Insulating an existing concrete floor

[Dan1976]

Hi All,

We are spending our first winter in our 1950's ex-council property and we have a very cold downstairs WC and utility room which I'd like to insulate.

The rooms have a solid concrete floor and solid masonry walls (which I'm going to dryline; and I'm going to insulate and plaster the underside of the concrete flat roof too) but I also want to insulate the floor and lay some floor tiles.

Any advice anyone has for a project such as this would be much appreciated but inaprticular can anyone advise a suitable type of insulation (I don't know if its better to use a plywood faced PIR that is glued to the floor and tiled over or to build a basic timber frame on the floor, insulate between the battens and lay chipboard/plywood on top to be tiled over?). The insulation would probably only be 30mm (ish) thick so I don't know if it will make any difference.

Has anyone done anything like this before? Did it work??

I would hate to go through this time and expense for no noticable improvement!!

Thanks in advance guys!

Dan.

 

[freddiemercurystwin]

Presumably this concrete floor level is the same as the rest of the house? So you'll end up with a step up into your wc/utility.

A tiled floor needs to be solid so either plywood (22 ideally) on joists with insulation between or insulation with probably a 60mm screed on top. The thicker the insulation the better so consider the overall height so whilst 30mm will be better than nothing 60 or 100 would be better.

PIR type insulations are better for their thickness than any other so the likes of Celotex or Kingspan etc. You're only gonna want to do this once so don't fit say 40mm on the walls when fitting 50 will only cost an extra £50 or whatever. Same applies to the floor and ceiling which wants to be the thickest of the lot. Don't forget insulating round any windows or doors either, you can get thin insulated plasterboard designed for this job.

 

[Dan1976]

Thanks for the reply Mr. Mercury!

There is actually a step down from the main house into the Utility/WC area so that isn't a problem - the limiting factor in terms of insulation thickness is the ceiling height (which isn't very much).

You've helped to make up my mind though ...

I'm going to put 60mm insulation on the inside of the roof and finish with thermal plasterboard, 50mm insulation and thermal plasterboard on the inside of all external walls and then timber battens infilled with insulation and finished with plywood and tiled for the floor at whatever thickness I can get away with.

Thanks again.

Dan.