You notice it one cold, winter morning - a gap between some floorboards that wasn’t there before. Or maybe it was there all along, only now it seems wider. You might start wondering if something has gone wrong, especially if your timber floors are new.
Don’t panic yet. In most cases, what you’re seeing is your timber floor doing exactly what it’s supposed to do.
Before you rush to buy your timber gap filler, remember some small gaps are normal. Timber is a living material, and it moves with the seasons. But not every gap is normal, and knowing the difference can save you from an unnecessary repair job or a problem that quietly gets worse. As the experts when it comes to timber floor care, we’ll walk you through why timber floor gaps appear in winter, and what to do (or not do) about it.
Why Do Timber Floor Gaps Appear?
Wood is a hygroscopic material
Timber is a hygroscopic material, which means it absorbs and releases moisture in response to the relative humidity and temperature of its surroundings. That characteristic doesn’t change just because it’s been taken out of the forest and installed in your home. Even finished timber flooring retains the capacity to interact with environmental moisture.
How the weather affects your timber
When the air is humid, timber absorbs moisture and expands. When the air is dry, it releases moisture and shrinks. In winter, particularly in homes with central heating running constantly, indoor air becomes significantly drier than at other times of year. The boards lose moisture, contract slightly across their width, and gaps open up between them. Come summer, when humidity returns, the boards expand again and the gaps close.
This isn't a defect. It's the floor responding to its environment the same way it always has. The movement is inherent to timber's organic nature and cannot be prevented. But the boards don't shrink uniformly in all directions, which is why gaps appear between boards rather than causing length changes.
Does the type of flooring matter?
The degree of movement depends on the species and cut of timber, how the floor was installed, and how variable the conditions in your home are throughout the year.
Solid hardwood floors tend to move more than engineered timber floors because engineered boards are constructed with a cross-layered core that stabilises them against changes in humidity. But even engineered floors move to some extent. Older floors, particularly in period homes, often move quite dramatically between seasons.
What's Normal: Identifying Seasonal Gaps
Some gaps are simply seasonal, and the best thing you can do is leave them alone. Here's how to recognise them:
- The gaps appeared gradually during the cooler, drier months and weren't there (or were much smaller) during summer
- They're relatively uniform across the floor, and you're not seeing one area dramatically worse than the rest.
- The boards themselves look flat and sound, with no lifting, twisting, or cracking.
- The gaps are small, generally in the range of one to two millimetres or less. And if you think back, the floor may have done the same thing last winter.
Why you shouldn’t fill them
If this describes what you're seeing, your floor is behaving exactly as it should. Unfortunately, they do look untidy, and they’re suddenly very visible, so the temptation to fill those gaps immediately is understandable.
But filling a gap that will close again in a few months is a mistake. When the boards expand back with returning humidity, they'll push against whatever filler you've put in. A rigid filler will crack, pop out, or, in the worst case, put enough pressure on the boards themselves to cause cupping or surface damage. The gap was the floor's way of accommodating natural movement, and filling it removes that accommodation.
In these cases, patience is the answer. Keep an eye on your floor through summer to see whether the gaps reduce or disappear.
Signs the gaps will close naturally
Normal gaps appear uniformly across the floor. To give you a rough idea of what to expect, a 130mm wide board might shrink around 0.75mm or more during the coldest months.
They also won’t collect excessive debris and will close up during humid months. Some floors stay tight with no observable gapping throughout their life, whereas others show gaps only during drier months.
When to Worry: Problematic Gaps vs Seasonal Movement
Not all gaps are harmless, and there are clear signs that something beyond normal seasonal movement is happening.
The gaps don't close in summer
If the gaps don’t go away when the weather warms up and humidity returns, they're not seasonal. This might indicate the floor was installed without adequate expansion allowance, or that the boards have dried beyond what the seasonal cycle can recover.
The gaps are wide
Gaps of three millimetres or more are worth investigating. Small seasonal gaps are expected; significant ones suggest something else may be going on.
The gapping is uneven or concentrated
Seasonal movement tends to be distributed evenly across the floor. If gaps are clustered in one area, near a wall or under a window, that can point to a localised moisture issue. That could be anything from a plumbing leak to one area of the floor being exposed to more direct heat than others.
The boards are doing more than gapping
If you're also seeing cupping (boards curving upward at the edges), crowning (boards raised in the centre), squeaking that wasn't there before, or any boards that feel loose or springy underfoot, these are signs of a more significant issue that should be assessed by a flooring professional before you do anything else.
The floor is relatively new and gapping heavily
A newly installed floor that develops significant gaps early in its life may not have been allowed to acclimatise properly before installation. Timber needs time to adjust to the humidity and temperature conditions of its new environment before being laid. If it hasn't, the movement after installation can be more dramatic than expected.
If any of these apply to your situation, get a professional assessment before reaching for the filler. Understanding the root cause first will save you from treating a symptom while the underlying problem continues.
Should You Fill the Gaps And When?
Assuming your gaps fall into the "worth filling" category, the next question is what to do about them. The golden rule is to only fill gaps that are stable. Filling a gap that will change with the seasons is setting yourself up for a failed repair and potentially a damaged floor.
Filling is the right call when:
- The gaps have been present across multiple seasons without closing.
- The floor has been sanded and refinished as part of a restoration project, and gaps need to be addressed as part of that process.
- The gaps are collecting dirt and grime, creating a draught through the subfloor, or posing a trip hazard.
- The floor is in a stable, climate-controlled environment, with minimal seasonal variation. In these cases, even gaps that might technically be seasonal are unlikely to close enough to cause a problem with a well-chosen flexible filler.
Waiting is the smarter call when:
- The gaps appeared in the last month or two of winter, and the floor has done this before.
- You haven't yet observed whether they close in summer.
- The floor is mid-movement, and conditions in the home are still dry.
If you're not sure, just keep an eye on your floor through to the end of the warmer months before making a decision.
Choosing the Right Gap Filler
Once you’ve confirmed filling is the right approach, choosing the right product comes down to gap size, floor type, and how much movement the timber is likely to have.
- Small gaps and nail holes (up to ~2mm): A fluid, fine-gap filler works best here. These are designed to flow into narrow joints and can be sanded flush for a seamless finish.
- Larger gaps and voids: A thicker, paste-style filler is more suitable, giving you better coverage and durability in wider spaces.
- Areas with movement (edges, thresholds, perimeter gaps): A flexible filler is the safer choice, helping prevent cracking as the timber expands and contracts.
You can browse the full range of timber gap fillers, applicators, and accessories at Quicksand Supplies. If you're unsure which product suits your floor type and gap size, reach out to our team for advice.
Tips to Reduce Seasonal Movement
You can never eliminate movement entirely from a solid timber floor, but if the seasonal gaps are bothering you, there are practical steps you can take to reduce them.
Maintain consistent indoor humidity
The biggest driver of seasonal movement is the change in humidity, not temperature itself. Aim to keep relative indoor humidity between 40 and 60% year-round. Ducted or reverse-cycle heating in winter strips moisture from the air, so running a humidifier in colder months can significantly reduce how much your floor dries out and contracts.
Be mindful of how you heat the room
Directing heating vents directly at the floor or placing portable heaters close to the boards accelerates localised drying. Where possible, distribute heat more evenly through the space.
Acclimatise new floors before installation
If you're having a new timber floor installed, make sure the boards are stored in the space for the recommended acclimatisation period before they go down — typically at least a few days to a couple of weeks depending on the species and product. This reduces the amount of movement once installed.
Know Your Floor and When to Act
Most winter gaps are normal, and they’re not a sign of a failing floor, poor installation, or an impending repair bill. They're the floor responding to drier air in the way that timber has always responded. In many cases, the correct response is simply to wait. But where gaps are permanent or becoming problematic, the right filler applied at the right time gives you a clean, stable result that lasts.
When you're ready to fill, make sure you use a product that suits your gap size and floor type. The Timber Gap Filler range at Quicksand Supplies covers everything from fine parquetry gaps to large board cavities, with the tools and accessories to do the job properly.
Still not sure what you're dealing with? Reach out to the Quicksand team. We know timber floors inside out and can help you make the right call.