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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorgravelld
    • CommentTimeJul 18th 2015
     
    I'm interested in how far EWI around a solid floor (I know, different, but still) will make up for no insulation under that solid floor.

    About 80% of heat loss through a floor is through the external perimeter I believe, so it feels like EWI right down as far as possible will go a long way to mitigating zero floor insulation. Given additional insulation elsewhere you could still have a very low energy retrofit with just this 'apron' and not have to dig out a floor.

    It has been discussed many times on the Home Style Green podcast.

    One thing I like about it is no need for scaffolding, could almost be done on its own?
    • CommentAuthortony
    • CommentTimeJul 18th 2015
     
    Needs to be no air or wind in the cavity.

    I like EWI or insulation against the wall (apron) to go down a long way

    Can help, you will then be warming the ground under the house making it much more thermally stable.
    •  
      CommentAuthorjoe90
    • CommentTimeJul 18th 2015
     
    I also like this idea and will be installing 300mm full fill cavity insulation all the way down to the strip foundation like the Golcar passive house. We have talked before on this forum about stable temps under a house with "wing" insulation of some sort. My thoughts with my new build is whether I need the underfloor insulation as thick as proposed (300mm)?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015
     
    Do you mean 300 underfloor insulation, or the 300 in the cavity? The former would defeat the purpose of the latter, if you did both.
    •  
      CommentAuthorjoe90
    • CommentTimeJul 18th 2015
     
    Posted By: fostertomDo you mean 300 underfloor insulation, or the 300 in the cavity? The former would defeat the purpose of the latter, if you did both.


    Hence my question fostertom, I originally wanted passive slab but because of clay and brick outer skin have decided to go the Golcar route which is full fill cavity down to strip foundation. Golcar still have under slab insulation (200mm) so there must be some need for this as they did PHPP calls for their build.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015
     
    Ah yes, perimeter only won't meet PHPP unless fantastically deep. But whether PHPP incorporates sophisticated understanding of in-ground seasonal heat flow/thermal mass effects, I doubt.

    My guess is that PHPP assumes straight-down loss to ground remains a fixed U value and doesn't allow for the 'lowering of the water table' of coolth (to shockingly misrepresent science!) which happens in the first 1 to 1.5 seasons. AFAIK, straight-down loss diminishes and diminishes to very little; the down/out/back up perimeter loss remains.

    With 200 u/floor insulation you won't get any of the beneficial stabilising effect of subsoil-coupling with the interior, even though you have the downstand perimeter insulation as 'coffer dam'. You've simply augmented a standard u/floor insulation arrangement so the actual u/floor bit needn't be quite so thick - and you have put most of the insulation in the perimeter zone, which is right and proper.
    •  
      CommentAuthorjoe90
    • CommentTimeJul 18th 2015
     
    So Tom, I remember the threads a long time ago where you talked of the effect of using ground stable temps with wing insulation as a very good thing. I am also a fan of thermal mass ( despite another forum having a member saying there is no such thing!!!) would it be the case that linking floor slabs to the ground would give too much thermal mass, I.e. Would take too long to heat from cold ? What are your thoughts on the Golcar foundations?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015 edited
     
    If expecting the building to warm up for breakfast, cool while out at work, and warm again for supper, then very light weight throughout is essential. Thermal massiveness dictates that temp remains pretty constant at all times, hence is only economic with v gd insulation/airtightness (or with v low losses anyway).

    Note that with a high %age of the heat input by radiation from the massive body rather by heating the air up, air temp will be 2oK or more cooler, for same subjective comfort, and another 1oK because of no draughts (which people counteract by turning the temp up).

    That in itself reduces losses pro rata - more than people realise, because they think that if rm temp wd have been 21oC and outside temp 0oC, reducing air temp by say 2oK wd reduce loss in the proportion 2/21. But in fact, over a heating season, av outdoor temp is prob say 9oC not 0oC, so over the season loss is reduced in the proportion 2/11.

    That's an unappreciated benefit of having a gently radiating thermal mass.
    • CommentAuthorgravelld
    • CommentTimeJul 18th 2015
     
    OK so if I may be so bold as to bring it back to my situation...

    Masonry cavity, solid floors. Let's concentrate on the EWI case.

    If getting the cavity airtight is paramount, is this practically possible? Some walls have cavity batts, partial fill. Some have EPS bead injected. However none will have anything below the DPC right?

    Sounds to me like this won't work unless fully EWI'ing and sealing top of cavity?
    • CommentAuthorgravelld
    • CommentTimeJul 18th 2015
     
    Oh and Tom you said you were working on a way to calculate the U for this case...
    •  
      CommentAuthorjoe90
    • CommentTimeJul 18th 2015
     
    Sorry gravelld, didn't mean to steal your thread !
    • CommentAuthorgravelld
    • CommentTimeJul 18th 2015
     
    Sorry, didn't mean to sound like that. I just meant I was particularly interested in the EWI outbound of the outer leaf case, but sure there are other configurations of interest.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2015 edited
     
    OK, briefly, without pics, my U value calc:

    Divide the floor into 0.5m squares - 0.25m2 ea. Measure the path length heat has to travel from ea square, curving down, outward beneath the 'coffer dam' and back up to surface. Group the squares by path length - 5.75m2 @ path length 2.6m, 3.25m2 @ path length 3.2m etc. Path length with conductivity of your subsoil gives say 5.75m2 @ 0.37W/m2.K = 2.13W/K, 3.25m2 @ 0.33W/m2.K = 1.07W/K. Sum those together, divide by total m2 and you get average U value W/m2.K for whole floor.

    Maybe add in just a little heat shortcutting thro the 'coffer dam' but that's tiny compared to the path-length thro the subsoil. Assume loss straight down is tiny, after 1 to 1.5 seasons.

    You'll soon see what order-of path length you have to create in order to achieve whatever target U value you want. L1 (new dwellings) has a long-stop U-value of 0.25; L2 (existing dwellings) has no long-stop. I'm currently OKing 0.35 for an extension, knowing I can more than make up for that lossiness by the rest of the superstructure's insulation. And that apparent lossiness is also compensated by the lowered internal air temp effect, mentioned above.

    I did set this up in LBNL Therm a little while back but didn't complete the calc as it was going in the right direction - wd be interesting to revisit that.
    • CommentAuthorgravelld
    • CommentTimeOct 21st 2015
     
    For anyone landing here from Google, Tom pasted the images in this thread: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13734&page=1#Item_6

    It's an interesting topic. I note Beattie Passive don't bother digging up floors and go with this approach (or so they said in a presentation to CoRE I saw on YouTube).

    How well does this work with UFH? The consensus seems to be insulation is essential for UFH, or you lose a load of heat to the ground. With this, a lot more of the ground would be heated, but there is *eventually* insulation, so would that work?

    Did you model this in THERM Tom?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 21st 2015
     
    Got no further with Therm so far.

    Where (on Beattie website?) do they show that? Any ref to the YouTube?
    • CommentAuthorgravelld
    • CommentTimeOct 21st 2015
     
    It's mentioned here but no reasoning so not convinced it's helpful. https://youtu.be/OxT5OYQJ4TY
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2015
     
    That is a deeply impressive presentation - all said together in one place, comprehensive.

    The approach is spot on for large-scale retrofit - as he says, no massive factories, all basic stuff, start tomorrow, full or near-PH.

    Because they have to cater for all kinds of existing structures incl the many kinds of dodgy 'industrialised' systems, they've gone full-on for an independent structural stud/rafter skin thrown right over the existing - takes the teacosy (he calls it T-cosy) concept one step beyond. The MHRV is perimeter-routed within that skin. Ample opportunity for dramatic re-styling if desired - he calls on local architects to step up to the mark. He gives a real taste of what 'Regeneration' can mean to occupant and community.

    The new structure even takes an independent bearing at foundation level. He states the impossibility of tearing up ground floors to insulate - hence the downstand insulation, part of the new structure. Yes, no details given as to efectiveness - just needs modeling in Therm.
    • CommentAuthormike7
    • CommentTimeOct 22nd 2015
     
    <blockquote><cite>Posted By: fostertom</cite>
    Divide the floor into 0.5m squares - 0.25m2 ea. Measure the path length heat has to travel from ea square, curving down, outward beneath the 'coffer dam' and back up to surface. Group the squares by path length - 5.75m2 @ path length 2.6m, 3.25m2 @ path length 3.2m etc. Path length with conductivity of your subsoil gives say 5.75m2 @ 0.37W/m2.K = 2.13W/K, 3.25m2 @ 0.33W/m2.K = 1.07W/K. Sum those together, divide by total m2 and you get average U value W/m2.K for whole floor.

    Maybe add in just a little heat shortcutting thro the 'coffer dam' but that's tiny compared to the path-length thro the subsoil. Assume loss straight down is tiny, after 1 to 1.5 seasons.

    .</blockquote>

    Hi Tom - I think if you tried sketching freehand the isotherms and heat flux lines you would soon see that the flux lines must diverge as they leave the bottom of the insulation barrier ( and a wee bit before). That means that the isotherms will also get further apart because the area has increased, and so the temp gradient must decrease. ( The flux and isotherm lines must cross at 90deg, and for a 2d situation the ratio of adjacent sides of each curvy square of your grid must keep constant ). A picture would help but...............

    Clear as mud then, but what it means is that you are under-estimating the heat loss from the non-perimeter areas.
    • CommentAuthorgravelld
    • CommentTimeOct 22nd 2015
     
    Posted By: fostertomThat is a deeply impressive presentation - all said together in one place, comprehensive....
    Surprised you weren't already aware of it Tom, also check out Energiesprong. Seems like the right way to do retrofit at scale for identikit houses (social housing etc). Shame my house isn't identikit!

    I'm interested as to how far skirt insulation is seen as adequate to support UFH.
    • CommentAuthorgravelld
    • CommentTimeOct 22nd 2015
     
    Here's a thermal image of my house btw, the red strip at the bottom is the DPC, which is uncovered, whereas everything above is rendered. Seems to suggest more heat comes from there than through the walls (filled cavities). "Well, obviously" you might say, but it's still a clear heat loss path in the case of zero floor insulation.
      IR_05372.jpg
    • CommentAuthorgravelld
    • CommentTimeOct 22nd 2015
     
    Posted By: mike7
    Hi Tom - I think if you tried sketching freehand the isotherms and heat flux lines you would soon see that the flux lines must diverge [...] A picture would help but...............
    Yyyyyup :bigsmile:
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2015 edited
     
    Posted By: mike7the flux lines must diverge as they leave the bottom of the insulation barrier
    Yeah but they also converge as they approach it - it's symmetrical so doesn't matter that happens to the flux lines in between. Cant quite picture 'ratio of adjacent sides of each curvy square of your grid must keep constant' but feels like that'll be symmetrical too.

    Must revive that Therm session - seems a topic whose time has come - things actually getting built.
    • CommentAuthormike7
    • CommentTimeOct 22nd 2015
     
    <blockquote><cite>Posted By: fostertom</cite><blockquote><cite>Posted By: mike7</cite>the flux lines must diverge as they leave the bottom of the insulation barrier</blockquote>Yeah but they also converge as they approach it - it's symmetrical so doesn't matter that happens to the flux lines in between. Cant quite picture 'ratio of adjacent sides of each curvy square of your grid must keep constant' but feels like that'll be symmetrical too.
    </blockquote>

    I recon my mud is clearer than yours :tongue:
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2015
     
    OK - Therms at dawn then!
  1.  
    Didn't someone on GBF have mice munching into their buried polystyrene insulation? (to make passivnests? For passivmaus??)

    A while back, someone else was thinking about wrapping it in fine wire mesh to keep them out.

    I like idea of wing / perimeter insulation but am put off by the short work the mice made of my interior insulation. Looking for rodent resistant alternatives.
  2.  
    •  
      CommentAuthorfostertom
    • CommentTimeOct 23rd 2015
     
    Would a few mouse tunnel/nests underground make much difference? How far inboard would they get? Isn't it a bit of a 'so what'?
    • CommentAuthorgravelld
    • CommentTimeOct 23rd 2015
     
    I thought there was already a mesh on which render was applied?
  3.  
    Nothing to stop you putting a base coat of render & fibreglass mesh on which would be a good deterrent against rodent damage. Wouldn't be a big job and would also protect the insulation from other mechanical damage.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 23rd 2015
     
    The mesh that's embedded in the render is 'nylon mesh'. Given that in much of Europe 'nylon' means any plastic, that doesn't tell us what it's made of - but not glass fibre I think. Would a plastic mesh offer any resistance to rodents? - I can kinda imagine that glass fibre might.

    Last job we did cover the u/g EPS with that mesh, on dabs of the render base coat - we certainly didn't expensively render, even just base coat, below GL. Any guess whether doing that was a waste of time?
   
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