you've stated the bare problem but given no context, details or background.
Here are some queries you need to consider if you wish to get relevant advice.
- How old is the house - year of completion?
- Are there any cracks on the external walls or render?
- Is the sealing around the opes complete, with no cracked sills, etc?
- Is there evidence of gutter or parapet blockage or pipe leakage internally?
- What kind of construction is used - cavity or solid wall, hollow block rendered or timber frame with outer leaf?
- How is the room used - highly used [how many occupants] with the windows never open, kept closed and unheated all the time with no window open to air the room?
- Is there an en-suite directly off the room?
- Where is the bathroom in relation to it and how frequently is this used - once or many times a day.
- Is the house is less new, is it vented mechanically with 5min overrun, 15min overrun, or more rapidly vented using a window?
- If the house is new and its sealed, is it mechanically vented using an MHVR system - if so when were the filters last changed?
- If there is an MHVR system who commissioned it and were they competent to do so including balancing flue lengths and sizes?
In general, where damp occurs on the inside face of the wall, its coming from inside as condensation or outside as water ingress. Usually condensation occurs on a surface that is colder than the rest of the house, or in an area of high relative humidity, so unventilated stairs landings or bathrooms are the likely areas even in poorly ventilated older properties.
Where damp occurs in bedrooms, one or all of the following factors may arise; -
- poor ventilation for the use [permavents sealed, rooms never aired properly]
- high incidence of water vapour in the air [this can arise from overcrowding, paticularly of adults]
- poor bathroom regime [poor venting including leaving door open to allow moist air to circulate to relatively colder areas]
- local missing insulation where walls are studded out
- local water ingress from gutter blockage/breakage or parapet detail failure.
In extreme cases opening up may be needed to trace the cause, which can occassionally be caused by a hairline crack in a render at high level on an exposed surface allowing water to get behind it and down, where the easiest way out if into the room, as opposed to through the waterproof render.
Similarly you can sometimes get a weep from a heating pipe near the joint which allows moisture to build up locally in even well insulated houses, reducing the effectiveness of the insulation, and causing a cold bridge and attracting air-borner moisture.
This isn't an exhaustive review of the causes, but you get the gist: it can be a locla porblem easily identified, or a problem of use where an overview of living patterns and ventilation routes is required.
Don't simply assume that re-rendering outside and adding a layer of dry lining insude will deal with the problem. This can create a space in which even more moisture will gather over time, called interstitional moisture, and this can be even harder to deal with if it migrates to another location in the house.
Seek professional advice.
ONQ.
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