Dry Rot Control


Dry rot control – What is it? timber decay of wood caused by wood rotting fungus Serpula lacrymans, which if left, can have devastating effects within a house.  Diagnosis of dry rot / timber decay in homes has the ability to strike terror into the heart of the recipient of this dismal news. However, to the untrained eye dry rot and wet rot can easily be confused. It is therefore essential that a correct diagnosis of a timber decay / fungal decay problem is formed. By using Damp Aid dry rot specialist treatment surveyors to carry out your damp & dry rot survey, a correct diagnosis is guaranteed, and the timber decay survey report will satisfy the mortgage lenders if required as part of the mortgage process. We also provide environmentally friendly dry rot control solutions for controlling dry rot in buildings.

Dry rot has the potential to cause serious damaging decay in timber found in homes throughout the UK, but dry rot control does not have to be outrageously costly to treat & repair if caught in time by property care dry rot specialist treatment companies.

A careful dry survey carried out by Damp Aid (an independent property care dry rot specialist company ) is required to first of all correctly identify if the timber decay affecting the wood is dry rot and not wet rot, which is often misdiagnosed by other dry rot treatment companies. The source of dampness will need to be located by dry rot surveyors, and repaired before dry rot treatment can take place. The dry rot outbreak is then controlled, & treated, in a very selective and targeted way. Timbers affected by decay are reinstated with industrial  pre-treated  timbers and isolated from damp masonry.
By using an independent specialist damp and dry rot company like Damp Aid, to control & repair dry rot, you will have the added assurance that any specialist dry rot repairs to timber flooring such as floorboards, timber joists, sub-floor structural timbers, skirting boards & roof timbers  will not only be carried out correctly but will benefit from a long term guarantee for wood rotting timber decay.

Enquire about  the cost of a dry rot survey here

Differences between Dry and Wet Rot Fungal Decay

The vital difference between dry rot and wet rot is the amount of moisture needed within the timber to allow fungal growth to occur. The term dry rot would suggest no moisture, but in fact a minimum moisture content of about 20% is needed for dry rot to flourish and establish itself. It’s often found in hidden voids such as the underside of wooden floors, beneath stairs & roof trusses – as it likes warm, damp unventilated areas. Wet rot is limited to very damp wood or plaster with a moisture content of at least 50% and will remain confined to a damp area. The high moisture content required for wet rot is often a result of defective plumbing, gutters or downpipes. We offer correct diagnosis of any type of wood rot affecting a property, and will tailor a control solution to protect it from further damage.

All wood-rotting fungi require both food (wood or other cellulosic material) and water, and the dry rot fungus is no exception; deprived of either, it cannot survive.  Much of the mythology surrounding dry rot is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry areas and for the fungus to ‘manufacture’ its own water. In reality, the delicate hyphae are the primary colonisers and the ability to conduct water is limited and can be counteracted by good ventilation.

The process of timber decay itself produces water but in this respect dry rot is no different from any other wood-rotting fungus and, likewise, its ability to produce moisture in this manner can be counteracted by ventilation. Decay will cease if the moisture content of the wood is reduced to below about 20 per cent, and many extinct outbreaks of dry rot are discovered in old buildings where the fungus has died out as a result of this happening, probably following building maintenance which has eliminated a source of moisture.


Because of the total dependency of dry rot on moisture, the primary control strategy must be based on environmental considerations aiming to restore and maintain dry conditions.

A detailed dry rot survey should be carried out by qualified specialist dry rot surveyors to identify and locate sources of moisture ingress. Particular attention will be paid  during a dry rot survey to roof, floor timbers, and rainwater systems with emphasis on gutters and down pipes, parapet roofs and roof coverings. Rain penetration can also be through renderings and flashing’s or around windows and doors. Rising dampness through missing, bridged or otherwise defective damp-proof courses must be rectified. Any plumbing should also be inspected by dry rot experts for leaks.

Rapid drying should be promoted through the provision of sub-floor ventilation and heating which may also require specific building work to prevent moisture ingress and transfer, and to encourage aeration. Dehumidifiers can remove moisture from the air but their effectiveness in aiding drying of walls depends on the rate of evaporation from the wall surfaces.

In many cases drying will take a long time, often taking years, especially where some types of older buildings are affected. Therefore, secondary measures will often be required to prevent further damage by timber decay fungus before it is effectively arrested by the drying process.


Once a suspected dry rot outbreak has been correctly diagnosed in a property, it is necessary for dry rot experts to determine how far the dry rot has spread, dry rot companies can then provide accurate costs for any timber decay works. All woodwork and sub floor timber / under floor voids in the vicinity of any dry rot outbreaks should be inspected for signs of timber decay defects by qualified damp-proofing and timber decay surveyors (C.T.I.S. or C.S.R.T.) to assess the extent of timber decay and the current moisture content of the timber. Extensive removal of plaster is necessary only if it is suspected that timber is embedded in the walls and is at risk to timber decay.

Perfectly sound floor joists, wood beams / skirting boards, and floorboards can become nothing but a crumbling rotting mess once they’re infected by dry rot, and, as the spores spread quickly, it won’t take long before all the structural timber in your home comes under attack by fungal decay. A single outbreak of dry rot in a home can cost anywhere between £500 and £10,000 to remove, and thousands of pounds more in home dry rot repairs.

Spotting dry rot before it takes hold is half the battle – if caught early enough, you can save a fortune in dry rot timber decay repairs and take action to prevent it coming back for good. Wood rotting fungus that causes dry rot in wood prefers warm, damp, dark and Unventilated  places to grow such as poor ventilated sub-floor voids & roofing timbers in lofts. While it’s usually associated with old properties that are being renovated, it can also appear in modern homes too. Don’t rule dry rot out just because your property is newly built; if you notice any symptoms of rot in your home, it’s important to identify it and embark on a course of dry rot treatment to eliminate it without delay.  Find out what causes dry rot, how to identify it and get it treated quickly, and, most importantly, how to deal with dry rot in the long-term.


Removal of all timber affected by dry rot is destructive but necessary in principle. Retaining affected timber presents problems for the structural integrity of the building and falling debris can be a hazard to occupants and others if decay continues. Timber already below 20 per cent moisture content presents little risk of further decay.   Special building measures are necessary if timber is to be retained, including isolation from damp masonry by way of incorporating a damp proof membrane or using metal joist hangers etc.



Although the dry rot strands can travel across masonry, the dry rot fungus derives no nourishment from it. The concept of killing the fungus within masonry by wide-spread irrigation with a fungicide traditionally has provided a ‘comfort factor’, but it has to be questioned in each case whether this procedure can be justified. First, it is usually difficult to achieve a thorough treatment and, secondly, the treatments introduce large quantities of water which then needs to be removed, increasing the risk of damage to the masonry, as well as prolonging the time it takes to dry the structure.

The most important role of chemical dry rot treatments of the masonry is to prevent the fungus from obtaining access to a fresh food supply in the form of timber in adjacent areas, or replacement timbers being introduced into the area. For this purpose, localised chemical treatments of the masonry (cordon sanitaire) can create a useful barrier between the dry rot fungus on the wall and the wood.



Environmental Dry Rot Control 
S. lacrymans, like any other biological entity, needs a specific environment in which to live. Indeed the environmental requirements of S. lacrymans are rather specific. It needs wood with a moisture content around the fibre saturation point (i.e. when there is free moisture in the timber), it cannot survive mildly elevated temperatures (temperatures as low as 30oC have been reported as being lethal), it is sensitive to air movements and requires a relatively high humidity environment and seems to have an absolute requirement for certain metallic elements, the lack of which can effectively prevent it from decaying wood. If any of these requirements are not met the organism will not decay timber and therefore eradication of the organism should be a relatively easy task. Indeed specialist companies in the UK and abroad are now offering services to correct dry rot infestations which rely solely on environmental dry rot control; keeping moisture levels in wood low and increasing ventilation to both favour low moisture levels and prevent the build up of high humidity. By inserting remote sensing moisture meters into at-risk timbers, e.g. beneath valley gutters or at the beam ends or in wall plates, it is possible to keep a check on a building without the need for complex and expensive inspection procedures.

This type of strategy is relevant in many situations and could theoretically be used in every situation. However it requires perfect building maintenance, co-operative users and a check on any structural modifications. As such it would appear likely that there are situations where the efficacy of environmental dry rot control could not be guaranteed despite the obvious appropriateness of the strategy. On account of this additional controls are necessary and these may well include the use of chemicals.

Heat Treatment
It has been known for many years that the dry rot fungus is peculiarly sensitive to relatively small increases in temperature. This lack of thermo-tolerance, which is reported as a range of different lethal temperature/ period combinations (e.g. any time period between 1 and 6 hours at 40oC), has resulted in the use of whole building heat treatments to eradicate dry rot. Total killing of organisms has been shown in this system though it is only the mycelial form of the fungus which is inactivated, active spores still persist. However given an appropriate drying regime for a building these spores are unlikely to germinate and produce destructive mycelia and indeed there are no reported recurrences of dry rot in buildings which have been heat treated. This dry rot control system has so far only been used in Denmark though its applicability in buildings in other countries seems likely and should be tested.

It could be argued that environmental control alone is sufficient to kill the dry rot organism and that heat treatment is therefore unnecessary. Heat treatment ensures the organism is rapidly killed at the start of the control procedure and also that any further degradation which might occur during drying is prevented. Of course, as in the case of environmental control more effective building management practices will have to be installed in order to prevent recurrences of dry rot infestations. The failure to maintain rigorous building management practices as a follow-up to heat treatment remains a major concern in the long-term protection of buildings. Currently there is no effective alternative to the use of chemical preservatives in poorly managed buildings or in buildings where constructional properties render it difficult to ensure that wetting of timbers does not occur.

We are often asked – How much does dry rot specialist surveys & treatment cost / How much does it cost to treat dry rot & timber decay in my house?

Cost of treating dry rot & cost of dry rot control will vary with each individual outbreak of the dry rot fungus.  Firstly, a dry rot survey has to be carried out by a fully qualified C.S.R.T. specialist damp and timber surveyor to correctly identify the fungal decay and determine if it really is dry rot and not wet rot as it is so commonly misdiagnosed during dry rot control investigations by other dry rot repair companies who are inexperienced.

The extent and causes of the dry rot infection in a house has to be determined, as this timber decaying fungus can spread behind wall plaster and under floors without being noticed until it attacks another piece of timber, such as a skirting board in a house or door/window frame, elsewhere in the property.  The source of the dry rot outbreak also has to be determined by the specialist dry rot surveyor. during his inspection including lifting of floorboards to inspect under floor void areas  for dampness to the sub-site walls. It is therefore not possible to provide an average cost of treating & repairing dry rot without carrying out a detailed specialist dry rot survey.


Maintenance and monitoring of the conditions in buildings cannot be stressed enough.  Dry rot develops very slowly, so early detection and curing of moisture ingress will prevent timber decay occurring in the long term. Routine monitoring can be as simple as regular visual inspection to check the integrity of the building fabric against ingress of moisture.


• Wood shrinks, darkens and cracks in a ‘cuboidal’ manner
• A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops under less humid conditions. This ‘skin’ can be peeled like a mushroom.
• White, fluffy ‘cotton wool’ mycelium develops under humid conditions. ‘Teardrops’ may develop on the growth.
• Strands develop in the mycelium; these are brittle and dry and crack when bent.
• Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface has wide pores.
• Rust red coloured spore dust originating from the fruiting bodies. Commonly described by specialist dry rot treatment companies as looking like brick dust.
• Active decay produces a musty, damp odour.

As we have shown it is very important that the type and cause of the fungal decay are correctly identified before any corrective dry rot control action can be considered. It is for these reasons that it is important that a detailed diagnostic dry rot inspection is carried out by qualified dry rot treatment specialists & surveyors.This inspection should be followed by the submission of a timber decay & dry rot report that details both the cause of the decay and the proposed remedial action.

If you need to arrange a specialist dry rot survey, would like further information regarding timber decay, how to spot dry rot, controlling dry rot in a house / flat that you may be in the process of buying / selling which is showing signs of a suspected dry rot out break, call Damp Aid UK property care specialists to speak to a specialist timber decay surveyor who I’m sure will be able to help and discuss which inspection you require and cost of dry rot survey.

 Birmingham, Cheshire, ChesterWrexham, Lancashire, Liverpool, London, Manchester,
Merseyside, Middlesex, North Wales, Shropshire, South East England, West Midlands, Wirral
& Yorkshire