Underpinning Made Simple – What It Is, When You Need It, and How Much It Costs

If you’ve ever seen cracks in your walls or a sagging floor, you might be wondering whether your house needs a stronger base. That’s where underpinning comes in. In plain terms, underpinning is the process of strengthening the existing foundation by extending it deeper into more stable soil. It’s not a fancy term reserved for engineers – it’s a practical fix many homeowners use to stop their homes from shifting or settling.

Why Underpinning Becomes Necessary

There are a few tell‑tale signs that your foundation is struggling. Horizontal cracks in walls, doors that won’t close properly, and uneven floors are common red flags. Often the cause is soil movement – maybe the ground has become softer after a leak or the original soil wasn’t compacted well enough.

When these problems appear, ignoring them can lead to bigger, costlier repairs later on. A weak foundation can damage structural walls, affect roof stability, and lower your property’s value. Underpinning stops the damage in its tracks by transferring the load to firmer ground beneath.

How Underpinning Is Done – The Main Methods

There are three popular underpinning techniques, each suited to different soil conditions and budgets:

Traditional mass concrete underpinning – This is the oldest method. Small sections of the existing foundation are excavated in stages, then filled with concrete that reaches down to stable soil. It’s reliable but can take several weeks.

Screw piles or mini piles – A steel rod with a screw‑like tip is turned into the ground until it hits firm soil. The rod is then tied to the foundation. This method is fast, often done in a day, and works well where space is tight.

Micropiles – Similar to screw piles but smaller and reinforced with steel. Micropiles are great for tight urban sites or where the existing structure can’t be moved.

Choosing the right method depends on the depth of stable soil, the size of the building, and how much you’re willing to spend.

For example, a homeowner who discovered a horizontal crack in a load‑bearing wall (see our post on Horizontal Foundation Crack Repair Cost) might opt for screw piles because they’re quick and cause minimal disruption.

If you’re dealing with water damage or broken pipes under the foundation (read our guide on Homeowners Insurance and Broken Pipes Under Foundation), you’ll likely need a method that also addresses drainage issues while the underpinning work is underway.

Cost is a common question. In the UK, underpinning can range from £80 to £150 per linear metre for traditional concrete work, while screw piles might cost £120‑£200 per metre. Prices vary based on soil type, depth required, and access to the site. Getting a few quotes from reputable contractors is the best way to nail down a realistic budget.

Before you book anyone, check that they have experience with underpinning, proper insurance, and good references. A solid contract should detail the method, timeline, and warranty.

In short, underpinning is a practical way to protect your home’s structural health. Spot the warning signs early, choose the right technique for your situation, and budget wisely. With the right approach, you can keep your house stable and avoid costly surprises down the road.