Building Pathology Flashcards
How do you apply your understanding of building pathology in your day-to-day duties?
As a Building Surveyor, my understanding of building Pathology is crucial in identifying and recording defects whilst analysing the causes and recommending appropriate remedial actions.
Could you elaborate on how the CPD events have been beneficial to your understanding of building defects?
The CPD events have been beneficial in keeping me updated on current standards and guidelines, learning about new technologies and their applications, and networking with fellow professionals.
Can you explain the limitations when using laser measure devices during building inspections?
Limitations of laser measuring devices include:
- Inaccurate readings due to obstructions
- Difficulty in sighting in bright light
- Short battery life.
Accuracy can be improved by taking multiple measurements and using visual markers where necessary.
What other forms of equipment have you used aside from a moisture meter, borescope and laser measure devices?
Infrared thermography for assessing heat loss and dampness.
What is Japanese knotweed?
Japanese knotweed is an invasive plant that can cause damage to foundations and structures.
What does Japanese Knotweed look like?
- Hollow bamboo like stems that can reach a maximum height of 3-4 m
- The leaves are are a shield like or shovel-shaped.
- The flowers are generally small, cream or white.
Why Japanese Knotweed an issue?
Knotweed can extend 7 metres horizontally making removal by excavation extremely difficult.
The invasive root is strong and can cause damage to foundations and structures.
The most effective method of control is by injecting with herbicide close to the flowering stage in late summer or autumn.
Why is Japanese Knotweed an issue for buildings and construction sites?
- There are legal restrictions on its removal and disposal.
- It is listed by the World Conservation Union as one of the world’s 100 worst invasive species.
- Cutting it down will just cause it to spread around the site therefore to irradicate it from a site it may take several attempts with herbicide injections which is time consuming.
- It can also be disposed in licensed landfill sites however this is a costly process.
What legal restrictions are there in dealing with Japanese Knotweed?
Classed as “controlled waste” in Britain under part 2 of the Environmental Protection Act 1990 which requires disposal at licensed landfill sites.
In the UK, it is an offence under section 14(2) of the Wildlife and Countryside act 1981 to “plant or otherwise cause to it grow in the wild”.
It was made illegal to spread Japanese knotweed in the UK by the Wildlife and Countryside Act 1981.
How does timber decay?
Decay of timber occurs when wood is allowed to remain damp over long periods.
Name me some timber defects?
- Dry Rot
- Wet Rot
- Insect Attack
How would you recognise dry rot?
- Wood shrinks and splits into large cuboidal cracking.
- The wood is light in weight, crumbles under touch and has a dull brown colour with a cotton wool type texture.
- Mycelium is often visible and greyish in colour when wet and yellow or purple when dry.
What’s the cause of dry rot?
- Airborne spores come into contact with damp timber which has a moisture content of more than 20%.
- This may be cased from leaking plumbing, poor ventilation leading to condensation or water ingress from a faulty roof or window.
- Causing shrinkage and warping of timber.
- Moisture content less than 20-35% which most would consider “damp not wet”.
How do you remedy Dry Rot?
- Removing the source of moisture.
- Remove all rotted wood by cutting away timber 300–450 mm beyond the last evidence of fungus or rot.
- In some circumstances, full replacement may be necessary depending on the extent of decay and site conditions.
- Applying a fungicide treatment to the remaining nearby timbers.
- Ventilation must also be ensured to prevent further occurrences.
Note: If structural timbers are affected, I would arrange a structural survey to determine whether structural repairs are necessary and, if they are, take appropriate steps to ensure structural integrity.
How would you recognise wet rot?
- Surface cracking where cracks follow the timber grain.
- Hyphae strands which are light brown & yellow (a key difference from dry rot).
- Infected timber turns dark brown in colour.
- Wood shrinks and splits on a smaller scale with the wood becoming darkened. Mycelium can be white, brown, amber, green or black with strands that are flexible when dry. The fruiting bodies can be a number of different colours and can occur both inside and outside.
What’s the cause of wet rot?
- Excessive moisture present over a long period of time.
- High moisture content 50-60%
- Leaking services
- Building material failure
How would you remedy wet rot?
- Removing the source of moisture.
- Wet rot is limited to areas in which wood has become wet: therefore, size of outbreak is closely linked to extent of wetting.
- Remove all rotted timber and replace – the wood that remains structurally intact and in a safe condition should be treated with a fungicidal spray to protect them whilst they dry.
How do you identify the presence of woodworm?
- Holes in the wood members in question are present typically 1 – 1.5mm in diameter.
- Live infestations showing powder known as frass which is faeces around the holes.
- Adult beetles will emerge from the wood and may be found in the summer months.
How do woodworms affect timber in buildings?
- The beetle’s lays eggs on, or just under the surface of the wood.
- The resulting grubs then feed on the timbers causing both structural and cosmetic damage.
- They then hatch as beetles which then breed, lay eggs, and repeat the process causing further damage.
How is a woodworm infestation treated?
- Woodworm infestation is generally controlled with chemical insecticides.
- However, I would ensure to solve the damp issues as damp timber may be re-infected at a later date.
What skills or knowledge did you gain from the timber defects CPD?
During the CPD event, I gained detailed knowledge about the causes of timber decay and defects, their effects, how to diagnose them and appropriate treatments.
Are you aware of any industry standard and guidelines related to timber defects?
BRE Publication on recognising wood rot and insect damage in buildings.
- BRE Digest 299: Dry rot: its recognition and control
- BRE Digest 345: Wet rot: its recognition and control
What is damp?
Where moisture becomes visible through discoloration and staining of finishes.
Or, causes mould growth, sulphate attack, frost damage or even drips and puddles.
How can you test for damp?
Moisture meters – Timber.
Speedy Carbide Meter – Masonry
Thermal imaging - used to record the temperature of building fabric and isolate areas that are either close to, or below dew point. These areas will suffer interstitial condensation and damp.
What is a protimeter / moisture meter?
- A protimeter works by measuring the electrical resistance between two applied electrodes.
- Protimeters are generally used to monitor the moisture content in wood, when used on other materials, the actual readings may be misleading however this approach does give a sense of moisture content.
What is a Speedy Carbide Meter?
- A speedy carbide meter is a device to measure moisture in masonry.
- Drilled samples are taken to determine the moisture content of walls, and the level of damp.
- Masonry dust generated into a sealed container with a known measurement of calcium carbide allows the moisture content to be determined.
- This works as the dust and calcium carbide releases a gas in proportion to the amount of moisture present.
The primary advantage of this procedure is the ability to assess the moisture content profile through the wall.
It allows us to establish whether the moisture content is higher towards the external face, suggesting wetting by rain penetration, or higher towards the inner face, suggesting condensation.
What are the main forms of Dampness?
- Penetrating Damp
- Rising Damp
- Condensation
How would you identify penetrating damp?
- Appearance of damp patches on walls, ceilings or floors.
- These patches tend to grow or darken after periods of heavy or prolonged rain.
What’s the cause of penetrating damp?
- Rain driving through exposed masonry walls.
- Defective roof covering.
- Cracked or detached rendering.
- Defects to window cills.
- Blocked cavity ties.
How do you remedy penetrating damp?
Remedies for penetrating damp include:
- Repointing of defective mortar joints
- Inspection of cavity ties to address any blockages.
- Inspection of areas of roofs such as chimneys, parapets and thresholds to address any defects in these elements.
How would you identify rising damp?
- Visible staining in the form of a tide mark at the point where the ground water has reached.
- Does not usually rise above 1.5m from internal ground floor level.
What’s the cause of rising damp?
Moisture rising from the ground via capillary action.
This can be caused either:
- Lack of a damp-proof course
- Defective damp proof course
- Where the damp proof course has been bridged by external features such as paving or blocked cavities.
How do you remedy rising damp?
- Removing the external feature causing bridging.
- The injection of water repellent chemicals into the brick work.
- Installing a new physical damp proof membrane.
How would you identify condensation?
Staining and mildew /mould growth.
Typically found in poorly ventilated areas with high humidity, kitchens, bathrooms, bedrooms and rooms used for drying clothes.
What’s the cause of condensation?
Causes of condensation include a lack of insulation, lack of ventilation and unheated areas of the building.
Where warm moisture in the air hits a cold surface it loses some moisture as condensation.
This water vapour comes from breathing, domestic activities such as cooking and bathing.
It can lead to staining at cold bridges, peeling wallpaper and mould growth.
How do you remedy condensation?
- Reduction in moisture generation
- Providing adequate ventilation
- Provide adequate heating
- Improving the building insulation.
Can you describe the process of elimination you use to differentiate dampness in a building?
Differentiating types of dampness involves a systematic approach:
- Visual inspection (internally & externally)
- Identifying symptoms like mould, peeling paint, efflorescence.
- Moisture meter to measure presence and degree of moisture in timber.
- Tactile inspection for temperature and moisture.
- In some complex situations, laboratory analysis of collected samples.
- Eliminating the source of moisture is key.
Are you aware of the Joint Position Statement, is so what is it?
The RICS collaborate with Property Care Association and Historic England to produce a joint position statement ‘investigation of moisture and the effects on traditional buildings’.
Could you explain further on the use of a moisture meter in identifying dampness in buildings?
A moisture meter is used to identify dampness on timber by passing a small, harmless electric current through the material and measuring its resistance.
If moisture is present, this will lower the resistance and hence indicate higher moisture content.
How do you ensure accuracy while identifying the cause of dampness using various surveying equipment?
Ensuring accuracy in dampness detection involves using calibrated and properly functioning equipment, interpreting readings in context of visual and tactile inspection findings, and corroborating findings with other lines of evidence.
What types of building movement defects have you learned about and how can they be identified?
I have learned about various building movement defects such as:
- Subsidence
- Settlement
- Heave
- Thermal movement.
These can be identified through signs like cracking patterns, distortion of building elements and monitoring over time.
What is subsidence and how would you identify this?
- A downward movement /shrinkage of ground beneath the foundations.
- In clay soil, the growth of large trees which remove water from the ground can cause this.
- Typically diagonal cracking at the corner of the property.
- The cracks will be larger at the top and thinner at the bottom.
What is settlement and how would you identify this?
- A downward movement 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.
- Hairline cracks may appear internally – doors and windows may become jammed.
What is differential settlement and how would you identify this?
If two sections of a building are constructed off different foundations or the ground is made up of different soil types, then one may settle more than another causing cracking between the two sections of the building.
This issue is most common with extensions.
What is heave and how would you identify this?
- An upward movement in the ground level.
- In 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.
- 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.
What is lintel failure and how would you identify this?
Lintel failure allows a triangular section of brickwork above the window to drop down creating a triangular crack from the corner of the window toward the centre.
How would you identify a 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.
Horizontal cracking.
What size cracks are of concern?
Cracks over 4mm that widen at any point or pass the through the DPC.
What is the BRE Digest 251?
BRE Digest 251 ‘Assessment of damage in low-rise buildings’.
This identified six categories of cracks together with the typical damage caused and the remedy required.
What are the categories of BRE 251?
Category 0: Hairline cracks. Less than 0.1 mm in width. No repair action required.
Category 1: Fine cracks: Up to 1 mm in width. Generally restricted to internal wall finishes. Easily treated using normal decoration.
Category 2: Cracks easily filled: Up to 5 mm in width. Not necessarily visible externally, but doors and windows may require adjusting to prevent sticking. Can be masked by suitable linings.
Category 3: Cracks that require opening up: Widths of 5-15 mm. Weather-tightness and service pipes may be affected. External brickwork may need repointing or, in some cases, to be replaced.
Category 4: Extensive damage: Width of 25mm. Windows and door frames become distorted, walls lean or bulge noticeably. Requires breaking-out and replacement of wall sections.
Category 5: Structural damage: Widths greater than 25 mm. Beams lose their bearing, walls require shoring, and the structure is generally unstable. May require major repair works.
If there was stepped cracking on the corner of a building, what might have caused it?
- Settlement.
- Subsidence.
- Heave.
When and why would you use a borescope?
To inspect a cavity wall to identify wall tie failure or breach of cavity.
What are the limitations of using a borescope in building surveying and how do we address them?
- Difficult access in restricted spaces.
- Low visibility due to cavity filled insulation restricting view of wall ties.
What are the common causes of concrete failure?
– Inadequate protection of reinforcement.
– Carbonation.
– Freeze-thaw action.
– Chemical attack.
– Crazing.
What is Carbonation?
– Carbon dioxide in the air affect the concrete.
– Carbonation changes the alkali nature of the concrete to acid.
- This causes cracking of the concrete cover exposing the rebar which is the suseptible to corrosion which will expand and spall the concrete.
– The risk can be reduced by providing as much cover as possible.
– To test for carbonation a small piece of concrete is broken off (not cut with a saw). The concrete sample is then sprayed with a solution (phenolphthalein) to measure the PH level.
– Alternatively, a more accurate test would be to send a sample to the lab for further investigation under a microscope to view the change in aggregate.
How do you treat carbonation?
Anti-carbonation coatings can be applied to the concrete with a life-expectancy of 10-years.
What is freeze-thaw effect in concrete?
- Concrete is a porous material subject to forces that absorb and release water.
- Absorbed water can freeze within the concrete and cause spalling and cracking.
What is Efflorescence of concrete?
– Efflorescence is more likely to be found on concrete that has been in place for a while.
– Concrete contains water-soluble salts.
– As water from the interior of the concrete migrates to the surface and evaporates, salts are deposited on the surface, usually as a white stain.
– Efflorescence can occur with concrete, brick, or concrete block construction. It can be removed with acid etching.
– The best way to prevent its recurrence is with adequate waterproofing.
What are Deleterious Materials?
Hazardous to health or
Affect the buildings performance or structure.
Can you name some Deleterious Materials?
- Asbestos
- Lead (when used in water pipes or paint)
- High Alumina Cement Concrete
- RAAC
Can you explain in more detail the different types of asbestos?
White: Chrysotile (Banned in 1999)
- Least dangerous (curly fibres)
- Cement sheeting
Brown: Amosite (Banned in 1985)
- Needle like fibres.
- Used for fire resistance (AIB board)
Blue: Crocidolite (Banned in 1985)
- Needle like fibres.
- Sprayed coatings (insulation).
What is the issue with lead based paints /lead water pipes?
- Due to the toxic nature of lead its use in plumbing was banned in the UK since the 1970s.
- Risk of contamination of drinking water.
- Risk of inhalation of lead dust during maintenance (paint).
What is High Alumina Cement Concrete?
- HAC found in structural concrete such as pre-cast concrete beams.
- First produced in 1925.
- Widely used in the UK from the 1950’s – early 1970.
- HAC concrete banned 1976 for structural use following a number of publicised collapses.
- HAC develops full strength very quickly; it equally loses its strength when it comes in contact with water.
- This process known as ‘conversion’ which is a mineral change.
- Once conversion occurs the HAC will reduce in strength and become vulnerability to chemical attack (poor roof detailing)
- Issues mainly stem back to manufacturing faults (high water content and high temperatures when casting).
- Testing should be carried out by chemical or laboratory testing of samples.
- If confirmed to be HAC the strength and durability should be assessed.
- Building Regulations Advisory Committee (BRAC) published guidance for design checks.
What type of property were you surveying when you identified damp staining at Grasmere Road?
I was surveying a residential house when I identified the damp staining.
The property was a 1900’s terraced building in Blackpool.
What level of survey did you undertake at Grasmere Road?
RICS Level 3 survey.
The property was in a poor condition and had been extended /altered extensively for a previouse use as a care home.
What RICS document outlines the levels of survey available?
– RICS Home Survey Standard 1st Edition (professional statement).
– This document sets out mandatory requirements for RICS members and firms who undertake residential surveys.
– You MUST ensure your services are benchmarked against one of the defined levels (1, 2 and 3).
Can you explain to me the different types of survey levels noted in the RICS Home Survey Standard?
Level 1: Least extensive survey, general condition of the building elements and grounds. No advice given on repairs or ongoing maintenance. Usually more suited to modern dwellings in satisfactory condition.
Level 2: General condition of the buildings elements with a more extensive visual inspection to include opening up roof spaces or basements where safe to do so. This report advises on repair and maintenance of building elements. Not suitable where the client intends to carry out extensive repair and refurbishment works or the property has been extensively altered in the past.
Level 3: Detailed visual inspection to include opening up concealed areas and although not tested they are observed in normal operation (such as drainage, flushing toilets and running taps etc.) Level 3 surveys should provide the client with all information they require without further investigation to make a decision if possible.
Grasmere Road; How far up from the internal floor level was the damp staining located?
The damp staining was located 2 metres up from the internal floor level.
I therefore ruled out the probability of rising damp which typically does not exceed 1.5m from the internal floor level.
Grasmere; Where on the property was the damp staining located?
The damp staining was located on the ground level of the property on the internal face of external solid wall.
The damp patch was localised and adjacent to the blocked rainwater goods externally.
Grassmere; What did you find when you inspected the area externals?
I discovered a significant build up of vegetation within the rainwater hopper.
This was causing rainwater to spillover and wash against the wall, which contributed to the damp stain.
What was the impact of the rainwater over spilling the hopper?
Large quantities of water penetrating the wall in one area, resulting in high moisture contents and localised damage. The moisture was then able to ingress internally leading to damp staining.
How did you record the location of damp?
I recorded the location of the damp using a detailed sketch of the property layout, specifically highlighting the affected area.
Grassmere; What did you advise your client on remedial works required?
- Remove vegetation from external hopper.
- Re point external masonry to the affected area.
- Hack off and remove contaminated plaster internally.
- Allow sufficient time for drying out the wall.
- Apply a lime plaster to the walls and decorate.
Grassemere; How long was required to dry out the wall and why did you advise this?
The wall needed drying out to prevent any trapped moisture damaging the new plaster.
I advised that the time required for drying would be dependant upon the extent of damage known once the internal plaster had been removed.
I recommended the use of dehumidifiers and improved ventilation were used to encourage the drying out phase.
As a rule of thumb, brickwork can take 1 month per inch of wall thickness for drying. (9inch wall could take up 9 months depending on conditions)
Grassmere; Did you photograph the affected area and if so, how was this information used?
Yes, I photographed the affected area.
These photographs were used in the report as visual proof of the situation and highlighted the need for immediate remedial action.
Grassmere; What was the construction type of the building?
The property was constructed early 1900’s with solid masonry wall (lime mortar).
Grassmere; How did you identify the construction type?
– The property was of solid wall construction.
– I identified this through the presence of header coursed brickwork.
– I also measured the window and door reveals with a tape measure to confirm.
What common issues can you find with sold wall construction?
Heat loss: No insulation as with cavity walls making the properties less efficient.
Dampness: Single skin can allow moisture seep in.
Inadequate repair works: cementitious pointing to solid wall causing moisture to become trapped.
How does lime mortar work, what happens to the moisture?
- Lime mortar is applied to solid wall construction to allow the moisture to evaporate and move out freely.
- When moisture levels are high the lime mortar can absorb water vapour preventing potential damage from moisture penetration.
- When conditions are dryer, lime mortar releases the trapped moisture back to the environment.
Grasmere; What were the probable causes you ruled out before identifying the actual problem?
I ruled out rising dampness due to the location of staining and the presence of a DPC that had not been breached externally.
I ruled out the presence of any embedded pipework - walls were solid wall with plaster. The wall plaster where deteriorated had no evidence of pipe work behind.
The staining was a localised patch adjacent the build up of vegetation externally - i determine the cause to be penetrating dampness.
Ashfield Rise; What was the purpose of the survey?
I was carrying out a residential building survey for my client who was looking to purchase the property.
Ashfield Rise; what type of property was this?
Fairly modern detached residential building constructed circa 1990 of cavity wall construction.
