Moisture in buildings

Dampness in buildings can come in many forms. Generally, buildings can deal with or have a degree of resistance to moisture that is either created or that enters a building.

A building will never be ‘totally’ dry there will always be some degree of moisture within the building fabric or internal environment. When a new building is being constructed or when an existing property is being refurbished careful consideration to the relationship of moisture and the structure should be thought of.

In the early part of the 20th century, the living standard in the UK was a stark contrast to what we expect in modern times. Other than affluent citizens most conditions were cramped, cold and building’s contained excessive amounts of moisture laden air. Despite the house being drafty with rattling windows and wind blowing through the eaves houses were damp, really damp. It wasn’t uncommon for clothes requiring drying in front of the fire before they could be worn.

The main cause of the damp was occupancy, it wasn’t uncommon for 5 people to share a room, this would give rise to horrendous amounts of condensation. At this point in time rising damp wasn’t considered an issue, the main priority was that there was a roof over your head.

Prior to the 1920’s most buildings were constructed without a damp-proof course. Until a new building standard was brought in to prevent rising damp. This was achieved using a slate damp-proof course. However, means of communication at the time were much slower than today and the propagation of this new standard to time to become fully established in the UK.

During this time and still common today is the incorporation of timber in buildings. It is strong, can be lightweight, can be durable and when used commercially can be cost effective.

However, timber is intrinsically linked with water. Water is required by the timber for growth. The drying process that it undergoes to change the materials properties to make it a satisfactory building material makes the timber a Hygroscopic material. This means that the timber will readily absorb atmospheric moisture and if placed in water will absorb moisture until it reaches saturation or fibre saturation point as it is known.

When a timber has elevated moisture content levels it creates a prime environment for fungal decay to set in. However, not all beetle infestations require this.

Although timber has a natural durability against degradation, it is limited. The degradation of timber can come in two forms either fungal decay or beetle decay and this is an important feature of nature so that the timber can remain part of the cyclical process known as the carbon cycle.

Timber decay and measures to avoid early degradation have been used for as long as timber has been used in buildings. In the UK, master craftsmen would use the heartwood or oak to create a long-lasting structure, even to this day it isn’t uncommon to see buildings from the 16th century using oak heartwood and the main structural support for buildings.

However, where most commercially used timber struggles is when it is constantly immersed in water in a scenario such as below ground. Timber can be embedded into solid walls and degrade quite rapidly if fungal decay sets in.

Therefore, to avoid structural failure inert material was and is used to from a below ground environment where the risk of permanent saturation is high.

In the UK, brick was often used to from a vault or retaining structure which created a storeroom or larder.

In modern times, materials such as concrete or blockwork are favoured due to speed of installation and strength of the material. However, in a below ground situation where there is retained earth a head of water pressure is created. This external water pressure creates a differential due to the space created by the retaining elements. Therefore, water will enter the structure through imperfections and will fill until the pressure has equalized.

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