Cracks that appear in winter: what the heating season does to walls

Why cracks show up just as the heating season starts

When district heating or a home's own boiler switches on for the season, indoor air dries out quickly, often dropping well below the humidity level the building had all summer. Timber, plasterboard, and the plaster skim on top of it all lose moisture and shrink slightly. Different materials shrink at different rates, and that mismatch is what opens a crack along a joint or corner.

In a Soviet-era panel block, the concrete panels themselves barely move with temperature and humidity, but the plaster skim and the filler in panel joints can. A crack tracing the line of a panel joint, especially near a corner or above a doorway, is usually that filler responding to the same seasonal shrinkage as everywhere else.

In a wood-frame house, especially the older stock in Kalamaja or Nõmme, the timber frame itself shrinks and swells with the seasons far more than plasterboard or plaster does. Once heating starts and the frame dries out after a damp autumn, the wall lining moves against the frame and cracks appear at joints between boards, around window and door frames, and where plasterboard meets a ceiling.

How to tell an ordinary shrinkage crack from something more serious

A seasonal crack is almost always hairline, under about a millimetre wide, and runs along a natural joint: where two sheets of plasterboard meet, along a cornice, around a window frame, or where a wall meets the ceiling. It does not go through solid material at an angle, and there is no step where one side sits higher or lower than the other.

A crack worth a proper look behaves differently. It is wider than a couple of millimetres, keeps growing over weeks rather than settling, runs diagonally across a wall rather than along a joint, or comes with a door or window that has started sticking. Any crack in a load-bearing wall, or one that follows a straight diagonal from a corner of a window or door opening, falls outside what we would treat as cosmetic.

We do not touch load-bearing walls ourselves, and if a crack pattern suggests movement in the structure rather than the surface finish, the right step is a structural engineer, not a coat of filler. Most of what turns up each winter is the harmless kind, but it is worth knowing the difference before you decide to just paint over it.

• Hairline width, along a joint or corner: normal seasonal movement
• Wider than 2–3 mm, or growing week by week: worth a closer look
• Diagonal crack from the corner of a window or door: get it checked
• Doors or windows newly sticking alongside the crack: get it checked
• Crack in a load-bearing wall: call a structural engineer, not a handyman

What you can reasonably do yourself before spring

If a crack is clearly the cosmetic kind, there is often no need to fix it mid-winter. Filling it now, while the building is at its driest and most contracted, means it can reopen slightly once the heating stops in spring and humidity rises again. Many people simply mark the date and width with a pencil and leave it to wait.

Where a draught comes through a crack around a window frame or skirting, a bead of flexible acrylic sealant is a reasonable interim fix that will not crack the way rigid filler does. Keeping indoor humidity from swinging too far, for instance with a humidifier or simply drying laundry indoors less aggressively, can also slow how much the timber and boards move.

What is not worth doing yourself is opening up a wider crack to inspect what is behind it, or filling anything in a load-bearing wall. That is a job for someone qualified to judge what they are looking at, not a weekend project.

When it is worth having someone look at it during winter

A handful of situations are worth a visit now rather than waiting for the thaw. If a crack is widening noticeably week by week, if it runs diagonally rather than along a joint, or if it appears alongside other signs such as a door that no longer closes properly, that pattern is worth having assessed while it is fresh rather than guessing until April.

It is also worth calling sooner if the crack lets in a cold draught that is pushing up heating costs, or if you are simply not sure which category it falls into. An odd-jobs visit, from 39 € per hour with a 25 € call-out in Tallinn deducted from the bill if the work goes ahead, is often enough to have someone experienced take a look and tell you honestly whether it is cosmetic or not.

If it turns out to be structural, we will say so and point you towards a structural engineer rather than attempt work we do not do. That is a better outcome for you than a filled-over crack that reopens because the underlying movement was never addressed.

Spring repairs: what the job actually costs

Once the heating season ends and humidity has settled back to a normal level, usually by late spring, is the right time to fill and finish most seasonal cracks properly, since the building will not shrink much further that year. For a plasterboard joint or a handful of hairline cracks, this is straightforward filling, sanding, and a coat of paint to match.

Plasterboard repair work starts from 28 € per job for smaller jobs such as re-taping a joint or patching a section around a crack. Painting and decorating to finish the repair and blend it into the surrounding wall starts from 12 € per job. Larger jobs, such as several rooms or a full ceiling, get a fixed quote valid for 30 days once we have seen photos or a description.

There is a 24-month guarantee on any work we carry out, which covers the work itself rather than further seasonal movement in the building. If the same crack reopens purely because of the next heating season, that is the building doing what panel blocks and wood-frame houses do every year, not a failure of the repair.