The pantry item homeowners are spreading on windowsills to stop condensation overnight

The first time I found water pooled on the windowsill, my mind went straight to plumbing trouble. It was a bleak January dawn - the sort where the air has a faint metallic bite and you can see your breath hanging in the room. I drew the curtains and saw it immediately: fat droplets sliding down the pane, gathering at the bottom and seeping into the timber surround we’d paid a ridiculous amount to have repainted. The radiator underneath was running and the room felt comfortably warm, yet the windows looked as though they’d been weeping for hours. It gave me that sinking feeling that the house was unravelling in the dark while we slept.

That was the moment I began asking the question plenty of homeowners are typing into Google at 1am: what can I actually put on my windowsills to stop this happening night after night?

The strange new life of the British windowsill

In winter, condensation has started behaving like an unwanted lodger in British homes. You go to bed feeling dutiful: the thermostat’s turned down, the curtains are pulled tight, maybe a draught excluder is wedged against the door. Then morning arrives and every window looks like the inside of a greenhouse - fogged glass, damp collected along the bottom edge, and black mould threatening to take hold in the corners. With the cost of living crisis pushing many of us to seal up and conserve heat, our homes have become so “sealed” that the moisture from breathing, cooking and showering has nowhere sensible to go.

Most of us know the ritual: you swipe a finger through the mist and doodle a little sad face, then instantly regret it when your sleeve brushes freezing, wet glass. It’s more than unsightly; it’s slow damage. Mould spreading along silicone sealant, timber frames swelling, paint blistering like bargain wallpaper in a steamy bathroom. Underneath it all is a nagging worry: if the windows are this wet, what is happening inside the walls?

So households have started improvising. Dehumidifiers whirring away in multiple rooms, bowls of salt perched near radiators, windows cracked open even when the cold makes your breath cloud the air. From that quiet, slightly desperate trial-and-error has emerged an oddly endearing habit: people rooting through kitchen cupboards and laying out a very ordinary pantry item along their windowsills before bed.

Bicarbonate of soda: the humble white powder that’s suddenly a hero

The surprise headliner? Bicarbonate of soda. Plain old bicarb - the stuff your nan kept in a jam jar under the sink. The same powder that deodorises fridges and doubles as “science” for children’s volcano experiments is now being sprinkled, spooned out and set in little dishes along British windowsills. It’s the kind of tip you hear and automatically assume can’t be real - until you try it on one window and find yourself checking the glass the next morning, mildly irritated that it’s made a difference.

The idea is straightforward. Bicarbonate of soda is mildly hygroscopic, which is just the technical way of saying it draws in and holds moisture from the surrounding air. Lay a narrow trail along a wooden sill or tip some into a shallow dish beneath the pane and it behaves like a tiny, silent sponge. As warm, damp air in a bedroom or kitchen hits cold glass and turns into droplets, some of that moisture is captured before it can become a puddle. Instead, it gets absorbed into the bicarb.

Those who rely on it describe it like you’d describe a slightly eccentric but dependable neighbour: not flawless, occasionally a bit untidy if you go overboard, but quietly getting on with the job while you sleep. One north London renter told me she started using bicarb “because it was literally all I could afford,” then woke up stunned to find her usually drenched bedroom window only lightly hazed, with much of the damp sitting in the powdery strip she’d set out the night before.

From TikTok tip to kitchen-table experiment

“I just grabbed what I had in the cupboard”

As with plenty of domestic mini-revolutions in 2024, this one has travelled via TikTok, Facebook groups and neighbourly WhatsApp threads. The clips are rarely polished: shaky footage of real windows in ordinary houses, a white line on a scuffed sill, and someone murmuring, “I thought this was a joke, but look at this.” You’re shown the “before” - dripping panes, black specks spreading in the corners - and then the “after”: a dry sill, with the bicarb no longer fluffy but slightly claggy, like damp sand.

A dad in Manchester recorded himself brandishing a teaspoon of bicarbonate as if he were about to attempt something reckless. “I know this looks like I’m about to bake a cake on my window,” he laughed, “but at this point I’d sprinkle flour on the ceiling if it meant not wiping these every morning.” That sums up the tone in a lot of households: a dash of humour, plenty of annoyance, and a strong desire not to spend every dawn shivering in a dressing gown, towel in hand, wiping down windows before work.

And, truthfully, hardly anyone manages to wipe every window daily, despite being told it’s what we should do. Real life intervenes. Between school runs, Teams calls, delayed trains and late nights, it’s suddenly the weekend and you’re eyeing a little thicket of mould creeping up the silicone. Anything that lets you skip a few guilt-ridden morning wipe-downs feels less like a trick and more like basic self-defence.

Why bicarb instead of the fancy stuff?

Of course, there are more polished options. There are dehumidifiers you can run from your phone, moisture traps housed in shiny plastic, and sprays that claim to tackle mould “at the root”. They can work, and if you’re able to place them around the house, that’s brilliant. Still, there’s something comforting about a 60p tub of bicarbonate you already own being repurposed into a quiet moisture magnet overnight.

Bicarbonate doesn’t buzz, light up or add anything to your electricity bill. You can lay it out with a spoon, then sweep the excess back into the tub once it’s done its job. No filter subscriptions, no complicated steps - just a soft, chalky powder that’s sat in cupboards for decades stepping in to help with a very current problem: tightly sealed homes that don’t breathe properly.

There’s also a simple psychological pull here. Using what you already have makes you feel capable rather than powerless. When the air feels damp and the budget feels tight, doing something small with cupboard basics can feel surprisingly reassuring.

How people are actually using bicarbonate of soda at home

Everyone I spoke to had their own slightly makeshift routine. Some insist on a neat, narrow line of bicarb laid along the front edge of the windowsill - almost like a chalk boundary between your wall and the damp trying to move in. Others want less mess and tip a couple of tablespoons into shallow ramekins or jar lids, spacing them out so they sit directly beneath the worst patch of glass. A few people with wooden frames hide it behind ornaments or photo frames, so it can do its work without making the room look like a chemistry demo.

A mum in Bristol, whose teenage son refuses to sleep unless the radiator is on full blast and the door is shut, lays out what she calls “a little bicarb runway” each evening. “If I don’t, his window literally drips,” she said, pulling a face as she recalled the smell of damp socks mixed with radiator-warmed air. “With the powder, the glass still mists up a bit, but I don’t get those horrible puddles on the sill that soak the curtains.” She replaces it twice a week, tipping the damp, clumped powder into the bin and laying a fresh strip.

With older painted timber sills, some homeowners take extra precautions. They place a strip of baking paper - or even an old envelope - on the sill first, then pour the bicarb onto that. It’s a small barrier that helps protect the paint while still allowing the powder to draw in moisture. One woman told me she’s come to enjoy the quiet evening routine: kettle on, lights lowered, then a slow lap of the house creating thin white borders at each window, as if she’s tucking them in for the night.

Does it really work, or is it wishful thinking?

No pantry trick can override physics. When warm, moisture-laden air meets cold glass, condensation will form - that’s simply what happens. Bicarbonate of soda can’t eliminate it completely, and anyone promising “zero condensation” from a spoonful of white powder is overselling it. What it can do - in a practical, no-nonsense way - is reduce the amount of loose moisture hanging around in the room overnight and provide an alternative place for some of that water to end up.

People who try it and keep going tend to describe improvements in increments, not miracles. A bedroom that used to wake up with heavy droplets and clear streaks might now have only a light haze and a dry sill. A bathroom window that used to leave a small lake at the corner of the frame may instead leave a little heap of compacted, damp bicarb. It’s not Instagram-perfect, but it’s gentler on the timber, the silicone, and your nerves.

There’s a modest satisfaction to it, too. You go to bed with thin white lines along the windows, not expecting magic - just hoping for “better”. Then, in the flat grey light of morning, you run your hand along the sill and feel powder rather than puddles. It’s a small, ordinary win that makes winter feel a fraction less relentless.

The limits of kitchen-cupboard heroics

For all its charm, this hack sits on top of a harder truth: condensation is usually a sign of something bigger. Homes end up warm in some spots and icy in others, double-glazed but short on ventilation, sealed up yet lacking trickle vents and extractor fans that actually get used. We dry laundry on radiators, simmer big pans of pasta in cramped kitchens, and take long hot showers as a reward for getting through the day. All that water vapour has to settle somewhere, and it often picks the coldest glass it can find.

Bicarbonate of soda is a useful ally, but it can’t take the place of airing a room occasionally - even when every instinct tells you to keep the heat in. It can’t solve the bathroom fan that rattles like a train and gets switched off at the isolator because it’s irritating. It won’t mend failed seals or dry out a wall that’s already saturated. It’s better thought of as a buffer: something that reduces the damage while you figure out the underlying issues.

A housing officer I spoke to put it plainly: “If a tub of bicarb is the difference between mould and no mould, the house probably needs more than a hack.” She wasn’t dismissing the idea - just pointing to reality. For renters who aren’t allowed to install vents or replace windows, though, that tub of bicarb can feel like a small piece of control when so much else is out of reach.

Why this tiny act feels bigger than it looks

There’s something almost gentle about seeing a windowsill edged with bicarbonate of soda. It’s a sign that someone is trying - quietly, between everything else in life - to look after the place they live. No major renovation, no drama; just a spoon, a box from the cupboard, and a few unhurried seconds. In a winter of eye-watering bills and homes that can feel oddly delicate, that counts for more than you might expect.

We’re used to “home hacks” being glossy and influencer-ready: perfect glass jars, spotless worktops, labels in designer fonts. This is the opposite. It’s inexpensive, slightly messy, and unapologetically functional. You may only notice it when you draw the curtains and see a pale, chalky line catching the lamplight. Yet it’s often these small, nearly invisible habits that make a home feel cared for, even when the paint is chipped and the curtain pole leans a bit.

On the coldest mornings, with radiators ticking and glass icy under your fingertips, that thin strip of powder is a quiet reminder you’re not entirely at the mercy of the weather or the gas company. You can still do something - even if it’s as simple as raiding the baking shelf for a little extra peace of mind. And perhaps that’s why the humble box of bicarbonate of soda is now appearing on so many British windowsills, ready for night to fall and moisture to rise.

When so much feels beyond our control, it’s oddly comforting to know a cupboard staple can keep watch while we sleep. It won’t win design awards and it won’t change the climate, but it may help keep windowsills dry until the first hint of spring sunshine finally shows up.