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  1.  
    New to the forum so apologies if I've missed a similar topic..

    Recently bought a mid terrace house built 1863. After lifting the carpets, linoleum and slate slabs, we discovered a compacted earth floor. Initially quite surprised, but after doing a bit of research it seems like these were the norm. We've dug a couple of exploratory holes and the foundations don't go very deep, so a suspended floor is not an option.

    So the choices we have so far are;

    a) leave the earth/slate down and live with a breathable/cold floor.

    b) dig down far enough to put in a dpm/concrete slab and float a floor on top, making for a warmer floor, but compromising breathability, and potentially sending more moisture into the walls.


    Would rather use as little concrete as possible, so would love to hear if anyone has any alternatives.

    Thanks
  2.  
    Can you raise the floor a bit? The thought - leave the slate floor, place 20mm or 30mm of insulation (e.g. high density EPS) - more if you can manage the thickness - less if you can't and put an engineered wood floor over. Take advice from the wood floor manufacturer about intervening membranes. Even an engineered wood floor (1/2" or so thick of the click fit type) on its own will make a surprising difference to the warm feel of the floor.
    • CommentAuthortony
    • CommentTimeSep 29th 2017
     
    Simplest is floating floor with insulation under, I always do a combined vb/dpm on top of the insulation.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 29th 2017
     
    A wide skirt of insulation laid horizontal just below ground level around the outdoor perimeter of the building - stop the downward-and-outward-back-up-to-cold-surface heat loss from the floor. A shallow french drain under it, to keep the top layers of the subsoil bone dry. Leca can double as the inorganic mineral insulation medium as well as the no-fines aggregate of the french drain. Then leave your old floors undisturbed.
  3.  
    The mid-terrace siting of this house will limit the effectiveness of the external wing insulation
  4.  
    You might also consider VIPs (Vacuum Insulated Panels) e.g. Kingspan Optim-R - would give good insulation for little additional depth, is a little fragile and wouldn't help with breathability. I think costs are about £60/sqm.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 29th 2017
     
    Posted By: Peter_in_HungaryThe mid-terrace siting of this house will limit the effectiveness of the external wing insulation
    All the better, as v little heat gets lost to next door's subsoil. Still french drain front and rear though, to keep upper layers of the subsoil bone dry.
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2017
     
    The walls of the house act as radiators connected directly to the soil, so heat doesn't need to flow out through the soil outside it can go straight up the wall and away.
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2017
     
    I'm with Tony and Peter. Install some insulation and a floating floor. Either by building the floor up a bit or by digging down a bit first.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 30th 2017
     
    With underfloor insulation the walls of the house still act as radiators connected directly to the all-warm slab (or screed) edge above the insulation, from where heat not only flows up but also down and out into the stone-cold surrounding ground. Also heat lost direct from room to wall not only flows up but also down and out.

    With outdoor perimeter insulation instead, yes the walls are connected to the edge of the block of floor plus subsoil, which goes from warm to cold with increasing depth, from where heat flows only upward, but not much down and out into surrounding ground because the ground kept warmer under its insulation skirt. Also heat lost direct from room to wall flows only up, not much down and out.

    The comparison would need Therm modelling, but I think would be close. Lack of ground floor disturbance remains though.
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2017
     
    No, there is perimeter insulation around the edge of the slab to separate it from the walls. Standard details.

    Obviously a plan to insulate the walls - and roof if not already done - would also be useful.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 30th 2017
     
    Slab perim insul is usually quite nominal.
    Perhaps what has dawned (on me) is that exterior insul to isolate found wall from cold surrounding ground (pref by vertical downstand where founds are deep, and/or horizontal skirt where founds are shallow) is worthwhile, whether or not slab is insulated and whether or not wall is insulated. On top of its great advantage of not having to disturb the ground floor.
    •  
      CommentAuthordjh
    • CommentTimeSep 30th 2017
     
    Posted By: fostertomSlab perim insul is usually quite nominal.
    Perhaps what has dawned (on me) is that exterior insul to isolate found wall from cold surrounding ground (pref by vertical downstand where founds are deep, and/or horizontal skirt where founds are shallow) is worthwhile, whether or not slab is insulated and whether or not wall is insulated. On top of its great advantage of not having to disturb the ground floor.

    Could you post your calcs that support your observations, please, since in their absence it seems quite unlikely to me.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 1st 2017
     
    I said
    Posted By: fostertomThe comparison would need Therm modelling
    i.e. not done (yet) - isn't it OK to throw a useful hunch into the arena?
  5.  
    Thanks for all the replies. Food for thought.

    Any thoughts on whether to put the insulation above or below the slab?
    Obviously if you were laying underfloor heating you'd insulate underneath, but are there any benefits if you're not?

    Thinking of using something like kingspan thermafloor and floating the floor on top of that..

    Any advice appreciated,
    Thanks in advance.
    • CommentAuthortony
    • CommentTimeOct 4th 2017
     
    I always put insulation below the slab and used EPS now graphite EPS, the mass which stores heat is then on the warm side of the insulation, I also put a combined vapour barrier/dpm on the warm side of the insulation.
    • CommentAuthorgravelld
    • CommentTimeOct 4th 2017
     
    Are you considering what to do about the walls? You might want continuity of insulation onto the wall, assuming IWI, so the insulation "cups" the slab.
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