Experts in Concrete Patio foundation stability

Why Patios Sink at the House Wall and How to Stop It

Have you noticed your patio dropping near the house wall? When the edge sinks, it’s not only unsightly it can redirect rainwater, block drainage, and even impact your property’s damp-proof course.

In this guide, we dive into the main reasons patio edges sink near walls in UK gardens including soil, drainage, and installation mistakes and show you how to fix and prevent this common issue once and for all.

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Main Causes of Patio Settling Along Walls

Patio edges close to walls are prone to sinking due to several compounding factors. Understanding each one helps prevent future problems.

Inadequate Compaction of Sub-Base

When the sub-base wasn’t compacted properly close to the wall either skipped to avoid noise or limited by digging access it settles under its own weight. Rainwater can then penetrate and erode the base. Over time, the concrete above loses support and sinks unevenly. UK ground, especially clay-heavy soil, is particularly prone to this.

Water Gathering and Poor Drainage

Without a fall away from the walls, run-off from roofs and patios ends up pooling at the edge. This water washes sub-base material out, particularly if there's no edge restraint or drainage channel. Recurrent saturation softens the foundation, and seasonal freeze–thaw cycles exacerbate the sinking by expanding and contracting the soil below.

Lack of Edge Restraint

Edge restraints (blocks, kerbs, metal strip) are designed to hold patio slabs in place. With no restraint, slabs close to the wall have no physical support. Over time, vibration and soil movement push them outward or downward. These slabs then drop under their own weight or allow the ground beneath to be displaced.

Tree Root Uplift and Soil Shift

Tree roots grow where they can, and often intercept patios near walls. While some roots lift slabs, others cause adjacent soil to sink when roots decay after surface damage. This shift leads to uneven ground support and sinking slabs in localized patches, especially near fencing or borders.

Sub-Par Installation Methods

Some installers shorten sub-base near walls to save materials, reducing structural integrity in those areas. Combined with missing compaction or unsuitable infill, this leads to rapid, uneven settlement that might only appear after the patio has aged for a year or two.

How to Repair and Prevent Patio Settlement

1. Re-excavate and Recompact Edge Area

Dig out the sinking slabs and old base to at least 150mm depth from the edge.
Add MOT Type 1 stone in 75mm layers and compact thoroughly using a plate compactor.
If space is tight, use manual tamping tools to ensure full compaction.

2. Add Proper Edge Restraints

Install concrete kerbs, block edge restraints or metal edging to hold slabs firmly in place.
Ensure it’s secured into firm sub-base with mortar or compacted stone behind.
This stops slabs sliding or tipping from soil shifts or freeze–thaw action.

3. Improve Drainage and Patio Gradient

Check and correct the fall so surface water leads away from walls at 1:80 slope.
Consider installing a slim channel drain where water collects most.
Redirect downpipes or water outlets away from patio edges to prevent pooling.

4. Treat Tree Roots Carefully

If roots are the cause, prune or barrier them using root-friendly methods.
Replace displaced ground with compacted aggregate rather than soil to maintain support.

5. Replace or Relevel Slabs

Once base is rebedded and restrained, relay patio slabs or concrete mix to suit new level.
Use spacers and string lines to align correctly with the wall and rest of patio surface.
Check consistency by walking edge it should feel solid and level.

6. Regular Maintenance and Monitoring

Inspect the edge annually for dips, cracks, or pooling.
Top-up aggregate behind restraints if minor settlement occurs.
Clean debris from drainage channels before autumn and winter freeze–thaw risk.

Frequently Asked Questions

Allow a small expansion gap typically 5mm between the patio and house. This prevents stress transfer and allows for drainage and movement from frost without pushing slabs.

Yes, but ensure each layer of aggregate is tamped firmly and evenly. Plate compactors are faster and more effective, especially in tight areas near walls.

Improved drainage helps prevent further sinking by keeping the sub-base dry. However, you still need to renew compacted layers and edge support to correct past settlement.

Sometimes. If roots are extensive, you may need to lift slabs, install root barrier, and rerun the sub-base. In less severe cases, pruning and infilling can fix minor shifts.

Check quarterly, especially after heavy rain or frost. Early detection lets you top-up aggregate or adjust drainage before slabs sink or crack.