Inspections and surveys for biodeterioration

A careful, systematic methodology is required when carrying out a building survey. One of the objectives is to assess the likely location or danger of dry rot, wet rot and insect infestation. Unless the property is new or relatively modern, it may be safe to start with the assumption that wet rot, dry rot and insect attack is probably present until proven otherwise. The aim in any inspection of a building for wet rot, dry rot and insect attack is to identify infected or vulnerable areas and to provide a logical assessment of the risks. This is usually best achieved if the same methodical approach used for a typical building survey is adopted.

Stage 1: Desk top study

Inspect records, drawings, relevant correspondence and previous treatment contract documents relating to the property. Consult owners/previous occupiers about problems with and alterations to the building. All of these sources may reveal valuable information about the building and may confirm or suggest previous outbreaks.

Stage 2: Primary inspection

Externally, work 'top down'.

Look for typical indicators of rot, such as algae growth on walls, damp stains on walls, choked/overflowing gutters, defective roof coverings, leaking/faulty rainwater downpipes, defective pointing/rendering.

Internally, work 'top down'.

Inspect all visible timbers, noting specific symptoms, such as warped or curled wall panelling boards, splitting and cracking of painted woodwork, strong mushroom smell in the vicinity of an outbreak, springing lintels or floors and, of course, fruiting bodies with a layer of red dust-like spores.

Stage 3: Secondary inspection

Once the 'at risk' areas have been identified, the surveyor is advised to recommend further investigations. These may involve an element of opening-up (e.g. lifting floorboards, removing sections of timber panelling). Using a fibre-optic endoscope will help to minimise such work (see below). Solum levels of subfloor voids, which are below the outside ground level, are potentially troublesome areas because they are prone to flooding and are difficult to ventilate adequately. If the finish of a suspended timber floor is at or near the outside ground level, the latter will be above the solum level, and this should be checked.

Objectives

There are 6 main objectives in carrying out the 3-stage investigation:

1. Building context: establish the client's instructions and the purpose of the investigation. Ascertain the property's age, form of construction and orientation. Investigation of its location and recent history, especially the level of maintenance and occurrence of adaptations (if any), may also be revealing.
2. Moisture zones: identify actual or potential sources of dampness.
3. Affected timbers: forecast the probable presence of hidden timbers within the building.
4. Dampness defects: identify and diagnose defects that can cause dampness.
5. Risk factors: pinpoint vulnerable areas (such as the floor, roof and wall voids) and look for external and internal indicators (such as dampness). If there has been previous infection, there is a higher risk of a further outbreak.
6. Reporting: accurately and impartially report the nature and extent of decay.

Figure 1: Non-destructive inspection of timber with the Resistograph