Groundsure medium-high subsidence risk - now what?

janipt

Hi all, according to Groundsure the property I am buying is within 50 meters of a medium to high natural and non-natural subsidence area but is, itself, in a "negligible - very low" risk area. It is a mid-terrace build between 1968 and 1974. There has been historic chalk mining in that part of Croydon. Which of these next steps would you consider essential and which are a waste of money?

What I have done:
- I have visited the the property and it looks like solid construction with no signs of subsidence. I have looked at the council records and there are 20 building control records that mention underpinning within the group of postcodes in the general 250m+ radius since 1998 (none are on the property's street or the same postcode and they are quite localised to certain streets only). I have enquired about reports that take surface insurance claims for subsidence but it seems like these only relate to coal mining, so the reports would not be relevant to chalk mining (is my current understanding).

What I could do in addition:
- The council would charge £25 for underpinning records on a specific address (I don't see much point in getting these, unless they cover pre-1998 era and properties beyond the ones in the building control records so I have enquired about this).  If I get the reports for the whole terrace it is £125.
- I have emailed the mining authority for a chalk-mining related search, also. Again - not too sure if it would be relevant. Sounds like £60-70 or so.
- I have enquired about a quote from a surveyor (thinking about the Homebuyer report at £600 as the property really does not have any signs of structural issues and it would be a waste of money to pay £300 more). I am actually trying to establish whether getting a structural engineer in might be better, instead of going down the surveyor route.

Just to be clear - I think I am at a bit of a risk here to overdo it as there is really no evidence of subsidence affecting the property itself and the report only turned up mid-high risk areas within 50m. What would you do if you had to prioritise which further measures to take?

Doozergirl

You can have a structural
engineer look it over, but I'd be interested in why the other streets had issues.  Have they built on landfill over the quarries, for example. If you aren't in the same position, you aren't at the same risk.  All environmental searches will pull up stuff around the houses that doesn't look all that healthy, especially in built up areas.  

A local structural engineer may well know the answer to why the localised subsidence, but also speaking to the land search department at Croydon Council might help interpret results.  I have found ours most helpful in the past.  

Interesting that it's a chalk base, but most of London is on a clay base which itself is the riskiest type of base and not that many people are affected by it or consider it a major risk.   Subsidence isn't pleasant, but it's not a kiss of death and I'm sure a chalk base is better than the clay you're surrounded by.   We recently had a very long hot summer that would have brought out many issues.  

The main point is that if you aren't happy with this then you may have to find a different area altogether to try and mitigate a risk that may not exist.   All houses come with risks and random defects.  And all houses move!  If this isn't showing signs, then that's as good as it gets.  

janipt

Thanks so much for your response. It is quite reassuring. 

Within 250m (which is the reach of my mining report radius) - 3 properties on 2 streets were built over infilled land. 1 property on a separate street sounds like it had tree related issue. The property I am looking at is outside the infilled land zone.

Within 500m (which is the reach of my natural subsidence report) and beyond (as I researched all of 238 active postcodes - Jackson Pollock madness mode) - it is either high risk of natural ground subsidence or my report does not cover the area. So could also be infilled. It is over 4 streets and most addresses are actually flats within 3 specific buildings. 

As you are saying, I think I am probably trying to mitigate a risk that really does not exist.