Mitigating the decay of timber

Mitigating Decay Risks of Timbers Embedded in Solid Walls

 

In traditional buildings the timber structures are built into the solid walls. These walls were often built with an earth-lime mortar mix and pointed with lime mortar. These materials readily take up and release moisture. During rainfall for example a moisture will soak into the wall and when the weather clears the wall is then able to release that moisture. This effect is interrupted with the use non-breathable materials (https://www.russetandsage.com/whyuselime).

It’s important to understand that moisture doesn’t get into the wall just from external sources (https://www.russetandsage.com/interstitialcondensation).

If a solid wall is unable to dry out sufficiently the risk of timber decay increases drastically. The timber relies upon the solid wall being able to adequately deal with moisture to keep its bedded sections dry. Timber decay can be caused by the following:

•     Moisture Entrapment: Solid walls with non-breathable materials can trap moisture within their structure. This trapped moisture permeates into embedded timbers, creating an ideal environment for fungal growth and decay.

•     Condensation Buildup: Interstitial condensation can occur within the solid wall affecting bedded timbers. This constant moisture exposure accelerates timber decay over time.

•     Capillary Action: Moisture from the ground or surrounding environment can be drawn into solid walls through capillary action. Embedded timbers in contact with these moisture-laden walls are susceptible to decay, particularly if ground levels are higher than internal floor levels.

•     Fungal Infestation: Damp conditions within solid walls provide a conducive habitat for fungi, including rot-causing organisms such as dry rot and wet rot. Once established, fungal infestations can spread rapidly, compromising the structural integrity of timbers.

 

To mitigate the decay risks associated with timbers embedded in solid walls with limited moisture release, proactive measures must be implemented:

•     Improved Ventilation: Enhancing ventilation within solid walls promotes air circulation and increases the rate of air exchange within a structure. This reduces the chances of condensation. If your building has air bricks they may have been installed specifically to ventilate underneath suspended timber floors. In the absence of a cellar, floor timber rotting will go un-noticed until the floor becomes springy - indicating the timbers have lost structural integrity.

•     Use of Breathable Materials: Utilising breathable building materials, such as lime mortar in wall construction facilitates moisture diffusion and prevents moisture buildup. These materials allow for the gradual release of moisture, reducing the likelihood of timber decay. Lime plasters will help balance internal conditions as well by taking in moisture when conditions are humid and releasing them again when conditions are drier. Repairing missing mortar joints and effectively maintaining weathered elevations will minimise the risk of penetrating damp. Pay particular attention to gable ends as purlins are often bedded through the wall and are exposed to weather.

•     Management of Drainage Systems: Faulty rainwater goods are one of the most damaging elements to a historic building. Overflowing gutters, blocked hoppers and even downpipes discharging to the base of a building can cause enormous amounts of damage. Implementing effective drainage systems, such as French drains around the perimeter of the building helps divert groundwater away from the solid walls and provides an evaporation strip to help dissipate the moisture. By minimising moisture ingress, drainage systems mitigate the risk of decay in embedded timbers.