If piling has been recommended for your project, it’s likely you’ve already heard two terms mentioned repeatedly. CFA piles and rotary bored piles. For most people, the difference between them isn’t immediately clear, and that uncertainty can lead to concerns about cost, disruption and whether the right decision is being made.
Both piling methods are widely used across the UK. Both are proven and reliable. Neither is automatically better than the other. The right choice depends on what’s happening below ground, how much space you have to work with, and what the structure needs to support.
This comparison matters because choosing the wrong piling method can introduce unnecessary risk or cost. Choosing the right one helps keep the project efficient, proportionate and controlled.
In this guide, we explain what CFA piles and rotary bored piles are, how they differ, and when one method is more suitable than the other, so you can understand why a particular solution is recommended for your site.
What are CFA piles?
CFA piles, also known as continuous flight auger piles or auger piles, are a non-displacement piling method commonly used on residential and commercial projects where ground conditions allow.
They’re often chosen because they’re efficient to install and produce low vibration, which makes them suitable for built-up or noise-sensitive areas.
What does continuous flight auger mean?
A continuous flight auger is a long, screw-shaped drill used to form the pile. The auger is drilled into the ground to the required depth, then concrete is pumped through the hollow stem as the auger is withdrawn.
This process means:
- The ground is supported throughout drilling
- Concrete fills the pile from the bottom up
- Surrounding soil isn’t displaced excessively
Steel reinforcement is then inserted into the fresh concrete.
CFA piles advantages
The main advantage of CFA piles is their versatility in most building projects. CFA piles can be used with most soil conditions, from medium dense sands to gravel, rocks or even rigid clays.
Additionally, CFA piles come with many auger dimensions available, that range from 300mm to 1200mm.
CFA piles are ideal for most business and residential projects as they come with a depth of up to 25 meters, making them efficient for low to mid-range loading.
CFA piles disadvantages
Although they are ideal for a large number of projects, CFA piles are not adequate for very soft clays or silts or any other types of ground that are too loose, for instance, some types of sand or gravel.
What are Rotary Bored Piles?
Rotary bored piles, often referred to as a bored pile, are another non-displacement piling method. They’re commonly used where ground conditions are more variable or where greater control during installation is required.
Rotary bored piling is often chosen when CFA piling isn’t suitable or where inspection of the ground during drilling is important.
What is a bored pile?
A bored pile is formed by drilling a hole into the ground and then filling it with reinforced concrete. Unlike CFA piling, the bore is drilled first and concrete is placed afterwards, allowing the ground to be assessed during drilling.
Like CFA piles, rotary bored piles have their advantages and disadvantages.
Rotary Bored piles advantages
The rotary bored piling technique can be used in almost all land conditions. It also allows for very high load capacity thanks to its attainable depth of up to 60 meters and diameter of up to 1.8 meters. This makes bored piles useful for constructions in soils that range from soft ground to hard rock.
Additionally, the risk to adjacent buildings is minimal because of its minimum vibration, making it a quick and effective method of installation.
Rotary Bored piles disadvantages
Bored piles can pose many challenges. The type of soil needs to be thoroughly analysed and land tests need to be conducted before choosing the best drilling method. Besides, although one of the main advantages of bore piles is that they cause minimal disruptions if there are buried blockages, they may cause vibrations.
Another disadvantage of bore piles is that the pilling process can be quite slow (it often takes around eight weeks). The process can be even longer if the soil type is very loose, which would require the use of steel cages or sustaining mud, adding complexity to the project.
The Key Differences Between CFA and Rotary Bored Piles
Both methods are non-displacement piling techniques, but they differ significantly in how they’re installed and how they respond to ground conditions.
Installation and control
- CFA piles are drilled and concreted in one continuous operation, without visual inspection of the bore
- Rotary bored piles are drilled first, allowing inspection and adjustment before concreting
Ground suitability
- CFA piles suit stable, cohesive soils
- Rotary bored piles suit variable or unstable ground
Speed and certainty
- CFA piling prioritises efficiency and low disruption
- Rotary bored piling prioritises control and certainty
The right choice depends on the site, not preference.
Ground Conditions and Suitability
Ground conditions are usually the deciding factor when choosing between CFA piles and rotary bored piles.
What ground conditions suit CFA piles?
CFA piles work best in stable, cohesive soils such as firm clays, where the bore won’t collapse during drilling.
When rotary bored piling is required
Rotary bored piles are typically used where ground is variable, prone to collapse, affected by groundwater or made ground.
A ground investigation identifies soil layers, groundwater and bearing strata. This evidence is what drives the piling choice, not assumptions.
Noise, Vibration and Disruption
Noise and vibration are common concerns on residential and urban sites.
Which method causes less disruption?
In most cases, CFA piling produces lower noise and vibration because drilling and concreting happen in one continuous operation.
How rotary bored piling compares
Rotary bored piling is still low vibration compared to driven piling, but it can involve more drilling noise, spoil handling and longer working time on site.
Noise considerations matter, but they don’t override ground suitability.
Access, Headroom and Site Constraints
Physical constraints often decide which piling method is practical.
- CFA rigs generally require more vertical clearance
- Rotary bored rigs can sometimes operate with sectional tooling
- Rotary bored piling usually generates more spoil, affecting space and logistics
If a rig can’t physically operate on site, the method isn’t viable, regardless of its other benefits.
Cost and Programme Considerations
Are CFA piles cheaper than rotary bored piles?
In suitable ground, CFA piling can be more cost-effective due to faster installation. In complex ground, rotary bored piling may cost more but offers greater certainty.
Which method is faster?
CFA piling is usually quicker in stable soils. Rotary bored piling is slower but more controlled.
Cost and programme are driven by ground conditions, pile depth, access and risk, not just the piling type.
Make the Right Choice for Your Site
As we’ve seen, bored piles usually have a larger diameter than the traditional continuous flight auger piles. Therefore, rotary bored piling can be used with higher loads and at a greater depth in comparison to CFA piles.
CFA piles are suitable for lighter loads, whereas bored piles are used for heavy-loaded constructs, to bypass underground impediments, and infiltrate the ground that is too hard to drill with a continuous flight auger.
If you are considering using CFA piles or bored piles in your next project, get in touch with one of our expert piling contractors today, for an initial discussion.