Do you want to know more about how prefabricated steel compares to in situ?

If you’ve had a bad experience building below-ground level using in situ concrete, you’re not alone. Maybe due to unforeseen issues, you ended up going over-programme. Or perhaps, upon completion of your construction project, the end-product wasn’t up to standard or within the tolerances required.

It may even have started to leak, leading to even more headaches and stress – especially if your project was in a high water table area.

What if I told you there was a better way?

Below, I’m going to use my experience as a subcontractor who specialises in prefabricated steel substructures, to compare in situ to prefabricated steel – including all the pros and cons you need to weigh up your decision.

In situ concrete

Also known as the most traditional below-ground construction method, main contractors and construction teams have been using in situ for the past 80 – 100 years. Very little is fabricated or constructed off-site, although sometimes the reinforcement or shuttering can be modular and delivered part-assembled.

This is typically a complete on-site approach that involves excavating a large hole, with timber shuttering and steel reinforcements all taken to site, pieced together with steel fixers and carpenters. The concrete is then poured between the shuttering.

Once the structure is built the waterproofing is then applied.

This method of below-ground construction may be traditional, but it can be very challenging. Often, the environment can be tricky, plus, you’ll need operatives to enter the excavation to complete the works. And that’s not even mentioning the weather conditions in the typical good old UK!

Not forgetting the logistics involved in moving the materials, and general site constraints. All of this can impact on the quality of the build, which can mean increased risk, stress and issues for you and your team.

TIP: In situ is probably still the best solution if your substructure must cover a large area – for instance (super basement).

The pros of in situ concrete:

  • It’s typically the cheapest method
  • It can be very effective when properly constructed
  • It’s a well-established method used for over 100 years
  • It works well on large-scale substructures

The cons of in situ concrete:

  • There’s a chance it can leak once constructed – often caused by reduced skill levels and on-site quality control when being constructed
  • It’s very labour intensive on-site work – and it can take a long time. You also have to wait for the concrete to cure before you can can load it
  • This method can easily be out of tolerance (at around +-20mm)
  • In order for your team to work safely, you’ll need a large excavation site
  • Quality control on the finish is not assured
  • It only lasts for around 30 years in the ground
  • It tends to create a lot of waste
  • Problems can occur if batches of concrete are mixed up. I.e. the wrong concrete mix is supplied during the concrete pour by the plant. This issue is only discovered after 28 days when the cube tests are completed and may lead to sections of concrete having to be broken out.

Ideally used for: Large-scale scenarios make in situ an effective choice – in fact, it’s often the only way large-scale projects can be completed. 

Typical costs: £500 – £2,000 per sq. metre

Prefabricated steel

You might be starting to get a good idea why a more innovative method might be a better alternative. This comes in the form of prefabricated steel. It’s manufactured entirely out of steel, off-site in a factory environment, with strict quality control, and constant monitoring and controlling.

Unlike in situ, this newer, almost revolutionary method won’t leak or crack, due to the unique way it’s constructed out of steel plates which are then welded together. Think of it as similar to the hull of a boat.

It’s a particularly good solution if your project is in a high water table area, or if time constaints are absolutely vital to your construction programme – as time on-site is reduced by 70 – 80%. It can also be built to very, very high tolerances (+-2mm/3mm), and lowers long-term maintenance costs.

TIP: Want to know more about steel prefabrication? Read my recent blog: ‘What is Steel Prefabrication Below-Ground and How Does it Work?’.

To sum it all up:

Pros of prefabricated steel:

  • Jobs can be completed 70 – 80% faster (typically in a matter of days compared to weeks/months)
  • This method will not leak
  • It’s built to very, very high tolerances (+-2mm/3mm)
  • The long-term costs are much cheaper, with less long-term maintenance required
  • Prefabricated steel substructures can last for over 100 years in the ground
  • It comes with a full design package from your subcontractor

Cons of prefabricated steel:

  • It can seem expensive
  • It’s an innovative method that  very few people are aware of yet. People who are unfamiliar with a concept are generally sceptical about it

Ideally used for: When your substructure is on the critical path of the programme, must be built to tight tolerances/precision engineering, or if a project is located in a high water table area and long-term water ingress is a concern.

Average costs: £1,000 – £3,000 per sq. metre

Advice from a specialist subcontractor

Still weighing up your options? It may be a good idea to seek out a subcontractor who specialises in prefabricated steel, so they can talk you through your options, and give you a better idea of what’s possible. It won’t always be that prefabricated steel is the best option – for instance, if your project is on a large scale.

However, it’s still worth having a chat. Most people tend to be skeptical of prefabricated steel as a method of below-ground construction until they’ve seen the product being made – or have installed and used them for themselves.

So, you could ask to see examples of their work, and even get in touch with some previous clients to ask them about their experiences.


I hope this blog has given you a better idea of how prefabricated steel measures up to in situ concrete – or in other words, the new vs the old. Traditional in situ concrete has been used for the past 80 – 100 years – and it’s still a good option for large-scale projects. However, there are several advantages to prefabricated steel (as mentioned above).

Do you have any questions about in situ vs prefabricated steel substructures? Feel free to leave a comment. I promise to reply!