Types of Underpinning and Lender Attitudes
There are several methods of underpinning used in residential properties in the UK. Mass concrete underpinning (also known as traditional underpinning) involves excavating sections beneath the existing foundation and filling them with concrete to a greater depth. This is the oldest method and is widely used for properties built on clay soils that have experienced subsidence.
Mini-pile underpinning involves drilling steel piles to a stable stratum deep below the surface, then connecting them to the existing structure with a reinforced concrete beam. This method is less disruptive and can be used where access is restricted. Beam and base underpinning (also called pier and beam) involves excavating piers of concrete at intervals beneath the existing foundation, connected by a reinforced concrete beam that transfers load to the piers.
Resin injection underpinning is a more modern technique involving injecting expanding resin into the subsoil to stabilise and compact it. This is less invasive and can be completed with minimal disruption. Lenders vary in their attitudes to different underpinning methods, and some specialist lenders take comfort from more modern techniques that come with longer guarantees. Your broker can identify which lenders are most receptive to the specific method used on your property.
Documentation Required to Remortgage an Underpinned Property
To give your remortgage application the best chance of success, you need to assemble a comprehensive pack of documentation before approaching any lender. The most important document is the structural engineer's completion certificate, which confirms that the underpinning was designed and supervised by a qualified structural engineer and that the completed works are structurally sound. Without this, almost no lender will proceed.
You should also obtain the original underpinning contractor's completion report, which details the method used, the depth of the new foundations, and any ongoing monitoring requirements. If the underpinning was carried out under an insurance claim, the insurer's sign-off documentation should be included. Many properties are also covered by a National House Building Council (NHBC) or similar structural warranty which can provide additional comfort to lenders.
Building regulations completion certificates are also important, as underpinning work is notifiable under Part A of the Building Regulations. A certificate from the local authority building control department (or an approved inspector) confirms the work was inspected and approved. A monitoring period log showing that no further movement has occurred since the underpinning is also helpful, particularly for more recent cases.
