“Buildings move. All buildings do.”

Brian Eckersley is a structural engineer. He set up Eckersley O’ Callaghan 12 years ago with James O’Callaghan. The practice has engineered some of the most world’s most ambitious glass structures and is the engineer for Ballymore’s Sky Pool at Embassy Gardens, designed by Hal Currey.

When the Sky Pool was unveiled last year, it created a media storm. Were you surprised?

It was a bit unexpected. We’ve done a lot of innovative things before, like the glass cube for Apple on 5th Avenue, so we didn’t see this as anything out of the ordinary. We’re used to working on extraordinary projects.

Wasn’t the excitement because it’s a world first?

As far as we’re aware it is. No one has spanned 150 tonnes of water 10 storeys up before and will it be a great technical achievement to pull it off but there are precedents.

Such as?

For the Sky Pool we’re using acrylic not glass so we’ve been looking at aquarium because they use acrylic too. Acrylic has a high degree of transparency and light passes through it in a straight line without any distortion. We’re taking it a step further though because we’re dealing with people not fish.

So I’ll be able to see the swimmers quite clearly from underneath?

Yes. That’s because acrylic is a lot less obtrusive than glass, which would have needed more laminating. The more you laminate, the less transparency.

I still don’t understand how the pool is fixed to the building

The pool is supported between two adjacent buildings with a clear span of 14 metres. Only this part is transparent. The remaining 11 metes sit in stainless steel tubs on bearings at each end of the acrylic span.

Why does it sit on bearings?

Because buildings move. All buildings do, so the bearings allow it to slide. Obviously you don’t feel the movement because it’s tiny – just a few millimetres - but you have to calculate what the effect of wind at that height will be as well the change in temperature. Both of these can cause a building to shift slightly.

It sounds amazing but a bit stressful.

Not really. The biggest challenge is dealing with the huge pressure on the structure because it’s carrying so much weight. The pool will hold 150 tonnes of water and the structure is 50 tonnes. Then you have to add the people- another 4 tonnes. But our job is to work out all the possible behaviours. Nothing is left to chance.

So how long before I can have a swim?

Not long. The first building is almost complete and piling has started for the second one. Before the second one is finished we’ll start construction. We ‘re thinking of having it entirely fabricated in the USA and then shipped across and hoisted up by a crane. I’m hoping it’ll be open by 2019.