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Extensive Dry Rot Damage Caused by Poor Sub Floor Ventilation

September 10, 2018

Premier Contractors were asked to investigate damage to floorboards and staining to downspouts and gutters. Our CSRT-qualified surveyors found True Dry Rot and identified the cause as a lack of sub floor ventilation.

Leaks from the gutters have created excess moisture which has penetrated the fabric of the building causing an outbreak of True Dry Rot

The moisture ingress has been absorbed by the adjacent timbers raising their moisture content to above 20% of their oven-dry weight. These conditions have resulted in the germination of the spores of the True Dry Rot fungus (Serpula lacrymans) bringing about the breakdown of structural timbers.

Floor timbers in the dining room were found to be seriously affected by dry rot and needed to be replaced.

Outside, gutter and down pipe joints were showing extensive staining which suggested leas and defects. Ideally, these need to be examined during heavy rainfall.

Dry Rot spores are ubiquitous and there is no environment free of them. However, they will not germinate or grow in timber with a moisture content of between 20 and 30 per cent. The fine fungal thread (hypha) digests the cellulose and hemi cellulose fractions of the wood but is unable to attack the structural lignin.

These remain as a brittle matrix which cracks into cubes under differential stresses. Cuboidal cracking is also a characteristic of many wet rots and does not automatically indicate the presence of Dry Rot. Fungal hyphae may clump together into a variety of structures known as mycelia which takes various forms depending on the surrounding conditions.

They may fill a humid cavity as a cotton wool-like mass or grow across the surface of the timber as grey-white skin. Active Dry Rot has a fresh white or greyish appearance. Some hyphae group together to form conducting strands. Their main function is the conduction of nutrients through inert non-nutrient materials (brickwork etc.) to permit eventual colonisation of other timbers.

Their relatively impervious outer layer, together with an unusual alkaline tolerance, allows them to survive in the mortar layers within masonry and walls and an infested area may be full of Dry Rot strands.

The Dry Rot fungus may tolerate relatively lower moisture contents and, through this and other quirks in its biology, is potentially capable of considerable destruction.

Premier advised and completed remedial repair works in two specific areas.

First of all, we designed and installed efficient sub floor ventilation to prevent any moisture build up and discourage the germination of Dry Rot spores.

In the dining room, the damaged floorboards and wall were replaced and treated to prevent further damage.

As with all our projects, the work is covered by an independent 10-year guarantee.

September 10th, 2018