in our vicinity, too, in the older Estates. (Luckily they can stay as they are older than our homes. My Insurance-provided Tree Inspector confirmed all this, along with the likely age.)

Maybe your potential neighbours know what was there. Or the seller, if it was taken down recently. Sometimes one can even find old photos on-line and also older Google Earth footage is sometimes still available.

If it was on Council Land, it might be the Council who chopped it down and they would have records with their Land Maintenance people. 

I believe qualified Tree Inspectors would know how to get to the bottom of what type it actually was and how old it was through testing and looking at the old stump, even if the Tree has been removed. 


When I said removing the Tree, I meant chopping it down completely (felling it) and also stump grinding the remaining stump so it does not regrow. or send up sprouts. Or injecting Poison in the Stump may have the same effect, but I imagine that is perhaps a bit slower method of killing all the roots. It also has to be done in the right place on the stump and immediately. 

One of mine was a Sweet Gum Tree (Liquidambar). Sent up sprouts for 2 years after being cut down, even though Council injected the Stump. Brother-in-law and I were going out and injecting any visible roots with the Poison both years. That did the trick. (We could see which remaining roots the sprouts were shooting up from and they had the same little leaves! I was on the warpath with them!)