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Closing cavities at the top of cavity wall on refurb.

Discussion in 'Building' started by paulandfrodo, 7 Feb 2014.

  1. paulandfrodo

    paulandfrodo

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    My gut feeling is yes... However, I would appreciate other peoples comments.

    I have refurbished a turn of the century property. It's a mid terrace brick under slate with 65mm cavities - brick on both inside skin and outside skin.

    I've taken all of the internal walls back to brick and re-wired/plastered (sand/cement) and moved a few things around. I've put 200mm insulation in the loft, 100mm between ceiling joists and 100mm over the ceiling joists.

    On the inside skin of the cavity wall I have a top plate that the roof sits on. Between the inside skin and outside skin (the 65mm cavity) should I put any insulation, so that the air between the two cavities warms up, and acts as a 'blanket' for the house. Or should I leave it open, allowing whatever cold or damp air is around to ventilate up and out...

    I would really appreciate your comments.

    Regards Paul.
     
  2. magiclintel

    magiclintel

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    Me too- I just missed my chance to do this as our scaffold is down now (re-roofed).... it struck me that I might have stopped the air flow and warmed the place up a little... will watch answers with interest.

    I guess I left it alone as I thought to leave it as designed, but am all ears...
     
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  4. Flyboytim

    Flyboytim

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    Sounds like a typical Portsmouth fin de si├Ęcle red brick terrace build. I doubt if closing the top of cavities with a little insulation would do much at all. Several of the cavity walls I have seen communicate with the outside through various holes and cracks in the outer skin.

    Have the original wrought iron wall ties between inner and outer leaf of brickwork been removed and/or isolated and replaced with stainless steel replacements like Thor Helicals?

    Are there horizontal cracks in the mortar where failed wallties have rusted and forced the mortar joints apart? Have these been repaired with cement mortar or re-pointed with the correct lime mix? Is there much spalling of the bricks? Are any walls finished with cement render or any cladding?

    I am also undecided. Considering the soaking we have had over the late Autumn /early Winter of 2012, and the Winter of 2013/2014, I am not going to consider this in my Fratton terrace until I have had some feedback from people who have had this done and their experiences with damp this winter, and the walls have a chance to dry in the summer. I have heard about catastrophes with damp bridging from loose-fill cavity insulation, but cannot tell if these are urban myths or not.

    It has been the worst season for internal damp we have had yet.
     
  5. noseall

    noseall

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    Fully filled cavities i.e. dritherm etc do remain open.

    This means that the cavity insulation can extend beyond the top of the wall and meet the loft insulation, forming a complete blanket.

    You should always try and limit air movement in a cavity. Air that moves over a surface ultimately cools that surface.
     
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  7. paulandfrodo

    paulandfrodo

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    I have to say, their is a 'little' movement in the wall in one place, so I will drill and put some more ties in before re-rendering the outside wall.

    The air movement over the inner skin concept makes sense, so I will go up into the loft and ram some rock wool into the top, to 'seal' the cavity from the top.

    I will then see if things improve !

    Thanks guys !
     
  8. DIYnot Local

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