You did nothing wrong by sleeping. Breathing puts moisture into a shut room, and the coldest surface collects it. Here is how to read it and fix it, cheapest first.
People breathe out moisture all night, and the Property Care Association and the Centre for Sustainable Energy both list breathing as a source of the water that condenses on cold surfaces. In a shut bedroom it has nowhere to go, so it lands on the window, the sill and the coldest corner. Open the trickle vents, keep a gap under the door, pull furniture off the outside wall and keep a little background heat in the room.
Look at the room on waking, before you wipe anything, and ask what is different from the rest of the house.
Pull wardrobes and beds a few centimetres off outside walls: the Energy Saving Trust and GOV.UK guidance both advise leaving a gap between furniture and the wall. Keep a modest background heat in the room. The Property Care Association says steady background heat is preferable to intermittent heating, though the Energy Saving Trust cautions that leaving heating on all the time just to avoid damp is not sensible, so aim for gentle and steady. A cheap hygrometer helps: the Centre for Sustainable Energy recommends 40 to 60 per cent humidity and says mould becomes a risk above 60.
If the cold spot is a gap in insulation, the Energy Saving Trust says to get insulation defects fixed, because gaps attract condensation and mould.
If the vents, gap, heat and furniture are sorted and bedrooms still run wet, controlling humidity across the home can help. A loft-mounted Dryzen system helps stop the conditions mould and dust mites need in an owner-occupied home with a loft. It is not suitable for rentals unless the landlord authorises changes, it will not stop a leak or rising damp, and mould that is already growing must be cleaned off.
We have not found published data on bedroom humidity in Chatham homes, so we will not claim a local pattern. The advice above is national guidance, and a week of readings from your own bedroom is the local evidence that counts. For the general causes in your area, see our pages for Gillingham, Rochester and Strood.
The Energy Saving Trust says most of us see condensation on our windows from time to time, for example on a cold morning, and it is not necessarily a problem if it clears up quickly. It becomes one when moisture builds up enough to cause mould or damage, so wipe it and watch for black spots on frames, sills and corners.
None of the sources we checked tells you to. The Energy Saving Trust advises keeping trickle vents open, and GOV.UK guidance describes a vent position, where a window is partly open but locked, for people worried about security. Noise, security and cold are real concerns, so use the vents first.
The sources we checked give no overnight figure for one person, so we will not invent one. The Energy Saving Trust says a household typically produces up to 100 litres of moisture a week from cooking, kettles, showers and breathing, and the Centre for Sustainable Energy lists breathing as a significant source in its own right.
Sources: Energy Saving Trust: How to get rid of damp; Centre for Sustainable Energy: Condensation, damp and mould; Property Care Association: Condensation in homes; Property Care Association: Condensation solutions; GOV.UK: Understanding and addressing the health risks of damp and mould in the home.
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