Level 3

Question 1

Describe the property (Grove Road, Hertfordshire )?

Answer 1

Two storey concrete tiled, hipped roof with double bay windows. Multiple occupiers and many pets including fish tanks and vivariums.

Question 2

What is mould growth?

Answer 2

Mould (sometimes referred to as mildew) is a fungal growth. Whilst mould itself is not toxic, some moulds can produce toxins that can have negative effects on human health, for example causing asthma

Question 3

What four factors are required for mould growth?

Answer 3

Mould spores.
Food (anything with carbon atoms).
Appropriate temperature.
Moisture (70%-).

Question 4

How does water enter buildings?

Answer 4

Condensation
Penetrating dampness
Rising dampness
Leaks (e.g. from pipework)
Trapped construction water (new builds)

Question 5

Describe the main consequences caused by dampness within buildings.

Answer 5

Health hazard
Reduce strength of building materials
Cause movement in building elements
Lead to timber decay (dry and wet rot, insect attack)
Cause chemical reactions in building components
Reduce effectiveness of insulation
Damage decorations

Question 6

How can you record damp in buildings?

Answer 6

Conductance Meter (aka Protimeter)
Carbide Testing (aka Speedy Meter)

Question 7

Explain how a conductance meter can be used to measure dampness.

Answer 7

1) When materials absorb water, they can conduct electricity
2) Conductance meters have two metal probes (electrodes) which are firmly pressed into the material being tested
3) Electrical resistance between the two probes can then be measured

Question 8

Explain how carbide testing can be used to measure damp.

Answer 8

Used for masonry products (e.g. bricks, blocks, mortars etc.)
Material is drilled slowly to minimise heating (and thus drying) then weighed and placed in a container
Specific amount of calcium carbide is added and container is sealed
Container vigorously shaken so two materials mix
Moisture in sample reacts with calcium carbide to produce acetylene gas, causing pressure inside the container, which gives a reading on the pressure gauge.

Question 9

Explain some of the limitations of carbide testing to measure damp.

Answer 9

Knowledge of material being tested is required as different materials will differ in the amount of moisture they can contain and still be regarded as ‘dry’
Destructive - requires several readings for accuracy

Question 10

What guidance is available in relation to dampness in buildings?

Answer 10

BRE BR 466 - Understanding Dampness

Question 11

Where was the mould growth found in the property?

Answer 11

The mould was identified behind furniture and on clothes within the cupboards. Water droplets were also found around the windows.

Question 12

What is condensation and how is it caused?

Answer 12

Condensation - change of water vapour naturally present in air into liquid water
The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
Once the air falls to a temperature where it can no longer hold the amount of water vapour present (i.e. it becomes saturated), liquid water will form on the cold surface

Question 13

What is meant by the terms ‘dew point’ and ‘relative humidity’?

Answer 13

Dew point - the temperature at which the air becomes saturated and will condense
Relative humidity - moisture content present within the air, referred to as a percentage of the amount of water vapour it can hold at that temperature

Question 14

What problems are associated with condensation?

Answer 14

Mould growth
Health risks
Timber decay

Question 15

How would you identify condensation within a building?

Answer 15

1) Wall has a ‘misty’ surface or stains or streaks of water running down a wall (particularly in bathrooms, kitchens and below windows)
2) Damp patches with no definitive edges or mould growth
3) Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
4) Localised dampness at potential ‘cold bridges’
5) Humidity (measured using a hygrometer), insulation and ventilation levels as well as heating and living patterns must also be taken into account

Question 16

Did you consider any other means of investigating if water ingress was present?

Answer 16

I did consult with a thermographer, however it was not the right season to carry out the investigation (middle of Summer).

Question 17

What steps would you recommend to eliminate condensation?

Answer 17

Short term - mould-affected areas can be washed using a fungicidal or bleach solution - do not use water as this will just spread the mould

Long term - combination of the following:
Reduce moisture generation (lids on pans, dry clothes outside, vent tumble dryers externally, do not use paraffin or bottled gas heaters, put cold water in bath before hot)
Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)

Increase air temperature by heating - warmer air can hold more water vapour without condensing
Increase surface temperature by thermal insulation (external or internal)

Question 18

What is interstitial condensation?

Answer 18

Occurs within the structure of an element, as opposed to on its surface.

Question 19

How would you deal with interstitial condensation?

Answer 19

If it occurs in a material such as timber, action will be needed to prevent risk of rot, usually by installing additional wall insulation
If internal inuslation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation

Question 20

What guidance is available in relation to condensation in buildings?

Answer 20

BS 5250:2011 - Code of practice for control of condensation in buildings

Question 21

What is condensation and how is it caused?

Answer 21

Condensation - change of water vapour naturally present in air into liquid water
The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
Once the air falls to a temperature where it can no longer hold the amount of water vapour present (i.e. it becomes saturated), liquid water will form on the cold surface

Question 22

How does modern living standards affect the occurrence of condensation within buildings?

Answer 22

Double-glazed windows can create a more ‘sealed’ building that lacks adequate ventilation
Trickle vents in windows (where present) are often kept closed

Balanced flue boilers (instead of open fires) reduce natural ventilation

Central heating systems are often used intermittently, meaning cold surfaces may coincide with high humidity levels

Question 23

What are the different mechanisms of water ingress relating to penetrating dampness?

Answer 23

Gravity
Capillary action
Surface tension
Kinetic energy (splashing)
Wind force
Differential air pressure (inside and out)

Question 24

What are the common causes and routes of penetrating dampness?

Answer 24

Slipped roof tiles
Inadequate chimney/parapet flashing
Copings without drips or not bedded on DPCs
Leaking gutters (lack of correct support, damaged joints, lack of regular clearing)
Overflowing hopper heads
Leaking downpipes (broken joints, rusting cast iron downpipes to rear against wall)
Continuously running cistern overflows (not discharging water clear of wall)
Blocked gulleys (resulting in water splashing against wall)
Cracked render or movement cracks in brickwork
Defective pointing (recessed joints that could lead to frost action)
Cavity ties (upside down so drip ineffective, mortar droppings resting on ties, uneven courses resulting in ties sloping toward inner leaf)
Inadequately fixed cavity insulation boards causing bridging of the cavity from outer to inner leafy
Poorly fitted windows and doors
Sills without drips
Poorly designed thresholds
Missing vertical DPCs
Driving rain on solid walls in particularly exposed situations (on cliff sides/west side of the Pennines)
Vegetation growth to damp/shaded brickwork
Repointing older buildings with cement mortar - stronger but less breathable than lime mortar, reducing the rate of evaporation. Also not as flexible so more likely to crack through drying shrinkage, thus allowing water ingress
Applying strong external renders (for the same reasons as using strong mortars)
Walls built in denser materials (e.g. granite or engineering bricks) - lack the ability to absorb water so most water runs down the face, which makes minor cracks more critical in allowing moisture ingress. Evaporation is also restricted

Question 25

How would you identify penetrating damp within a building?

Answer 25

Distinct damp patches with well-defined edges Often in localised areas Moisture readings show sharp change from wet to dry Patches of efflorescence (crystallisation of sulphates and carbonates present in building materials) Timber in area of damp has high moisture content External inspection may reveal obvious defects (e.g. cracked render/brickwork, damaged downpipes etc.) Deep wall probes indicate high readings in centre of wall Line of dampness on internal plasterwork corresponding with mortar joints where cement mortar/dense wall materials have been used Measure wall temperature, air temperature and RH to eliminate condensation Salt analysis shows zero level of nitrates and chlorides, eliminating rising damp

Question 26

What steps would you recommend to eliminate penetrating damp?

Answer 26

Identify the source of penetrating damp and remove or provide a barrier, for example: Replace defective rainwater goods Introduce DPCs beneath copings or vertical DPCs around openings Repair cracked render/brickwork Unblock gulleys/rainwater goods Replace poorly installed cavity ties Application of a hydrophobic masonry paint (repels water but still allows the wall to breathe) may also be beneficial for solid walls that experience excessive rain penetration

Question 27

What is rising damp and how is it caused?

Answer 27

Ground water rising by capillary action through pores of the wall or floor material (Tide Line/1m)

Question 28

Give some examples of how rising damp can be caused?

Answer 28

Causes: Lack of/ inadequate lapping/failure of DPC/DPM Bridging of an existing DPC/DPM (often by external rendered finishes or raised ground levels) or splashing from rain. Increase in ground water levels (e.g. man-induced changes to the water table, leaking drains, blocked land drainage systems, leaking water mains and springs) - likely if rising damp occurs fairly suddenly.

Question 29

What height can rising damp reach and what factors can affect this?

Answer 29

``` Rarely higher than 1.5m Depends on: Supply of water Pore structure of materials Rate of evaporation Heating within building Chemicals in ground and walls - efflorescence can block capillaries through which water evaporates, thus driving water further up the wall ```

Question 30

What problems are associated with rising damp?

Answer 30

Lead to outbreaks of dry or wet rot under the right conditions Reduce the strength of building materials, such as chipboard and plasterboard Reduce the effectiveness of insulation Damage decorations

Question 31

How would you identify rising damp within a building?

Answer 31

1) Visual inspection of possible causes (lack of / bridging of DPC/DPM etc.) 2) Characteristic tide mark that does not extend beyond the lower part of the wall 3) Damp contours can be pinpointed with a moisture meter 4) Damp limited to usually 1m-1.5m above ground and readings above peak will drop quickly 5) High percentage of moisture content in timber skirtings 6) Salt analysis using a calcium carbide meter determines a high level of nitrates and chlorides, which are contained naturally in the subsoil 7) Areas of dampness appear to get wetter in humid conditions due to hygroscopic salts (nitrates and chlorides) brought up from the ground, which attract water in from the atmosphere 8) BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) contains detailed guidance on rising damp identification and remediation

Question 32

What steps would you recommend to eliminate rising damp?

Answer 32

Identify the source of rising damp and remove or provide a barrier, for example: Lower the ground level (where DPC is breached or ground level is not 150mm below DPC) Repair leaking drains/water mains Unblock land drainage systems Replace DPC or provide new where non-existent Replace plaster/finishes where hygroscopic salts may still be present Renew to height 300mm above level of rising damp Re-plaster with a cement-based plaster (not gypsum plaster as most of these cannot prevent the passage of hygroscopic salts and quickly breakdown in wet conditions), preferably containing a waterproofer or salt inhibitor

Question 33

What different methods of installing/replacing DPCs are available?

Answer 33

Installation of any type of DPC must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works: Physical replacement - more expensive, disruptive and can only be laid on horizontal course (not suitable for rubble walls) Chemical injection - cheaper, lines the pores with a water-repellent solution (usually silicone/latex) however effectiveness depends on its successful penetration of the wall and lack of 'viscous fingering' (chemical spreads out and does not form a continuous barrier) Electro Osmotic DPC - a titanium wire (anode) is secured around the wall at DPC level and connected to a small power supply, which causes moisture molecules to repel down the wall back into the ground (not supported by the BRE)

Question 34

What guidance is available for rising damp problems?

Answer 34

BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) - rising damp identification and remediation BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs

Question 35

What methods can be used to minimise dampness within a basement?

Answer 35

Dense Monolithic Concrete Tanking Bund Wall System Drained Cavity System

Question 36

What are the disadvantages of using tanking as a method of waterproofing a basement?

Answer 36

Water is not drained, merely pushed to other areas around the structure, which could cause problems elsewhere Only external tanking will protect the structure from aggressive sulphates that may be present in the surrounding soil, which is not always possible

Question 37

What is a bund wall and how can it be used as a method of waterproofing a basement?

Answer 37

Construction of an inner non-load bearing wall to form a cavity joined to special triangular tiles laid to falls This enables moisture to collect in the cavity and drain away into a sump, where it can be pumped into the surface water drainage system Cavity should be ventilated

Question 38

What is a drained cavity system and how can it be used as a method of waterproofing a basement?

Answer 38

Plastic membrane in an egg-crate type formation applied to the wall and floor with properly bonded overlap joints in one continuous system Allows air and moisture to circulate and drains water into a sump, where it can be pumped into the surface water drainage system

Question 39

What guidance is available for waterproofing basements?

Answer 39

BS 8102:2009 'Protection of Below Ground Structures against Water from the Ground'

Question 40

How would you differentiate between rising damp and penetrating damp (RISING DAMP)?

Answer 40

For rising damp: Positive salt analysis (containing nitrates and/or chlorides) Visible tide mark to lower part of wall Limit of dampness usually 1m-1.5m above ground Moisture readings quickly drop above tide mark Areas of dampness appear to get wetter in humid conditions (due to hygroscopic salts drawn up from the ground) External inspection may indicate missing or bridged DPC

Question 41

How would you differentiate between penetrating damp and condensation (PENETRATING DAMP)?

Answer 41

For penetrating damp: Moisture content is usually localised/isolated Moistures readings identify an epicentre of the water entry High moisture content within fabric of element, not just on its surface Evidence of an external defect (e.g. wall cracking, defective downpipe etc.) Measure wall temperature, air temperature and RH to eliminate condensation Mould growth unusual

Question 42

How would you differentiate between rising damp and condensation (CONDENSATION)?

Answer 42

For condensation: Water is usually on the wall face when wiped with hand Negative salt analysis (no nitrates or chlorides) Moisture readings may occur across the full height of a wall (although higher readings at lower levels as warm air rises so less chance of condensation) Moisture content of skirting normal but may contain staining due to water run-off Deep wall probes indicate low readings in centre of wall Mould growth likely Surface temperature is below dew point temperature (established by measuring air temperature and RH)

Question 43

What are hygroscopic salts and are they problematic?

Answer 43

Salts that absorb moisture in from the air As they absorb water, they continually re-dissolve, which prevents any crystallisation Often associated with rising damp, as nitrates and chlorides (both of which are hygroscopic) naturally present in sub-soil are drawn up through the wall with water and are left behind on the surface once the water evaporates, causing surfaces to become wetter from moisture in the air as well

Question 44

What is efflorescence and is it problematic?

Answer 44

Temporary white powdery substance often seen on the face of new brickwork and in cases of rising damp Caused by sulphates and carbonates naturally present in building materials crystallising as water evaporates, due to their relatively insoluble nature These salts are not hygroscopic and merely indicate that moisture is evaporating from the structure They may only be problematic in cases of rising damp, as the crystals can sometimes block pores in brickwork, thus preventing evaporation and driving damp higher up the wall Can be brushed off if appearance is causing a concern

Question 45

Where should a DPC be located?

Answer 45

Should be 150mm above ground level

Question 46

What materials would you expect a DPC to be constructed from?

Answer 46

Pre 1900 - slate 1900s onwards - bitumen Modern - polymer materials

Question 47

What is the process with physically retro-fitting a DPC?

Answer 47

Cut out the brickwork and insert (access required from both sides) Can cause issues with services within wall Very costly and very disruptive

Question 48

What is the process with chemically injecting a DPC?

Answer 48

Holes are drilled in brickwork at 120mm centre Chemical cream is injected at low pressure External holes should then be plugged Must be allow to dry before plastering Can be difficult to ascertain the quality, best to ensure a guarantee for the work is provided

Question 49

What is thermal bridging?

Answer 49

Thermal bridging, often known as cold bridging, is caused where there is direct contact between internal and external faces of a building due to thermal properties of the fabric being poorer than that around the area. Will often cause localised condensation and therefore mould growth

Question 50

Why did the tenants refute the findings of condensation?

Answer 50

They believed that external factors caused water ingress such as a leak, with the source not being of internal causes.

Question 51

Educated on lifestyle changes to eliminate sources of moisture (humidity) EXAMPLES

Answer 51

* Drying clothes outdoors | * Ensuring kitchen and bathroom doors are closed when occupied

Question 52

Increasing the exchange of internal air (ventilation). EXAMPLES

Answer 52

* Move furniture away from external walls | * Make use of extractor fan when showering

Question 53

Controlling the moisture capacity of the air (heating) EXAMPLES

Answer 53

Ensure property is adequately heated.

Question 54

Describe the buillding you found this on (Gibb Croft- Harlow)?

Answer 54

End of terrace with pitched roof, concrete tiles, two storey cavity walls with render to upper floors. C.1990s.

Question 55

Who was the client?

Answer 55

Social Housing Association

Question 56

What was the soil type?

Answer 56

London Clay

Question 57

How did you know what type of soil it was?

Answer 57

British Geological Soil Map

Question 58

What are typical defects of 1980's terraced properties?

Answer 58

Blocked guttering, poor workmanship, lack of lateral restraint, condensation issues, i.e. mortar on cavity walls, sealant issues.

Question 59

What is the Burland Scale?

Answer 59

Used to describe or measure the damage (or risk of damage) to properties as a result of changes such as subsidence.

Question 60

Why did you sketch the crack?

Answer 60

As another point of reference, as photographs in certain light can not give a clear picture.

Question 61

How wide were the cracks?

Answer 61

Moderate (Burland Scale). Widest was 7mm.

Question 62

What are the typical effects for cracks that are moderate (5-15mm)?

Answer 62

Repointing/some brick replacements. Doors and Windows sticking Service pipes ma be fractured Weathertightness impaired.

Question 63

What other checks did you do?

Answer 63

Neighbouring property, and also the external gable of end of terrace.

Question 64

Why do buildings crack?

Answer 64

``` Drying shrinkage (sand-lime bricks, too strong rendering mixes) Thermal movement (lack of vertical movement joints) Frost action (freeze-thaw cycle) Ground movement (settlement, subsidence, heave) Wall tie failure Chemical reactions (carbonation, chloride attack, sulphate attack, ASR) Lack of lateral restraint ('book-end' effect) Overloading (roof spread, increase of internal imposed loads) Vibration ```

Question 65

Why is cracking a problem?

Answer 65

Structurally unsafe, Water penetration = damp problems Could lead to (frost action, carbonation, wall tie failure)

Question 66

How do you monitor cracking and what are the procedures?

Answer 66

Proprietary calibrated tell-tale - measurement grid/scale is placed over the crack, however they are not always clear to read and are more easily affected by weather and vandals. Glass tell-tale - placed over the crack and breaks if there is movement, therefore the least effective method, as it only indicates movement has happened, nothing else

Question 67

Categorise the severity of cracking.

Answer 67

BRE Digest 251, Table 1 (gives 6 categories of cracks based on size, with 0 being hairline cracks and 5 being cracks over 25mm) Burland Scale.

Question 68

What is subsidence?

Answer 68

Downward movement of a building foundation caused by loss of support beneath

Question 69

What are the common causes of subsidence?

Answer 69

Influence of trees on shrinkable (cohesive) soils Washing away of non-cohesive soils (e.g. leaking drains, burst water mains or underground streams) Change in ground-water levels (e.g. abstraction or land drainage) Mining Nearby excavations

Question 70

How can trees cause subsidence?

Answer 70

Trees and shrubs in close proximity to the building can cause the soil to become desiccated and lose its cohesion as a result of water being taken up through their roots Worse throughout periods of hot, dry weather (soils can become desiccated even without the presence of trees) As a tree grows it will extract increasingly more water from the ground, which can still cause desiccation even without hot weather Introducing new trees causes more water to be removed from the ground, thus heightening the problem

Question 71

How can subsidence be rectified?

Answer 71

Repair/alleviate the cause (e.g. repair/replace leaking drains, reduce height of trees) Consult with an arboriculturalist when removing/gradually reducing the height of trees is concerned Monitor the cracks and if no further movement occurs, repoint/patch/replace as necessary Where movement is excessive and on-going, underpinning may be required Where movement is slight and thought to be seasonal (usually where trees are concerned), it will be necessary to monitor the movement

Question 72

Who usually pays for damage caused by subsidence?

Answer 72

Most insurance policies cover the cost of repairing the loss and damage caused by ground movement, but not necessarily the cost of preventing further movement

Question 73

What is heave?

Answer 73

Upward movement of a building foundation caused by the expansion or swelling of the subsoil

Question 74

What are the common causes of heave?

Answer 74

The removal of trees on shrinkable (cohesive) soils | The freezing of ground water in frost-susceptible soils

Question 75

How can trees cause heave?

Answer 75

The ground slowly regains moisture that was once taken up by the tree roots Can last up to 10 years so care is needed when building on sites soon after trees have been removed

Question 76

How can freezing ground water cause heave?

Answer 76

After a period of high rainfall, water fills the voids between the particles and in freezing weather expands as it turns to ice Additional damage can be caused when the ice thaws and the ground settles Worse if ground has a high water table

Question 77

Explain the process of diagnosing ground movement cracking.

Answer 77

1) Inspect the cracks - location, size, direction, age 2) Investigate the site - ground profile, soil type, tree proximity, drains testing, mining area 3) Determine the cause of the cracks from steps 1 and 2 4) Begin remedial action - alleviate cause, provide underpinning if necessary 5) Monitor cracks - minimum 18 months 6) Assess action for trees (if necessary) with an arboriculturalist

Question 78

What features of a crack may indicate that it has been caused by ground movement?

Answer 78

Extends above and below the DPC Affects both internal and external surfaces Diagonal in direction (stepped along brickwork) Tapered

Question 79

Describe the typical cracking in subsidence?

Answer 79

Diagonal/stepped. | Wider at the top, tapering through weak points (window/door opening)

Question 80

Where is subsidence more likely to affect?

Answer 80

Extensions/Bays rotate away = foundations different.

Question 81

Name the two likely causes of Subsidence?

Answer 81

``` Trees= Mature trees removing moisure from cohesive soils. Drainage= Damaged drains, erosion/alluvial deposits. ```

Question 82

Describe the typical cracking in heave?

Answer 82

Vertical or tapered stepped cracking wider at the bottom.

Question 83

Name the likely cause of heave?

Answer 83

Removal of trees = expansion of cohesive soils.

Question 84

What are other causes of ground movement (Excluding heave/subsidence)

Answer 84

Sink holes, mining, landslip

Question 85

Is there a test for tree removal in relation to heave?

Answer 85

Yes, If tree is same age/younger- no risk of heave. If tree is older= risk of heave.

Question 86

What type of soil is usually affected by settlement?

Answer 86

Cohesive soils (viscous liquid squeezing out of a sponge). Sands/gravels do not usually exhibit settlement issues.

Question 87

What is thermal movement?

Answer 87

When the construction materials expand/contract as the temperature varies.

Question 88

What are some typical examples of thermal movement?

Answer 88

Oversailing DPC, Bulging, Fractures (tension/shear).

Question 89

What is lintel failure?

Answer 89

Diagonal cracks above window/door opening. Caused by failure of lintel or inability to deflect.

Question 90

What can cause bowing/leaning?

Answer 90

``` Lack of lateral retraint. Walls too slender Additional storeys Increased floor loads Vibration. ```

Question 91

What prevents bowing/leaning walls?

Answer 91

Lateral restraint: Historically- tie bars/wall plates. Modern- Lateral straps (Floor>Wall)

Question 92

What is roof spread?

Answer 92

Weight of the roof produces outward force to the top of the walls.

Question 93

What do you know about chemical reactions and building movement? (Chimney stacks/Parapet walls)

Answer 93

Soluble sulphate salts in clay bricks (efflorescence) react with portland cement and increase in volume.

Question 94

What is freeze that action?

Answer 94

Water trapped in pores of porous building material, freezer resulting in expansion. Coatings that trap water can make it worse. Left untreated can cause structural issues.

Question 95

Which tree types extract the most water from the ground?

Answer 95

Broad Leaf- Poplar, willow, oak, elm, horse chestnut and sycamore

Question 96

As a general rule, how far away should trees be from buildings?

Answer 96

Full mature height away from a building and one and a half times when part of a group/row However, this does not necessarily mean they should be removed if closer, especially mature trees

Question 97

What RICS guidance is available in relation to ground movement and what information does it contain?

Answer 97

``` Guidance for professionals involved in subsidence claims, including: Causes of subsidence, heave and landslip Causes of other building fractures Policy cover details Handling claims Repair techniques Recoveries and contribution Relevant voluntary agreements ```

Question 98

What is underpinning?

Answer 98

Process of strengthening the foundation of an existing structure by transferring the load carried by the foundation from its existing bearing level to a new level at a lower depth

Question 99

Explain the sequence of work involved in underpinning a strip foundation.

Answer 99

Soil beneath the existing foundation being excavated and replaced in phases with foundation material, normally concrete 1500mm long are excavated in a strategic order so there are never adjacent bays being worked on at the same time

Question 100

Detail some alternative methods of underpinning.

Answer 100

Jack pile underpinning: Used where depth required is too deep for traditional underpinning Precast concrete pile is hydraulically jacked beneath existing foundation. Existing foundation must be in good condition as it must rest on the pile caps once the pile has been inserted Needle and pile underpinning: Used where condition of existing foundation is unsuitable for traditional or jack piling Reinforced concrete beams (aka 'needles') are connected to small diameter bored piles which take the load Can be cantilevered where access beneath existing foundation is restricted. Expanding foam: Relatively modern technique where foam is injected into foundations, filling any voids and solidifying No excavation required.

Question 101

What guidance is available in relation to underpinning?

Answer 101

BRE Digest 352 (Underpinning) contains further information

Question 102

What was the effect of the two mature trees on the cracking?

Answer 102

Uptake of water = drying out clay.

Question 103

What would dropped concrete paving slabs indicate?

Answer 103

That there has been ground movement beneath.

Question 104

Why did you advise a SE to follow up the investigation?

Answer 104

To confirm the findings and recommend appropriate remedial action. Qualified and competent to do so (The Institute of SE)

Question 105

What would an arboriculturist report assist with?

Answer 105

An arboricultural survey (or tree survey) is a technical document produced by an arboriculturist (tree expert), which is used to assess and record trees within a particular site or area.

Question 106

What is pollarding/tree removal?

Answer 106

Pollarding is pruning of upper branches.