Spongy Floors

Dickdastardly1

I have heard that the delamination or spongy spots of internal floors is due to the solid insulation breaking down due to footfall and creating crumbs of the insulation, thereby not offfering any support. My understanding is that a simple hole can be drilled
into the floor from underneath and expanding foam inserted. The upper floor would need to be weighed down to avoid warping.. Any views on this?