Are you tired of below-ground construction methods taking so long?

Imagine if there was a faster way than traditional in situ below-ground construction methods. In fact, as you may even have got the hint from the title; there is.

It could even save you an astonishing 70 – 80% of time spent on-site!

As a subcontractor who specialises in prefabricated steel substructures, I’m going to talk you through this innovative method.

But first…

Why does in situ below-ground construction take so long?

Traditional in situ construction involves building the entire structure on-site. It involves digging up the earth, battering the sides of the excavation to 45 degrees before the blinding, DPM, reinforcing and concrete slab is then poured. Reinforcement starter bars for the walls are left exposed, to allow reinforcement and then formwork for the walls to be constructed ready for the walls to be poured. Land drains and the necessary waterproofing is then installed before the structure is backfilled with earth or fill material.

To cut the story short, and as you can probably tell, it’s all very labour-intensive on-site – and it can take a while.

To give you an idea, let’s say you needed a 4m wide x 10m long x 1.5m deep below-ground substructure for your project. The plans have been drawn up for in situ poured concrete, and the conditions are pretty good; a stiff clay location.

You’d be looking at roughly 24 working days to install your substructure with in situ concrete.

This method hasn’t really evolved since it was first established; some adjustments have been made though. For instance, shuttering and reinforcing can now be delivered to site in the correct sizes. It’s just not particularly economical, as most substructures vary in size, and pre-making some components can be more expensive.

An alternative to in situ poured concrete

Now, let’s look at the alternative (and I’m not talking about precast). Prefabricated steel substructures have been around for over 35 years, but not everyone is aware of the benefits yet.

In the same scenario as above, you could install a prefabricated steel substructure in just seven or eight working days. This is because they come pre-built in an off-site facility. This method does require more time upfront, however when it comes to starting your project, your substructure will already be built, delivered and ready to go.

So, how could steel prefabrication work for you?

As a rule of thumb, you’d typically be looking at around four to six weeks’ lead time, which is why it’s important to approach a subcontractor who specialises in prefabricated steel well before your project is due to begin – preferably in the early tender or design stages, so this method can be incorporated into the construction programme.

The four to six weeks is usually broken down into two weeks for design, and then another two – four weeks for fabrication. This varies, depending on the size and scale of the project (as it will be custom-built to your exact specifications).

The bottom line is that your prefabricated steel substructure is specified upfront and ready to go, so you’d be starting on the same day as in situ. Potentially saving you up to 70 – 80% of time spent on-site! It also eliminates the risk of leaking, and can be built to extremely tight tolerances.

Advice from a specialist subcontractor

The most important thing to remember is that because prefabricated steel has a longer lead time, it’s absolutely vital to engage with a subcontractor who specialises in prefabricated steel substructures as soon as possible, so it can be incorporated into the programme of works without any issues. Ideally, this should be early on in the tender or design process.

Your chosen subcontractor will then be able to listen carefully to your needs, and offer free, impartial advice. They should also be able to show you previous examples of their work, along with client testimonials, so you can have peace of mind that your substructure is in the right hands. They should also be happy to take on the risk, so you can have complete confidence.

I tend to find that once any of our clients have installed a substructure via a prefabricated steel route, they very rarely go back to in situ or precast traditional methods. The benefits far outweigh any cons – as along as you engage a subcontractor in plenty of time.


By now, you should have a better idea of how prefabricated steel can be a much faster alternative to in situ below-ground construction. As long as you approach a specialist subcontractor early enough, what could usually take weeks or even months on-site, could be completed in just a matter of days.

This is all because prefabricated steel substructures arrive on-site already pre-built. This method completely changes the way you think about below-ground construction, and has so many other benefits, including eliminating the risk of leaks (particularly ideal if your project is in an area with a high water table).

Do you have any specific questions about this alternative to in situ below-ground construction? Just pop me a comment below – or get in touch directly. I’m always happy to help!