Underpinning costs

Underpinning is when extra support is added beneath a building to prevent it from subsiding (sinking into the ground). You might have to do this if you or your neighbours are dealing with subsidence, or if you’re planning on building an extension. To help you out, we’ve laid out the typical underpinning costs.

Underpinning costs UK

No matter whether you’re underpinning your house’s foundations or underpinning a conservatory, costs will vary depending on a number of factors including:

• Location: For example, labour is more expensive in London and there’s also less space between buildings which makes the work harder.
• Size: Pricing will depend on the depth and width of your foundations.
• Type of property: For example, prices for apartments and bungalows will usually be lower than prices for a three-bedroom house.
• Slopes: If your property is built on a slope, prices could be higher.

All this will help to determine what method of underpinning is required, which will arguably have the biggest impact on price.

Underpinning costs per metre

The average cost of underpinning per metre squared is in the region of  £1,500 to £2,600. The cheapest method is generally mass concrete pour, which has an average cost of £1,500, while piling is the most expensive at £2,600.

Costs of underpinning

There are a number of costs you’ll have to factor in on top of the cost of underpinning itself. These include:

• Party wall agreements: If you live in a semi-detached or terraced house, you’ll need to give your neighbours two months’ written notice. If they don’t agree to the work or they don’t respond, you’ll have to get a surveyor to inspect the boundary wall and draw up an agreement that lays out the condition of the wall. You’ll need one for each neighbour who refuses to consent.

• Building control notification: Before you start work, you’ll have to notify your local building control office. The fee for this will vary depending on your local council.
• Structural engineer: You may need a structural engineer to carry out extra structural inspections and trial pit tests, or to give advice on what underpinning method to use and help you acquire planning permission.
• Building contractor: You may need a building contractor to carry out additional inspections to do with how accessible the site is and whether the work can be done by hand.
• Tree surgeon: The job might require a tree surgeon to remove trees or dig root barriers.
• Remedial work: When the work is finished, you may want a decorator to repair any cracks, a plumber to check for leaks or a gardener to replace damaged turf.

Types of underpinning

Here are the most common methods of underpinning:

Mass concrete

Mass concrete pour involves digging holes beneath the existing foundation. These holes are then filled with concrete. Usually, this can be done by hand without any big excavation equipment required.

Beam and base

The beam and base method is very similar to the mass concrete method. In this case, holes are dug beneath a wall. These holes are then filled with concrete and a load-bearing beam is laid on top. The aim of this is to spread out the weight of the wall above.

Piling

Piling is usually only used when very deep foundations are required, such as foundations that are over five metres deep. Because this method uses specialist equipment and expertise, it’s normally the most expensive.

Costs of underpinning foundations key takeaways

• Underpinning is intended to prevent subsidence.
• The cost will depend on the method used as well as the type of property, its size and location.
• You’ll need to notify your local building control office before you start work.
• If your neighbours don’t consent to the work and you share a wall, you’ll need a party wall agreement.