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Advice on insulating north facing box room

Discussion in 'Building' started by rob7475, 30 Nov 2017.

  1. rob7475

    rob7475

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    Hi,

    My son's bedroom suffers from condensation on the walls behind his bed. The house his a 1920's semi and has virtually no cavity and we've been advised it's not worth filling.

    His bedroom is at the corner so has two external walls - one north facing and the other west. His bed his on the external wall and we get condensation building on the wall behind the bed due to lack of air flow.

    My plan is to insulate the two walls but as the room is tiny, I need the best option whilst losing as little space as possible. So far, I'm thinking of the following options:

    1. Line walls with wallrock lining
    2. Found a product called aerotherm which looks good and is only 1mm thick - I'm not conviced though.
    3. Strip walls back to brick and put up insulated plasterboard or celotex with p/board on top (I'd only be able to go to 25mm insulation max plus 12.5mm plasterboard due to needing to fit a bed in.

    Any thoughts or other suggestions would be appreciated.

    Thanks,
    Rob
     
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  3. ^woody^

    ^woody^

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    First see if you can deal with the condensation by better extraction at source or altering heating patterns. You may need to do this anyway with whatever option you choose.

    If you are not trying to insulate, but just need to take the cold surface away to deal with the condensation issue, then a polystyrene liner (wallrock or similar) could be enough. But without actually working dew points and temp/humidity gradients out then it will be trial and error.

    Thermal plasterboard or celotex and plasterboard will stand a better chance of success and will add insulation value too. But then it’s the cost, disruption and loss of space to factor in.
     
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  4. John D v2.0

    John D v2.0

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    Have you thought of external insulation? We had the same situation with the same age house, the whole wall was black. We put 50mm polystyrene on the outside and rendered over. No loss of space and less chance of thermal bridging etc
     
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  5. rob7475

    rob7475

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    Unfortunately, this isn't an option as we had the external re-pebbledashed last year.
     
  6. John D v2.0

    John D v2.0

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    Shouldn't be a problem, you don't have to clean it off, as long as air doesn't move behind it. Pebble dash on polystyrene is fine, ours is actually rough cast (the old rough cast is still on underneath and the new is on the outside)
     
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  8. rob7475

    rob7475

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    We leave the window open most of the day to help dry things out which works to some extent. The culprit is the bed - it has drawers built in underneath it so there's no air circulation behind the bed. The wall behind the bed constantly feels cold and this is the area that feels damp in a morning. We have an extractor in the bathroom and kitchen.

    I'm not too fussed about insulation - I just need to stop the wall being cold which will hopefully cure my problem. If I go down the thermal plasterboard route, I can do the work myself so only have material costs to consider. I'd rather not have the mess of ripping the 100 year old plaster off the walls but if that's going to be the best option........
     
  9. TrevP

    TrevP

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    Hi,
    we had the same problem with a box room. In the end I stripped off the plaster dot and dabbed it with 25mm (insulation + board) insulated board;. Whilst it is not very thick it has done the job. It has improved the warmth in the room. On removing the plaster I found that an air brick had been covered so I also left this opened up.
    That is another option; put in an air brick to allow ventilation. Whilst this will involve a bit heavier work getting through the brickwork it should work.
    Another option that it may be worth considering is putting a Positive Input Ventilator(PIV) unit in. My daughter's flat has serious condensation issues and I installed one of these this year and it has cured the problem. Essentially this is a unit that fits into the ceiling in the hallway and takes filtered air from the loft and circulates it around the house. It is whisper quiet and easy to fit (some electrical work). They are made by Nuaire and cost around £250 (see i-sells.co.uk) As I say it has completely resolved the issue throughout my daughter's flat
     
  10. John D v2.0

    John D v2.0

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    Another other suggestion to reduce the condensation is to apply heat - so run a warm pipe from the heating all the way round the room? Or a small rad on the cold wall
     
  11. JP_

    JP_

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    I slept in a box room like that as a student. Was horrible. What is the floor / ceiling like? Is it above a kitchen at the back that has no heating at night? (mine was).
    Maybe lots of insulation in the ceiling and floor will compensate what cannot be achieved in the walls, and get a really good window put in with trickle vents, and a bigger radiatior.
     
  12. DIYnot Local

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