Question 1

Why is my wooden floor cupping or gapping?

Accepted Answer

Because wood **moves with moisture**, and both symptoms are the same mechanism producing opposite results.

**The underlying principle.** Wood absorbs and releases moisture until it reaches equilibrium with the surrounding air. Absorbing moisture makes it swell; releasing it makes it shrink. Crucially, movement is **anisotropic** — considerable across the grain, negligible along it. So boards change in width, not length.

**Cupping** — board edges higher than the centre, giving a concave surface.

This means the **underside is wetter than the top**. The bottom swells while the top does not, and the board curls upward at the edges.

**Causes:** moisture beneath the floor — a damp subfloor, a leak, no damp proof membrane, a crawl space or basement with high humidity, wet-mopping the surface, or a spill soaking through joints. It can also occur when a floor is laid over a slab that has not fully dried.

**Crowning** is the reverse — centre higher than edges — usually caused by sanding a cupped floor flat before it dried out, so it crowns as it equalises.

**Gapping** — visible gaps between boards.

This means the wood has **dried and shrunk**. Almost always **seasonal**: heating in winter drops indoor relative humidity substantially, boards lose moisture and narrow, and gaps open. They typically close again in summer.

**Causes:** low humidity from central heating, underfloor heating run too hot or brought up too fast, or wood installed at too high a moisture content that has since dried.

**What prevents both:**

**Acclimatise before installation** — leave boards in the room for the manufacturer's specified period so they reach equilibrium before being fixed.

**Control relative humidity**, ideally 40–60% year round. A humidifier in winter is the single most effective measure.

**Leave expansion gaps** at the perimeter, covered by skirting or beading.

**Never wet mop** — damp only.

**Address subfloor moisture first**; sanding a cupped floor before it dries guarantees crowning.

Question 2

Why does my door stick in summer but not in winter?

Accepted Answer

Timber absorbs moisture from the air and expands, then releases it and contracts. In humid summer conditions a door can grow enough to bind in its frame, and in dry winter air it shrinks back and

Question 3

What is subsidence, and what should you actually do about it?

Accepted Answer

The downward movement of the ground beneath a building's foundations, causing the structure to move with it. It is the most feared word in home ownership, and the fear is disproportionate to how most

Question 4

What is thermal bridging, and why is one corner of my room always damp?

Accepted Answer

A thermal bridge — sometimes called a cold bridge — is a path through the building fabric that conducts heat out faster than the surrounding structure. The surface on the inside of that path stays

Question 5

How do I tell rising damp from condensation and penetrating damp?

Accepted Answer

The three have completely different causes and completely different fixes, and misdiagnosis is expensive — most damp diagnosed and treated as rising damp is actually one of the other two.

Question 6

What causes a musty smell in a room?

Accepted Answer

A musty smell is produced by mould and mildew growing somewhere, releasing compounds you can smell before you can see any growth. Air freshener masks it; finding the moisture source is the only real

Question 7

How do I stop floorboards creaking?

Accepted Answer

A creak is friction — two pieces of timber, or timber and a nail, rubbing as the board flexes under weight. Fixing it means removing the movement, so the first job is locating exactly where it comes

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