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    • CommentAuthordelprado
    • CommentTimeOct 11th 2017
     
    For those of you who have done it, or recommend it, with what authority have you done it or recommend it, to not be worried about moisture build up?

    Thanks
    •  
      CommentAuthorfostertom
    • CommentTimeOct 11th 2017
     
    Moisture - meaning condensation originating from the interior, or ground water?
  1.  
    large thread on it somewhere
    • CommentAuthortony
    • CommentTimeOct 11th 2017
     
    No problems, moisture moves away from warm (higher partial,vapour pressure) areas to cooler places where the
    (pvp) is lower.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 11th 2017
     
    That's my thinking. Provided there's no water penetration into the subfloor by groundwater, leaking drain etc, that just leaves water vapour from the interior.

    If it's not condensing on the floor surface it's not going to condense in the warm topmost layers of the EPS beads.

    It may well condense on whatever's on the cold side of the EPS beads - the inner face of external founation walls or the solid ground beneath. But is that harmful?
    • CommentAuthortony
    • CommentTimeOct 12th 2017
     
    Even with water on the sub floor it is still ok as the above process still operates.

    The insulation helps keep the substructure warm enough for there to be no problems of the type you mention.
    • CommentAuthordelprado
    • CommentTimeOct 12th 2017
     
    Thanks all. Isn't the consequence that it is going to try and drive more moisture up the walls and hit the DPC?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 12th 2017
     
    Not necessarily, but if so, that's OK - what DPCs are for.
    •  
      CommentAuthordjh
    • CommentTimeOct 12th 2017
     
    Tom, have you ever calculated to show that the temperature of the bottom of the joists is well above the dewpoint there when there is free water on the ground?

    (I'm presuming the bottom of the joists are still the coldest timber in the space)
    •  
      CommentAuthorfostertom
    • CommentTimeOct 12th 2017 edited
     
    No but I do know approx where danger of interstitial condensation becomes more than merely rare and insignificant, in a highly insulated wall sandwich. To be very adequately safe, there should be no timber within the outer 40% of that sandwich.

    Compared to such a wall sandwich, the underfloor sandwich being discussed here terminates 'outboard', or rather down below, at a temp (subsoil temp at depth) that is worst-case higher than the worst-sustained-design-temp that a wall sandwich experiences.

    Therefore I'd feel very safe as long as say a quarter or one third of the insulation of the total floor-sandwich, lies beneath the joist undersides. Sure, if there's very litle insulation thickness between joist undersides and top of subsoil, then that might be more unsafe.

    But having said that, there's more - the act of putting a heated building on top a piece of subsoil, with or without a void space between, gradually and 'unnaturally' warms the upper layers of that subsoil.

    That is, once you've stopped up the through-ventilation of the void. While it's through-ventilated, the subsoil effectively 'sees' outside air, uninfluenced by the house above, so its temp wil be approx same as the 'natural' temp at depth of the surrounding ground.

    Once the through ventilation is stopped up e.g. by filling the void with EPS granules, then the subsoil becomes coupled to the house's interior temp - albeit only weakly influenced because of the insulation - but nevertheless slowly equilibriating at a higher-than-natural subsoil-at-depth temp.

    Thus reducing interstitial condensation risk still further. Perhaps 15-20% of the insulation thickness beneasth the joist undersides?

    Still, don't take my word for any of this, unless paying me a consultancy fee - as Dave says, if in doubt do the calc.
    • CommentAuthortony
    • CommentTimeOct 12th 2017
     
    Anyone interested in applying for a grant and developing this area?
    • CommentAuthordelprado
    • CommentTimeOct 13th 2017
     
    I've just made contact with Sophie who is looking for houses to test.

    https://www.sheffield.ac.uk/architecture/people/academic/sofie-pelsmakers

    http://www.sofiepelsmakers.com/
    • CommentAuthordelprado
    • CommentTimeOct 13th 2017
     
    As another thought - is condensation the only concern, though?

    Surely even if in the air, is there is warm moist air just sitting around the joists permanently then that isnt good either?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 13th 2017
     
    That's fine - late summer outside air is often 90%RH. Moisture only becomes a threat to timbers when it's liquid i.e. condenses. Tho admittedly there are many puzzles about just what happens within the pores of timber at high RH.
    • CommentAuthordelprado
    • CommentTimeOct 13th 2017
     
    Thanks Tom.

    Does filling with eps to the joists then going between the joists with woodfibre change this dynamic at all? I dont think it does and it anything would improve the situation since the wood fibre can take in some moisture whereas the eps cant? I am thnking about it because a) i have batts to use and b) its better at sound insulation at 43kg cubic metre
    •  
      CommentAuthordjh
    • CommentTimeOct 13th 2017
     
    Posted By: delpradoDoes filling with eps to the joists then going between the joists with woodfibre change this dynamic at all? I dont think it does and it anything would improve the situation since the wood fibre can take in some moisture whereas the eps cant? I am thnking about it because a) i have batts to use and b) its better at sound insulation at 43kg cubic metre

    The woodfibre has poorer lambda and using batts instead of beads means there will probably be more flaws in the insulation. Sofie's paper is a good read, thanks for the pointer! Why do you care about sound insulation underneath a ground floor? Better to use the woodfibre almost anywhere else I would have thought - ceilings, lofts, walls etc.
    • CommentAuthordelprado
    • CommentTimeOct 13th 2017
     
    I suppose I might be worrying over nothing - if the airbricks are sealed - which they would be - the floor would be no worse than the walls I guess? If I had to ventilate underneath I would certainly prefer batts for the attenuation. And in fact its looking at the price of an acoustic air brick (Greenwoods are 140 quid each!) that has made me consider this whole idea!
    •  
      CommentAuthorfostertom
    • CommentTimeOct 13th 2017
     
    Attached is the drawing I keep posting as this question keeps coming up - was a newbuild extension so not quite what you have in mind, but it argues the principles. The Building Inspector accepted it and AFAIK it's succesful to this day. The whole idea is to couple the interior environment to the subsoil in a controlled way - through-ventilating under the 'filled' void negates that, in fact is just conventional suspended floor insulation, not the filled void that's being discussed.

    If you'd like a fully legible pdf, email me (click on 'fostertom')
      285Ja-ufloor 330KB.JPG
  2.  
    If the ground is wet, what is to stop capillary action? And once that has started, whats going to clear it?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 13th 2017
     
    Are EPS beads very capillary? Leca certainly isn't.
  3.  
    Posted By: dimengineerIf the ground is wet, what is to stop capillary action? And once that has started, whats going to clear it?
    Hi Tim, I must have pumped EPS bead into the floors of at least 50 Renovations since 2007, never had a problem or call back from a client.
    One of the first things tested in the early days was the capillary effect of bonded EPS beads, 10mm holes were drilled every 20mm on the side of a 110mm sewage pipe and filled it with EPS bead, the holes were stuffed with blotting paper and it was stood vertically into a basin of water for a week. After a week the moisture levels of the blotting paper was tested with a moisture meter, the paper 10mm up from the water was a few % higher in moisture than the rest. The conclusion was that the capillary effect of EPS bonded bead is minuscule to non existent. The floor beneath my own 1850's house was fully pumped about 10 years ago. A Thermocouple placed at the soil/EPS junction reads a constant temperature of about 14 degrees, heat drives moisture out making the soil beneath the house drier than the surrounding soil.
    Sophie Pelsmaker attended the UK PassivHaus Conference in 2010 where I presented 4 EnerPHit Renovation projects, 2 of them had the floors fully pumped with EPS bonded bead sparking Sophie's excellent research!
    An interesting paragraph in the Canadian House Building Manual says that 10mm of EPS Insulation nailed to the outside of a roof rafter reduces the risk of condensation on the rafter by 90%.
  4.  
    Posted By: delpradoThanks Tom. Does filling with eps to the joists then going between the joists with woodfibre change this dynamic at all? I don't think it does and it anything would improve the situation since the wood fibre can take in some moisture whereas the eps cant? I am thnking about it because a) i have batts to use and b) its better at sound insulation at 43kg cubic metre
    Hi Paul, pumping the void beneath the floor with EPS beads warms the floor joists and eliminates condensation risk.
    Your kitchen table or internal doors won't rot from the moisture in the air because its the same temperature as the air so there's no condensation risk, same with the floor joists after you fully pump the void beneath the floor with EPS beads.
    Wood is made up of cell walls and cells filled with air, the humidity level in the air within the cells is usually similar to the average daily house humidity. If the wood cell wall gets too cold the moisture in the air within the cell can condense, insulating the void beneath the floor ensures this never happens.
  5.  
    Posted By: delpradoThanks all. Isn't the consequence that it is going to try and drive more moisture up the walls and hit the DPC?
    Insulating one side of a rising wall warms it a few degrees reducing the capillary action. If you pump beneath the floor with EPS and dryline the external wall the heat-loss from the room is concentrated at the wall/floor junction heating it up further.
    • CommentAuthordelprado
    • CommentTime4 days ago
     
    Hi Viking

    Can we chat offline about this? Would really appreciate it
  6.  
    <blockquote><cite>Posted By: tony</cite>Anyone interested in applying for a grant and developing this area?</blockquote>

    Yes, what are the details?
    • CommentAuthordpmiller
    • CommentTime22 hours ago
     
    <blockquote><cite>Posted By: Viking House</cite><blockquote><cite>Posted By: dimengineer</cite>
    Sophie Pelsmaker attended the UK PassivHaus Conference in 2010 where I presented 4 EnerPHit Renovation projects, 2 of them had the floors fully pumped with EPS bonded bead sparking Sophie's excellent research!
    An interesting paragraph in the Canadian House Building Manual says that 10mm of EPS Insulation nailed to the outside of a roof rafter reduces the risk of condensation on the rafter by 90%.</blockquote>

    This interests me. Is there a sensible way to implement this into a normal "cold" sloped roof? Say, laid with ventilating gaps beneath a standard breathable membrane. Or would it still then demand counterbattening?
    • CommentAuthortony
    • CommentTime16 hours ago
     
    Sophie's work is excellent but almost unknown, saving over 90% of the heat being lost through a suspended wooden floor should headline news

    I have an opportunity to repeat that work using a test-bed house also looking at influence on air tightness which will offer further savings.

    Do we think that that would be worthwhile exercise?
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