This article outlines some of the more common defects in buildings and property related to timber decay, and similar issues. It is relevant to residential, commercial, and industrial buildings.
In the construction of buildings, we take timber for granted; it is used for a wide variety of applications, from structural members, (such as beams and joists), to joinery and panelling.
Timber is an inherently durable material, and is resistant to most biological attack, provided that it remains dry. It is, however, more vulnerable to fungal attack and subsequent decay, in situations where certain conditions exist.
Such conditions can be created by raised levels of moisture; typical causes may be missing or defective roof tiles, defective flashings, inadequate eaves ventilation, blocked or leaking gutters, defective flat roof coverings, cracked render, defective brickwork pointing, and leaking internal services. Any of these situations can result in damage to timber occurring, which can prove both costly and disruptive to the occupants.
The air is full of fungal spores, but they are so small we don’t notice them. They settle on materials within buildings and externally, waiting for moisture to increase to enable them to germinate and spread within timber.
Dry rot and wet rot
Not all fungi found in buildings will cause timber decay, however, the presence of any fungal growth indicates damp conditions; which are also suitable for the wood rotting species.
When timber in buildings becomes damp, it is vulnerable to attack from two main types of fungal growth; wet rot and dry rot.
Wet rot includes two groups of rot, (brown and white), each of which has characteristic signs of decay. Brown rots cause the timber to become darker in colour, and to crack along and across the grain. White rots cause the timber to become lighter in colour and fibrous in texture, without cross-cracking. All brown rots and white rots are collectively referred to as wet rot, except for one brown rot, (Serpula lacrymans), which is commonly called dry rot.
Building surveyors are trained to identify the potential for timber decay, and often encounter different types of timber decay and rot during inspections; in particular wet rot, but also the much more destructive dry rot. Some of the symptoms of the different types of rot are common, so experience is required to make an accurate assessment and diagnosis.
A source of moisture over time could result in first wet rot occurring, followed by a dry rot attack. Dry rot has a much higher potential to cause failure of structural members, (lintels, beams, joists, roof rafters); as well as damaging joinery, (fascia boards, skirting boards and floor coverings). A surveyor is often called in to carry out a building defects report for the occupant, landlord, or managing agents.
Legal consequences of timber rot and fungal spread
Opening-up works may often be required, to establish the condition of the structure, and how far the timber decay has spread. The surveyor will need to check masonry structures such as walls, as dry rot can easily penetrate through walls and floors using long, fine, fungal strands called hyphae, and mycelium, and can even contaminate adjacent property. In such circumstances, there may be legal consequences, because if it can be proved that the problem started in your property, (and has spread next door), you might be liable for their costs of reinstatement.
Listed buildings and conservation
Timber decay that may lead to structural failure is often only discovered when a consequential problem becomes apparent; such as putting afoot through the flooring, or noticing skirting boards wrinkling and cracking. Such a situation can conceal more serious damage to adjacent floor joists and timber wall plates. Whilst there are many timber specialist firms out there, willing to solve your problem, be cautious. Most are in business to sell you their services and products, and are usually far from impartial.
With wet rot to timber, removal of the source of moisture should usually be the main plan of attack, and some damp timber may even be salvaged using modern resin-based systems; removing the need for wholesale replacement. This could be important in listed buildings, and conservation projects; where retention of original fabric is the priority. The end-grain of timber, (at the ends of joists and rafters), is particularly vulnerable to both water penetration and subsequent wet rot; the timber can quickly lose it’s integrity, and become soft and spongy.
Planned maintenance inspections by building surveyors on larger properties can be beneficial in identifying roof coverings about to fail, rainwater goods becoming defective at joints, poor joints to internal service pipes and hot water cylinders. This can be nipped in the bud, bydealing with routine maintenance issues before they lead to a structural problem. But let’s face it, most people don’t go down that route, and some panic when there is a major leak, or they discover wood rot in their office or home.
Conditions for rot and decay in timber
The moisture content required to generate the various types of fungal decay varies, depending upon the type of fungus. Dry rot can commence when the moisture content is above 20%; wet rot may require a much higher moisture content. Dry rot is sensitive to high temperatures, (over 25˚C), and lower moisture content, (below 20%), and is therefore rarely found on exposed timber, or in situations where conditions fluctuate. Making the correct diagnosis of what we have on site is critical to avoid financial waste and unnecessary disruption. Wet rot might even precede an outbreak of Dry rot, later on.
Finishes such as decorations, wall coverings and plasterwork, cornices, panelling, etc., will often be adversely affected. Opening-up the areas carefully, will enable the building surveyor to make an examination, and carry out tests. Remedial works can be brief and straight-forward, or lengthy and complicated. In some cases, the remedial works may form part of an insurance claim; unless there has been neglect in maintenance by the owner.
A building defects report should provide information on the extent of the damage, whether it is structural in nature, or not, and whether there is the need for further opening-up required. Identifying the source of the moisture and origin of the rot is important, to avoid recurrence.
In some cases, specially trained dogs, (who have good olfactory senses), can be used to assist surveyors to detect dry rot, and, and can save valuable time and remove the risk of causing unnecessary damage to important timber fabric. Experienced building surveyors are effectively ‘detectives’, and naturally curious to examine the site and find evidence and key information pointing to the cause or causes of the defect. A tiny area of cracking timber skirting in a room or area could conceal serious structural damage adjacent, when opened-up more extensively.
Specialist tools for surveyors and inspection methods
Use can be made of optical borescopes in difficult to access areas, to view tight spaces which are too small for a person to crawl inside. The surveyor will have in their arsenal, a range of instruments and solutions to tackle timber decay. They are also often required to specify the repairs and supervise the specialist contractors that execute the works.
The client can either just request an inspection and report by a building surveyor, or ask for a full service including specifying and programming the remedial works, dealing with insurance loss adjusters, and managing builders to remedy the problem. Sometimes, all that is really needed are a few more air bricks to aid ventilation of a sub-floor space. That alone might be enough to keep dry rot at bay, as stagnant air is the preference of dry rot fungus.
It is surprising how much money has been wasted over the years by many people simply failing to follow simple, good practice. Good practice is the core of a building surveyor’s knowledge and experience.
More than one defect and investigation
Wood-boring beetle infestation can be another major problem with timber in buildings. It is sometimes the case that there is a combination of defects with rot and infestation, which needs action.
Arun Associates have building surveyors experienced in investigating timber defects and timber decay, and in providing property defects reports. They are also aware of client, contractor, and designer obligations under the Construction (Design and Management) Regulations 2015, for Health and Safety on sites.