Buying a house with high risk of shrink-swell hazard

gsermaid

Hello, I'm in the process of buying a house which is 4 years old and still has 6 years to go under the NHBC warranty.

The land searches report has come back indicating the following risks:
- High risk of shrink-swell hazard
- Moderate risk of natural ground subsidence

This is apparently due to the house sitting on clay soil which is not seasonally stable; most properties in that estate seem to have the same risk profile.
The report also states that "building characteristics are taken from Office for National Statistics Lower Super Output Area data, and as such are generalised to give the
most likely characteristics for the property. Any assigned rating should not be relied upon if the property is a new build", which I guess the property in question is.

I've had a full structural survey done on the property which didn't indicate any signs that subsidence has taken place (no cracks inside or outside of the property, other than hairline cracks above door openings and along the lines of plasterboard joints "which are not unusual or structurally significant" according to the surveyor). The surveyor tells me that this is a modern property that would have adequate foundations for this type of soil and that no further action is needed.

Despite the reassurance from the surveyor, I'm still am very concerned about this risk...

Am I meant to just trust that the developers did a proper job and put adequate foundations in place for this type of soil?
Should I ask the seller to see some plans/evidence that the developer put adequate foundations?
Is anything else that you'd recommend I do to ease my mind?

Many thanks

Doozergirl

To put this in context, most of London is built on clay.  Most of London's housing stock doesn't have foundations.  It is a risk there and people buy and live perfectly happily. 

It is likely that your entire area is clay, so if it isn't this house, it would need to be somewhere else entirely.

Your house had to be built to regulations, no one will get a mortgage without that certificate. 

The thing you do have is a structural warranty.  The value of those is debatable but it is certainly better than no foundations and/or no warranty. 

You need to put this out of your mind.  Your at less risk than others locally.     

JJR45

The foundations are likely to have been dug to a depth to take this into account and building control would have signed it off at the foundation level so it should be fine.
With the extreme weather, we have seen over the last few years if there were an issue it would have likely shown up by now.
We had a house made in the 70s with shrink/swell soil and it was fine (with most probably less strict foundation rules then), the garden will get uneven over time though.

GDB2222

Doozergirl said:

To put this in context, most of London is built on clay.  Most of London's housing stock doesn't have foundations.  It is a risk there and people buy and live perfectly happily. 

It is likely that your entire area is clay, so if it isn't this house, it would need to be somewhere else entirely.

Your house had to be built to regulations, no one will get a mortgage without that certificate. 

The thing you do have is a structural warranty.  The value of those is debatable but it is certainly better than no foundations and/or no warranty. 

You need to put this out of your mind.  Your at less risk than others locally.     

As you say, most of london is on a shrinkable clay subsoil. We own a Victorian house, and when we were thinking of turning the cellar into habitable space we hired a builder to dig down to expose the footings in a couple of places. He allocated most of the day to do the work, and turned up with a big kango.  It actually only took him a few minutes to dig down the six inches needed. The house has never moved.

TripleH

My parents' home (Victorian house) was built on clay. (Clay for bricks was dug out the earth a few metres behind their house).

It suffered subsidence in 1976 and the cellar flooded in 1987 and 2007 not helped by the clay soil.

No evidence of further subsidence was found when it was sold in last couple of years.

user1977

Have a look at the planning papers on the council website - chances are they will include much more detailed reports on the ground conditions than the very sketchy desktop search you're looking at (which never seem to be particularly useful).

I wouldn't be concerned about a very recent build not having taken the conditions into account