Choosing the Best Foundations for Different Soil Types

Before you start any construction project that needs foundations, it’s worth analysing what’s beneath your feet.

The type of soil on your property directly affects which foundation system will work best for your project.

Get it right, and your structure will stand firm for decades. Get it wrong, and you could face expensive problems down the line – from sinking and tilting to complete structural failure.

Here, we’ll investigate the main soil types you’ll find across the UK and explore which foundation options work best for each. We’ll help you avoid costly mistakes by matching the right foundation system to your specific ground conditions.. 

Understanding Different Soil Types Throughout the UK

Before picking a foundation system, you need to know what you’re building on. Here are the main soil types you’ll encounter across the country, with tips for where they tend to be located across the country. 

It’s worth mentioning that these are broad categories – soil can take many forms even across a relatively small local area, with different rock types, sediments, and nearby plants or trees all playing a part. 

Moreover, the soil type doesn’t account for obstacles you might encounter in the soil itself – tree roots, large rocks, old pipes. 

Don’t worry too much, though – with so many types of foundations available, there’s luckily nearly always a solution, which we’ll come to shortly. 

Clay Soils

Clay soils are widespread across much of England and parts of Wales, though is most common in the south and south east. The biggest issue with clay is how it swells when wet and shrinks when dry.

During rainy weather, clay expands and forces upward on foundations. In dry spells, it shrinks and can leave parts of your foundation unsupported. Clay’s consistent seasonal movement can be problematic for concrete systems that don’t properly flex with the soil.

Often, you’ll need to entrench the foundations deep below the clay’s ‘movement zone,’ demanding extensive excavation. Plus, it’s worth mentioning that clay is notoriously hard to work with when it’s wet – it’s sticky, slippery, and impermeable when strongly compacted. 

Sandy Soils

Sandy soils, as you might expect, are commonest in coastal areas and parts of East Anglia. You’ll also find sandy soils next to some river floodplains. While they drain well, they lack cohesion, strength, and stability.

The main problem here is settlement – foundations can sink unevenly as the sand moves under constant pressure. The closer you are to water, the greater the risk.

Foundation systems in sandy soil typically need to either reach substantial depth or spread the load optimally to prevent sinking over time.

Peat and Organic Soils

Peat soils – far more common in Scotland than elsewhere in the UK – can pose a nightmare scenario. While rare, peat soils compress dramatically under heavy load, triggering severe settlement issues in some cases.

Peat also has extremely high moisture content, which changes seasonally, drying in summer and expanding in autumn and winter, altering its volume and support capacity. 

Rocky or Stony Ground

Rocky ground can offer excellent load-bearing capacity, but its properties vary significantly depending on the type of rock. 

Across the country, you can encounter everything from soft sedimentary rocks like chalk and limestone, to hard metamorphic and igneous types like granite, basalt, or flint.

• Chalk is common in southern England – including the South Downs, Wiltshire, and the Chilterns. It’s a relatively soft rock with good bearing strength, but it can dissolve in water over time, especially if fractured or porous, which may lead to cavities or subsidence.
• Limestone, widespread in areas like the Cotswolds and the Peak District, is stronger and denser than chalk but can also be affected by groundwater erosion over the long term.
• Granite, found in places like Cornwall and parts of Scotland, is extremely hard and stable – excellent for load-bearing, but very costly and time-consuming to excavate.
• Flint and siltstone, common in southeastern and eastern England, can make excavation challenging due to their unpredictable size, strength, and distribution. Flint nodules in particular can be tough to break through.
• Shale and mudstone, seen in areas like Yorkshire and parts of Wales, tend to be weaker and can break down when exposed to moisture.

Each rock type brings its own nuances and complications to the table. Solid, uniform rock can reduce foundation costs, while fractured, uneven, or layered strata sometimes demand creative solutions to deal with point loads or potential water ingress. 

Excavation into rock – especially harder metamorphic rocks such as flint and granite – may require specialist equipment or blasting, increasing time and cost significantly.

Made Ground or Fill

Made ground is common in towns and cities. Urban sites contain soil that’s been affected by construction, mixing natural soils with rubble, concrete, and synthetic materials. 

Made ground can take many forms with lots of different components and additives, making foundation design particularly challenging. 

Since made ground is unpredictable, different areas within your site – even those divided by a couple of feet – may have completely different characteristics, causing unstable or uneven settlement.

Main Foundation Options for Different Soil Types

Let’s turn our attention to different foundation types and how they interact across common soil conditions:

Concrete Bases

Concrete base foundations create a solid concrete slab that extends under the entire footprint of the building. They effectively spread the load across a much larger area than strip or pad foundations, making them useful for certain challenging soil conditions.

These foundations involve excavating the entire building area, adding substantial reinforcement, and pouring a thick concrete slab. The building then sits directly on this stable platform.

Here’s how concrete base foundations interact with different soils:

• Clay soils: Better than strips at handling movement, but still susceptible to edge heave
• Sandy soils: Good performance as they spread weight evenly, but expensive overkill for many projects
• Peat: Still problematic unless the entire area can reach stable ground
• Rocky ground: Very expensive due to extensive excavation requirements
• Made ground: Provide good bridging over minor inconsistencies but at significant cost

While offering excellent stability, concrete bases are typically the most expensive option due to the volume of materials required and extensive groundwork. They also create significant site disruption and are highly weather-dependent during installation.

Strip Foundations

Strip foundations are continuous trenches filled with concrete that run under the load-bearing walls of a building. They distribute the building’s weight along linear pathways in the ground, forming a solid base for the walls above – reliable when soil conditions are reasonably consistent.

Here’s how strip foundations perform across soil types:

• Clay soils: Poor without extreme depth – prone to cracking with seasonal movement
• Sandy soils: Require wider footprint to prevent sinking, increasing material costs
• Peat: Completely unsuitable unless reaching firm ground below
• Rocky ground: Prohibitively expensive excavation costs
• Made ground: High risk of differential settlement across variable fill materials

Concrete Pad Foundations

Pad foundations are individual concrete squares or rectangles that support load points rather than entire walls. 

Commonly used under posts, columns, or at the corners and junctions of timber-framed structures, these foundations concentrate the building’s weight at strategic points.

The primary restriction associated with concrete pads is their point loading, which concentrates weight in specific areas. Here’s how this interacts with soil:

• Clay soils: Vulnerable to uneven lifting during wet periods and sinking in dry spells
• Sandy soils: Risk of uneven settlement as individual pads sink at different rates
• Peat: Inadequate without reaching stable ground below each pad
• Rocky ground: Easier than strips, but still challenging to level on uneven rock
• Made ground: Highly unpredictable performance as soil conditions vary under each pad

Ring Beam Foundations

Ring beam foundations consist of a continuous reinforced concrete perimeter that forms a rigid frame around the building’s footprint. 

Unlike strip foundations that follow only load-bearing walls, ring beams create a complete circuit around the entire structure, providing edge support and helping to resist ground movement.

Here’s how ring beam foundations interact with different soils:

• Clay soils: Require deep trenching below movement zone
• Sandy soils: Need wider dimensions to prevent sinking
• Peat: Impractical without reaching stable substrate
• Rocky sites: Extremely difficult and expensive trenching
• Made ground: Risks uneven settlement along the beam length

While they create a solid edge for buildings, ring beams share most of concrete’s limitations – weather dependency, curing time, and the inability to adjust once installed.

Adjustable Jack Pad Systems

Jack pad systems combine concrete pads with adjustable steel supports that can be raised or lowered as needed. 

The system generally consists of a concrete base pad, a threaded steel post, and an adjustable head that connects to the building frame. This enables excellent leveling control across most sites. 

Performance limitation across different soils:

• Clay soils: The concrete elements still face seasonal movement issues
• Sandy soils: Can sink unevenly unless properly sized
• Peat: Inadequate without substantial ground improvement
• Rocky ground: Difficult to achieve level concrete bases
• Made ground: Adjustable elements help with minor settlement, but not major issues

Ground Screw Systems

Ground screws are large, helical steel piles that are rotated into the soil to create secure foundation points. 

Each screw consists of a steel shaft with spiral flights that cut into the ground as they’re turned, creating minimal soil disturbance while providing superb load-bearing capacity.

Installation involves no excavation or concrete – the screws are simply driven into the ground using handheld equipment or small machinery. 

Once in place, brackets, which can either be fixed or adjustable, are attached to the top of each screw to connect with your timber frame or deck structure.

Here’s how ground screws interact with the different soil types we’ve explored:

• Clay soils: Can be installed below the zone of seasonal movement
• Sandy soils: Helical flights provide outstanding resistance to settlement
• Peat: Can reach through soft layers to find stable ground beneath
• Rocky ground: Can work around obstacles or be positioned to avoid large rocks
• Made ground: Can bypass problem areas to reach competent bearing strata

The complete ground screw system offers immediate load-bearing capacity with no curing time, making it a brilliant choice for projects with tight timeframes or access issues.

Why Ground Screws Suit a Variety of Soils

So why have ground screws become so popular in recent years? Simply put, they solve numerous problems that traditional foundations can’t handle.

Unlike concrete that fights against natural soil movement (and usually loses), ground screws work with the ground. Their clever helical design cuts through soil rather than excavating it, keeping the natural structure intact. This makes a massive difference in how they perform in the long term.

The installation process is refreshingly straightforward, too. Forget mixers, diggers and multiple site visits – ground screws can be installed using handheld equipment for smaller projects or compact machinery for larger jobs. That’s a game-changer for sites with tight access where getting concrete in would be a nightmare.

Perhaps the most significant advantage? You can build immediately. There’s no hanging around for days while concrete cures, hoping it doesn’t rain. With ground screws, you can install your foundation in the morning and start building by lunchtime – perfect when you’re working to tight deadlines.

Making the Right Choice for Your Project

As we’ve seen, each and every soil type presents different challenges that are too often overlooked. 

Selecting the optimal foundation for your soil type can save you from problems down the line. 

Ground screws work effectively across a wide range of soil conditions:

• Clay soils: Reach below the movement zone without extensive digging
• Sandy soils: Hold firm with their helical design, where pads would sink
• Peat: Can be driven through the soft stuff to find solid ground beneath
• Rocky sites: Work around boulders instead of requiring costly removal
• Made ground: Bypass dodgy areas to reach good soil below

At Ground Screw Centre, we’ve helped thousands of customers find the right foundation solution for their specific soil conditions. 

Our range includes ground screws designed for everything from light garden structures to heavy commercial buildings, with options suitable for all soil types.

Ready to find the perfect foundation for your soil type? Try our Ground Screw Calculator to determine exactly what you need, or contact our team for advice about your specific ground conditions.