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Housing - Renovation: Internal insulation question

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    • CommentAuthorDan McNeil
    • CommentTimeOct 3rd 2008 edited
     
    We have a small porch extension on our solid wall stone cottage, the porch is cavity wall construction, breeze-block internal wall and brick external. The internal walls on the porch get very cold, as does its (single-storey) ceiling. It's a real heat-loss zone, and we intend to fix it asap.

    I strongly suspect that the muppet who built it around 12 years didn't insulate the walls or the roof-space. So, I'm going to pull down the ceiling, stuff the void with insulation and then replace the standard plasterboard with 45mm thermal board.

    On to the walls...money and access are a real issue, so the options of cavity insulating or external insulating the walls are not an option for us. So, we're going to dry-line it with thermal board. Here's the question...would the advice be to:

    a) glue the thermal board directly to the internal wall (once the nasty woodchip has been striped off)?

    b) attach battens to the wall and then thermal board over the battens, leaving an air gap?

    c) same as b), but stuff insulation between the battens before putting up the thermal board?

    Re. the battening option...would it help/not help to attach horizontal battens as well, in effect to create "zoned areas" of battens beneath the thermal board, to minimise/stop air circulation underneath the board?

    Everywhere I look, I see different opinions. Guess here will be no different...

    I'm guessing one advantage of options b) and c) are that I could batten straight over the woodchip?

    Thanks.
    • CommentAuthorskywalker
    • CommentTimeOct 3rd 2008
     
    I think that Kingspan/cellotex etc produce boards for both mechanical fix and dib dib dob/glueing. There are good guides on both websites.

    I would be inclined towards careful dobbing ensuring good contact around all edges and joins to prevent air movement behind the board.

    I suppose the advantage of the batten method would be the inclusion of an extra vapour membrane but you will end up with many mini thermal bridges in the form of screw heads & unless you can get a good thickness of fleece in there probably not worth the effort - might as well get thicker insulation on the plasterboard. In a conservatory/porch environment the screw heads may well cause you problems (or at least be unsightly tiny damp patches). Most of the thermal plasterboards are backed with foil faced foam (exept gyproc I think) and so have a good vapour seal anyway.

    Hope this helps.

    S.
    • CommentAuthorcaliwag
    • CommentTimeOct 3rd 2008
     
    Is there any heating in this porch or is it just a draught lobby?
  4.  
    skywalker - thanks for advice - useful.
    caliwag - porch faces off from kitchen, which is linked to sitting room, which will shortly be running a stove to heat all of downstairs. porch is important though, as we use it's door as our main exit, rather than front door.
    • CommentAuthortony
    • CommentTimeOct 3rd 2008
     
    Why not keep it as a porch unheated and then you could save the cost of insulating it. And the time too.
  6.  
    Tony - porch is open to kitchen (so no separating door), therefore it needs insulating, otherwise heat from sitting room and kitchen leaks out of porch. In any case I'm very surprised you suggest not insulating, as this seems to be one of your hobby horses.
    • CommentAuthortony
    • CommentTimeOct 3rd 2008
     
    It is not a porch then!
  8.  
    Tony - if I say it's a porch, then it's a porch. And even if you disagree with the term, I've explained the situation and the layout very clearly. So - do you have anything useful and constructive to contribute?
  9.  
    What will you be using the "porch" space for ?. If just for boot/coat storage do you have the option of adding a door to the kitchen, this would save the cost of insulation etc.
  10.  
    Hi Crofter,

    The porch space is somewhere we hang coats, store boots etc.; and it's also the way out into the garden and the woodstore. Very limited space really, and the option of adding a door between it and the kitchen doesn't exist unfortunately, hence the need to bring the insulation levels up to a decent standard.
    • CommentAuthorMike George
    • CommentTimeOct 3rd 2008 edited
     
    Option A without a doubt. Dead easy on a flat wall. I would use PUR laminated plasterboards stuck with very wet adhesive and also mechanical fixings to be sure it stays there. Lots more here http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1070&page=2#Item_2
  12.  
    Thanks Mike!
    • CommentAuthorsinnerboy
    • CommentTimeOct 3rd 2008 edited
     
    I would use battens - including horizontals at floor and ceiling level and all around any door and window openings - for the reasons you have stated yourself - see page 31 of this document

    http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,16557,en.pdf

    I would then fix kingspan boards , foil faced both sides and foil tape the joints - to maximise air and vapor resistance

    Then platerboard and skim over

    I would not leave the woodchip in place . It would support the development of mould growth behind the insulation
  14.  
    Nice document sinnerboy. I notice it also gives bonding plaster as an option on page 31. What benefit do you see in using battens?
  15.  
    Agree option A. Type 'CE184' into google, and take the EST publication it offers you. Very good.
    • CommentAuthorsinnerboy
    • CommentTimeOct 3rd 2008 edited
     
    To Mike George - you can inspect the support system of the insulation before it is applied - ensuring the air paths are segmented - in a way you cant really ensure bonding ribbons are all present and correct . Also they facilitate the "splitting" of the insulation and plasterboard. Again - it is easy to check all board joints are taped before applying the plasterboard over
  17.  
    Sinnerboy, have you seen the PUR laminated plasterboards? Why would you fix insulation and then plasterboard when you can fix the two in one go?

    I agree about the difficulty of using ribbons on uneven walls, but on flat walls [like this case] its just like sticking on a giant wall tile - easy peasy. Just use the adhesive nice and wet. Also the mechanical fixings used to complement the adhesive are failsafe really.
    • CommentAuthorsinnerboy
    • CommentTimeOct 3rd 2008
     
    Composite insulation and plasterboards (CPB) - yes I have used them many times - they are convenient I agree . But I have just recently started to specify this alternative . In Ireland as in the UK we are seeking to make dramatic improvements in building energy performance * . So when dry lining we face the prospect of increasing from say a 62 CPB ( 50+12) to a 92 CPB ( 80 +12 ) When one insulates to such a high degree - the weak points ( joints in the case of CPB's ) become more vulnerable, relatively . I like the "comfort" of the foil taping of the joints - in terms of build quality . With composites you always have the nagging doubt that the skim over may be hiding poor jointing ....

    The battens cavity also provide a neat space for cables and pipes . I like to provide 25mm pur in the cavity local to power points / light switches - to prevent condensation there ( worst place for it to happen ) . A nice "Brucie-bonus" is you can run rad pipes here too to serve rads via the wall . not the floor - easier to hoover below then

    *( That link I posted earlier is to the recently published Part L of the Irish regs - intended to affect a 40 % improvement in energy/C02 performace - in 2010 - another revision is due to affect a further 20% improvement - by 2015 - passive haus is set to become B regs standard )
    • CommentAuthorMike George
    • CommentTimeOct 5th 2008 edited
     
    I've been thinking about this.. I can see some of the advantages, but also some downfalls as I see them:

    1. If you put CH pipes in the air space on the cold side of the insulation you are introducing unnecessary heat losses to the outside
    2. This also means that there is a natutal path for air infiltration/lossses wherever the pipe runs go
    3. It is very difficult to seal all air paths around electric cables/sockets.

    I am also against any cavity which can exacerabate the risk of deteriation of the existing fabric, which can be very unpredictable in old buildings. If there is no ventilation [which you're obviously trying to avoid] then there is the risk of temperature and humidity levels which can promote rotting of unknown existing timbers.

    The latter though is a generic problem with all internal insulation and is why I only use it in some situations.
    • CommentAuthorsinnerboy
    • CommentTimeOct 5th 2008
     
    Absoultely aggree Mike . Pipes in the cavity sould be sleeved - should have mentioned that before . Cables should be selaed with intumescent sealant where they enter the back ( Kasier do a range of air tight back boxes but they are expensive ( in Ireland anyway ) .

    http://www.betonbaudose.de/Pressetexte/Englisch/L-B-EnEV/KAISER-Light-Building2008-EnEV-06-04-08.pdf

    Got the be careful to ensure that plasterboard is sealed to elec points - good fill of skim as opposed to skim over

    Around Dublin we have a plentiful legacy of dry lined hollow block walls , rendered externally . Ironicaly I think the poor air infiltration nature of render and hollow block has"saved" the battens over years in these houses , providing unintended , but necessary ventilation .

    Dan has breeze block internally so this will help keep dew point closer to the external . To be super safe Dan , you could use these extenally to releive ( ventilate ) potential interstitial condensation

    http://www.drillvent.com/

    They are intended to provide ventilation , through the block or brick skin in front of a timber framed house - you clould "liken" your breeze block to a timber frame in your case .
    • CommentAuthortony
    • CommentTimeOct 5th 2008
     
    It still does not sound to me at all like a good idea to have a ventilated cavity behind insulated plasterboard.

    You will then effectively be living in tent made of insulated plasterboard and wasting all the insulating and thermal meas features of the walls of the house.
  22.  
    Sinnerboy, my last post wasn't very clear in that I assumed you were trying to avoid ventilating the cavity. I now see that you are suggesting ventilation.

    I agree with Tony on this and it reinforces my opinion that battens should not be used in such scenarios - We will have to agree to disagree.
    • CommentAuthorsinnerboy
    • CommentTimeOct 5th 2008
     
    I am not suggesting ventilating the battens cavity . I am suggesting ventilating the cavity between the breeze block and the brick
  24.  
    Ah, sorry, my mistake. I think we are at cross perposes between Dan's situation and other more general situations. For Dan's situation, I would opt for the adhesive solution myself.

    Generally speaking, Venting a masonry cavity will not mitigate any risk to, for example, existing timbers built into masonry - such as joist ends. And where the walls are stone, there is probability of inbuilt timber lintels as well. I don't see any advantage to using battens, only disadvantages - we'll have to agree to disagree.
    • CommentAuthorsinnerboy
    • CommentTimeOct 5th 2008
     
    :cry:

    Just kidding - fair enough Mike . I think there are benefits but I accept you don't

    I have to say - another " agree to disagree " point perhaps - that (assuming no insulation in the cavity ) that venting a masonry cavity would help joist ends built into the inner leaf . Damp clammy environment in that cavity - joist ends would be vulnerable
    • CommentAuthortony
    • CommentTimeOct 5th 2008
     
    I only see dry drafty cavities. The heat lost from the house keeps them that way

    I must now as is it sane (or worse) to live in a single half block wall house with a ventilated cavity or a 225mm solid brick house (with twice the insulation)

    I bet the hot box makes cavity walls look far better than they are in the real world.
    • CommentAuthorMike George
    • CommentTimeOct 5th 2008 edited
     
    Posted By: sinnerboy
    I have to say - another " agree to disagree " point perhaps - that (assuming no insulation in the cavity ) that venting a masonry cavity would help joist ends built into the inner leaf . Damp clammy environment in that cavity - joist ends would be vulnerable


    Yes, it would no doubt help, but that ventilation would not get to the airspace in a battened cavity. I wonder what a condensation risk analysis would tell us?
    • CommentAuthorMike George
    • CommentTimeOct 5th 2008 edited
     
    Just done one for Plasterboard, 50mmPUR, 25mm battened cavity

    Result:

    Clear in a cavity wall
    Risk in a solid masonry scenario

    PS if you could install a very good vapour barrier then maybe OK. Not sure how you would fix it though without puncturing it

    Note. not to be relied on by anyone as condensation risk analysis is VERY specific to a particular construction
    • CommentAuthorsinnerboy
    • CommentTimeOct 5th 2008
     
    Did you use the Buildesk software Mike ? Vapour barriers are a bit of a "silver bullet" - i.e. include one and we are told condensation risk is eliminated. I am skeptical about the real life situation . And so - to try to achieve the best vapour barrier i can think of - battens , PUR boards over - joints foil taped . Yes the plasterboard fixings do compromise the barrier i accept that . But the butt joint between composite boards - i believe- poses a greater risk of vapour migration .

    And Tony - I hate cavity wall construction . ( After 25 years years of dealing with them - as an architectural technician ) I don't believe it ever delivers in practice what we calculate it to . With partial fill boards you can expect to find horizontals joints fouled by mortar droppings, vertical joints not cut true or parallel, boards which lean forward away from the inner leaf . All of which leads to thermal looping and consequent degrading of the thermal performance .
  30.  
    I used TAS - no vapour barrier [as you say it is a silver bullet]- although the vapour permeability of the other materials is considered. I don't think there is an effective VB for this application in reality, whether battened or stuck on, vapour will get through the punctures and/or joints.

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