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Housing - Renovation: Cavity wall insulation concerns

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  1.  
    • CommentAuthorjivingjon
    • CommentTimeOct 5th 2007
     
    I am renovating a 1958 semi detached house and am thinking about cavity wall insulation. I have had seen so many different ideas and opions that I getting more confused. So here are some more questions to add to my confusion.
    My main concern is created damp spots on internal walls if I go ahead with cavity wall insulation.

    My upstairs windows do not have lintels. There are however a concrete slabs across the front and back of the house which acts as window lintels and includes the outside gutter that I think goes across the cavity and becomes part of the internal wall. Firstly could these blocks be part of the inside wall? Does this become a cold bridge into the house and thus becoming a place for vapour to condense? If this is the case is there any point in using cavity insulation?

    Secondly I am guessing that there a metal ties between the 2 walls. By introducing insulation could I increase the likelyhood of condensation created on the ties dripping on to the plastic beads of the insulation and then get carried into the internal wall? If condensation does get created on the ties won't this just rot them away?

    Any thoughts are welcome.

    jon
    •  
      CommentAuthorfostertom
    • CommentTimeOct 5th 2007 edited
     
    Unmessed-with unfilled cavities are a great asset - keep them that way! http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=723&page=1#Item_0
    • CommentAuthortony
    • CommentTimeOct 5th 2007
     
    You are very unlikely to generate damp spots on the walls or to get condensation in the cavity. The concrete things will likely be cold bridging the cavity.

    I would still fill the cavities with insulation as this will save energy, make the house more comfortable to live in and greatly reduce air infiltration.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 5th 2007 edited
     
    Posted By: tonyI would still fill the cavities with insulation as this will save energy, make the house more comfortable to live in and greatly reduce air infiltration
    and, as a short-future half-measure, make the house harder to raise to really low energy standard in future, affecting its capital value in a few years time as fuel prices go through the roof.
    • CommentAuthorNeil
    • CommentTimeOct 5th 2007
     
    Hi Fostertom,

    New to posting on site so excuse if this has been debated...

    What cavity insulation product /system is on the horizon making filling cavities now a bad idea?

    Neil
    •  
      CommentAuthorfostertom
    • CommentTimeOct 5th 2007
     
    • CommentAuthorNeil
    • CommentTimeOct 5th 2007
     
    The 'dense cavity fill - external insulation' idea's about trying to store heat for longer than the diurnal term temp swing then? Didn't I read otimum thermal mass (concrete) is about 50mm, diurnally?
    • CommentAuthortony
    • CommentTimeOct 5th 2007
     
    the problem with not filling the cavity is that effectively you are living in a half brick wall house. Cavities are are connected to outside and so cool the house dreadfully. Air often, if not always, gets in from the cavity to under the floor making the houses even colder. Better off in a mud hut?

    I agree with Tom about high thermal mass and ideally we should be filling the cavities solid and doing external insulation but planners are a problem then.

    Neil -- We are interested in longer term thermal stability than diurnal.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 5th 2007
     
    Tell us more Neil - what's the floor construction? If solid, is there u/floor insulation? - if not, then you're in luck - see http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=685&page=1
  10.  
    My first post too.

    I can see the point having large quantities of high thermal mass in a passive house or house designed to except large amounts of solar gain, but we are refering to retro insulating the existing housing stock which are neither of the above.

    Surely insulating the cavity initially and then later adding external insulation is not a "bad" plan, you will still have 100mm plus of concrete block to act as thermal mass on the inner leaf, and quite likely, masonry internal walls too.

    Could you explain why in a "normal" house refurb you would want to iron out anything more than the day and night temperature fluctuations.
    • CommentAuthorNeil
    • CommentTimeOct 5th 2007
     
    Okay, say a 250mm 'solid' (filled cavity) masonry wall is insulated externally (say max 100mm because of usual detailing, best U=about 0.3?), what longer term thermal stability is sought, what period of 'extreme' temperatures can this sink absorb, roughly speaking. Any ideas? & is it pricipally a tool to temper overheating?
    I agree in principle, but wonder if the (very cheap) economic of insulating a 50mm cavity now & retaining 100mm thermal mass (in conjunctionwith other insulation & infiltration upgrades) could give more valuable savings / payback than much bigger expense of insulating externally. I see the potential in more external insulation and quite exciting (& inspiring) changes in the appearance of our building stock, but without the mandate & support of planners?...more fights? I guess deeper insulation could be possible with (as a minimum) shallower eaves sprockets giving a wider eaves?
    Is it possible to hoover up polysterene bead cavity fill at a later date for replacement with dense fill?
    •  
      CommentAuthorfostertom
    • CommentTimeOct 6th 2007
     
    neil and richardab, you're right to question whether 50 or 100 of mass is actually enough for everyday practical thermal store purposes, and my insistence on 250 cd be pointless. I'm not yet able to answer that convincingly - currently getting set up to computer-model these things - however my amateur-scientist's gut feeling is that the thicker the better. Maybe the point is that with just a bit more understanding, other things can be readily arranged to positively bring the extra thickness into play. As always, comments on this site provoke fresh thought - a true university of the air!
  13.  
    Most writing on this subject seems to suggest that 100mm is optimal and that 150 is excessive and 35mm or less a waste of time

    Robert + Brenda Vale, New Autonomous House, 2000, Thames + Hudson
    Sue Roaf, EcoHouse 2, 2004, Architectural Press
    Simos Yannas, 'Solar Energy and Housing Design', 1994, DTI +Architectural Asociation

    Also interesting graph + refs on greenspec...
    http://www.greenspec.co.uk/html/design/PassiveSolarThermalMass.html

    Also, any body any ideas re interstitial condensation and following set up:

    102 brick, 100 retro filled cavity, 102 brick, + future external insulation system.

    J
    • CommentAuthortony
    • CommentTimeOct 6th 2007
     
    Not sure that I agree with the ideas of efficiency in the context of thermal mass. The heat (or coolth) expelled from the thermal mass is effectively free if it was solar gained therefore efficiency is totally irrelevant and gross ammount are important.

    Nice link and in answer to your question; In general interstitial condensation usually forms on the surface or the very outermost later ( the cladding ) so will not be a problem
  15.  
    Point taken about mass in theory, but for the penniless environmentalist in the 1930s semi/terrace, cavity fill is pretty cheap and you can often get help from power companies etc, and so start saving C02 straight away rather than waiting till you can afford external insulation. The thermal mass in this context is only free if you work for an external insulation company :wink:

    External insulation is definitely the best solution technically and in the long term for existing housing stock...

    ...but then there's the local planning authority.....:devil::devil::devil: with their peculiar obsessions with the sanctity of the holy brick.... ...don't get me started on planners.... :fierce:

    J

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