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    •  
      CommentAuthorfostertom
    • CommentTimeFeb 8th 2010
     
    The guiding principle for floor insulation, is the average through-soil path length, to outside air, from an average bit of the floor.

    Obviously, from the centre of the floor to outside air, you can't help but have a good long path length, so that 'thickness' of the subsoil, however mediocre its insulative value, even if without any formal insulation, adds up to considerable thermal resistance, and can probably do without any formal insulation at all.

    Conversely, from the edge of the floor, it's but a short path length, downward, curving outward and coming up through the nearby soil surface. For any floor, loss from its perimeter parts far exceeds loss from its centre.

    One way is to therefore add underfloor insulation, thickest around the perimeter.

    Another way to deal with the perimeter loss is to rely on increasing the through-soil path length, as 'seen' by the perimeter parts of the floor. That is achieved if that underfloor perimeter insulation is instead placed vertically, i.e. the upper wall insulation is in principle continued downward, unbroken, to underground e.g. to bottom of foundation level.

    Then heat, travelling downward through the perimeter of the slab, can no longer turn immediately outward, but must go right down below the vertical edge insulation, before turning outward and up to the surrounding soil surface. Through-soil path length is increased by twice the downstand of the vertical edge insulation.

    So that's another solution to an existing uninsulated floor slab - forget insulating the slab horizontally, instead dig a trench round the outside of the building and fit vertical insulation against the foundation wall, down as deep as you can.
    • CommentAuthorbrig001
    • CommentTimeFeb 8th 2010
     
    fostertom, any idea how effective this would be with a cavity wall? I am considering this, but it's quite an undertaking as you can imagine.
    •  
      CommentAuthorali.gill
    • CommentTimeFeb 8th 2010
     
    With a cavity wall the cavity should be filled below ground level with mortar. dpc should be at least 150mm above ground level.
    If the cavity is not insulated then you'll get thermal bridging through the inner leaf into the cavity.
    So if the cavity is uninsulated or only partly insulated then i'd recommend Springvale Ecobead
    http://www.springvale.com/products.asp?InfoID=525&mySub=517

    For the shallow insulation / cold floor problem i'd spec http://www.jupiter-system.com/system_ideal.php
    "Solid or engineered timber floors can be laid directly either as a floating floor or nailed to floating battens."

    For the external trench and insulation fill you could use Leca
    http://www.claytek.co.uk/leca_home.htm
    rather than trying to fix a foam product to the outside of your walls.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 8th 2010
     
    Posted By: ali.gillWith a cavity wall the cavity should be filled below ground level with mortar
    I don't, at least I didn't till i gave up cavity walls (nasty things). For a long time I carried the cav wall insulation (in impermeable foam-plASTIC insulation) DOWN TO TOP OF STRIP[ FOOTING - no one minded. (sorry - caps lock).

    Posted By: ali.gillrather than trying to fix a foam product to the outside of your walls.
    What could be easier or simpler?
    • CommentAuthorSaint
    • CommentTimeFeb 8th 2010
     
    Tom, agree totally. Question: How hard can it be to fix foam to the outside of your walls externally below ground level anyway??
    However using XPS high compressive foam insulation in the cavity is just so simple and works very well.
  1.  
    Fostertom says that the most significant heat losses from flooring are via the loop to external air, rather than vertically down to the 'stable' 7-10 degrees of the 'deep' earth - I can't say whether that is correct or not, but if true, doesn't it imply that you could improve your heat losses by laying say EPS horizontally out from the wall base, thus increasing the path length to air ? It would save on excavation depth and would seem appropriate to old buildings with shallow foundations. Any problems anyone can see with this?
    • CommentAuthortony
    • CommentTimeFeb 9th 2010
     
    That is called wing insulation and yes indeed it does work,
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 9th 2010 edited
     
    It will take a year or more for the subsoil within the perimeter of insulated found wall to get heated up, as the opening 'leg' of the linear temp gradient that you've created.

    You may want to tweak that gradient a little, by slightly increasing the resistance of the first bit, so that the floor surface/screed is warmer than it would otherwise be. Something like 25mm of EPS under the screed - not enough to greatly change the principle of insulation by long subsoil-path length, but so the screed contains more of the warmest end of the gradient. Note, that 25 of EPS would be all over the slab, not just at the perimeter. Thanks to Paul T of http://thehealthyhome.co.uk for that tip.
  2.  
    Slightly off topic, but none of this works for suspended floors right?

    In which case, having taken up the floor boards to insulate beneath them, would it be better to just pour a floor of...ahem... some kind of *crete, rather than putting them back down again?

    If not, in the case of a ventilated suspended floor, is there any point in insulating the founds externally if the inner surface of the wall is still leaking heat into the ventilated space under the floor?

    Peter
    • CommentAuthortony
    • CommentTimeFeb 9th 2010
     
    Suspended floors are very heat leaky -- much more so than ground bearing

    There can be structural reasons for not bearing a floor on to the ground but in all other cases ground bearing is definitely best in terms of saving energy and comfort.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 9th 2010
     
    Posted By: Peter Clarkin the case of a ventilated suspended floor, is there any point in insulating the founds externally if the inner surface of the wall is still leaking heat into the ventilated space under the floor?
    If 'ventilated' then definitely no point, but if 'unventilated', then that wd be a gd question, which I haven't thought thro yet, but was about to arise on a project (with got cancelled). To avoid underfloor stagnation, instead of thro ventilation I was beginning to think of plumbing it into the MHRV.
  3.  
    Posted By: fostertombut if 'unventilated'


    How could the underfloor not be ventilated? I thought they had to be.

    Peter
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 9th 2010
     
    See my last sentence. The Approved Documents are not The Building Regs, just 'one way of satisfying the Regs' - worth going back to the legal Statutory Instrument sometimes - other ways to satisfy the objectives set out there. In this case, I'm not sure what the SI says, but most Building Insps are reasonable men!
  4.  
    Posted By: fostertomIf 'ventilated' then definitely no point,


    Unless you also insulated the internal face of the external wall? sounds terrible pain, would you dig down and insulate the internal of the founds?

    Would it not make more sense to take out the joists and pour a solid floor, then external insulation of founds(or wing insulation) with EWT?

    is this a mad idea? Is it likely to be very much more expensive initially?

    Peter
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 9th 2010
     
    Posted By: Peter Clark
    Posted By: fostertomIf 'ventilated' then definitely no point,


    Unless you also insulated the internal face of the external wall?
    That wd be invalidated by the through-ventilation.
    • CommentAuthorPeter Clark
    • CommentTimeFeb 9th 2010 edited
     
    Posted By: fostertom
    Posted By: Peter Clark
    Posted By: fostertomIf 'ventilated' then definitely no point,


    Unless you also insulated the internal face of the external wall?
    That wd be invalidated by the through-ventilation.


    Surely not entirely.

    The wall would then be inside the insulation envelope, apart from the cold bridge straight down and the draught contacting the sides of the ventilation aparture, the under floor void outside it?
    Maybe room for insulated pipe to line the ventilation aparture through the wall?

    But what about my main question, how practical to turn a suspended wood floor into a solid floor, thus avoiding the hassle of insulating the wall with the suspended wooden floor in place?

    Or alternatively, the best way to insulate the wall if leaving the suspended wooden floor?

    Peter
    • CommentAuthorseascape
    • CommentTimeFeb 12th 2010
     
    Back to concrete slab insulation. I was going to insulate under my concrete slab with kingspan kooltherm 100mm load bearing insulation, with upstands at edge to create 'envelope'. I had reservations as I was worried that dpm would create 'swimming pool effect' if build was delayed due to cost, as manufacturers state it should be stored in dry conditions. Lots of wind and rain here. Also had heard (unverified) stories of rats making nests in insulation if under the slab! Had visions of my building suddenly dropping 100mm! I suppose I could have rendered round edge to stop that happening? Anyway, in the end decided to proceed with dpm/slab and then insulation. The discussion about extending insulation downwards on vertical wall makes sense to me.

    Question: I want to make a change to my floor plan! I have just contacted a concrete cutter and am waiting for a reply. Any one had any experience of increasing or reducing exsisting slab?
  5.  
    I'm intending to insulate above an uninsulated concrete slab. This is for workshop use. I'm intending to lay 40mm studs, with 40mm rockwool in-between and then 18mm T&G chipboard on top. The solid brick walls surrounding the slab have a dpc two courses above the level of the existing slab. Do I need to involve a vapour barrier in this floor design? The floor currently has no visible signs of damp.
    • CommentAuthortony
    • CommentTimeMay 26th 2010
     
    Technically yes. However a lot of people dont do them on floors for some reason -- I always do.

    I would use sheet insulation (EPS) rather than fibrous materials.

    I would also do it as a floating floor -- loads easier and quicker too.
  6.  
    cheers for advice. Do you think EPS is strong enough for floor? I'm not so keen on board insulation as I'd have to level the existing floor first, so would have to apply a screed / self-levelling compound first. I was planning on using plastic shims underneath the studs to level them, with the benefit of providing a gap underneath the studs.

    re; vapour barrier: Would you install a polythene sheet directly onto the concrete and then the new floor on top? Will this encourage any damp the slab has to make its way up the walls? Or a variable Intello-type membrane between the insulation and the floating floor?
  7.  
    Posted By: spoonandforkre; vapour barrier: Would you install a polythene sheet directly onto the concrete and then the new floor on top? Will this encourage any damp the slab has to make its way up the walls? Or a variable Tyvek-type membrane between the insulation and the floating floor?
    A polyethylene vapour barrier should go on the warm side of the insulation, i.e. directly under the floor boards. Is there already a damp proof membrane under the slab? Has it been kept dry/heated? Are there any signs of damp?

    David
  8.  
    no signs of damp, has been unheated. I don't think there is a dpm under the slab. The building is old, approx 1900s, but there is a dpc in the brick walls. I think if I put a polyethylene barrier on the warm side, below the floorboards, the studs below will be prone to rot. Or, if I went for XPS (or similar non-breathable insulation) or used a barrier, I could be encouraging damp to migrate up the walls.
  9.  
    actually it's easier to level the floor with compound and then lay EPS and floating floor than to bolt and level battens down every 2', so perhaps your way is the way forward, tony.
    • CommentAuthortony
    • CommentTimeMay 26th 2010
     
    :bigsmile:
    • CommentAuthortony
    • CommentTimeMay 26th 2010
     
    It is surprising how much of an undulation a floating floor can cope with

    it is also possible to lay a dry mix of sand and cement instead of leveling compound

    There are also said to me damp proof leveling compounds too.
  10.  
    hmm, still not confident about the damp proof procedure. If I lay plastic straight onto slab, the damp could go up the walls. Also would then need to have secondary membrane above insulation to prevent condensation on the lower sheet. If I have no membrane, the floor could breathe but may be less insulating as it is potentially more damp... I don't know. I'm tempted to not use a membrane, as the floor seems dry (I will test this) and because of past experience of laying floor dpms - damp walls.
    • CommentAuthortony
    • CommentTimeMay 26th 2010
     
    Don't worry about the floor --- go from bottom up, insulation EPS, vapour barrier, sheet flooring and you will have no problems.
  11.  
    do you favour EPS over PUR and XPS because of embodied energy of the materials?
    • CommentAuthortony
    • CommentTimeMay 26th 2010
     
    price!
    • CommentAuthorCWatters
    • CommentTimeMay 26th 2010 edited
     
    <blockquote><cite>Posted By: tony</cite>price!</blockquote>

    http://www.secondsandco.co.uk/
   
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