Building Pathology

Question 1

Name the six common groups of rot to affect timber in the UK

Answer 1

1) Brown Rot
2) White Rot
3) Soft Rot
4) Stains
5) Moulds
6) Plaster Fungi

Question 2

What are the main differences between brown rots and white rots?

Answer 2

Brown rots –
* Cuboidal cracking
* Becomes darker as a result of the attack
* Can cause severe timber decay and loss of strength quickly
* Crumbles between fingers
White rots –
* Fibrous consistency, similar to lint
* Becomes lighter in colour as a result of the attack – almost as though bleached.
* Cracking tends to be along grain.
* Generally has a higher moisture content.

Question 3

What is wet rot?

Answer 3

Coniophora Puteana – the decay of timbers exposed to high levels of moisture, often greater than 50%.
Can often be found in external timbers that are exposed, bath surrounds etc.
It is treated by fixing the source of the water and removing/replacing the affected timbers.

Question 4

What is dry rot?

Answer 4

Serpula Lacrymans – can be identified by a fruiting body, mycelium, orange/red dust (spores), cuboidal cracking etc.
More expensive to treat than wet rot as it can spread through a building, even through brick and mortar.
To treat remove the source of moisture and replace all timbers affected and those within a 1m radius and replace with pre-treated timbers.

Question 5

What are the four main types of dampness?

Answer 5

1. Rising
2. Penetrating – cracks to roughcast, external wall, leaking downpipe/gutter etc.
3. Condensation – identified by black mould growth
4. Leaking plumbing.

Question 6

Which areas would you typically test for dampness?

Answer 6

• Lower walls
• Chimney breasts
• Windows
• Beneath flashing/parapet and valley guttering
• Roof voids
• Adjacent walls to bathrooms/WCs

Question 7

What are the 4 main types of wood-boring infestation found in the UK?

Answer 7

1. Common Furniture Beetle – Softwoods, Round emergence holes 1-2mm, frass is cream colour.
2. Deathwatch Beetle – European hardwoods (usually only damp/decayed timber), round emergence holes 3mm, frass is brown colour.
3. House Longhorn Beetle – Softwoods (tends to only be found in London and home counties), emergence holes are 6-10mm and oval, often ragged, frass is cream colour.
4. Powderpost Beetle – Seasoned woods (Oak, Ash etc), emergence holes 1.5mm, frass is cream coloured and talc-like.

Question 8

What do you know about nail sickness?

Answer 8

It is the corrosion of the nails attaching the external roof covering to the timbers and is caused by moisture between the sarking and the covering. The slates and tiles become loose and slip. Depending on the extent of the nail sickness it may require full re-roofing or patch repairs.

Question 9

What is the lifespan of a flat roof?

Answer 9

Typically 10-20 years but I’m aware some firms now offering 25 year guarantees.

Question 10

Why are flat roofs problematic?

Answer 10

In Scotland, where the climate is relatively wet, it can lead to ponding of water which can then penetrate through any cracks. Other issues are insufficient run-offs, poor workmanship, vegetation growth, thermal movement etc.

Question 11

What issues can be caused by parapet/valley guttering?

Answer 11

Debris/vegetation and water can gather causing water ingress, particularly if the lead flashing/damp proof course is defective. This can lead to rot to internal timbers as a result.

Question 12

What does a Protimeter measure?

Answer 12

Wood moisture equivalent (dampness). It can be tested using the calcheck device supplied with the meter.

Question 13

What is wood moisture equivalent?

Answer 13

This is the moisture level in any building material as if it were in close contact and in any moisture equilibrium with wood expressed as a % moisture content in wood. Any reading above 20% in any material is hazardous and should be investigated.
It is calculated by (Wet weight – Dry weight)/ Dry weight x 100% moisture content

Question 14

What are the moisture content levels for different materials?

Answer 14

4% 12%
Wood Extremely Dry Air Dry
Mortar Dry -
Brick Damp Saturated
Plaster Very Wet Not Possible

Question 15

What moisture content % can lead to rot?

Answer 15

The figures most commonly referred to are in the 20-22% range for dry rot, anything above can lead to wet rot.

Question 16

What is the difference between an inherent defect and a latent defect?

Answer 16

An inherent defect is a defect in the design or material that has always been present.
A latent defect is a fault to the property that could have not been discovered by a reasonably thorough inspection of the property.

Question 17

What can cause heave?

Answer 17

The removal of a nearby tree may cause heave. The water that would have normally been absorbed by the tree saturates the subsoil/clay causing it to expand and push agains the foundations of the property, and can cause structural damage as a result.

Question 18

What would horizontal cracking in the brick outer-leaf of a dwelling possibly indicate?

Answer 18

Possible wall tie failure, usually from mortar dropping on the wall ties during construction/renovation works. The mortar creates a bridge where moisture can travel causing the wall tie to corrode and expand, resulting in the cracking.
The cracks usually occur at ever fourth or fifth course.

Question 19

What can cause cracking to a lintel only?

Answer 19

Possibly due to different materials e.g. an older timber lintel that has been affected by timber pest/rot or a concrete lintel affected by carbonisation.

Question 20

What is bossed roughcast? How is it identified?

Answer 20

It is when the roughcast has detached from the external wall. It can be tested using the end of a screwdriver or metal object by tapping or running the screwdriver across the roughcast. If defective it will sound hollow.

Question 21

What causes frost damage?

Answer 21

Excessive moisture in walls, which are susceptible to freezing temperatures. The moisture freezes and expands causing the surface of the wall to spall.

Question 22

Have you come across rising damp?

Answer 22

Yes in a ground floor tenement flat. The moisture meter readings were higher at the base of the wall and gradually got lower as you went higher. Rising damp usually comes up to 1.5m.

Question 23

What common defects would you expect to find in a Victorian tenement flat?

Answer 23

 Rising damp at lower wall levels.
 Erosion/weathering of stonework to walls, chimneys and skews.
 Slipped/chipped/missing roof slates/tiles.
 Weathering to single glazed units.
 Defective mastic around glazed units.
 Dated wiring/fusebox.
 Structural movement.
 Corrosion/defective rainwater fittings
 Etc.

Question 24

What common defects are associated with non-traditional construction?

Answer 24

Concrete construction
* Carbonisation of concrete which results in the reinforcing steel to rust. This is a greater issue in PRC (Precast Reinforced Concrete).
* Poor thermal performance, can lead to issues like condensation.
Steel Frame Construction
* Corrosion to steel frame.
* Thermal issues again.
Timber Framed Construction
* Moisture and consequent timber decay.
* Insulated cavities can cause issues with moisture also.
* Differential movement between timber frame and brickwork.

Question 25

Give some typical signs of structural movement in a property?

Answer 25

Externally: Distortion to the main walls, cracking affecting the walls greater than 5mm, off level/cracked lintels and sills.
Internally: Cracking in room corners, ‘ruffling’ of wallpaper in corners, run/slope of floor, canted doorways

Question 26

What is the difference between settlement and structural movement?

Answer 26

Settlement: The downward movement of the ground, or any structure on it, which is due to the load applied to the structure.

Subsidence: The vertical and downward movement of the ground which is not caused by the imposition of the building and/or financial loads i.e. loss of support from the sub-soil. The two main causes are trees and defective drains. Other causes are mining and made ground e.g. landfill.

Question 27

How could you identify if a crack is recent?

Answer 27

It may feel sharp when you run your hand along as it has not been blunted by weathering. Older cracks tend to be darker and dirty.

Question 28

What are the typical defects of a flat roof? What are the remedies?

Answer 28

Crazing –
Surface crazing is caused where there is a lack of adequate protection from the harmful effects of exposure to the sun or, in rare occasions, chemical attack. If this is only in small localised patches no treatment is necessary but should be regularly rechecked. If more widespread the areas will have to be re roofed and specialist protection introduced.

Blistering –
Blisters can be caused by water vapour pressure occurring below the roof covering. The blister should be cut and then re bonded to the underlay allowing any trapped moisture to escape first. The source of the moisture should also be traced and rectified.

Question 29

What other sorts of cracks would you expect to see on a brick building and what might have caused them?

Answer 29

Subsidence –
A movement down in the ground level. In clay soil, the growth of large trees which remove water from the ground can cause this. This can lead to vertical cracking if in the centre of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the top and thinner at the boo vertical cracking at the bottom.
Heave –
A movement upwards in the ground level. In the clay soil the removal of a tree will lead to an increase in the moisture content of the soil which will cause the soil to swell. This leads to vertical cracking if in the centre of the building or diagonal cracking if at the corner of the property. The cracks will be larger at the bottom and thinner at the top.
Settlement –
A movement down due to an increased load. Buildings will settle when first constructed or if there is a change in the load as the new load settles to the bearing capacity of the soil.

Question 30

What is Damp?

Answer 30

A building is only considered to be damp if the moisture becomes visible through discoloration and staining of finishes or causes mould growth, sulphate attack, frost damage or even drips and puddles.

Question 31

How can you test for damp?

Answer 31

The use of a protimeter moisture meter or a speedy carbide meter can be used to establish the moisture content of walls, and the level of damp occurring.

Question 32

How would you identify rising damp? What are the causes? How would you remedy it?

Answer 32

Identification –
Inn high tide mark, peeling and blistering of wall finishes, musty smell, rotting of timber, hyproscopic salts. Use of a moisture meter, the readings with moisture meter results in high surface readings, often with slight decline, finishing with sudden cut off.
Causes –
No damp proof course, DPC bridged by pointing, render, soil, paving, mortar droppings, affected both solid and suspended floors.
Remedy –
Remedy DPC problems, remove bridging of DPC, chemical injected DPC.

Question 33

What type of soil is susceptible to heave and what are the possible causes?

Answer 33

Cohesive soils such as clay. Possible causes include removal of trees, change in water table, leakig drains or inadequate foundations that are built within the movement zones.

Question 34

What are the common defects associated with flat roofs?

Answer 34

Common defects associated with flat roofs include blistering and splitting of covering, sagging (due to failure of decking between joists), ponding (due to insufficient falls), damage to flashings, inadequate solar protection.

Question 35

What should you take into account when deciding whether to repair or replace a flat roof?

Answer 35

Its age and life expectancy, the overall condition i.e. are the defects localised or affecting the whole roof, what type of defect is it and does it relate to a localised factor or is it an issue with the whole roof, are they affecting the surface layer or the roof structure. Clients intentions for the building, their budget, the building use, disruption caused and possible phasing required?
Age / condition / extent of defect / cost / use / life cycle costing / disruption associated with repair and replacement.

Question 36

How long would you leave brick/plaster to dry out before commencing work?

Answer 36

Minimum 3-4 months.

Question 37

How would you tell the difference between rising damp and condensation with a moisture meter?

Answer 37

Rising damp is damp that comes up from the ground and only extends up to 1m up the wall. Therefore if you take readings at 300mm centres going up the wall from the bottom and it is damp at the bottom and becomes increasingly less damp as you go up the wall to the point where it is not damp above the 1m mark then it suggest rising damp.
Condensation would cause uniform dampness and is most often found at high level in corners where the hot air has risen and then condensed on the cold surface in a poorly ventilated corner or the room. Condensation has distinctive mildew which forms black spots.

Question 38

You are inspecting a building and identify a number of cracks in the external wall take me through your thought process?

Answer 38

I would firstly note the material the wall is constructed from and what form of construction the building is. If there are any local factors which could be causing the cracking such as trees or stumps, if there have been any alterations to the building, of there are drains in the vincinity of the crack. If there have been any alterations to the building such as extensions, room in the roof or internal layout alterations.

Question 39

What other sorts of cracks would you expect to see on a brick building and what caused them?

Answer 39

Subsidence- A movement down in the ground level. In clay soil, the growth of large trees which remove water from the ground can cause this. This can lead to vertical cracking if in the centre of the building or diagonal if at the corner. Cracks will be larger at the top and thinner and the bottom.

Heave- A movement upwards in the ground level. In clay soil the removal of a tree will lead to an increase I moisture content in the soil which will cause the soil to swell. The cracks will be larger at the bottom and thinner at the top.

Settlement- A movement down due to an increased load. Buildings will settle when first constructed or if there is a change in the load as the new load settles to the bearing capacity of the soil.

Differential Settlement- if two sections of a building are constructed off different foundations or ground is made up of different soils , one may settle more than the other causing cracking between the two sections of the building.

Thermal movement- Either expansion or shrinkage of the masonry, is often characterised by vertical cracks with a relatively constant width if appropriate expansion joints are not present.

Lintel Failure- Lintel failure allows a triangular section of brickwork above the window to drop down creating a triangular crack from corner of the window towards the centre.
Corroded steel lintel- Where a steel lintel has been used above an opening and the edge is exposed or close to the surface this can corrode over time and expand causing cracking.

Cavity wall tie failure- Corrosion of large steel fishtail ties will lead to cracking every 4 to 5 courses as the steel expands.

Internal Alterations- Where a wall has been removed and a steel beam put in its place without consideration to the increased load acting upon the wall the beam is bearing on. Or where a stair case has been moved without thought to the lateral restraint of the flank wall.

Question 40

What size of cracks raise concern?

Answer 40

Up to 2mm – Very slight / Aesthetic
2-5mm – Slightly / Aesthetic
5-15mm – Moderate / serviceable
15-25mm – Severe / serviceable
Over 25mm – Very severe / stability

Question 41

What types of timber defects are there?

Answer 41

The main timber defects are dry rot and wet rot, insect attack

Question 42

Describe the different types of rot and how you would recognise them?

Answer 42

Dry Rot — Wood shrinks and splits into large cuboidal cracking, the wood is light in weight,
crumbles under fingers and has a dull brown colour, cotton wool type mycelium is often visible
greyish in colour when wet and yellow/purple when dry, strands are brittle when dry, a fruiting body
can also occur with a reddish brown colour, only incurs inside of buildings.

Wet Rot — Wood shrinks and splits on a smaller scale, wood becomes darkened, mycelium can
be white, brown, amber, green or black, strands are flexible when dry, the fruiting bodies can be a
number of different colours can occur both inside and outside.

Question 43

What are the remedial measures to dry/wet rot?

Answer 43

Locate and eliminate the sources of moisture, promote rapid drying, remove rotted wood
(450mm beyond last indications of rot and burn), surface application of fungicidal fluid,
introduce support measures if required.

Question 44

Explain the life cycle of a rot?

Answer 44

The 4 main dry rot lifecycle stages are as follows:
1. Spore: Spores are omnipresent. In very large numbers dry rot spores appear as a fine orange
brown dust. The spore are activated when combined with timber and moisture.
2. Hyphae: Where timber and moisture are present the spore will produces very fine white strands
called hyphae, which allow the dry rot fungus to grow by feeding on the timber. Thereby
breaking down the structure of the timber while it grows to form a mycelium
3. Mycelium: The resulting hyphae mass is known as mycelium. Mycelium has the ability to grow
over a significant distance and a variety of materials, which allows an outbreak to progressively
destroy the structural timbers of an entire building if left undetected.
4. Fruiting Body: To perpetuate itself the fungus will create a fruiting body (sporophore). This
mushroom-like forms function is to pump out spores into the atmosphere that can be transferred
by air currents to other susceptible areas within the building allowing them to germinate and create
a new attack of dry rot, thus bringing us back to the beginning of the dry rot lifecycle.

Question 45

How do you identify the presence of woodworm?

Answer 45

Holes in the wooden item, with live infestations showing powder (faeces) around the holes. The
size of the holes varies, but are typically 1nnnn to 1.5mm in diameter for the most common
household species. Adult beetles which emerged from the wood may also be found in the
summer months.

Question 46

How do woodworms affect timber in buildings?

Answer 46

Typically the adult beetles lay eggs on, or just under the surface of, a wooden item. The resulting
grubs then feed on the wooden item causing both structural and cosmetic damage, before
pupating and hatching as beetles which then breed, lay eggs, and repeat the process causing
further damage.

Question 47

What is a woodworm infestation likely to indicate?

Answer 47

Most species of woodworm require that the wooden item contain a higher moisture content than is
normally found in wooden items in a typical home. A building with a woodworm problem in the
structure or furniture probably/possibly also has a problem with excess damp.

Question 48

How is a woodworm infestation treated?

Answer 48

Woodworm infestation is generally controlled with chemical insecticides. However, it is also
advisable to investigate and solve possible damp issues, as dry wood is not usually affected, and
wood that remains damp may be re-infected at a later date.

Question 49

Deflected timber floor in early 19th century building. What methods are available to deal with
this if the client requires a level floor?

Answer 49

Confirm the cause of the deflection, notching, rot, insufficiently sized joists, insufficient centres,
overloading, deterioration of sleeper walls etc. Confirm if issue can be remedied and timber floor
retained. Potential to supplement the timber joists, potential to overboarded, potential to remove and
replace with suspended timber floor or alternative solid floor.

Question 50

Name the three types of asbestos and examples of where they are found in buildings.

Answer 50

Chrysotile - the most common form of asbestos found in buildings. The most common use is
within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages.

Amosite - is found most frequently as a fire retardant in thermal insulation products and ceiling tiles.

Crocidolite - Spray on insulation, pipe lagging, loose fill insulation, gaskets and cement sheeting.

Question 51

You find a leak at high level on a first floor of a 2 storey building constructed with
traditional cavity wall construction. Please outline the process which you would go
through in assessing the cause for the defect. Also, what are the potential causes of
such a defect?

Answer 51

I would review any existing building information available before inspecting the property. I
would look at the building as a whole to get an understanding of its construction, and the
materials used, assess whether there had been any alterations to the building.
I would inspect the leak and talk to the building owner/user. I would look at the extent of the
leak and the damage caused and ask questions relating to the history of the leak. When did it
occur does it happen all of the time or just on occasions is it affected by the whether? I would then assess whether there were any external elements that could be the cause and then any internal elements that could be the cause. My first thought would be a roof leak so I would
assess the roof both externally and internally for signs of defective or missing roof covering, defective or missing flashings around roof penetrations etc. Then when in the roof space I would look for evidence of leaking pipes.

Question 52

How does cavity wall tie failure present itself? How would you fix it?

Answer 52

IDENTIFICATION — Horizontal cracking in every 5 or so brick course or in render. It’s the corrosion of old steel ties such as large fishtail. The corrosion increases the steel up to 4 times leading to the cracking.

REMEDY — use boroscope to determine the defect is wall tie failure. Locate wall ties and isolate or removed to ensure no further damage. Install replacement stainless steel mechanical fixed ties secured with an epoxy resin if required

Question 53

What is Japanese knotweed?

Answer 53

Japanese knotweed is a large, herbaceous perennial plant.

Question 54

What does Japanese Knotweed look like?

Answer 54

Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo. While
stems may reach a maximum height of 3-4 m each growing season, it is typical to see much smaller plants in
places where they sprout through cracks in the pavement or are repeatedly cut down. The leaves are broad oval.
The flowers are small, cream or white.

Question 55

Why is Japanese Knotweed an issue?

Answer 55

It forms thick, dense colonies that completely crowd out any other herbaceous species. Its can extend 7 metres
(23 ft) horizontally and 3 metres (9.8 ft) deep, making removal by excavation extremely difficult. The plant is also
resilient to cutting, vigorously re-sprouting from the roots. The most effective method of control is by herbicide
application close to the flowering stage in late summer or autumn. In some cases it is possible to eradicate
Japanese knotweed in one growing season using only herbicides. In 2010 over £150m was spent annually on Japanese knotweed control

Question 56

Why is Japanese Knotweed particularly an issue for buildings and construction sites?

Answer 56

It is listed by the World Conservation Union as one of the world’s 100 worst invasive species. The invasive
root system and strong growth can damage to foundations and structures. There are legal restrictions on its
removal and disposal. Cutting it down will just cause it to spread around the site therefore to irradiate it from
a site may take several attempts with herbicide injections which is time consuming or dig up the extensive
root system and dispose of all of the soil in licensed landfill sites which would be a costly process.

Question 57

What legal restrictions are there in dealing with it?

Answer 57

In the UK, it is an offence under section 14(2) of the Wildlife and Countryside act 1981 to “plant or otherwise
cause to grow in the wild” Japanese knotweed. It was made illegal to spread Japanese knotweed in the UK
by the Wildlife and Countryside Act 1981. It is also classed as “controlled waste” in Britain under part 2 of
the Environmental Protection Act 1990. This requires disposal at licensed landfill sites.

Question 58

How should it be dealt with?

Answer 58

It should be injected with a suitable herbicide at the correct time in their growth cycle or
excavated along with their extensive root system and disposed of in a licensed landfill site.

Question 59

What is Deleterious Materials?

Answer 59

Typically classed as materials that;
- Are harmful to health
Are harmful to safety
Are harmful to the environment
Are not suitable for their intended purpose; or,
Pose a risk where they have been used.

Question 60

What are some Hazardous Materials

Answer 60

 Asbestos
 CFC’s (Chlorofluorocarbons) (think air conditioning refrigerants)
 HCFC’s (R22. Banned from January 2015)
 Crystalline Silica (Found in building materials. Dust can result in silicosis (lung
disease)).
 Formaldehyde (Carcinogenic material used in foam and timber-based
building materials)
 Lead (used in roofing, waterpipes and paint) (Carcinogenic and teratogenic)
 Machine Made Mineral Fibres (MMMF) (Respiratory issues)
Continuous filament (glass wool)
Insulation (rock wool or slag wool)
Ceramic Fibre
Special purpose fibre