Dampness
Dampness in a building is one of the more common defects picked up by surveyors during Home Survey Reports. It can result in unforeseen cost, time and aggravation.
To categorise where dampness comes from, we can consider three locations:
- From ‘Inside the house’ – This could include condensation and plumbing leaks.
- From ‘Outside the house’ – Most commonly, this involves rainwater; either windblown rain, penetrating rain, or concentrated rainwater from gutter/downpipe leaks.
- From ‘Below the house’ – Possibly from inadequate ground drainage or defective/bridged damp proof courses.
If a surveyor does identify dampness in a property, it is important that they ‘follow the trail’ and give a professional, informed opinion as to what is causing the dampness. Unfortunately, in today’s litigious society, many surveyors are happy to defer the matter to a commercial damp company. Of course, it could be argued that commercial damp proofing companies have a vested interest in carrying out damp proofing works. This may lead to homeowners spending money on unnecessary or over complex repairs without the real cause of the dampness having been properly assessed by an independent Chartered Surveyor. As well as being costly, many of these ‘repairs’ can be damaging to the fabric of a building – particularly historical properties. It is therefore very important to firstly establish exactly where the dampness is coming from so that an informed decision on remedial works can be made. It is my opinion that surveyors should not defer the matter without having first given an opinion on the likely cause – they are the professional and you are paying them for their expertise.
Dampness from ‘Inside’
Apart from in extremely dry and arid environments, the air around us always carries a degree of moisture. The warmer the air temperature is, the more moisture it can hold. Cold air is unable carry the same amount of moisture. Therefore, when warm air suddenly meets a cold surface, the moisture is given up as condensation.
The temperature at which moisture in the air condenses is known as the ‘dew point’.
Increased levels of insulation, coupled with reductions in the levels of ventilation, does not always sit well with some older types of property.
With an ever increasing need to be more energy efficient, our homes have had to keep pace with hermetically sealed windows and increasing the levels of insulation within the floors, walls, and roof spaces. These improvements to insulation, coupled with reduced ventilation and modern central heating systems, means that the average air temperature in the home has increased from 12C in 1970 to 17.7C today (source: BRE). Although well-meaning, these improvements do not always sit well with some older types of property.
A surprisingly large amount of moisture is produced within our homes from normal activities such as cooking, washing/drying clothes and simply just breathing. The warmer air temperatures created by increases in insulation means that more of this moisture can be held in the air. However, unless it is safely vented to an external point, the warm moist air could come into contact with cold internal surfaces in the home. In these areas it will condense and, over time, localised damp staining, sometimes with accompanying mould growth will occur.
Typical locations where condensation can occur within the household include:
- Roof voids with high levels of insulation above the ceiling joists but limited ventilation (or possibly where the existing soffit vents have been inadvertently blocked by insulation).
- Bathrooms that have no ventilation or perhaps where the owners have switched off mechanical extract vents due to noise issues from overrun timers.
- Around windows where cold bridging has occurred due to poor design or workmanship.
- To the inner face of cavity walls that have been retrospectively filled with insulation. The insulation can slump or there may be empty pockets resulting in variable temperatures which are vulnerable to condensation.
Many owners of Listed buildings will appreciate that these older properties tend to be much draughtier than more modern homes. This is not, however, such a bad thing as draughts from gaps around windows or from open fire fireplaces also provide a level of ventilation which is missing in many of today’s more modern buildings. The materials adopted in these older buildings also tend to help when it comes to condensation. Lime based renders and mortars are naturally porous and breathable. They have the ability to absorb moisture when relative moisture level in the air are high but can also release moisture back into the air when the relative humidity level drop – in effect they act as a natural ‘sink’. Furthermore, the alkalinity of lime can help prevent mould growth by killing spores that may dwell on the surface.
Dampness from ‘Outside’ (Penetrating Dampness)
From a practical point of view, penetrating dampness from the outside can be the easiest type of defect to diagnose. It tends to occur during periods of heavy driving rainfall and the associated damp staining is usually obvious as it visibly expands during the period that it is raining. Therefore, the next time it rains, take the opportunity to walk around the outside of your home to assess the condition of the rainwater gutters and downpipes together with any gullies or hopper heads which may be overflowing from blockage.
Penetrating Dampness – Leaking gutters and downpipes
Internally, carry out an inspection around the perimeter of windows and doors where leakage between the framework and the masonry reveals maybe occurring. If you are able, enter the roof void and look for signs of staining to the rafters or moisture damage to the underfelt. Pay particular attention to the underside of vulnerable locations such as valley gutters.
Look around the external perimeter of the property to ensure that ground levels have not increased over time to a point where they may be ‘bridging’ the damp proof course. Similarly, check that external hardscaping works such as patios and block paviours have not been laid at height closer than 2 brick courses to the damp proof course level.
Penetrating Dampness – Bridging of damp proof course – soil build-up
Most traditional building materials such as stone, brick, timber, or lime mortar tend to have a degree of porosity or breathability. This varies with the specific material but their ability to absorb a certain degree of moisture during wet conditions means that they act as a natural ‘sink’, similar to the lime render mentioned above. They are then able to safely dissipate the moisture back into the air just as readily during a period of drier conditions. The thickness of the external wall also means that, by the time inclement weather conditions have passed and the drying process has begun, the moisture will not have reached the internal surfaces.
Modern surface finishes to external walls such as cement renders do not rely on breathability, but rather their inherent permeability to prevent rainwater penetration. Unfortunately, cement render is prone to shrinkage and therefore cracking. The cracks allow rainwater to track behind the render where it becomes ‘trapped’. Over a period of time, this build-up of ‘trapped’ moisture leads to saturation of the structure and internal penetrating dampness. A detailed inspection of any cement-based render to identify cracks is therefore a critical aspect of property maintenance.
Dampness from ‘Below’
A huge industry has grown out of the dreaded term ‘rising damp’. Many damp proof contractors are more than willing to carry out damaging remedial works involving chemical damp proof injections whilst mortgage lenders insist on the work being carried out simply because a ‘guarantee’ will be provided. A damp proof contractor (or surveyor) who is worth his salt will be able take a step back, assess the situation from a practical point of view, and look instead at the two main causes of dampness to walls at low level. These being, high external ground levels (compared to the internal finished floor levels), and excessively wet grounds around the perimeter of the property, possibly caused by high water tables or leaking gutters. Removing the sources of the moisture, either by lowering external ground levels, inserting perimeter ground drainage, or fixing leaky rainwater goods is a much easier and effective way of dealing with the dampness. Forming barriers does not address the root cause of the problem no matter how impressively worded a guarantee might be.
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David Cosby Chartered Surveyors & Estate Agents
