I just bought a house which had an extension done 12 years ago. I am about to do some work in this area and want to understand what has been done before. Below is a screen shot of the bits of the planning drawings relating to the concrete floor construction.

enter image description here

What does this say? (it is hard to scribe something when you don't fully understand it)


  • 30mm screed on
  • 175 bar concrete oversite
  • on 50mm Jablite
  • on 1200 polythene damp proof membrane
  • on 75mm hardcore (usually recycled concrete).

Does this have sufficient insulation properties or would you recommend I add more?

What is the likely-hood of this being level/smooth when I remove the existing tiles from the floor?


2 Answers 2


I'm only answering because an educated guess is hopefully better than no information at all. Is this in the UK? I'm not recognising some of the terms, and of course metric units are alien to us Yanks :) I hope you get a more definitive answer, but in the mean time...

A 30mm screed topping layer just means it was struck off level, there is no indication of finish quality. It may be anything from level with a rough finish to a very smooth finish. This is on a 175bar concrete slab of unknown thickness. 175bar is a typical utility strength concrete.

I would expect the next 50mm layer to be some sort of granular material. It may be something like expanded slag which has some insulating value. A poly (polyethylene) sheeting layer as the next layer is very typical, I've no idea what the remainder of the description line means.

I'm hoping the final 75mm layer is some sort of insulation board like extruded polystyrene. If so, 75mm is a good thickness. The problem is I've no idea what this material really is. As I said, this is an educated guess based on construction knowledge in a completely different country. It could be the 50mm is insulation and the 75mm is is a granular base, or they're both insulation, or neither are, I really don't know for sure.

I am reasonably confident you have a level floor that is properly insulated. Best of luck getting a better answer.


I am not a building professional, so I can't comment on how current these specs are but:

The third line is 50mm Jablite, a brand of polystyrene sheet insulation. http://www.jablite.co.uk

The next line is a 1200 g polythene damp proof membrane.

The last line is 75mm hardcore (usually recycled concrete).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.