Biological Defects on the Buildings

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21 May 2021 - 10:59, by , in Waterproofing, No comments

Why is biology a problem

• Many building materials have great attraction to living organisms

– As food

– As shelter

• Some organisms just push buildings out of their way

• Some organisms change the environment that a building exists in


• Fungi (moulds) are amongst the most damaging biological agents in buildings

• Funga.I spores are present everywhere in the atmosphere

• They require water, heat and food

• Buildings provide the warmth and food, usually timber. If moisture is present, fungi will always grow

Types of fungi

• Black spot: not damaging but disfiguring. Lives on damp surfaces

• Wet rot: a range of 1moulds which grow in and digest wet ti1mber (1moisture content over 20°/o) – If the source of moisture is removed, the mould will die off

• Dry rot a mould which grows in slightly da1mp, wanm timber (1moisture lless than 20°/o.

– Extremely damaging. The hyphae can grow through solid brick walls and carry water to dry locations.

– Inf ected areas will need sterilisation to remove the mould

Changing the environment

• Most building da1mage from trees results from the water content of the sub-soil being clhanged by the tree

• If a tree grows near a building it can dry out and shrink the clay under the building, causing it to subside.

• Conversely , removing a Ilarge tree can resullt in the ground swelling because water is no longer extracted

Pllants can push builldings over

• Slow growing plants can exert huge, destructive pressure on buildings

– Trees : the roots can push into foundations, under floors, into cellars and into drainage pipes

– Ivy:the stems grows into cracks in walls f or support and protection. As they grow, they f orce the masonry units apart

– Virginia Cre·eper is not a serious problem as it just clings to the surf ace


• Insects can eat buildings

– Termites – only a tropical problem, currently, but a big one Death watch beetie Most other wood boring insects only live for a few weeks as adult beetles but can live as wood boring larvae f or several years

– “Woodworm”, the Iarvae of a range of insects • Common furniture beetle • Powder post beetle – notifiable· • House longhorn beetle – notifiable • Ambrosia beetle· – Dutch elm disease vector-doesn’t affect buildings

Masonry Bees These don’t eat limestone, but they do bore into it for nesting. Rarely a serious problem

There are several types of biological growth on buildings:

  • Trees and Shrubs
  • Ivy and Creepers
  • Lichens
  • Mosses
  • Fungi
  • Algae
  • Slime Moulds
  • Bacteria
  • General Issues

Trees and Shrubs

Damage may be caused by trees and larger shrubs in various ways, including root action on walls, foundations, pavings, monuments and below-ground drains; trunk and branch contact with walls and roofs; blockage of rainwater disposal systems by leaf fall; and shading of surfaces. The genus Buddleia, which includes deciduous, semi-evergreen or evergreen shrubs or trees, requires fertile, well-drained soil. Growth is often seen at high level, such as chimneys and gutters, or where there is saturation of defective masonry.

A proactive management regime may include felling, topping, lopping and/or selective pruning, subject to legislative protection. Removal of trees may result in the volumetric expansion of shrinkable soils (heave) and changes to sub-surface water levels. Where shrubs and trees have established themselves in built structures, such as in walls of buildings , it is essential that root systems and woody growth are dealt with thoroughly, preferably by removing them, as re-growth and compressible decay may result in damage. However, localised chemical treatment of root systems may be an acceptable alternative if extensive dismantling is to be avoided.

Certain flowering plants such as Wallflowers (Cheiranthus) may be retained on the basis that shallow root action is accepted relative to enhanced aesthetic value.


This genus of evergreen, woody-stemmed trailing perennials and self-clinging climbers with adventitious rootlets prefers well-drained, alkaline soils, and species such as common English ivy (H helix) are commonly found on buildings and monuments.

Aerial roots and woody growth can penetrate open joints causing displacement of bricks or stones, while with broken walling there is risk of the facing material being forced from the backing or core. Suckers and tendrils can damage surface features and leave a pattern of marks upon removal.

Rainwater goods may become blocked and extensive growth can force gutters and other fixtures from the wall. The shading effect of extensive growth may also reduce moisture evaporation from wall surfaces.

Mature ivy and creeper growth may be treated by cutting a section out from the main stem(s) and allowing the plant to die back naturally over a period of time. The parent stem(s) should also be treated using an appropriate chemical paste or crystal product.

Physical removal of established growth can cause displacement and detachment of building fabric (such as flint facings). Woody growth and root systems, which may have penetrated into walling, must be removed as noted above. Use of sprayed chemical defoliants is often precluded due to the presence of agricultural crops or water course, together with health and safety issues associated with spray drift.

Where decorative growth is to be retained on a wall it can be carefully isolated and reinstated on a system of trellising or support wires. Spacers should be used to maintain an air gap between wall surface and growth, and the plant pruned or trimmed away from eaves, gutters, and openings.


Lichens are a symbiotic association of photosynthetic micro-organisms held in a mass of fungal hyphae, with growth in various shrublike (fruticose), leaf-like (foliose) or encrusting (crustose) forms. The photosynthetic partners are typically unicellular or filamentous green algae or cyanobacteria. The fungus usually gives the lichen its overall shape and structure, with the algae or cyanobacteria present just below the lichen surface. In such a symbiotic relationship, the algae provide carbon compounds, the cyanobacteria fix nitrogen and provide organic nitrogen, and the fungi provide a suitable environment for growth. The hyphae retain moisture and minerals, and the fungi secrete acids that aid the uptake of minerals.

The presence of lichen on roof coverings and wall surfaces often has aesthetic appeal and can contribute to the appearance of the building or monument. Growth can, however, cause deterioration of sheet metals (such as copper and lead flashings and roof coverings) and other inorganic materials, and assist in the colonisation of surfaces by mosses, and other plants. Inscriptions on headstones and monuments may also become unreadable.

Management of lichens, where acceptable, can be achieved on small areas by physical removal. Chemical control using appropriate biocidal products may also be appropriate, but generally they should only be considered in exceptional circumstances. There may be a presumption in favour of retaining established lichen growth on surfaces during repair or maintenance works (such as re­ painting open and/or defective joints), and advice should be sought on identification and suitable action from the diocesan ecological adviser or local wildlife organisation.

Essential reading on the treatment of lichens includes Control of Lichens, Moulds and Similar Growths (BRE, 1992) and Control of Biological Growths on Stone (BRE, 1995). The Norwich diocese has a policy for conserving stonework plants during work to churches (Norwich DAC, 1996).


Mosses are an example of a non-vascular plant (Bryophytes), which, unlike larger plants, do not have vascular tissue to transport water and nutrients. Other non-vascular plants include liverworts and hornworts. Mosses are particularly common and widespread, with the wetland genus Sphagnum forming deposits of partially decayed organic matter commonly known as peat. Mosses are typically green and photosynthetic when young, turning brown or red-brown when ready to release spores.

Like lichens, mosses can contribute to the overall character and appearance of historic fabric. Their presence on porous materials such as roofing tiles can, however, result in frost-related damage and large growths can restrict moisture evaporation. Deposition of mosses may also block rainwater disposal systems.

Mosses may be successfully managed by physical removal on small areas and/or controlled by application of appropriate biocidal products.


Fungi (heterotrophs) cannot make their own food as plants and algae can, nor can they ingest food. Instead they digest their food while still in the environment by secreting enzymes that break down molecules into smaller compounds that may be absorbed. Species may live as decomposers (saprobes), parasites and symbionts, with saprobic fungi breaking down and absorbing nutrients from non-living organic material.

Fungi associated with timber decay in buildings may be divided into brown rots and white rots. Brown rots, such as Dry Rot (Serpula lacrymans) and Cellar Fungus (Coniophora puteana), destroy cellulose and cause darkening of the decayed timber, while white rots, including Oak Rot (Donkioporia expansa), digest cellulose and lignin that results in lightening of the decayed timber.

Moulds, which appear as a coloured mass of spores and pigmented hyphae, are an imperfect form of higher fungi. These feed on free sugars on the timber or on surface deposits, and produce powdery spores that may constitute a health hazard. Essential reading on the identification and treatment of fungi, which is beyond the scope of this article, includes Recognising Wood Rot and Insect Damage in Buildings (Bravery, Berry, Carey & Cooper, 3rd ed, 2003) and Timber Decay in Buildings: The Conservation Approach to Treatment (Ridout, 2000).


Algae are ‘protists’, a photosynthetic, plantlike organism that is not a plant, animal or fungus. Most protists are unicellular, although some are colonial or multicellular.

The largest and most complex algae are brown (phaeophytes) and red (rhodophytes) algae, which include many species commonly known as seaweeds. Green algae are closely related to land plants and are divided into two main groups – chlorophytes and charophyceans. Chlorophytes may live symbiotically with fungi as lichens. Treatment includes eliminating sources of excess moisture and removing surface growths.


While initially considered as fungi using fruiting bodies to disperse spores, slime moulds (mycetozoans) are now considered in the Amoebozoa group of species and identified either as plasmodial or cellular slime moulds with distinguishing life cycles. Slime moulds consume bacteria within affected timber and become visible on the surface when producing fruiting bodies. Treatment includes eliminating sources of excess moisture and removing surface growths.


Cyanobacteria are the only prokaryotes with plant-like, oxygen-generating photosynthesis. They occur in abundance where there is water. Metabolic co-operation in some prokaryotic species may occur in surface-coating colonies (biofilms).Treatment includes eliminating sources of excess moisture and removing surface growths.


Biological growth can enhance the appearance and character of buildings and structural monuments, but certain species can cause direct and indirect damage to materials and elements of construction. Managing such growth requires consideration of various factors and an assessment of risk that balances actual and potential damage against ecological and aesthetic benefits. Legislative protection may restrict or remove treatment options.

The key to avoiding damage, while retaining a level of external vegetation, lies in planned preventive maintenance, particularly with regard to rainwater disposal systems and proactive trimming or pruning or plant growth. Internally, where biological and microbiological growths typically indicate past or present problems of excess moisture, treatment must be carried out with an appreciation of environmental factors (temperature, humidity, health hazards) and the likely effects of growth and removal on often sensitive surface layers and materials (including wall paintings and funerary monuments).

The effects of climate change need also to be considered in the longer term, particularly in relation to environmental conditions (such as increased relative humidity), plant growth patterns, soil moisture content, and the performance of existing rainwater disposal systems. For further information, see Climate Change and the Historic Environment (Cassar, 2005).

Useful guidance on flora and fauna in relation to buildings is available in Wildlife and Buildings: Technical Guidance for Architects, Builders, Building Managers and Others (National Trust, 2001). For a wider coverage of plant forms and ecology, see Biology(Campbell and Reece, 7th ed, 2005), which has been used in writing this article.

Dampness Penetration Through Walls

Dampness penetration through walls can be a serious matter, particularly to buildings located near water sources. Not only does it deteriorate building structures but also damages to furnishings. The main cause of dampness is water entering a building through different routes. Water penetration occurs commonly through walls exposed to prevailing wet wind or rain. With the existence of gravity, water may penetrate through capillaries or cracks between mortar joints, and bricks or blocks before building up trap moisture behind hard renders. Water may also drive further up the wall to emerge at a higher level. Dampness also occurs in walls due to other factors such as leaking gutters or downpipes, defective drains, burst plumbing and condensation due to inadequate ventilation. Dampness may also enter a building from the ground through cracks or mortar joints in the foundation walls.

Insect or Termite Attacks

Timber can deteriorate easily if left exposed to water penetration, high moisture content and loading beyond its capacity. Insect or termite attacks pose a threat to damp and digestible timber found in wall plates, the feet of rafters, bearing ends of beams and trusses, as well as in timbers which are placed against or built into damp walling. It is unwise to ignore timber that is lined with insect or termite holes because they may in time soften the timber and form further cracks. Affected timber can be treated by pressure-spraying with insecticide or fumigant insecticidal processes.

Defective Rainwater Goods

Problems associated with the defective rainwater goods include sagging or missing eaves, gutters, corroded or broken downpipes, and leaking rainwater heads. Other problems include undersized gutters or downpipes which cause an overflow of water during heavy rain, and improper disposal of water at ground level. Due to inadequate painting, iron rainwater goods can rust and fracture. Lack of proper wall fixings, particularly by projecting lead ears or lugs can cause instability to the downpipes. If routine building inspections and maintenance have been neglected, rainwater goods can be easily exposed to all sorts of defects.

Decayed Floorboards

Widely used in many heritage buildings including churches, schools, residences and railway stations, some timber floorboards have been subjected to surface abuses and subsequently deteriorated: leading to structural and public safety problems. The main causes are pest attacks, careless lifting of weakened boards by occupants, electricians or plumbers; lack of natural preservatives ; and corroded nails.

Defective Plastered Renderings

Defective plastered rendering occurs mostly on the external walls, columns and ceiling. In a humid tropical climate like Malaysia, defective renderings are normally caused by biological attacks arising from penetrating rain, evaporation, condensation, air pollution, dehydration and thermal stress. Other causes may be the mould or harmful growth, insects, animals and traffic vibration. Prior to being decomposed and broken apart, renderings may crack due to either shrinkage or movement in the substrate.




The following factors contribute to moisture in buildings

Penetrating Damp
Building Disaster( fire and flood) Construction moisture
Building Defects

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