Installing a Screw Isn't the Same as Installing a Foundation

Something happened this week that reminded me why the ground screw industry still has some important questions to answer.

And it wasn't about whether ground screws work.

It was about what happens when somebody wants them installed, but the evidence to demonstrate that the proposed foundations are suitable isn't there.

It started with a fairly straightforward enquiry. A customer wanted ground screws supplied and installed for an outbuilding.

Nothing particularly unusual about that.

But when the installer arrived on site, things weren't quite as straightforward as they'd first appeared.

There were significant differences in ground levels, limited information about the proposed foundation arrangement and, as it turned out, the project would also be subject to Building Control.

Suddenly, a relatively simple installation enquiry had become something rather more complicated.

And that's when I was asked for advice.

Looking at the available information, my first concern wasn't actually the weight of the building.

It was the ground underneath it.

Publicly available geological information suggested the possibility of shrinkable clay, with nearby trees introducing another consideration.

In other words, there was a potential for seasonal ground movement that needed to be understood before deciding what foundations would be suitable.

And here's the bit I struggle with.

Imagine you've got a one-metre ground screw that's perfectly capable of carrying the weight of your building.

Brilliant. Job done?

Well, not necessarily.

What if the upper layers of ground are potentially affected by seasonal movement?

That screw might support the weight perfectly well, but if the ground it's relying on is shrinking and swelling throughout the year, you've got a rather different problem to consider.

And pointing to a manufacturer's published load capacity doesn't answer that question.

There's a difference between carrying the weight of a building and providing a foundation that performs acceptably over time.

That's why ground conditions matter so much.

In this situation, the information available suggested that movement could potentially affect ground deeper than the proposed screws.

Now, that doesn't automatically mean the proposed arrangement wouldn't work. It means there's a question that needs answering through appropriate investigation and engineering.

And that's what I explained.

The customer, however, was keen to proceed.

From their perspective, an engineer had already been involved, a foundation arrangement had been proposed and the installer had been instructed to get on with the job.

I can understand the frustration.

Nobody wants to be told they might need further investigations, calculations or changes to a project they thought was ready to proceed.

But here's the thing.

Not every foundation needs the same solution. Every foundation does, however, need a solution that can be justified.

You wouldn't necessarily approach a small garden room in the same way as a substantial two-storey extension. The level of assessment should be appropriate to the structure, the site and the risks involved.

But if you've identified a potential ground movement problem, simply choosing a screw length because its published load capacity looks sufficient isn't really answering the question.

And just because somebody has produced a drawing showing where the screws should go doesn't automatically demonstrate that the foundations have been properly designed.

There may be supporting engineering information, of course. But somebody needs to establish that the proposed arrangement is suitable for the actual ground conditions.

Which brings us back to the installer.

What are they supposed to do?

They've got a customer who wants the work completed, an instruction to proceed and a business to run.

They also have concerns about whether the proposed foundations have been adequately justified.

Do they walk away and potentially lose the job?

Do they carry out the installation because somebody else has apparently taken responsibility for the design?

Or do they insist that the outstanding questions are answered before proceeding?

It's a difficult position, particularly when there may well be another contractor willing to undertake the work without asking the same questions.

One suggestion that sometimes comes up in situations like this is a customer signing a waiver to accept responsibility for the foundation design.

And there's nothing inherently wrong with separating design and installation responsibilities, provided those responsibilities are properly defined.

But a waiver doesn't make an unsuitable foundation suitable.

Nor does it automatically remove an installer's responsibility for the work they've carried out.

If someone is being asked to install screws without clearly defined positions, levels, founding requirements or acceptance criteria, how can they confidently demonstrate that the installation satisfies the intended design?

That's the distinction I think we need to understand.

A correctly installed screw isn't necessarily a correctly designed foundation.

And it works both ways.

An engineer can produce a perfectly reasonable foundation design, but if the installation doesn't follow that design or the required verification isn't completed, the finished foundation may not meet its intended requirements.

The design and installation need to work together.

That's ultimately what I believe we should be aiming for across the industry.

Not more paperwork for the sake of it. Not making every small project unnecessarily complicated.

Just making sure the right questions have been asked, the relevant risks have been considered and everybody understands what they're responsible for.

I've spent years working with ground screws, and I remain convinced they have an important future in construction.

But if we want customers, engineers and Building Control professionals to have confidence in them, we need to demonstrate that we're providing properly considered foundation solutions, not simply products installed into the ground.

And that brings me back to the situation that prompted this article.

There's a customer ready to proceed, an installer with a job waiting to be done and a very real possibility that somebody else will happily take the work.

But there's also a question that hasn't been satisfactorily answered.

And I think that's where the difference between installing a screw and providing a foundation really becomes apparent.

Sometimes doing the right thing means being prepared to ask a question that might cost you the job.