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    • CommentAuthorconverse
    • CommentTimeNov 11th 2020
     
    I am sure i have read somewhere about an approach to insulation from heat losses to the ground where the perimeter of the building is insulated vertically, but the floor slab itself is a large deep heat sink type construction laid on top of a damp proof membrane, without insulation. I'm sure it was a thread on here but can't find it. I have a site with a lot of spare crushed concrete to use, and also a need to build the levels up significantly, so i wanted to read up on this. Cant find anything on it so am starting to think I imagined it.
    • CommentAuthorEd Davies
    • CommentTimeNov 11th 2020
     
    No, you didn't imagine it, that sort of thing's been discussed here often. Search engine fodder which might help: “perimeter insulation”, “umbrella”.

    Not sure it'd be my first choice of a new build, though.
    • CommentAuthorconverse
    • CommentTimeNov 11th 2020
     
    Great, found the mammoth thermal store thread. Thanks
    •  
      CommentAuthorfostertom
    • CommentTimeNov 11th 2020
     
    try 'downstand perimeter'.
    •  
      CommentAuthordjh
    • CommentTimeNov 11th 2020
     
    I have a suspicion you might have problems convincing a BCO it meets regs?
    • CommentAuthorjms452
    • CommentTimeNov 30th 2020
     
    Posted By: converseneed to build the levels up significantly.


    300+mm of polystyrene plus a concerete slab will help build up your levels - you normally have to go down to get a good level of floor insulation.

    Crushed concrete might be able to be reused as a bottom layer of sub base for your drive...
    • CommentAuthorbxman
    • CommentTimeDec 1st 2020
     
    AIUI
    Heat loss is directly proportional to the Delta and heat losses through the floor are insignificant apart from at the perimeter when the exterior walls are not insulated on their exterior.

    To my mind that insulation would be better used elsewhere. if you can incorporate EWI you will get some thermal mass which will stand you in good stead.
    • CommentAuthordereke
    • CommentTimeDec 1st 2020 edited
     
    I've been wondering about doing this in my house. I've been insulating under the suspended floor but it is a pain in the arse to do and the part I've started with is the easiest as there is a roomy 600mm of clearance. It is less elsewhere.

    I'm thinking of ripping all the floors out (they are not fixed to the walls, like piers in the middle holding it all up) laying down insulation on the ground and walls then infilling with hardcore and putting a screed and underfloor heating in. I think the thermal mass would be useful for getting the most out of my heating system and also switching to an agile tariff (turning off the heating for a few hours at peak time should not have a big impact).

    Hell of an upheaval though. Please don't mention it to my wife!
    • CommentAuthorconverse
    • CommentTimeJan 25th 2021
     
    <blockquote><cite>Posted By: bxman</cite>AIUI
    Heat loss is directly proportional to the Delta and heat losses through the floor are insignificant apart from at the perimeter when the exterior walls are not insulated on their exterior.

    To my mind that insulation would be better used elsewhere.</blockquote>
    Yes, agreed. Crucial point is from DJH above - I have no idea what Building Control would think. Ground water levels are also going to be an issue, though there is a handy ditch running the length of the plot that can take groundwater away. Has anyone used Geocell in this sort of application?? - looks like it could provide drainage and insulation at the same time.
    •  
      CommentAuthordjh
    • CommentTimeJan 25th 2021
     
    Posted By: converseHas anyone used Geocell in this sort of application?? - looks like it could provide drainage and insulation at the same time.

    Yes, it will provide drainage and a capillary break. I'm not quite clear as to its relevance for your scenario?

    FWIW, I believe tomorrow's Grand Designs will be about an earth-sheltered house with an uninsulated floor and lots of underground perimeter insulation. Should be interesting.
    • CommentAuthorconverse
    • CommentTimeJan 25th 2021
     
    Relevance is manufacturers claim Geocell can be used for perimeter insulation as well. I guess a bonded EWI would work better, but I'm trying to minimise number of trades on this design.
    • CommentAuthorconverse
    • CommentTimeJan 25th 2021
     
    •  
      CommentAuthordjh
    • CommentTimeJan 25th 2021
     
    converse quoth "Like this"

    That looks a lot like a diagram of a passive slab.

    There's a PDF about the system we used at
    https://www.glavloc.com/downloads/KORE-Passive-Slab-Design-Guide.pdf
    We had to dig a big hole and part-fill it with loads of hardcore (recycled from some industrial process), then the EPS 'bucket' and then the concrete slab. French drain around the outside. I got one firm of groundworks contractors to do everything.

    You can obviously extend the insulation out further from the edge of the raft. EPS is what they use but geocell should work as well. It's not normal/necessary to bond the sheets of EPS together AFAIK. Maybe to allow drainage?

    There's an article that discusses both systems at https://passivehouseplus.ie/magazine/guides/the-ph-guide-to-insulating-foundations
    • CommentAuthorconverse
    • CommentTimeJan 29th 2021
     
    Hi, yes, the diag I posted is indeed a passive type slab. But if you moved the expensive geocell from under the middle of slab proper, and shifted more to the outside perimeter as deeper and wider perimeter strip, wouldn't you have something that performed better and used much less of the Geocell? I appreciate there might be arguments with the Building inspector and probably wouldn't pass building regs in UK as I read them, but does seem a better use of resources to me. I'm probably missing something.
    •  
      CommentAuthordjh
    • CommentTimeJan 29th 2021 edited
     
    Posted By: converseI appreciate there might be arguments with the Building inspector and probably wouldn't pass building regs in UK as I read them

    I think you're mostly right, but the GD episode had no insulation under the floor AIUI so it's possible to get around the regs (or at least the Approved Documents) if you know what you're doing.

    They like most people used EPS for the insulation they do have rather then Geocell. I'm not sure why we're spending so much time discussing Geocell? Do you have some particular reason to want to use it?
    • CommentAuthorconverse
    • CommentTimeJan 29th 2021
     
    I don't particularly want to use Geocell, but I do want to move away from EPS and am thinking what else could work in an economical way. My doubts about EPS are firstly environmental issues associated with its production, but I also have reservations about its longevity. It's not as if it could be easily replaced if it's underneath a building, so its not a solution that would fail very gracefully in that situation.
    •  
      CommentAuthordjh
    • CommentTimeJan 29th 2021
     
    Posted By: converseI also have reservations about its longevity. It's not as if it could be easily replaced if it's underneath a building

    Indeed. There's 400 mm underneath our building so I hope it lasts! There have been some tests of longevity and I think there are links somewhere on this forum. But the thing that made me relax about the question was when I realised that railway embankments and some motorways are held up by EPS 'hardcore'.

    I don't like its environmental credentials, but it is a very useful material at a reasonable price with a lot of track history so I'm happy to live with it as I live with my concrete slab.
    • CommentAuthorPetlyn
    • CommentTimeJan 30th 2021
     
    If you are looking for an economical alternative to Geocell, then we have 12m3 of an identical product - 4-8mm, remaining from our build. We also have a large hopper blower which is single phase running from a standard 13 amp plug which will blow the beads 8m approx.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2021
     
    AFAIK EPS has very much nicer eco credentials than any of the other plastic insulations inclusing Extruded polystyreme (XPS).
    There is a good case for using petroleum oil to make insulations, when their use saves many times their oil content, in energy that doesn't have to be burnt subsequently for space heating.
    There's that aspect of eco credentials, in which EPS is about on a par with the other plastic insulations; AFAIK it's in the other kinds of chemical pollution, which is IMO more insidious and long-reaching, that EPS shines compared with the others.

    Posted By: djhYou can obviously extend the insulation out further from the edge of the raft. EPS is what they use but geocell should work as well
    This is where I hesitate to use plastic insulations, as horizontal skirt outboard of the building perimeter. Here it really is a little or a lot or accidentally exposed to the elements, and to mechanical distruption due to imposed ground loads varying over time.
    The idea of it lying what - 300mm? - below finished GL, covered with topsoil, paving or whatever sounds really poor.
    If topsoil, roots will soon enough penetrate and disrupt, even with root barrier overlay. The thin topsoil layer, isolated from deeper massiveness, will scorch is summer, freeze in winter and struggle to retain moisture stability.
    Much better to use inert mineral Geocell, or my preference LECA, tho 2x or 3x thicker (for given insulation) and more expensive - but less so if you order LECA not in bags like garden bedding compost with fancy silicone coatings etc, but by the lorry load (or dumpy bagged or even blown-tanker load) in civil engineering grade.
    Then it becomes just a mineral geological stratum compatible with topsoil and subsoil, tolerant of mechanical disruption or root penetration, and leaves the topsoil less liable to temperature swings.
  1.  
    Posted By: fostertommy preference LECA


    How far out from the building would you go with this? and how deep?
    We have a plain rectangular building 14.5m x 10m
    Perhaps extend it 1m out from the perimeter and 500mm deep?
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2021
     
    Good question. I have been trying to model this in a crude way, as I find Therm software too tiresome. I think of the 'wing' more as extending the wall insulation, not so much the floor insulation - in fact to me it's a way of not having any floor insulation, instead letting the floor benefit from direct connection with the great temperature-stability of massive subsoil.

    This thread started as the latter but is tending to veer off into an insulated slab, perhaps supplemented with a perimeter horizontal 'wing'.

    1m of downstand is worth 2m of 'wing', and the bulk of the loss through it is where it's closest to the building, so it needs to be thickest there, tapering off outward.

    A horizontal 'wing' of perimeter insulation may only be necessary instead of a downstand 'coffer dam' of insulation, where depth can't be achieved because the foundation is shallow, maybe built off shallow bedrock, but even then some more or less vertical EPS against the wall or at say 45o against vestigal foundation, like attached. Make it up as you go along!

    To calc, I postulated 21C at floor/inner wall surface, 0C exterior ground surface. Therefore 0C ground temp at the far tip of the 'wing'. Other ground temps at 0.5m intervals diminishing from 21C to 0C. At each interval, use the local delta-t and conventional U value to calc heat loss for that 0.5m strip. From that you can see where the 'wing' thickness needs to be thickened and where it can be allowed to diminish. Turns out, what's shown on the attached isn't really thick enough - but a lot better than nothing and prob works better than it should, as the floor is, as I say, heavily temp-stabilised by direct connection with subsoil - shattered rock/shale in this case. At any rate, the downward temp gradient of the floor is hugely flattened.

    Familiarity with the principle should achieve convincing of an open minded Building Inspector, at least in an existing building.
      319Ca-44.JPG
  2.  
    Posted By: fostertommore or less vertical EPS against the wall or at say 45o against vestigal foundation


    Thanks that’s really helpful. I think it will be a case of making it up as we go along. There is some depth to foundations, but ground levels differ all the way around (it’s possible that the foundations are actually level all the way round) So can do some vertical then slope off at 45 degrees from the strip foundations (under the blockwork walls) and then there is also to deal with big square foundations for the steel uprights!
  3.  
    Hi, I developed the Passive Slab used by djh and marketed by KORE so a few things;
    Wing insulation increases the temperature of the ground beneath the insulation, I modeled this and found that increasing the temperature of the ground beneath 300mm of insulation by 10 degrees reduces the heat-loss of a 200m2 house by 30kWh/annum, about ÂŁ5, so the return on investment could be about 100 years.
    Last time I looked the Embodied energy of foamed glass on the ICE Database was 2-3 times higher than EPS.
    Frost protected insulated footings were used as early as the 1930s by Frank Lloyd Wright in the Chicago area.
    But since that time, the Europeans have taken the lead in applying this concept over the last 60 years.
    There are now over 1 million homes in Norway, Sweden, and Finland with insulated shallow footings which are recognized in the building codes as a standard practice.
  4.  
    Posted By: Viking Houseinsulated shallow footings


    Hi VH
    I can fully see the benefit of a passive slab on a new build, but
    What would you recommend in our retrofit situation?
    a plain rectangular building 14.5m x 10m
    Hoping for EWI then continue down to foundations.
      B2EB5848-826C-48C9-9A68-C5EE9EF5375C.jpeg
  5.  
    Just to add, we were wondering if we would not have to insulate the existing concrete floor slab in this building if we EWI and continue it down. Hoping to design out a heating system if possible!?!?
  6.  
    That's good, dropping external insulation 500mm below finished floor level improves the temperature at the skirting by almost 3 degrees. Photo 5 shows the perimeter trench http://www.viking-house.ie/passive-house-renovation.html#prettyPhoto Scroll down to see the skirting temperature improvement.
  7.  
    <blockquote><cite>Posted By: Dominic Cooney</cite>Just to add, we were wondering if we would not have to insulate the existing concrete floor slab in this building if we EWI and continue it down. Hoping to design out a heating system if possible!?!?</blockquote>

    I don't believe you'll achieve what you hope Dominic, I believe the ground will never heat up enough and will remain cold, any heat you put in will conduct away through the ground. The closest we got to no heating was this house http://www.viking-house.ie/solar-enhanced-passive-house.html
    The 40m2 Solar Roof reduced the heating demand from 15kWh/m2/annum to 1kWh/m2/annum and the hot water demand from 20kWh/m2/annum to 1kWh/m2/annum. It has a 50m3 insulated gravel Thermal Store beneath the house and has an annual heating/hot water and electricity cost of €120.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 8th 2021 edited
     
    As I see it, dowstand and/or 'wing' perimeter insulation is great in a 'near-PH' renovation as you can then consider not tearing up the floors to insulate. But it only (considerably) reduces the floor loss as well as cutting risk of lowest-skirting condensation, as VH says. It's def not up to scratch as a full-PH or newbuild tactic - VH's Passive Slab is the way to go. I have no opinion on downstand or wing insulation added to an insulated floor.

    I would add - why VH only go 500mm deep? The deeper the better, without going an inch deeper than the base of the found - or only by cutting outward at flatter-than-45o. In the pics I attached is was on bedrock, but still we came outward at 45o.

    I'm sure there are really serious 'wing' designs that would achieve near-zero floor loss - that would look more like ground-coupled/earth-sheltered cave-like principle.
  8.  
    Hi Tom, I believe at the time we were just trying to avoid condensation at the skirting, yes you can always go further, the top of the footings was down 500mm so we stopped there. On a side note I never actually saw the benefit of improving the airtigtness below 1ACH@60pA.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 8th 2021
     
    I didn't find a way in Therm to model downstand and/or wing perimeter insulation around an uninsulated slab, where the thermal gradient from the floor surface carries on extending deeper (and therefore 'flatter', but at diminishing rate) in theory forever! It's just a guess, to set a boundary at say 10C at a depth below floor surface. I suppose you could play around, set numerous combinations of depth and temp, see what combination is least sensitive to changing the numbers, at which point you're perhaps close to an equilibrium, tho not really - it's asymptotic.
   
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