Are you a main contractor looking for the best alternative to precast concrete?

If you’re anything like many of our clients, you may even surprised to learn that there is one! (Aside from traditional in situ concrete, of course)

There IS another method of below-ground construction; a method that can help address unskilled labour and eliminate the risks of cracking and leaking associated with precast concrete.

As a specialist subcontractor, I’m going to tell you more about prefabricated steel substructures, and why they make such a great alternative to precast concrete.

The risks of precast concrete 

Don’t get us wrong. There are a lot of benefits when using precast concrete substructures – especially when you need one that’s a relatively small size, due to the weight the labour that goes into physically constructing the necessary moulds. Smaller repetitive precast substructures are also easier to transport than ones on a larger scale.

They also work out as less expensive, and they can be designed and constructed, whilst standing up to tighter tolerances than traditional in situ concrete.

However, there are also some risks:

  • In order to be economical, the chosen structure shapes should be modular and repetitive
  • Joints between panels can fail
  • The process involved in curing concrete can often lead to cracks 
  • If cracking occurs, it will cause your substructure to leak -especially if you’re in a high water table area
  • It can be expensive to construct this way (£1,500 – £2,500 per sq. metre)
  • Due to their weight, larger precast concrete substructures can be tricky to transport and move into position
  • You’ll need a crane to lift your substructure whilst on-site

If you do use precast concrete and run into some of the above issues, there’s also the risk of running over-programme. If your substructure is on a critical path of the programme, this can lead to major headaches for all involved.

So, what can you do instead? Well…

A better alternative

Prefabricated steel substructures are a newer, more innovative alternative to precast concrete. They’re manufactured entirely out of steel, via an off-site factory environment. Once your substructure if complete, it’s then transported to your site and fixed into position, before being back-filled with concrete between the earth and the substructure.

And because this method is constructed uniquely out of steel plate that’s then welded together, one of the greatest benefits of prefabricated steel is that it completely eliminates the risk of leaking.

This makes prefabricated steel a much more viable option, if cracking and leaking are a main concern – particularly in high water table areas. And if time is a main concern, prefabricated steel substructures can reduce the time you spend on-site by 70 – 80%.

Not to mention, it can withstand much tighter tolerances than precast (+-3mm43mm), and can last for over 100 years in the ground.

That doesn’t mean there aren’t any downsides:

  • Much like precast, it can seem like an expensive option (£1,000 – £3,000 per sq. metre)
  • It’s a newer, innovative method that many haven’t caught onto yet – and not everyone will be prepared to change plans for a project that’s already been specified for precast (however, as part of the a prefabricated steel system a full design package should be completed).

Advice from a specialist subcontractor

If you think a prefabricated steel substructure could be a good option for your next project, my advice is to approach a subcontractor who specialises in this method well ahead of time (at least six weeks’ in advance, and preferably in the early design stages). They should be happy to provide you with some free, impartial advice.

You should also be able to look at previous examples of their work, and see client testimonials to get a better idea of whether they were happy with the end result.

The main thing to consider is the end-user of your substructure, and whether prefabricated steel could be a better alternative to precast. A specialist should be able to help advise further.

We’ve completed a project recently where we had some intricate shapes. Fortunately, the client in question had done their research and carefully compared their options against precast concrete. However, as it turned out, the precast method just wasn’t suitable for the job, as it would have required half of the works on-site being constructed traditionally.

Therefore, it wouldn’t really have saved much time on-site, and in the end they opted for our approach.


Thanks for reading. Prefabricated steel can be a great alternative to precast concrete, and can help to eliminate a lot of the risk involved when constructing below-ground. However, it’s important to bear in mind that it’s a very different way of working.

Do you want to know more about prefabricated steel substructures and whether they’re the right choice for your project?

Feel free to leave me a comment below – or alternatively, get in touch with me directly. I’d love to hear from you!