1. Hi Matt,

      first of all I’d try and find out for certain if it is a problem with condensation or water getting in from the outside. Flaking paint suggests water from outside to me. As the outhouse was never designed to be habitable, its damp-proofing doesn’t seem very good (in my case).

      If it’s a problem with condensation increasing the ventilation should help.I presume your outhouse is not part of the habitable house ie it’s not heated and has an external-type door between it and the kitchen. If so you don’t need to worry about losing heat from the outhouse through ventilation so an extractor fan (perhaps humidity controlled) could help.

      Sorry to disagree with Marc but I don’t see much point in insulating an unheated room as there won’t be much heat to keep in! If you do insulate it I would be careful to make the lining air and vapour tight otherwise you risk condensation forming behind the insulation and rotting the battens.


      1. Its only a little bit on the walls (ive knocked through so its one long outhouse if that makes sense) and in the toilet area as not having any windows that open cant help alot!

        the outhouse isnt part of the habitable house though it does have a radiator out there, should i be turning this off? i am thinking of replacing the wooden door with a window that can be opened as more air flow can only help surely?

  1. Thanks for the thorough reply, I thought this would be a quick fix…all walls appear solid, is it concrete block? The lean to roof is asbestos sheet as well!

    I thought the roof may have been asbestos. If it is anything like the out-houses that I have worked on there should be more than enough ventilation coming in through the roof edges as the asbestos sheets being corrugated do not form an air tight seal. Often when it’s windy you can feel the strong draught inside the building. I think in your case Matt the moisture is coming directly from the dryer and the warm moist air is cooling on the nearest cold wall. If it’s a vented dryer you could always fit the vent pipe onto the outside wall so all the warm air will go straight outside. It’s not going to be so easy if it’s a condenser dryer though.

  2. Hi Matt, the problem that you describe is typical of a BISF outhouse, particularly where the front and rear walls are constructed from a single brick skin wall. (Not all are)
    Obviously the heat generated inside the space from the dryer or just the warmth coming in from the house will quickly condensate onto the brick wall causing moisture to drip down and also to blow the paint coating which looks like blisters. The water can also mix with salts inside the wall which doesn’t help the paint.
    Putting in some standard grid vents won’t do much to prevent this though, even putting in a powered extractor like you see in bathrooms will only help a little, it will not in itself prevent the moisture build up.
    The best solution would be to internally insulate the single brick walls by way of fixing battens vertical battens. In between the battens you fit a layer of insulation such as Kingspan type panels and over this you screw on foil backed plasterboard.
    If you want an instant finish you can use decorative cladding panels which are often used in bathrooms. They are easy to fit, and easy to wipe and come in a range of finishes.
    I myself prefer to tile over the plasterboard (in the toilet area) as no plastering in required.
    What you haven’t said is what the side walls of your outbuilding are made from as some are timber and some are block work.
    I have a customer at the moment who is having the exact same issue on the toilet wall in her garage. In her case it looks like it will be a similar job to above except we are using battens a breathable membrane and insulated plasterboard as she is not decided what finish she wants and space here is very limited. She also has a dryer in the room so I am also installing an electric extractor fan which will also help reduce moisture.
    Also you must make sure that moisture isn’t penetrating in from outside, so check your render / paint finish for signs of deterioration or obvious signs of water ingress from the roof area.
    This reply is probably not as quick and easy a solution as you may have wanted but it will be a better solution in the long run.