Hollow summerhouse concrete base!?

[Wynney34]

Hi, home this is the right part of the forum to post this on!
i've been staying in my mates summerhouse for 18 months and recently I've noticed that some part of the floor sounds hollow!

Apparently he laid a concrete base when he built it, maybe 4/5 years ago.

I'm not sure when the hollow sounds started but they definitely became prominent and large enough in area on the floor for me to notice when walking around!

Just wondering if anyone has experienced this before and should we be concerned?

 

[bernardgreen]

Buoyancy Rafts or Hollow Box Foundations in Building Construction

Buoyancy rafts or hollow box foundations also known as the floating foundations is a type of deep foundation is used in building construction on soft soils.

theconstructor.org