Sunday 4 January, 7:10, back bedroom: 76%. Window streaming. Isla still asleep. That's the first line of a notebook that has lived on the landing windowsill for three weeks, with a pencil tied to it on a bit of string, the way the biro hangs on the sign-up sheet at school.
I bought two hygrometers, £8 each, on 2 January. They're small digital things with a screen that shows the humidity and the temperature, and a memory for the highest and lowest readings. I have been wiping condensation off the bedroom windows most winter mornings for years without ever knowing what the air was actually doing. I wanted a number. Rob said I wanted a hobby.
Week one: changing nothing
One hygrometer went in Isla's room at the back and one in Alfie's box room at the front. Every morning at 7:10, before anyone was up, I wrote both readings in the notebook. In the first week, 4 to 10 January, Isla's room read between 71% and 78% and Alfie's between 68% and 74%. The temperature column told its own story: 16 degrees in Isla's room and 15 in Alfie's at ten past seven, even with the heating on since five. The back bedroom window ran with water every single day, and there's a paw print in the notebook margin from the morning Mabel walked across the page. The worst morning was Thursday 8 January, at 78%, the day after a bedding wash with the airer tent full downstairs.
I'm not a damp surveyor and I'm not trying to be one. At work this month the phones have been all "no heating" and "why is my house wet", so I know I'm not the only one with streaming windows. What I can tell you is what I measured in my own house with an £8 gadget.
Week two: the dehumidifier goes upstairs
In the daytime the 12-litre dehumidifier lives in the lounge next to the airer. For the second week I carried it up to the landing at bedtime, put it on a timer plug from 11:00 to 5:00 and left the bedroom doors open about 10cm. It costs 28p a night at our current electricity rate, so £1.96 for the week. The tank was nearly full most mornings, about two litres, which I tipped down the bathroom sink and tried not to think about.
The readings fell straight away. Isla's room dropped to between 54% and 58%, and Alfie's was much the same. The window stayed dry on all seven mornings, which hadn't happened since October. The hum is louder than I'd like when you're lying awake at midnight, but I've stopped hearing it, the way you stop hearing a fridge.
Week three: back to normal life
In the third week I put everything back as usual: bedding on the airer, towels on the radiator, Wednesday being Wednesday. The dehumidifier stayed on the landing at night. The numbers held at 53% to 60%. The only time they crept up to 60% was the morning after a bedding wash, so the washing still matters, but the upstairs air stays on the right side of dry.
On three mornings I swapped the second hygrometer into the bathroom. At 7:40, after my shower, it read 91%. The bathroom has no extractor fan and hasn't since we bought the house in April 2017, and a dehumidifier on the landing can't do much about a room with a closed door and a bath full of steam. That's a problem for another post.
The numbers in one place
- Bedroom mornings before the dehumidifier moved upstairs: 68% to 78%
- With it on the landing overnight: about 55%
- Bathroom after a shower: 91%
- Cost of the whole experiment: £16 for two hygrometers, 28p a night in electricity, and a hum
None of that tells me why the house is damp, or whether the cause is the washing, the walls, the windows or four people breathing in a 1930s semi. If I were worried about damp in a wall, I'd ask somebody who does that for a living rather than a notebook. But the windows are dry in the mornings, and I'd call that something.
Today's entry, Saturday 24 January, 7:10, back bedroom: 55%. Window dry. Isla asleep, Mabel on her feet.
