Despite the adoption of modern materials, timber remains a critical structural component in many buildings. From lintels to window frames, timber components are still lauded for their insulative properties as well as their structural robustness.
However, London’s ageing property stock, risks associated with flooding, and damp environments make fungal decay a serious concern for any building where a lot of timber materials are used. For commercial landlords and property managers, early and correct identification of rot prevents costly structural repairs.
In this blog, we’ll discuss the two types of fungal decay, wet rot and dry rot, how to identify them, and what you can do to protect or repair your property after an outbreak.
Why is Fungal Decay a Major Risk in Commercial Buildings?
Fungal decay is an ever-present risk for any building. Both wet rot and dry rot spores are considered omni-present. That means that it’s difficult to completely remove them from any environment, meaning that any small changes in your property’s moisture content could promote future fungal growth.
Depending on the type of fungal decay, it may respond differently depending on what type of defect is feeding it. For example, wet rot requires a consistent source of moisture to feed it, but its spread will be limited to this moisture source. Conversely, dry rot often only needs an initial amount of moisture to germinate, and will then spread over masonry and plaster to reach new sources of moisture.
More dangerous is the fact that many structural timbers in roofs, floors, and basements are hidden. Floorboards often have decorative flooring laid over them, and basements and roof voids are concealed spaces only accessible through small hatches or trapdoors. If you’re less likely to use a space, it’s more likely that fungal decay can take hold without you even realising it’s there.
As with any property care concern, deferring maintenance, especially in larger buildings or a portfolio of properties, can significantly increase the cost of repair and treatment. Significant outbreaks of fungal decay can also damage a person’s health as well as a building’s structural integrity, leading to business closures or temporary tenancy moves if a property manager is find to have ignored any concerns with fungal decay.
What Is Wet Rot?
Wet rot is the natural decay of timber due to the increased presence of moisture. Wet rot is a general term used to describe several different species that exhibit the same behaviours. One such example is Cellar Fungus (Coniophora puteana), a type of wet rot that occurs in cooler environments such as basements or roof voids. Regardless of species, each wet rot fungus breaks down damp timber and feed on the nutrients within, reducing the wood’s structural strength as it feeds.
Causes of Wet Rot
Wet Rot often germinates due to persistent moisture exposure, such as a plumbing leak or a roof defect causing penetrating damp into a property. It is also associated with areas of poor ventilation, which prevent the moisture from evaporating as quickly and escaping the room. Instead, the moisture remains in or on the surface of the timbers, promoting the growth of the fungus.
Common Signs of Wet Rot
Wet Rot has some telltale symptoms, including:
- Darkened timber
- Crumbling or softened wood
- A musty smell
- Localised timber decay on moist timbers.
What Is Dry Rot?
Dry Rot is used to describe a specific strain of fungal decay (Serpula Lacrymans). Contrary to its name, it often begins germinating in initially damp wood. However, it is a resistant organism, able to grow even across masonry or behind plaster in search of new moisture sources. It is also possible for dry rot to spread from already infected material.
Causes of Dry Rot
Dry Rot often germinates from an initial source of moisture. A combination of poor ventilation and increased moisture allows the fungus to settle in damp wood, germinating quickly and feeding on the wood. Once established, dry rot fungus will often grow cotton-like hyphae that spread underneath floorboards or behind plaster in search of new moisture sources.
Signs of Dry Rot
Dry Rot also has some telltale symptoms, including:
-
- Cracked or cuboidal decay in timber
- Grey or white fungal growth (hyphae or mycelium)
- Orange/red spore dust from fungal body (sporophore)
- Rapid spread across timber, masonry, or plaster
Wet Rot vs Dry Rot: Key Differences
Both wet rot and dry rot are commonly misdiagnosed for the other, as they often both appear, at least initially, in similar damp conditions. We’ve provided a table below to help illustrate the differences between both kinds of fungal outbreak, but you may also wish to check out our companion blog, Identifying the Differences Between Wet Rot and Dry Rot, for more information on correctly diagnosing fungal decay in your property.
|
Feature |
Wet Rot | Dry Rot |
|
Moisture Requirement |
Requires a constant moisture source |
Can spread once established |
|
Spread |
Localised |
Unrestricted |
|
Structural Risk |
Moderate |
Severe |
|
Typical Location |
Roof timbers, window frames |
Floorboards, door frames, hidden structural timbers |
| Treatment Complexity | Usually localised repair, sometimes replacement in severe cases |
Often requires extensive treatment |
Where is Rot Most Likely to Occur in Commercial Buildings?
Fungal Decay occurs in areas with a certain level of moisture (usually between 15-20% in timber). Roof voids, basement structures, floor joists, window frames, and structural timbers are all likely to develop rot issues provided enough moisture exists around them.
In London properties, the most likely culprit of rot forming is flooding. Groundwater flooding from rapid urbanisation or river flooding from the Thames both contribute an increased moisture level into ground-level timbers, especially floorboards. Below-ground structures such as basements or cellars are equally at risk.
Condensation is also a significant risk factor, especially in ageing Victorian and industrial buildings. As the way we heat buildings has changed, the previous methods of ventilating an older building have changed along with it. Older buildings often lack manual or passive ventilation such as extraction fans or wall vents, allowing fungal spores to settle and germinate in ideal conditions.
How Can Rot Affect Commercial Property Value and Compliance?
The prevalence of a rot issue causes a significant compliance risk, as well as reducing the value of any assets found to be harbouring a fungal infestation.
Both wet and dry rot can reduce the integrity of structural timbers, rendering them weakened or, in severe cases, capable of full collapse. Leaving structural timbers to rot increases the risk of further structural damage, as well as risking the health and safety of any tenants or employees inhabiting the building.
Failure to disclose a rot issue can also result in the cancellation of insurance, or the increase of insurance premiums for both buildings and contents insurance.
Early treatment of rot issues is also essential to reduce the disruption to commercial operations. Leaving a rot issue to worsen not only increases the risk of having to close a business for treatment, the costs of treatment also escalate the longer a rot issue is left to spread or worsen. For example, rot treatment with fungicidal solution is more cost-effective than having to repair or replace an extensive area of structural timbers.
Prevention Strategies for Commercial Landlords and Property Managers
As with all property maintenance cases, prevention of an issue far outweighs the costs of curing an established concern. Here are a few things you can do to prevent a rot issue from becoming more severe, or preventing a rot issue from germinating to begin with.
Control Moisture Sources
Your property should always be maintained in a watertight condition. You should ensure your roofing and guttering are checked periodically for slipped or missing tiles, and ensure that any blockages are cleared to reduce the likelihood of penetrating damp within the roof void.
At ground level, you should address any signs of rising damp, such as moist internal plaster, tide marks on walls, or sagging timber floors.
If your property develops a leak, either from a plumbing fault or an external defect, this should be fixed promptly to ensure that rot does not have a consistent water source to feed from and germinate.
Improve Building Ventilation
Once any leaks are repaired, you should next consider the air flow within your building. Moist, stale air is a likely contributor of fungal decay, and so controlling how moist air escapes your home will help prevent the onset of a fungal outbreak.
Your roof void and basement should both include passive ventilation such as air bricks or wall vents. This will allow any moist air to circulate and escape.
In areas of high humidity, such as wet rooms or those with plants or fish tanks, additional measures such as mechanical ventilation fans should be installed to control the humidity within a room. Newer hydrostatic fans will detect when moisture in a room reaches a certain level and turn on automatically to remove this moisture.
Conduct Regular Timber Inspections
Make it a habit to check your properties periodically for decay, especially in older London buildings. Older timbers do not carry the same treatments as modern timbers, and so carry a greater risk of developing rot concerns than modern timbers.
Having your property assessed annually is usually enough to identify any rot concerns before they spread. However, you should assess any high-risk areas such as cellars, basements, or roofs more frequently, especially if you’ve had a history of rot issues. You should also conduct checks during refurbishments or tenancy changes, as unreported leaks and accidental damage during redevelopment can result in an increase in damp forming.
Commission Specialist Timber Surveys
Professional surveys identify hidden decay early. Services such as these will require access to all areas of a property, and may require the removal and reinstatement of sections of decorative flooring or fixtures to ensure a thorough survey can be conducted.
You can request a survey to have one of Timberwise’s expert surveyors attend your property and provide an assessment of its condition and any required remedial work.
Commercial Timber Maintenance Checklist
If you are a property manager, you should check the following areas in your annual property checks:
- Roof leaks, either from slipped or missing tiles or damaged flashing
- Blocked guttering or downpipes
- Poor ventilation in roof spaces or wet rooms
- Dampness in basements or cellars
- Signs of fungal growth or cuboid cracking in timbers
- Timber warping, especially in ceiling or floorboards
When to Call a Specialist Timber Surveyor
You should contact a specialist timber surveyor whenever you suspect a property of having a damp or condensation-related issue. Here are some of the signs that your property requires professional investigation:
- Structural cracking near timber supports, in floorboards, or roof joists
- Musty odours in enclosed areas
- Visible fungal growth on decorative or structural timbers
- Repeated or serious exposure to flooding events
- Recurrent damp issues
Protecting London’s Commercial Buildings from Timber Decay
The age of London’s commercial properties, their increased risk of groundwater or river flooding, and the increase in damp retention from inadequate ventilation all make fungal decay a serious concern for any property manager in the capital.
Proactive inspections will identify any issues before they become serious structural repairs, reducing the risks of deep-seated fungal decay and its spread.
Early intervention is often more cost-effective than large-scale remedial work, reducing the closure time of affected businesses or tenancies, and protecting the health of any occupants within the property.
If you suspect your property to be at risk of fungal decay, speak to a Timberwise Specialist about rot treatment.
FAQs
What is the Difference Between Wet Rot and Dry Rot in Commercial Buildings?
Wet rot and dry rot are both forms of fungal timber decay caused by excess moisture. Wet rot usually affects timber exposed to persistent damp conditions and tends to remain localised. Dry rot is more destructive, as it can spread beyond the original moisture source and travel through masonry to attack additional structural timber.
Is Dry Rot More Serious than Wet Rot in Commercial Properties?
Yes. Dry rot is generally considered more serious because it spreads rapidly and can affect hidden structural timbers such as floor joists and roof supports. If left untreated, dry rot can compromise the structural stability of a commercial building and require extensive repairs.
What Causes Timber Rot in Commercial Buildings?
Timber rot typically develops when timber is exposed to prolonged moisture. In commercial buildings this may result from roof leaks, plumbing defects, poor ventilation, rising damp, flooding, or condensation in poorly ventilated spaces such as basements or roof voids.
Where is Timber Rot Most Likely to Occur in Commercial Buildings?
Timber rot is commonly found in areas where moisture accumulates. These include roof timbers, timber floor joists, basements, window frames, plant rooms, and concealed structural timbers in older commercial buildings.
How Can Property Managers Prevent Wet Rot and Dry Rot?
Preventing timber rot requires effective moisture management. Property managers should ensure roofs and gutters are maintained, repair leaks promptly, improve ventilation in enclosed spaces, and arrange periodic timber inspections to identify early signs of decay.
How Quickly Can Dry Rot Spread in a Building?
Dry rot can spread rapidly once established, particularly in poorly ventilated and damp conditions. The fungus can travel through masonry and plaster in search of additional timber, which is why early identification and professional treatment are essential.
Do Commercial Buildings Require Specialist Rot Surveys?
Yes. A specialist timber or structural survey can identify hidden fungal decay, determine the cause of the moisture problem, and recommend appropriate remedial works. These surveys are particularly valuable for older commercial properties or buildings that have experienced flooding or persistent damp.
