Damp and Mould growth in tenanted properties
In our experience, the most common claim made by a tenant is for dampness and mould growth.
Tenants, not unlike most people, don't want to spend money heating a house, whilst seeing that same money disappear out of a window to aid ventilation and reduce condensation and mould growth.
Every day the
average household puts about 12 to 15 litres of moisture into the internal
environment through normal domestic activities and just breathing.
Warm, moist air is
mobile and will permeate throughout the internal space of a dwelling, resulting
in condensation in contact with colder areas. This can be seen on colder
surfaces through thermal (cold) bridging on corners of external walls and lintels.
In poorly ventilated dwellings condensation will invariably lead to the growth of mould. Landlords can't make tenants leave the windows open and consequently mould growth tends to be inevitable; but it can be reduced.
Typically in a tenanted house, the most common areas where mould growth is found are:
1) The bathroom due to high levels of moisture
2) On the internal face of the external walls on the first floor typically close to the ceiling where the walls are likely the coldest.
3) On the first floor ceiling close to the external walls, again due to temperature differentials
4) Behind furniture due to low levels of ventialtion
Moulds can be
described as simple fungi (Fungi imperfecti) and are often referred to as micro-fungi.
They have the ability to adapt almost immediately to their prevailing
environment and are associated with damp conditions in buildings, predominantly
caused by condensation.
growth can occur if the relative humidity remains above 70% but, for
active growth, prolonged spells of over 80% relative humidity are
generally necessary or continued access to direct moisture supply within
the material upon which they will form. The spores of fungi are
ever-present in the air in most buildings and so are nutrients; thus,
the factor controlling growth is this supply of moisture.
The moulds can cause
severe disfigurement and damage to surfaces, fittings and fabrics. Prolonged
exposure to mould growth can cause disintegration and disruption to some paint
films. Paper and certain fibre building
fabrics may also be softened and deteriorate as some mould species are capable
of digesting cellulose.
There have been approximately
one hundred species of micro-fungi detected in dwelling houses. The species
most commonly encountered are Penicillium, Cladosporium, Mucor and Aspergillus. It is this high number of species that
gives a wide range of colours in mould growth from black, green, grey, white,
yellow to pink.
There can be an
unpleasant “musty” odour associated with the presence of mould and there have
been health concerns with regard to the micro-fungi. In the past these concerns
have tended to be confined to susceptible individuals such as the young or
those suffering from asthma or with other respiratory problems.
and ground floor flats and bungalows
Old properties and
ground floor flats and bungalows can be more susceptible to mould growth due to
the following reasons:
Many older houses have an earth sub-floor, which can be
affected by ground water penetration, this causes a damp sub-floor environment,
which in turn can affect the levels of moisture internally.
penetrating damp due to the lack of effective damp-proof courses and/or solid
walls with no cavity to resist the transmission of damp from the outer face of
the wall to the inner face.
flats and bungalows
The unwillingness of
the occupants to vent the building by leaving windows open due to the fear of
burglary or intruders.
Advice on the
prevention of mould growth in the UK
The following are
methods of reducing mould growth and the visual effects of the same:
1. The best emulsion paint to use is that designed
for bathrooms, as it usually has an anti-fungicidal ingredient.
2. Ventilate the property regularly, even if this
means losing heat. Unless one purges the
property of the moisture produced by general living activities, condensation
and mould growth will occur.
3. If mould does occur, clean the surface with an
anti-fungicidal wash or mild bleach solution.
4. Do not use un-vented driers.
5. Do not use paraffin or other un-vented
hydrocarbon fuelled heaters.
6. If one dries clothes internally, vent the room
in which they are dried.
7. For ground floor flats and bungalows, leave
windows on night vent as much as possible when the property is occupied.
8. Install a humidistat fan in the bathroom
Most mould problems
we have found in the UK are simply down to not enough ventilation. The cost of heating
a building has risen dramatically in the last few years. Consequently few people wish to see the heat
they have paid for disappearing out of an open window. Sadly this increases the build up of moisture
and increases the likelihood of mould growth.
Rising damp is caused due to ground
moisture filling the pore structure of the walls. Usually the height it can reach is around one
metre, although we have experienced it slightly higher than this. Modern buildings have a p.v.c. layer
(damp-proof course) built into the walls to prevent this phenomenon.
Older houses (built before 1920) often have
no damp-proof course and are therefore very prone to rising damp. After 1920 it is common to see bituminous
damp-proof courses (sometimes Hessian based).
This type of damp-proof course can deteriorate over the years and become
By the 1960’s p.v.c. damp-proof courses
were used and these tend not to deteriorate and usually perform adequately.
Remedial damp-proof courses
Injection and electro osmosis damp-proof
courses started being installed in the 1970’s. An injection damp-proof course is based on
filling the pore structure of the brick with a water repellent fluid. Problems can arise because: If a property has rising damp the pore
structure of the brick is usually already filled with water. Hence the system relies on the belief that
the low pressure injection system will displace the moisture from the brick and
replace it with a water repellent fluid.
Our experience of injection and
electro-osmosis damp-proof courses suggests that they are rarely effective and
usually rely on the water-proof render coating applied to the walls to prevent
dampness coming through to the internal wall surface.
In addition in respect of both injection
and electro osmosis damp-proof courses, we have found that the guarantees
offered, are often of dubious value.
Penetrating damp is usually caused by:
Ø The lack of cavity (solid walls)
Ø Leaking gutters and rainwater pipes
Ø The lack of a damp-proof course in a chimney stack where it exits the roof
Ø Bridging of a cavity by debris or the walls of a flue.
Ø Wind blown rain entering via gaps in the structure or being forced back under tiles or slates.
Methods of reducing rising and penetrating damp
The following notes give information one ways to reduce rising damp, and/or the effects of the same.
The best form of protection against rising damp is to install an in-situ damp-proof course. This is when the brickwork is cut out and p.v.c. is inserted to form a waterproof layer. This is a very expensive and time consuming process and rarely ever carried out.
As an alternative an injection or electro osmosis damp-proof course can be installed. An injection damp-proof course is based on filling the pore structure of the brick with a water repellent fluid.Problems can arise because: If a property has rising damp the pore structure of the brick is usually already filled with water. Hence the system relies on the belief that the low pressure injection system will displace the moisture from the brick and replace it with a water repellent fluid. Our experience suggests that this form of damp-proof course is rarely fully effective and usually relies on the water-proof render coating applied to the walls to prevent dampness coming through to the internal wall surface.
In respect of both injection and electro osmosis damp-proof courses, we have found that the guarantees offered are often of dubious value. If one intends to install such a damp-proof course it would be prudent to have it independently tested before settling the invoice.
One method of reducing the effects of rising damp which in essence means reducing the levels of dampness present on the internal surface of the wall, is to ‘Sika’ render the internal surfaces of the walls to a height of one metre. This is a water repellent internal render coating.
Another method of prevent damage to plasterwork is to coat the walls (after the existing plaster has been removed) with a heavy-duty urethane or water-proofing compound such as ‘Cellarcote’. These are water-proof coatings that prevent damage to plaster, however the coating should be poly-bonded prior to re-plastering to ensure good adhesion of the plaster to the water-proof membrane.
Alternatively one can dry-line the walls. This is when a visqueen membrane is placed against the wall and timber battens and plasterboard are used to form a new wall surface. The timber battens should be pre-treated against rot and decay.
In respect of chimney breasts it should be noted that unless one uses the flues as they were intended (to vent solid fuel fires), penetrating dampness tends to be difficult to eradicate completely. One can reduce the chimney-stack below roof level (in the case of shared stacks you will need the permission of the owners of the adjacent premises) and use a purpose made gas-ventilating cowl to vent any gas fires if such are required. Other methods of reducing dampness centre around overhauling the flashings, re-pointing the masonry, and treating the masonry with a water repellent fluid.
A considerable amount of water is used during construction for the mixing of mortar, concrete and plaster and such like.
For brickwork alone, as much as one tonne of water may be used in building the average house. Some of this constructional water is immobilized in the hydration of cement and plaster, and some evaporates before occupation of the building.
In any event a lot of water used for mixing purposes will still be retained and can be slow to dry. Not a lot can be done about this moisture, though good ventilation and the judicious use of heating in the first year will assist drying.
An average house, with masonry walls, is likely to contain several tonnes of water just after completion. At least a year is likely to elapse after occupation before the moisture level drops to that in equilibrium with normal internal humidity conditions.