The document summarizes various types of biological and mechanical damage that can affect buildings over time. It discusses how fungi, insects, plants, animals, and environmental factors can deteriorate building materials when conditions are suitable. It also outlines different mechanical stresses like wear and tear from use, vibration, shocks, and thermal expansion/contraction that gradually break down structures. The key message is that proper design and maintenance are needed to prevent defects and extend building lifespan by mitigating destructive biological growth and movement stresses.

1. Building defects due to
biological agents and
mechanical damage
Shaken, stirred and eaten
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Agricultural
College

2. 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
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3. Fungi
• Fungi (moulds) are amongst the
most damaging biological agents in
buildings
• Fungal spores are present
everywhere in the atmosphere
• They require water, heat and food
• Buildings provide the warmth and
food, usually timber. If moisture is
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present, fungi will always grow Agricultural
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4. Types of fungi
• Black spot: not damaging but
disfiguring. Lives on damp surfaces
• Wet rot: a range of moulds which
grow in and digest wet timber
(moisture content over 20%)
– If the source of moisture is
removed, the mould will die off
• Dry rot: a mould which grows in
slightly damp, warm timber
(moisture less than 20%.
– Extremely damaging. The hyphae can
grow through solid brick walls and
carry water to dry locations.
– Infected areas will need sterilisation to Royal
Agricultural
remove the mould College

5. Invertebrates
• Insects can eat buildings
– Termites – only a tropical
problem, currently, but a big one
– Death watch beetle
– Most other wood boring insects
only live for a few weeks as adult
beetles but can live as wood
boring larvae for several years
– “Woodworm”, the larvae of a
range of insects
• Common furniture beetle
Masonry Bees
• Powder post beetle – notifiable
These don’t eat
• House longhorn beetle – notifiable
limestone, but they do
• Ambrosia beetle – Dutch elm
disease vector-doesn’t affect
bore into it for nesting.
buildings Rarely a serious Royal
problem Agricultural
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6. Damage by large animals
• Building foundations
can be undermined by
burrowing animals
• The species depends
on the location, in the
UK badgers are the
only significant one
• Problems usually occur
when a building is
constructed on an
existing badger sett. Royal
Agricultural
College

7. Plants can push buildings 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 for support
and protection. As they
grow, they force the
masonry units apart
– Virginia Creeper is not a
Royal
serious problem as it just Agricultural
clings to the surface College

8. Changing the environment
• Most building damage from
trees results from the water
content of the sub-soil being
changed 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
large tree can result in the If the sub soil is a
ground swelling because shrinkable clay, it will
water is no longer extracted contract as water is Royal
removed by transpiration Agricultural
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9. What is mechanical damage?
• Wear and tear
– Using a building wears it out. This is not a
defect, just a fact of life. Rapid wear is a
defect.
• Damage due to movement
– Buildings are essentially designed to stay still.
If they move, and they do, damage is likely
– Rapid repetitive movement – vibration
– Sudden movement – shock
– Slow, possibly repetitive movement – stress
and fatigue Royal
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10. Wear and tear
• Damage due to internal traffic.
– People walking over floors
– Rubbing against walls
• Damage due to other use.
– Repeated opening and shutting of doors and
windows, wears out ironmongery and can
damage walls
– Thermal cycling due to automatic central
heating
(heating/cooling = expanding/contracting)
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11. Internal Traffic damage 1
Stair treads wear
from foot traffic. It
is so slow as to be
undetectable, but
the damage
accumulates
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Agricultural
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12. Internal Traffic damage 2
Hospitals are notorious for suffering
traffic damage to walls and doors.
Walls can be designed to have smooth
edges, with reinforcements at points of
contact.
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Agricultural
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13. Vibration
damage
Repetitive vibration can
result from nearby
construction work,
traffic, industrial
activities
Vibration damage tends
to build up slowly,
which can make it
difficult to establish the
cause
Damage is various:
cracked walls, gaps
between floors and Royal
walls, spalling Agricultural
plasterwork College

14. Shock damage
Earthquake damage.
Masonry buildings
very prone to
earthquake damage.
Lincoln Cathedral was
demolished by an
Royal
earthquake prior to Agricultural
1200. College

15. Thermal stress
• Buildings expand and
contract with changes in
temperature.
• The interior of inhabited
buildings tend to be kept
at constant
temperature, the exterior
varies with the weather. Damage due to thermal
expansion on “short return
• Stress is set up between walls”
the interior and exterior Most damage can be controlled
elements where they are through use of movement
in contact. joints. Don’t try to stop
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movement, you can’t.
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College

16. Buildings do just wear out
eventually…
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The casings of the pyramids were removed by people,
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but the sphinx eroded through wind-blown sand