Insulating over stone floor.

[Sailfish18]

Hi.

Looking for some opinions and/or guidance.

I have a small mid-terraced house circa 1880. Ground floor is stone flags just laid over rubble/clay/ mixed stone etc. I have 2 issues which i would like to address, namely some damp patches showing through the stone flags and cold floor.

 

I have considered various options including:-

1. Excavating and laying DPM, concrete, insulation etc.

2. Excavating and laying geotextile membrane, foamglass, screed and timber floor on top.

3. Constructing suspended timber floor above existing using decking feet. This would mean minimum 150mm void, ventilation and associated introduction of cold air which in turn means insulation on top of the 150mm already.

 

Due to location up a flight of stairs onto a raised terrace, and very limited access at the back, every builder has sucked their teeth, hummed and haaaard and then not come back, cut off contact or submitted daft quotes to avoid the work. Presumably because they are put off at the prospect of a bit of physical work and want a quick buck.

 

I have a lot of experience in property renovations so am happy to carry out the work myself but don't want the upheaval of digging the floor up (currently living in the house), especially as i would be doing it on my own and by hand.

 

Ground floor rooms are high ceilings, so i do have height to play with. I am now considering the following.

 

25mm blinding sand over the stone flags to level them out.

DPM lapped up to current DPC (Chemical)

100mm EPS.

Vapour layer.

18mm T&G OSB3

Underlay.

Engineered wood floor.

 

I would appreciate any observations or suggestions, preferably constructive ones!

 

TIA.

[Mr Punter]

If you do the floating floor it is best to use 22mm t&g chipboard and bond the engineered floor to it.  The adhesive is pricey but it feels a lot more solid.

[JohnMo]

If you are only adding 100mm insulation upgrade to PIR.

[saveasteading]

That seems a pragmatic solution, as long as you don't want to keep the stone on show.

One concern is that the stones might rock / move differentially over time, but the very flexible construction above should absorb it. Another good reason for upgrading the board.

I'd also upgrade to waterproof osb. There shouldn't be damp, but this depends on keeping it completely away from the walls.

The flooring must be allowed to move/ shrink/expand and must be kept off the wall. Have you a plan?

 

 

BTW geotextile is completely porous so don't consider it.