Dry Rot vs Wet Rot: How to Tell the Difference and Why It Matters

Two Types of Wood Rot,Two Very Different Problems

If you've spotted crumbling, discoloured or cracked timber in your home, the instinct is often to assume the worst and panic. But before anything else, you need to know which type of rot you're dealing with — because dry rot and wet rot are not the same thing, and treating one as if it were the other can make the situation considerably worse.

Both destroy timber. Both spread if left alone. But they behave differently, they look different, and they require different approaches to fix properly.

What Is Wet Rot?

Wet rot is the more common of the two. It happens when timber is exposed to persistent moisture — think leaking pipes, faulty guttering, or poor ventilation in a bathroom or basement. The wood absorbs water over time until it starts to break down from the inside.

Signs to look for:

• Timber that feels soft or spongy when you press it
• Darkened or discoloured wood, often darker than the surrounding timber
• Paint that bubbles or peels for no obvious reason
• A damp, musty smell coming from floors, window frames or skirting boards

Wet rot tends to stay localised to wherever moisture is present. Fix the water source, and you remove the conditions it needs to survive. That said, the damaged timber still needs to be assessed and likely replaced — softened wood has lost its structural integrity, and that's not something to ignore.

What Is Dry Rot?

Dry rot is a different beast entirely, and it's the one that homeowners and surveyors tend to be more concerned about. Despite the name, it does need moisture to get started — but once established, it can spread through masonry and across materials that aren't even timber. It produces a fungus called Serpula lacrymans that sends out fine strands called hyphae, which can travel significant distances in search of new timber to feed on.

Signs of dry rot include:

• Timber that cracks in a distinctive cuboid or 'cuboidal' pattern — almost like deep squares
• A grey or white silky skin on affected surfaces
• Rust-coloured spore dust around the affected area
• Mushroom-like fruiting bodies growing from walls or floors

Because dry rot can travel through walls and behind plasterwork, it's rarely as contained as it first appears. A small patch visible on a skirting board might be connected to a much larger problem underneath the floor or inside a wall cavity.

Why Getting the Diagnosis Right Matters

Wet rot treatments focus on eliminating moisture and replacing or treating damaged timber. Dry rot requires a more extensive approach — removing all affected material, treating surrounding masonry, and making sure the source of moisture is fully resolved. If you treat dry rot the same way you'd treat wet rot, there's a good chance it'll come back.

This is exactly why a professional survey matters. Rot often hides in places that aren't immediately visible, and what looks like a surface-level issue can have roots — sometimes literally — that go much deeper.

When Should You Call Someone In?

As soon as you notice anything suspicious. Soft timber, unexplained smells, bubbling paint, or visible fungal growth are all reasons to get eyes on the problem quickly. Both types of rot accelerate in autumn and winter when properties tend to be colder and condensation builds up, so if you've been putting off investigating something, now is the time to act.

A proper inspection will confirm which type of rot is present, how far it has spread, and what needs to happen next — giving you a clear picture rather than a bill of guesswork.