Pre-purchase due diligence helps identify gypsum risk

NHBC’s Land Quality Service (LQS) team began working with Keepmoat Homes on two sites in the North East of England in 2025. By consulting with NHBC and undertaking due diligence prior to the purchases Keepmoat Homes was able to make informed decisions and mitigate potential risks relating to gypsum below the sites.  

Background:  

The LQS team were commissioned after an initial ground investigation. In both instances NHBC’s role was to assess the information, identify where additional work was required and inform on any potential for abnormal costs related to the noted gypsum risk.  

The team’s advice allowed the customer to understand potential risks, NHBC's requirements regarding the gypsum geohazard and supported the accurate estimation of what future works were required.  

By gaining a clearer view of the approximate time and costs involved Keepmoat Homes were better able to make informed commercial decisions in relation to the purchase and any abnormal costs relating to the future residential developments.  

Why is pre-purchase due diligence important?  

Prior to consideration for new home development both sites were deemed greenfield land and had been in solely agricultural use for some time.  

However, gypsum bedrock underlies these areas. This meant there is a potential dissolution risk, presenting a challenge for residential development and requiring further ground investigation. It could also mean the need for bespoke engineering solutions to mitigate risks and ensure new home warranty criteria could be met.  

In Ripon the development is situated on an outcrop of gypsum where there is a high risk of sinkholes developing, necessitating the accurate mapping of the area to enable the development to be located away from it. The LQS team were able to provide technical advice on how to further delineate high-risk areas.   

At the Darlington site a geophysical investigation was used as the primary evidence for the dissolution assessment. It found six areas of interest which had not been investigated further using conventional methods. Again, LQS was able to confirm the requirements for additional investigation to determine the degree of risk presented at this site.   

Support from NHBC’s Land Quality Service:  

The LQS team provided the Technical Memo service, which specifically considers one aspect or query from a customer in relation to our Technical Standards Section 4.   

This allowed the team to assess the current ground investigation and provide pre-purchase advice, particularly regarding the level of risk and likely impacts of gypsum dissolution.   

As Sam Fuller, Specialist Geotechnical Engineer at NHBC explained “By engaging with LQS before both the land purchase and the start of any development, Keepmoat Homes were able to obtain NHBC’s insight on the ground investigation already undertaken as well as what additional investment, both in terms of time and financial resources, could be required. This provided both a view on the future work needed and any previously unanticipated costs associated with gypsum risk management.”  

Developing the site:  

The Ripon site is now moving forward with more Ground Investigation planned. Once complete, the 10-hectare site will provide up to 190 high-quality new homes.  

Brian Cunningham, Technical Director at Keepmoat Homes commented “At Keepmoat Homes we’re committed to providing high-quality homes and we work hard to ensure that is the case from the start of each project. By engaging with the team at NHBC we’ve been able to make informed decisions about the sites from the very beginning and adapt our plans for development if necessary. Early engagement and proactive discussions have enabled us to make the right choices for our business, our developments and most importantly for our customers.”