Damp in Commercial Property
Damp is incredibly common among the commercial properties we survey. Our commercial building surveyors provide detailed diagnoses of the causes of damp, as well as advice and estimated costs for remedial works to prevent it recurring.
All building types and materials will deteriorate to some extent over time. Water ingress and damp are an almost inevitable consequence of this deterioration.
Understanding the causes of damp is crucial to effectively maintaining a commercial property. Being aware of potential water penetration points can guide appropriate repairs to prevent water ingress and associated damp issues.
It is also important to understand that, depending on the building and construction type, a certain level of moisture is inevitable and acceptable. Knowing how to manage moisture flow in and out of a building, and how to run and maintain the property to prevent damage from that moisture, will keep a commercial property functioning safely and effectively.
The age and construction type of the building should also be taken into account. Whereas a modern brick or portal frame building will have a damp proof course and use materials that prevent water penetration, such measures are inappropriate for an older building. This is because the materials used to build such properties were designed to manage damp by allowing moisture to circulate in and out. Blocking moisture circulation with modern, non-breathable materials can trap water within the walls of a period property, resulting in damp and damage.
Risk Factors for Damp
When carrying out a condition survey or pre-acquisition survey, surveyors look for signs of damp both inside and outside the property. Externally, damage to masonry, mortar, cladding and roofing are obvious entry points for moisture; often, corresponding internal areas of the property will have visible damp, mould, water staining or high moisture meter readings. Likewise, absence of, or breaches of, a damp-proof course (DPC) are often evident externally, with corresponding damage seen inside the property.
Building surveyors will also be assessing whether a building, or an area of a building, is at higher than average risk of damp. Commercial properties that are at high risk of damp include those that are exposed, such as those in rural or coastal areas. Buildings or elevations facing the prevailing wind can be at higher risk, as can those in valleys or wind tunnels, because they are vulnerable to wind-driven water. Properties with spaces below ground level are particularly vulnerable to damp if appropriate tanking has not been carried out.
The quality of the external envelope of the building is critical to resisting water entry. Key aspects include:
- The pitch of the roof.
- Flat roofs are most vulnerable to water ingress, particularly if the falls are inadequate, or flashing is insufficient or damaged.
- Shallow pitch roofs also put a property at high risk, particularly when combined with inadequate gutter falls, resulting in water backing up between the roof and the wall.
- The age of the roof.
- Some commercial roofing materials have a fairly limited lifespan.
- For example, asbestos sheeting, which was commonly used in the 60s and 70s, has an expected lifespan of 35 years. This means that most examples of asbestos roofing are now beyond their life expectancy and starting to substantially degrade and even fail.
- Some commercial roofing materials have a fairly limited lifespan.
- Absence of window sills.
- Poor quality window fittings.
- Ramps up to entrance doors.
- Building on sloping ground.
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Signs of damp
Damp can affect buildings in various ways, and the construction of the building plays a big part in how damp will manifest.
Externally
With warehouses, modern office blocks and industrial units, damp will usually show up externally as water staining, delamination and corrosion to metal finishes. Algae and plant growth highlights areas where water has been able to collect, indicating poor drainage and a risk of internal damp. Roofing that is older than its expected lifespan will show obvious areas of deterioration where water may be able to leak into the property.
Typically, many retail and hospitality properties are within older buildings, built using traditional construction methods. In these cases, water staining to brickwork is usually visible in areas of damp, and we frequently see cracking, deteriorated or missing mortar, cracks, damage to render, and algae growth. On a standard pitched roof, we would be looking for missing, damaged or slipped tiles, which could result in water leaks.
Rainwater goods are crucial areas for inspection in any building. Water staining around and underneath pipework and guttering indicates that the drainage is insufficient. Similarly, blockages, breakages and misalignment of rainwater goods all provide opportunities for water ingress.
Internally
In moderate to severe cases, damp is easy to identify internally. Mould growth occurs and is obvious visually and by the musty smell it creates. Water staining and damage to flooring and paint finishes are common, as are damaged plaster and rotting woodwork.
Suspended ceiling tiles are common in commercial buildings and quickly appear soiled if damp is present.
In roof voids, inspection of the insulation will reveal areas of discolouration. The insulation itself may be wet if there has been recent rainfall. Timbers may also show signs of rotting and degradation. Active woodworm can also be a sign of damp, as moist conditions support the survival of the beetles and their larvae.
A moisture meter is an important tool in assessing damp internally. It may identify widespread damp; alternatively damp can be localised to specific areas, indicating areas of poor pointing externally, cold spots or areas where cavity wall insulation has been bridged.
Causes of Damp in Commercial Properties
The causes of damp are numerous and varied. The main sources can be grouped into several categories.
Firstly, poor design and workmanship can set up a building for damp even without any deterioriation; for example, if drainage is insufficient or inappropriate, the DPC is absent or too low, appropriate tanking has not been carried out, or the building design breaches the DPC.
Secondly, external deterioration provides entry points for damp. This could include damage to the roof structure, whether that is tiles, metal, concrete or asbestos sheeting, or felt and bitumen. Damage to mortar joints, brick and stonework, and metal corrosion can also provide entry points for moisture.
Thirdly, a lack of maintenance can exacerbate problems arising through normal wear and tear. Failing to remove vegetation can lead to moisture being held against a structure, leading to damp and further damage. Failure to repair render and damaged mortar compounds the problem.
Lastly, the use of the building can affect levels of damp. Inadequate heating and ventilation and result in a build up of condensation, particularly if the building is being heavily used. This can result in deterioration of internal fixtures and finishes, as well as mould growth.
Here are some of the causes we come across most frequently when surveying commercial buildings such as schools, shops, warehouses, pubs and office buildings:
- Failed seals between constructions elements, such as between metal frames and brickwork.
- Poorly fitted or damaged window frames.
- Damage to render creating entry points for moisture.
- Damaged roofs, perished areas of bitumen, damaged or distorted flashing.
- Poorly designed roofs with insufficient pitch or falls are also an issue.
- Perished stonework.
- Perished mortar joints or failures around chimney flashing.
- Render connections to the ground creating a path for water to rise up and breach the DPC.
- Vegetation growth holding moisture against a structure.
- DPC too low, so that driving rain can breach it; or ground level raised above a low DPC.
- In some cases, the DPC is completely absent.
- Drainage not carrying water away from the structure, resulting in pooling water on flat roofs, or at ground level next to a wall.
- Drainage blockages and leaks resulting in water backing up towards the structure.
- Cavity being bridged.
- Inadequate heating and ventilation.
- Absence of adequate tanking where internal levels go below external ground level.
Remedial works for damp
Understanding the degree of damp and where it is coming from is imperative when determining the remedial works that are needed. These can range from small repair jobs to entire roof replacements costing tens of thousands, so getting an assessment before purchasing or leasing a property is crucial for enabling you to budget accurately and decide if the property is worth the lease or purchase price.
If a building has been well maintained, remedial works are often fairly straightforward, and can include re-pointing areas of damaged mortar, repairing damaged areas of render, clearing out gutters and replacing missing roof tiles.
In cases where a commercial property has been neglected, repairs can run into tens or even hundreds of thousands. Roof failure requiring complete replacement is one of the most costly requirements we come across. Similarly, tanking basement areas and carrying out underground drainage repairs can be costly.
It can also be challenging to determine who is responsible for the remedial works when dealing with a leased property.
If a tenant is on a full repairing and insuring (FRI) lease, then they will be liable for the costs of repairs.
When a tenancy is based on an internal repairing insuring (IRI) lease, the situation can be more complex. If the source of the damp is internal, such as down to a leaking wash basin, the tenant is liable. However, if the source of the damp is external, it can be difficult to know where to draw the repair line. It can be argued that the landlord is responsible for external remedial works, and the tenant for internal redecoration, but often these cases are not clear cut.
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