Building Pathology

Question 1

What typical building defects might you expect to see on a Victorian residential property?

Answer 1

Damp:

• • Penetrating
    Roof leaks (no underfelt), gutter leaks, low capacity Ogee guttering, degraded mortar pointing
• Rising
  Raised external ground levels, poor rainwater surface drainage, buried cracked pipes
• Condensation
  No ventilation provision, poor thermal performance, building not designed for modern washing/living/occupancy, subfloor vents covered
  -Salts in chimney columns, unlined flues, damp buildup without chimney vents

Structural:
- Cracking from ground movement (clay / effect of trees), corbelled brick foundations, partial cellars/basements, different foundation construction,
- Roof spread / original slates changed to heavier concrete/clay tiles
- Lack of wall restraint, bowing/bulging
- Spine wall or rear additions of different foundations to rest of house, differential settlement/movement

• Degraded timber rafters/joists/bressumers, sagging brickwork/windows sticking etc

Services:
- Lead water pipes, old VIR electric cables failing, old buried gas pipes corroding

Timber:
- Rot of various types, sagging/deflection, wood boring insects
- Joists built straight into masonry walls (damp/rot)

Other:
- Nail fatigue, slipped slates, asbestos wall lining and tiles

Question 2

How would you identify condensation in a property?

Answer 2

Look for surface water droplets, use moisture meter in pin/search modes, use hygrometer, check for blown plaster/flaking paint, look for mould.

Question 3

If a property was suffering from dry rot, what might you expect to see?

Answer 3

Orange spore dust, white mycelium, white hyphae strands, fruiting bodies.
Affected timber – light brown colour, very dry, cuboidal cracking, easily friable, loss of strength, likes sapwood rather than heartwood, may pass through masonry walls

Question 4

Are there any limitations with the use of a damp meter?

Answer 4

Yes – only measures electrical conductivity, can give false readings if metal present (lathes, foil etc).

Calibrated for timber only, other materials have different values at which they could be considered “damp”.

Must be calibrated by user, must be used properly, only useful in physically accessible locations.

Question 5

Where a property is suffering from subsidence, what type of cracking might you expect to see?

Answer 5

• Diagonal stepped cracking through mortar joints
• Generally tapered, wider at the top
• Can follow weaknesses in wall, ie. door and window openings

Question 6

What is a deleterious material?

Answer 6

Materials that are:
- dangerous to human health
- cause failure in buildings
- could be environmentally damaging.
May work fine, until in certain conditions

Question 7

What are the problems associated with high alumina cement?

Answer 7

HAC – used in marine applications and to develop concrete strength rapidly, particularly in 1950s – 70s.

However, loses strength over time, and vulnerable to chemical attack in the presence of water

Question 8

What is carbonation?

Answer 8

CO2 in the air reacting with the concrete to form calcium carbonate AND reacts with water to form “carbonic acid”, gradually carbon “front” moves through concrete and reacts with concrete close to steel reinforcement. Reaction lowers alkalinity which protects steel along with the “passive layer”, which then rusts/expands/corrodes/pops concrete off. Moisture
worsens it. At least 50mm coverage needed (post WWII buildings had poor coverage or concrete).

Question 9

Explain the testing procedure when testing for concrete carbonation

Answer 9

In-situ or lab testing – apply a pH indicator (spray phenolphthalein), high pH = pink (good!),
lower pH = clear (bad)

Question 10

Explain how you would test a masonry wall for the possible presence of damp

Answer 10

Visual inspection:
- Staining
- Mould
- Flaking paint
- Salt deposits/crystals
Tap it – listen, blown plaster?
Conductance meter – check readings both in search and pin mode.
Could use thermal infra-red camera, although may not be conclusive. Can show up penetrating damp during tests though.

Question 11

How else could you test for damp conditions in a wall?

Answer 11

Speedy carbide test – for understanding accurate moisture content in non-timber.
- Take physical sample of material, weigh it
- Add to sealed cannister with calcium carbide, specific measure of it
- Shake, chemical reaction given off. Gas accumulates in cannister.
- Gauge reads off amount of gas that corresponds with moisture content

Question 12

When investigating structural cracking to brickwork in residential/low rise property what recognised standards would you refer to assist in classifying the cracking?

Answer 12

BRE 251 – Assessing cracks in houses (0 to 5)

Question 13

When investigating structural cracking to brickwork caused by adjacent trees what recognised standards would you refer to assist in assessing the risk posed by the trees present?

Answer 13

BRE Digest 240 / 241 – “Low-rise buildings on shrinkable clay soils: part 1 / 2”

BRE Digest 298 – “Low-rise building foundations: the influence of trees in clay soils”
BRE Digest 412 – “Desiccation in clay soils”

BRE – “Subsidence damage to domestic buildings: a guide to good technical practice (FB 13)”

All the above available on NBS
NHBC has a raft of further information sources (inc. the digests above)

Question 14

Tell me about the subsidence in the Victorian Terrace in Hackney.

Question 15

What is the RICS “joint position statement” on damp?

Answer 15

“Investigation of moisture and its effects on traditional buildings: principles and competencies”. Created by RICS and several other stakeholders, (Historic England, PCA, amongst others).
Details best practice guidance on investigating moisture issues in traditional buildings.

Question 16

Can you describe how you would take moisture the readings for a full room?

Answer 16

Use conductance meter in pin and search modes, use add-on tools for difficult-to-reach places. Systematically take readings, plot results on plan, take photos of readings, concentrate on areas visibly affected

Question 17

What are the signs of dry rot

Answer 17

Orange spore dust, white mycelium/hyphae strands.
Very light brown timber, cuboidal cracking, easily friable and weak
Deflected/sagging area of timber floor in adjacent bedroom

Look for Fruiting bodies

Question 18

What % moisture readings would you see on a protimeter for dry rot?

Answer 18

Between 20-22%. Potentially very dry in areas dried by the rot

Question 19

What is the correct name for dry rot?

Answer 19

Serpula Lacrymans. Brown wood-rotting fungus.
Fungi are basically plants with no chlorophyll, do not photosynthesise, but feed off cellulose-based fuel (wood).

Question 20

What is a building defect?

Answer 20

A material, component or finish which does not meet its expected performance criteria.

Question 21

What type of survey’s can be used to identify asbestos?

Answer 21

Asbestos can be identified by two distinct survey types:

Management survey
Refurbishment and demolition survey

Question 22

Three types commonly found in pre 1999 buildings are:

Question 23

What is Deleterious Materials

Answer 23

A deleterious material is one which was used in good faith at the time of installation but has proven to be a risk to the building over time.

Question 24

How does a Calcium Carbine Meter work?

Answer 24

An accurate measurement of moisture in walling materials. A weighed sample of mate-rial is placed within the Calcium carbide moisture meter, water within the sample is then mixed with calcium car-bide which releases acetylene gas. As the gas forms, the pressure in the sealed container increases. The pressure gauge indicates the moisture content of the sample. This test is very useful as it can be done quickly on site and gives more specific results than the electrical resistance meter. However numerous tests can be destructive as samples need to be drilled.

Question 25

What is the name for dry rot?

Answer 25

Latin name, Serpula Lacrymans.

Question 26

What are the dry rot distances?

Answer 26

• Cut back the affected joists to 500mm beyond the last recognised point of infection
• Stripping off of plaster to 1m beyond the last identified point of infection

Question 27

What’s the latin name for black mould?

Answer 27

Strachybotrys chartarum. Sometimes referred to as “toxic mould”.

Question 28

What is a deleterious material?

Answer 28

Deleterious materials

Deleterious materials are those which break down causing properties to experience problems.

Question 29

What is the BRE cracking guidance:

Answer 29

0 - Hairline cracks less than 0.1mm.
1 - Fine cracks of up to 1mm.
2 - Crack widths up to 5mm.
3 - Crack widths of 5 to 15mm (or several of e.g. 3mm).
4 - Extensive damage, cracks 15 to 25mm.
5 - Structural damage, cracks greater than 25mm.

Question 30

What was your specification for the lime based plaster? Why not normal plaster?

Answer 30

Lime plaster is the name given to a lime mortar that is applied to cover internal walls and ceilings, it has been used to finish interior surfaces for thousands of years.

It is a mixture of traditional lime, sand and water.

Unlike the modern gypsum plaster found in most homes today, lime plaster is breathable. Not only does it allow moisture to escape and evaporate from the structure, it effectively draws moisture out from the structure thanks to its exceptional capillary properties.

Lime plasters are always applied and built up in thin layers called coats, the traditional three coat system is the recommended method:

1 Scratch Coat Thickness 10 Drying time 10
2 Float Coat / Brown Coat 10 10
3 Finish Coat / Skim Coat 4 4

Question 31

Did you use a damp meter at Sylvan Avenue for the rising damp?

Answer 31

You didn’t use a moisture meter to test the damp because the salts could give a mis-leading reading.

Question 32

What is the optimum moisture content for dry rot?

Answer 32

Mositure content requied for propogation is in excess of 20%, but likely optimum range is 35%. Will die if exposed to temperatures of 40 degrees for a short period. Growth is 1m pre year.

Question 33

West Bank: Did you consider a root barrier?

Answer 33

It is not easy to completely isolate the structure from the influence of trees. Cutting through roots may also damage the tree. Expense of digging the trench. If tree removal would not be acceptable, then consideration may be given to this. But the tree was not under a TPO, so removal or hard pruning would be an easier more considered solution.

Question 34

What are the water demand of a Eucaliptus & an London Plane

Answer 34

Eucaliptus - High
London Plane - Moderate.

Question 35

Reasons for cracking in buildings:

Answer 35

Differential Settlement
Settlement
new brickwork / timber - movement
calcium silicate brickwork
rusting metals - can expand to four times the size!
chemicals such as sulphates - (expand when damp).
shrinkage - clay /
Peat - reduction folowing loss of moisture.
expansion caused by vegetation such as buddleigh.
Over loading - such as roof spread.
Ground failure.

Question 36

What did you look for at West-bank.

Answer 36

The presence of filled cracks may help the surveyor locate where cracks have been. - look for signs of repeat movement. Identify when the repair was carried out.

Lime mortar - more tolerant of cracking.
Internal plaster re-inforced with horsehair so that plaster cracking was less evident.

. It is suspected the property sits on clay formation which is susceptible to tree root related soil desiccation resulting in high volume change potential. The foundation of the building would typically be shallow and often is founded on made ground. Below the made ground will be the London clay.

If an insurance claim is pursued then it is likely that insurers will request 12 months crack monitoring to prove progressive and ongoing movement.

• In summary, there is subsidence movement associated with tree root related soil desiccation, by separate forces to the front and rear of the property, but this will need to be confirmed by a soil investigation.
• A trial pit will be required to determine the foundation profile of the footing including a 5m deep borehole to confirm the soil strata and its properties.
• It is recommend an Arboriculturalist advice is sought on pollarding the trees in close proximity to the property and maintained note most of these trees are in neighbouring land. The trees are mature, and their influence will thus be greater and can potentially cause further movement to the property.
• A drainage survey is recommended as a precautionary measure to mitigate leaking drains as a possible cause of the movement.
• If an insurance claim is pursued then it is likely that insurers will request 12 months crack monitoring to prove progressive and ongoing movement.

classified as moderate under BRE digest 251.

1mm-5mm - SLIGHT
5-15 - MODERATE
15-25 - SEVERE
+25 - VERY SEVERE

Is the crack clean or dirty. dirt build up in the crack may give an indication as to its age.

Question 37

What is the possible volume change in London clay?

Answer 37

10% due to water content.

Question 38

What information did you include in the Pre-Construction Information for the Homerton Building project?

Answer 38

• Project description
• Key project dates of the construction phase
• Project directory
• Client considerations and management
• Environmental restrictions
• Significant design and construction hazards- Health and Safety File requirements

Question 39

Tell us about the methods of assessing flat roof defects you learned about?

Answer 39

Electronic leak detection whereby a weak electrical field is created on the dampened surface
and any current that ‘earths’ into the building changes the nature of the field locally. This should
pinpoint the penetration or just as importantly show when water penetration is not caused by a
roof leak. Also Firstly a thermographic examination could y be carried out to identify areas of
leaks

Question 40

What measurement would you expect for a solid brick wall measurement for the inside window.

Answer 40

A solid brick wall is usually about 22 cm thick, a cavity wall between 27 cm and 30 cm thick, and a solid stone wall could be as much as 50 cm. The age of your home can also be a good indicator. As a general rule, if it was built before the late 1920s it is unlikely to have a cavity.

Question 41

What is the standard size of a brick?

Answer 41

Standard bricks are 215mm x 102.5mm x 65mm

Question 42

How did you review geological records?

Answer 42

UK Soil Observatory British geological survey.

Question 43

What damp % does wet rot require?

Answer 43

Wet rot is called Coniophora Puteana. Needs 50% to 60% not below 40%

Question 44

How would you make a specific identification of wet rot?

Answer 44

• Use the BRE digest or handbook
• Differentiate by: fruiting body, strands, mycelium & decay
• It’s not always critical or possible to identify exact type
• It’s more important to eliminate causes and treat damage
• The principal cause is usually poor maintenance or design
• Always use a damp meter to test the moisture content, which will aid the diagnosis

Question 45

What is the foundation depth in relation to distance from London

Answer 45

NHBC The driest and hottest areas in the UK generally exist in southeast England; therefore, the greatest risk occurs in that area and diminishes with distance north and west. A 50mm decrease can be made to the foundation depth determined in accordance with this chapter for every 50 miles distance north and west of London.

Question 46

Why do we monitor cracks?

Answer 46

Why do we monitor cracks – see the pattern. Which part of building moves and when; by how much, and what rate.- this can then assess the cause. Most buildings need 18 months to establish a reliable pattern.

Question 47

Why do we dig boreholes/soil investigations?

Answer 47

Ground investigation – trial holes – will see foundation depth and quality of ground beneath. – see tree roots as well.
Bore or auger tests. – will show composition of the ground and compressible materials below which may contribute to problem. These will be lower than foundation.

On drain survey on clay soil? yes because we don’t know if its made-up ground.

Question 48

What should you look for with cracks?

Answer 48

1. Note construction and age of building.
2. Classify each crack
3. Establish age of crack
4. Apply golden rule and follow lines of evidence
5. Note how the servicablity of the building has been impaired.
6. Is the crack progressive?

Question 49

How do you measure cracks?

Answer 49

Ruler.
Vernier Calliper - (2 pins - meaure distance).
Tell-tales

Question 50

What is soil plasticity

Answer 50

The plasticity of a soil is its ability to undergo deformation without cracking. It is an important index property of fine grained soil, especially for clayey soils. The adsorbed water in clayey soils is leads to the plasticity of soil. Adsorbed water in the clay particles allow the particles to slip over one another.

Question 51

Name some deleterious materials:

Answer 51

• Calcium silicate brickwork - shrinks which causes cracking.
• Calcium chloride additive - Reduces passivity of concrete in damp conditions. Subsequent risk of corrosion of steel reinforce-ment.
• High Alumina Cement (HAC) used in marine applications and to develop concrete strength rapidly, particularly in 1950s – 70s. However, loses strength over time, and vulnerable to chemical attack in the presence of water.

Question 52

What is carbonation?

Answer 52

CO2 in the air reacting with the concrete to form calcium carbonate AND reacts with water to form “carbonic acid”, gradually carbon “front” moves through concrete and reacts with concrete close to steel reinforcement. Reaction lowers alkalinity which protects steel along with the “passive layer”, which then rusts/expands/corrodes/pops concrete off. Moisture worsens it. At least 50mm coverage needed (post WWII buildings had poor coverage or concrete).

Question 53

What are the 5 steps to assessing cracking?

Answer 53

Step 1 – Note the Construction of the Building
Step 2 – Record and Classify Each and Every that is clear in its interpretation would suffice.
Step 3 – Try to Establish the Crack Age
Step 4 – Apply the Golden Rules and Follow the Lines of Evidence
Step 5 – Note How the Serviceability of the Building Has Been Impaired
Step 6 – Is the Crack Progressive? Will a Structural Engineer Be Required?

Question 54

Describe the cracking you saw at West Bank

Answer 54

Flat B

1. The main areas of damage to the property are within flat B on the first floor. The kitchen area of this property located on the rear right hand side of the building is significantly sloping to the right hand side.
2. There is tapered cracking approx. 1m in length and 7mm wide around the window frame in the kitchen, rear elevation right hand side.
3. Similar tapered cracking is on party wall around chimney breast in kitchen rear elevation.
4. Appliances do not stand upright due to sloping floor.

Flat A

1. Various cracking to front elevation bedrooms.
2. Cracking to front bedroom right had side on flank wall. 2m length hairline to brickwork.

The level of damage is MODERATE, and is classified as category 2 in accordance with BRE Digest 251 - Asessment of damage in low-rise buildings.

Question 55

What do you include in your reports:

Answer 55

• site address
• preface
• executive summary
• purpose
• contents
• building description
• observations
• defects
• remedial
• diagnosis
• prognosis
• Conclusion
• limitations

Question 56

What do you include in your reports:

Answer 56

• site address
• preface
• executive summary
• purpose
• contents
• building description
• observations
• defects
• remedial
• diagnosis
• prognosis
• Conclusion
• limitations

Question 57

Foundations related to soil desication:

Answer 57

It is suspected the property sits on clay formation which is susceptible to tree root related soil desiccation resulting in high volume change potential. The foundation of the building at 4 Belmont Avenue would typically be shallow and often is founded on made ground. Below the made ground will be the London clay. The rear double height extension at 2 Belmont Avenue is likely to have deeper foundations of around 1m, due to it having been built after 1970, and will unlikely suffer the cracking seen in the property next door.

Tree roots can be troublesome in cohesive (clay) soils because they can induce
volumetric change. They are rarely troublesome in non-cohesive soils (sands and gravels etc.) other
than when they enter drains, in which case blockages can ensue.

Tree roots can be troublesome in cohesive (clay) soils because they can induce
volumetric change. They are rarely troublesome in non-cohesive soils (sands and gravels etc.) other
than when they enter drains, in which case blockages can ensue.

Question 58

Describe the process of Carbonation

Answer 58

What is carbonation? Taken from RICS training;

CO2 in the air reacting with the concrete to form** calcium carbonate** AND reacts with water to form** “carbonic acid”, gradually carbon “front” moves through concrete and reacts with concrete close to steel reinforcement. Reaction lowers alkalinity which protects steel along with the “passive layer”, which then rusts/expands/corrodes/pops concrete off. Moisture worsens it. At least 50mm coverage needed** (post WWII buildings had poor coverage or concrete).