but don't UK builders tend to just show the regulations have been met in one of the units per development - ie soundproofing and thermals? The rest never get checked to the same or any extent, do they?
The UK building inspectors are not that stupid, they examine the cavity's to make sure that they are clean and the insulation is fixed properly, if they are suspicious that something has been left out, they can make you knock a hole in the wall or floor and God help you if anything is missing or out of place/incorrect size. They can make you knock the whole building down and start again, your name would be recorded and any future project would be scrutinised. I am not saying that there are no fly by night builders.
Isn't it the polystyrene or rockwool that keeps Polish flats thermally insulated?
Its usually 140mm thick Styrofoam sheets fixed to a single skin 225mm thick concrete/terracotta block wall, 75mm thick Styrofoam sheets are installed under the sand/cement floor screed. Rockwall (fibreglass) is now only used in the loft space, usually to a thickness of 250mm.
I've never seen the same level of insulation in UK flats, look at a UK flat and there is no outer "jacket" of insulation. There might be cavity wall insulation but not polystyrene slabs etc, surely?
You will not see this level of insulation on newly built flats in the UK because the weather is not that extreme, more dampness than freezing. Insulation is usually in the cavity but I know that several new projects were going to use the external Styrofoam slabs as it was more cost effective and of course, more efficient. Cavity wall insulation in the UK is usually 1200 X 600mm X 50mm Polystyrene slabs or Rockwall "Batts"., outer skin is either 100mm thick brick or block work, 50mm cavity, insulation is fixed to cavity side of 140mm insulation block (pumice) by clips on the wall ties which hold the inner and outer skin together. The higher the two skins go, cement drops into the cavity and hits the wall ties, this can cause a "bridge" for moisture to travel along so it is essential that the ties are cleaned off " as you go up" before they are unreachable. One serious problem that has now been resolved was that the ties were made from galvanised, steel wire, brickie's had the habit of twisting the ties flat which caused the galvanised coating to crack away from the steel and over the years the moisture got to the steel which resulted in the ties rusting and expanding, made the walls crack and become unstable. There is a fix for this (fairly expensive and time consuming) but its not the end of the world. Nowadays they use stainless steel or plastic ties, so no problem.
At the end of the day, they are going to use the cheapest, most cost effective way to build in whatever country you are in but there has to be regulated standards for safety, nobody wants to see a building collapse, certainly not like you see these Chinese schools do on a regular basis when large amounts of cement/reinforcing bars are left out so the builder can make more profit.
Sorry if this seems like a lecture but its the only way I know how to explain the building process.