Timber contains moisture, and its moisture content changes with the environment around it. During wetter periods it can absorb moisture. During prolonged warm and dry weather it loses moisture again.

As that happens, timber can expand and contract. On fencing, this may become visible as slightly wider gaps between boards, small changes along an edge or an individual board that is no longer quite as straight as it appeared when first installed.

That alone does not mean there is anything wrong with the fence.

DIFFERENT FENCING BEHAVES DIFFERENTLY

Closeboard fencing, individual vertical boards, horizontal screening and prefabricated panels all respond differently because the timber is arranged and fixed differently. The dimensions and type of timber matter too.

A narrow board fixed individually has different freedom to move from a larger framed panel. Horizontal boards can make movement visible in a different way from vertical ones.

This is why we do not think it is useful to judge every fence by one rule about how much movement is acceptable.

We need to look at what has moved, how the fence was constructed and whether that movement is affecting its function.

FIXINGS HAVE TO ALLOW THE FENCE TO DO ITS JOB

Fixings may be small, but across a fence there can be hundreds of them.

Their material, position and condition all matter. A fixing has to hold the timber securely while spending years outside with moisture, changing temperatures and movement in the timber around it.

The combination of metal, timber and moisture also deserves consideration. In some situations, deterioration or reactions around inappropriate fixings can lead to staining or affect the connection itself.

Simply adding more fixings is not necessarily the answer. The fence needs to remain secure while still allowing timber to behave like timber.

THE POSTS TELL A DIFFERENT STORY

Movement in the timber boards and movement of the entire fence are not the same thing.

If boards shrink slightly during a very dry summer, that can be normal. If the whole fence begins leaning or posts are moving significantly in the ground, we would look at that differently.

The posts are what transfer wind loads and the weight of the fence into the ground. Their condition and stability therefore tell us much more about the structure than a small seasonal gap between two boards.

We have been building timber fencing for many years, and during that time the materials available to protect timber posts have continued to develop.

One example is products such as PostSavers, which add protection around the particularly vulnerable area where a timber post passes between the ground and the air above it.

That transition zone repeatedly experiences changing moisture conditions. Over the life of a fence, this can have a significant effect on the timber.

Where appropriate, we use this type of protection because we have found it genuinely useful. It does not replace good installation or suitable timber, but it can provide another layer of protection to the post.

The way we built a fence many years ago does not have to remain exactly the way we build one today. When better materials or details become available and prove useful, it makes sense to incorporate them.

Ground conditions also vary. A fence installed in one garden may be dealing with completely different soil from a similar fence only a few streets away.

THE BOTTOM OF THE FENCE DESERVES ATTENTION

Timber that remains continuously close to wet soil or trapped organic material experiences very different conditions from timber that can dry properly.

The relationship can also change after the fence has been built.

Soil levels can change, planting grows, leaves accumulate and mulch may be added. Over time, material can build up against timber that originally had more space around it.

A detail that worked properly when the fence was installed can therefore be affected by changes in the garden around it.

BOTH SIDES OF A FENCE MAY LIVE IN DIFFERENT ENVIRONMENTS

A fence may divide two gardens, but that does not mean both faces of the timber experience the same conditions.

One side might receive direct afternoon sun while the other remains shaded. There may be dense planting on one side and an open patio on the other. Irrigation or a sprinkler may regularly wet one face while the opposite face remains relatively dry.

Those differences can affect moisture movement and the way individual boards behave.

The conditions can change over time too. A hedge that was small when the fence was built may eventually create permanent shade and reduce airflow.

When we look at movement in fencing, the immediate surroundings are therefore part of what we look at.

SOME SUMMER MOVEMENT MAY REVERSE

After a prolonged dry period, gaps can become more noticeable and boards can appear drier. When moisture levels increase again, some of that movement may reduce.

That is one reason not to judge every visible change as soon as it appears.

There is an important difference between seasonal movement and progressive failure.

The question is whether the timber is responding to temporary conditions or whether something in the material, fixing or structure is continuing to deteriorate.

WHEN SHOULD MOVEMENT GET ATTENTION?

A significantly loose post, boards pulling away from their fixings, persistent distortion, damaged components or areas that remain continually wet deserve investigation.

Context matters.

One board changing slightly during an unusually dry summer tells a very different story from an entire section of fencing beginning to lean.

The aim is not to expect timber to remain perfectly still. It is to recognise the difference between the normal behaviour of the material and a change that may indicate a problem elsewhere.

A FENCE SHOULD BE ALLOWED TO AGE

Timber fencing does not need to look exactly as it did on installation day to remain healthy. Colour changes, small movements occur and the garden around it evolves.

Good construction cannot stop timber being timber. Nor should it try to.

The aim is to build the fence so normal timber movement remains normal, while the structure continues doing its job year after year.