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Understanding wood17 Understanding wood →

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Understanding wood: how it moves, lasts and decays

The Wood Guide · Understanding wood

Section · Understanding wood

Understanding wood

If you know how wood behaves, a small crack won't alarm you, you'll choose the right species for the right place and you won't miscalculate. The basics, in plain language.

  • Movement and durability
  • Calculating in cubic metres
  • Woodworm and fungi
heartwood, sapwood and growth rings
The basics

Four concepts that explain almost everything

Wood moves

It absorbs moisture and releases it, swelling and shrinking as it does — mainly across its width. That is where gaps, small cracks and warping come from. How wood moves · when does wood expand.

Heartwood and sapwood

The inner part of the trunk is usually more durable than the lighter outer ring. That is why one board differs from the next, even within a single species. Heartwood and sapwood.

Durability classes

From 1 (very durable, like teak) to 5 (not durable). The class tells you how long the heartwood lasts outdoors without treatment. Durability classes of wood.

Calculating with wood

Wood is sold by the cubic metre, by the running metre or by the piece. If you know how to convert between them, you can compare fairly. How much is 1 cubic metre of wood.

From understanding to choosing

Once you know how wood behaves, choosing the right species is easier: the full register is under Wood species, the buying guides under Choosing & buying, and maintenance under Care & finishing.

The Understanding wood section

All pages

Calculations and sizes

How much is 1 cubic metre of wood?

Quick answer

Frequently asked questions about wood

Why does wood move?

Wood absorbs moisture from the air and releases it again. As it does, it swells and shrinks, mainly across its width and much less along its length. That is why the gaps between boards get wider and narrower with the seasons.

What is a durability class?

A scale from 1 (very durable) to 5 (not durable) that tells you how well the untreated heartwood of a species resists wood-destroying fungi. Teak is class 1, spruce class 4.

What is the difference between heartwood and sapwood?

Heartwood is the inner, often darker part of the trunk and is usually more durable. Sapwood is the lighter outer ring that still carried sap while the tree was alive; it is more vulnerable to fungi and insects.

More in The Wood Guide

From understanding to choosing

Understand wood, and you choose better — and maintain less.

The wood register Buying guides Picnic tables

A question about wood? Just ask.