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Housing - Renovation: Stone walls - U values and insulation

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  1.  
    • CommentAuthorpostwall
    • CommentTimeFeb 13th 2009
     
    Does anyone have some empirical data on the U/R/K values of stone walls? I live in a fridge with 800mm stone walls (two skins of dense dolerite stone) roughly bedded in mortar with an inner cavity/rubble fill between). There seem to be at least three possible ways of calculating U:
    1) Assume the wall is solid. U=1.7
    2) Assume the rubble fill acts as a cavity: U = 1.4
    3) Assume that there is a howling draught in the wall and that the wall is effectively only 350mm thick, U= 2.8.

    All the figures are grim and I’d like to do something about it. I’m not keen on drylining and consequent visual effect. I thought of using an insulating plaster. This has the advantage of retaining some of the character of the building and allows for thinner layers around critical areas such as door frames and window reveals. A perlite: lime mix seems quite promising. A 50mm layer (? R= 0.5) should at least halve the heat loss through the walls and get rid of any draughty cracks. Does anyone have experiences of trying to do something similar? Should I try to scrape the emulsion paint off the walls first?
    •  
      CommentAuthorrogerwhit
    • CommentTimeFeb 13th 2009
     
    I am emotionally inclined to suggest that the U-wall is far less than 2.8. The rubble cavity is likely to be drafty but still sheltered from outdoors so its airflow will be tempered somewhat. 1.7 to 2.0?

    I would scrape off any modern emulsion myself - horrible stuff - would rather the new plaster & existing wall were contiguous in terms of moisture gradient & transmission. Ideally.

    There, I've stuck my head above the parapet.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 14th 2009
     
    Bang - splat
  4.  
    ''Bang - splat''. Fostertom, do you mean: Bang splat knocked Rogerwhit off the parapet, or Bang Splat right? Rogerwhit's gut feeling equals mine. I did a survey the other day (c 500mm rubble fill) and reckon c 1.8.

    Nick
  5.  
    Your biggest problem is the thermal capacity of the walls. Solid stone has a huge thermal storage ability - it will stay cold for ages, so to heat the room, the only way will be to insulate internally, much as you don't want to. If you can stand it till summer, the house will stay lovely and cool in the summer! Not much compensation as you shiver though!
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 14th 2009
     
    Posted By: Nick ParsonsBang splat knocked Rogerwhit off the parapet
    just obliging his invitation!
    Posted By: Nick Parsonsor Bang Splat right
    Maybe - would depend greatly on the individual wall construction and condition - how much internal void space, how well ventilated to outside air. Could differ widely, from 500mm of truly soild massiveness, to just living in a plaster-thickness tent! If anything less than the former, then grouting is indicated - I've been wondering whether sloshy Hemcrete cd be used for that?
  7.  
    I am in a similar boat, although my walls are only 450mm thick and very well pointed on the exterior. At the moment I am drawn to Hemcrete on the inside but have no idea what thickness to aim for. I guess more is better, but one of the rooms is only 2800 deep (the other is 3800) and i don't want to lose too much space inside.
    Saying that, it is built into the hillside at the back so I could dig out and insulate externally along the back wall instead - but don't know if a mixture of the two will cause problems?
  8.  
    Something like 300mm EPS on exterior of back wall, french drain and backfill; then 200mm hemcrete on the inside of the front and side walls?
    • CommentAuthorTheDoctor
    • CommentTimeFeb 16th 2009
     
    how much overlap at side walls to rear walls

    300 outside to 200 inside leaves a vertical cold bridge in each rear corner.
    is this 'the price to pay' for this solution?
    is it a worry?
    • CommentAuthorNoyers
    • CommentTimeFeb 16th 2009
     
    Your walls are similar to mine, 500 - 800mm stone (nominally solid but with multiple cavities for bees, bats, mice etc), here in SW France. I would agree that this produces a lovely cool house in the Spring/Summer/Autumn.
    The French approach is to thoroughly point both internal and external faces, apply a coat of "hydrofuge", fit underfloor heating and light the wood burner. In those few warm stone houses that I have visited they also have good windows and good roof insulation. it looks lovely but the winters are short, if cold, hereabouts - it may not be applicable to the UK (and I should think would be hopeless in Scotland or any upland area).

    In the absence of the above measures (the house I am living in) these stone houses are appallingly cold!

    I am doing two things: Lounge - the French approach plus a VERY large wood burner, the kitchen/diner - drylining using both multifoil and rigid foam.
    I have no real idea of the U value I will achieve with this dry lining approach and have a thread running in the "Energy Assessment" section seeking an answer to U values of internally insulated stone walls.

    My guess is that the effective U vale of these unimproved old stone walls is so terrible and that the thermal mass (so beloved by some) is so large that any normal heating system simply cannot raise the wall temperatures to sensible levels.

    I read somewhere that the cost of renovating an old property to near Passivhaus standards was >75% of the cost of new build. If I have a brain storm and ever take on an old stone house again I will be starting with a very large JCB.
    • CommentAuthorpostwall
    • CommentTimeFeb 17th 2009
     
    Thanks for the comments and splats - poor old Rogerwhit. It seems everyone agrees that these walls are bad news The lovely-and-cool -in -the -summer benefit is rarely necessary here. I've tried Noyers big woodburner approach. It's hard work in the Welsh maritimes and I reckon his/her JCB solution might be a more appropriate solution. Whilst I'm plucking up courage, has no one experimented with perlite and lime? In theory it should be a lot easier to apply than hemcrete. I reckon it should give a fairly good insulation gain for the effort involved and no nasty cavties for loitering rodents and damp air.
  12.  
    I'll still be going for the Hemcrete, JCB is not an option.
    • CommentAuthorNoyers
    • CommentTimeFeb 18th 2009
     
    I'm with Brazenscroll; do not dryline, use hemecrete or equivalent (Perlite?) solution. Thermal mass is all very well but you can have too much of a good thing. It is much easier to create a draught proof, vermin proof solution using a nice solid insulant than to do the same with drylining. I am currently doing the latter and would not recommend it as the labour element involved is too great. That said, if you had nice straight vertical walls then you could use the internal rigid foam approach (if you don't mind the worry of off-gassing).
  14.  
    Can I re-open this one? I've been looking at a house with 800 limestone wall (probably, almost certainly, rubble fill) with 30mm EPS dry-lining. The 'raw' figures are fantastic, based on a figure from http://people.bath.ac.uk/absmaw/BEnv1/properties.pdf for thermal conductivity of limestone, and give me U = 0.33. I find this extremely unlikely. Apart from a gut feeling to 'discount' this to somewhere in the 0.6 to 1.0 region, anyone got any other thoughts? Air-tightness is not fantastic, but not awful.
    • CommentAuthorCWatters
    • CommentTimeJul 13th 2009 edited
     
    I think you made a mistake. The document..
    http://people.bath.ac.uk/absmaw/BEnv1/properties.pdf
    ..says the thermal conductuvity of limestone is 1.5 W/mK.

    The Thermal Conductivity of a sample (in W/mK) is the same as the U-Value of a 1 meter thick sample (in W/m^2K). So the U-Value of 800mm is 1.5 x 1000/800 = 1.9 W/m^2K approx.

    The Thermal Conductivity of EPS is given as 0.035 W/mK (I thought it was worse than that) so the U-Value of 30mm is 0.035 x 1000/30 = 1.16 W/m^2K

    The U-Value of the combination is

    1 / (1/1.9 + 1/1.16) = 0.72 W/m^2K (so your estomate of 0.6-1.0 isn't far off).

    Running the numbers backwards.. To get to 0.3 W/m^2K you would need insulation with a U-Value of..

    1 / (1/0.3 - 1/1.9) = 0.36 W/m^2K

    The Thermal conductivity of Polyeurathane variants like Celotex is around 0.025 W/mK so you need this thickness..

    1000 x 0.025/0.36 = 70mm

    instead of the 30mm EPS.

    but do check my sums!

    Edited: to get the units consistent.
    • CommentAuthorCWatters
    • CommentTimeJul 13th 2009 edited
     
    PS When was the house lined with EPS? If done recently that might be a breech of the building regs if my sums are correct. I wonder what the HIP report says?
  17.  
    Aha!!

    I had already converted R to U (0.53 to 1.88) for the stone, then forgot, and added the other R values to it to give my erroneous answer! Thankyou for the check. I could not believe it, hence the Q in the first place. "If it looks too good to be true it probably is..."

    Re the EPS, I was using 0.38, but pretty close.

    Thanks a lot.

    And finally, no, the EPS was done 10+ years ago. I can't persuade them to hack it all off! Mind you, I feel the same at home - 38 - 50mm XPS 20 years ago (CFC blown, of course!) and I wish I'd done a lot better.

    Nick
  18.  
    My full calc (with Rs and Us in the right place!) is as follows:

    0.8(m)/1.5 = 0.53 Stone wall

    0.03(m)/0.038 =0.79 30mm EPS

    Pl'bd R =0.19 (depends whose figures you read) 12.5mm plasterboard

    Rsi and Rse = 0.15 Internal and external resistances

    Total R = 1.66

    1/1.66 = 0.6ish, allowing for no thermal bridging.
    • CommentAuthorCWatters
    • CommentTimeJul 13th 2009
     
    Yes much easier to do the sums if you stick to thermal resistance and R-Values rather than conductance and U-Values. I should have done that.

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