During the design works as well as planning application (dependant on your local council), various site and ground conditions might need to be confirmed. For this reason, some of the below investigations will need to be carried out:
Ground and Soil Investigation – this report would include details such as existing ground conditions, ground contamination and water table levels. Your engineer will base his design on the information provided by this report so you will most likely need to appoint a company to carry one out. As the soil and ground conditions are an important design factor, this will highly affect the outcome of the overall cost of a basement conversion or the new basement constructions costs.
Basement Impact Assessment – this report will include a desk study to check the history of the site, to determine the geological and hydrogeological conditions and risk of surface water flooding, to assess the risk of slope stability problems. Dependant on your local council, a ground stability analysis may also be required which to show that any ground movements will not have a detrimental effect on surrounding structures.
Walk Over Survey – this would typically be included in the Basement Impact assessment and consists of a site walk thru carried out by the surveyor to assess existing site conditions such as: the structural condition of the property; potentially contaminative features, materials or land use within the site or in its immediate vicinity which are likely to give rise to significant contamination risks.
Tree Survey Report (Arboricultural Report) – should you have any trees in the vicinity of the basement, a survey will mostly be required which will assess if the new structure will affect the tree and to come up with any recommendations for the designing engineer as well as your appointed contractor.
You can search specialised companies who can carry out detailed soil and ground investigations required at design stages here
In the party wall award, it may be imposed that the structural works (mainly during the house underpinning works) a monitoring system will be installed to all properties involved. The purpose of this is to detect at early stages any movements within the structures. The system to be installed consists of target points affixed to your as well as adjoining properties. These target points will be read at the agreed intervals and if any movement is detected the underpinning of the foundations, the appropriate actions will need to be taken and the underpinning methods revised.
Experts in monitoring of ground and building movement, settlement and vibration during basement projects are available here