Basements and underpinning: the party wall position

Notices you are likely to need

• Excavation notice, because the dig will go well below your neighbour's foundations
• Party structure notice, if you will underpin or cut into the party wall
• Sometimes notices to neighbours further along, under the 6-metre rule

What the award is likely to cover

• Detailed structural drawings and calculations, reviewed for the neighbour
• The sequence of underpinning, often in short sections
• Temporary propping and support
• Movement monitoring of the neighbour's property during the work
• Drainage and groundwater measures
• Working hours and vibration limits

Costs

Basement awards cost more than those for lofts or extensions because there is more to review and inspect. The neighbour's surveyor may need a structural engineer's input, and that cost usually falls on the building owner. Your neighbour can also ask for security for expenses, a sum held back in case the project is abandoned part-way.

Timetable

Allow longer. A basement award can take several weeks of review on top of the notice period. Starting the party wall process early, while the engineer is designing, saves time.

Underpinning without a basement

Underpinning to deal with subsidence, or to deepen foundations under a shared wall, is also party structure work and may involve excavation. The same principles apply on a smaller scale.