Building Pathology

Question 1

What are the causes and remedies for some of the defects associated with flat roofs?

Answer 1

• Crazing - Generally caused by UV rays from the sun. Protection can be provided by solar reflective paint. Isolated areas are acceptable, but should it spread then replacement will be needed.
• Ponding - Ponding occurs when the gradient (min. 1:40) is not sufficient. Standing water can drastically reduce the lifespan of a felt roof.
• Thermal Movement - Cracks and splits can occur when there is differential movement between the substrate and the membrane. Likely require replacement with more accommodating membrane.
• Blistering - Commonly caused by water vapour trying to escape the roof build-up. Blister should be cut and re-bonded to the underlay. Source of vapour should be identified and remedied.
• Defective Flashing and Falls around Openings - Poor workmanship, or deterioration of the flashing details can lead to water ingress. poor detailing or construction of the structure can lead to structural movement around roof lights.
• People - Punctures and rips are most often caused by impact damage by personnel or loose debris. Localised repairs required.

Question 2

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

Answer 2

1 - Electronic Roof Detection - A weak electrical field directed onto the dampened surface. Any current that ‘earths’ into the building changes the reading locally, helping to identify ingress points.
2 - Thermographic Imagery - Particularly useful when there is a large temperature differential between internal and external conditions. Will highlight areas of retained moisture.

Question 3

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

Answer 3

1 - Age , Life Expectancy, and Overall Condition
2 - Are the defects localised or affecting the whole roof, and is it affecting the surface layer or the roof structure.
3 - What are Client’s intentions for the building?
4 - Budget
5 - Disruptions

Question 4

You are asked to inspect a flat roof. Take us through the inspection process.

Answer 4

1 - Historical information gathering - Current or previous issues with the roof.
2 - Arrange access and prepare RAMS
3 - Undertake non-invasive inspection.
4 - Further inspection (if needed).

Question 5

What is damp?

Answer 5

Damp is the presence of unwanted moisture within a building.
Symptoms may include;
- Mold growth
- Discoloration
- Salt presence
- Timber rot

Question 6

How can you test for damp?

Answer 6

There are various types of moisture meters which can be used to assess for the presence of damp.
- Pinless Moisture Meter
- Pin Type Moisture Meter
- Hygrometer
- Data Loggers
- Calcium Carbide Meters
- Gravimetric Testing
Alternative tools available might include thermal imagery cameras.

Question 7

What is a protimeter / moisture meter?

Answer 7

A device used to measure moisture in wood. WME readings are provided when testing alternative materials.

Question 8

What is a speedy carbide meter?

Answer 8

• A device to measure moisture in masonry.
• Sample put into sealed container with a measurement of calcium carbide allows the moisture content to be determined.
• Reaction releases a gas which pressurises the container and provides a reading.

Question 9

Describe three issues and associated remedies for rising damp.

Answer 9

1 - Absence of a DPC - Reinstate breathable wall materials.
2 - Bridging of a DPC - Bridging material (ground levels or cavity debris)
3 - Failure of a DPC - Replace with either a physical or a chemical DPC

Question 10

How would you identify penetrating damp.

Answer 10

Can be identified through the appearance of damp patches on walls, ceilings, or floors. Typically occur during or following periods of rainfall.
Caused by defective elements within the building envelope, allowing surface or ground water to reveal itself on the internal finishes.
Caution should be applied to not jump to conclusions about where the source of the ingress is based on location of symptom.

Question 11

What is a cold bridge?

Answer 11

A cold bridge is created when materials that are of poor thermal performance extend from a cool space to a warm space allowing heat to escape.
To eliminate the occurrence a thermal break will need to be inserted, or the component replaced with one that is more thermally efficient.

Question 12

What are the causes of condensation, and how would you remedy it?

Answer 12

An imbalance between the amount of water vapour contained in the air, the ambient temperature, and surface temperatures.
When water laden air contacts a cooler surface at the dew point it condenses and forms condensation.
Key mitigation measures would include:
1 - Reducing production, and management of, water vapour.
2 - Maintaining ambient internal air temperatures, and subsequently surface temperatures.
3 - Eliminating cold bridging and provision of (carefully considered) insulation.

Question 13

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

Answer 13

Dependent on seasonal conditions.
Finishes are required to be dry before application of decoration. Guidance should be sought from manufacturers data sheets, but acceleration of process may be available though careful use of ventilation and dehumidifiers.

Question 14

What ways could moisture enter the building, and how could you differentiate between the different types?

Answer 14

Penetrating Damp - Porous materials within the building envelope allowing transfer of surface water from outside to the internal parts. Possibly through bridging of cavity, moisture being trapped within the fabric by impermeable materials, or from a simple issue such as a slipped or displaced roof tile.
Rising Damp - Found at low level of ground floor up to approx. 1m in height. Tide marks may be present, together with presence of visible salts. Cause likely to be elevated ground levels of blocked cavities allowing bridging of the DPC to occur.
Condensation - The most common cause of damp. Typically identified during the cooler months though the presence of condensation to windows in first instance, but also mould to surfaces of external walls.

Question 15

You are inspecting a building and identifying a number of cracks in the external wall. Talk us through your thought process.

Answer 15

1 - Building construction, age, and material type.
2 - Pattern of the cracking.
3 - Movement joints.
4 - Local factors which may be contributing to the movement such as trees or stumps, any recent alterations, or presence of drains.

Question 16

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

Answer 16

Vertical Cracking - May be caused by solar gain in long stretches of masonry without sufficient expansion joints. Would typically occur at junctions or returns where a weak spot is present.
Horizontal Cracking - May be caused by corrosion or failure of metal wall ties or beams resulting a bowing effect forcing a small gap between the brickwork courses.
Diagonal Cracking - May be associated with subsidence caused by failure of the foundations. This may be due to erosion of the supporting strata caused by defective drains.
Misalignment - Typically found at intersections between bay windows and the main structure of a house. It occurs when there are differing settlement rates between the foundations which may have been poured to different depths.
Triangular Cracking - Typically found over bay windows when timber lintel has failed.
Craze Cracking - Freeze thaw action which might locally be seen on face of brickwork before spalling. Can also be seen on concrete or plastered surfaces and caused by excessive drying.

Question 17

What size cracks are of concern?

Answer 17

Up to 2mm - Very slight concern
2-5mm - Slight or aesthetic concern
15-15mm - Moderate concern
15-25mm - Severe
Over 25mm - Very severe with stability concerns

Question 18

If there is stepped cracking on the corner of a building, what might have caused it?

Answer 18

• Settlement
• Subsidence
• Heave

Question 19

What if the cracks were present on concrete?

Answer 19

Consideration of the common concrete defects such as carbonisation, chloride attack and silica reaction, as well as issues relating to structural movement and poor design and construction.

Question 20

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

Answer 20

Cohesive soils such as clay.
The possible causes revolve around changes in the water content of the soil, causing expansion and contraction. Expansion of the soil forces the ground to swell, forcing the substructure upwards in an event known as heave.

Question 21

What types of timber defects are there?

Answer 21

The main timber defects are
- Dry Rot
- Wet Rot
- Insect Attack

Question 22

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

Answer 22

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 cotton wool like texture. Mycelium is often visible and greyish in colour when wet, and yellow or purple when dry.
Wet Rot - Wood shrinks and splits on a smaller scale with the wood becoming darkened. Mycelium can be white, brown, amber, 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.

Question 23

What are the remedial measures to wet and dry rot?

Answer 23

To locate and eliminate the sources of moisture and promote rapid drying whilst removing the rotten wood.
There can also be a surface application of fungicidal fluid and introduction of support measures if needed.

Question 24

The ends of the joists in a timber floor built into an external wall have been seriously affected by dry rot. How will you recognize this type of rot, and what action would you take to resolve the problem?

Answer 24

Typical indications of dry rot include:
- Wood shrinkage and dark cracks of a cuboidal manner.
- A silky grey to mushroom colored skin frequently tinged with pitches of lilac and yellow which often develops under less humid conditions.
- This ‘skin’ can be peeled like a mushroom.
- White fluffy ‘cotton wool’ like mycelium develops under humid conditions.
Any affected timbers should be removed and replaced with pre-treated timber. Any remaining timbers at risk of being affected by the dry rot should be treated with an effective fungicide.
Where the dry rot has passed through masonry, it should be isolated using physical containment and / or masonry sterilization.

Question 25

The ends of the joists in a timber floor built in an external wall have been seriously affected by wet rot. How will you recognize this type of rot and what action will you take to resolve the problem?

Answer 25

Wet rot results in high moisture contents of around 50-60% to propagate and spread.
- It is usually found in areas where there may be a water leak, or building failure, such as along window cills and in roof voids.
- Indications of wet rot outbreak include surface racking where cracks follow the timber grain, hyphae strands which are light brown and yellow (a key difference from dry rot), and infected timber turns dark brown in color.
- The first step to remedy wet rot is to find and eliminate the source of dampness to prevent timbers becoming damp.
- All infected and / or damaged timber should be removed, as there may be structurally impaired dur to the decaying action of the wet rot, and the remaining timber treated with a suitable preservative.
- If the wet rot is in a confined space, such as a cupboard or loft space, it may be necessary to consider methods of improving the ventilation.

Question 26

What are the remedial measures for dry rot?

Answer 26

• Remedial action for dry rot is far more intrusive.
• The first step is to establish the full extent of the outbreak, many parts of which may be initially concealed from view underneath floorboards, behind furniture and panels.
• Affected timber needs to be cut out and replaced, including those within approximately 300-450mm beyond, to allow for possible further contamination.
• All surrounding timbers should be treated with a chemical biocide to ensure all strands and spores are killed off.
• Affected plaster that has come into contact with the dry rot also needs to be removed, and wall surfaces treated with a sterilizer or biocide.
• Lastly, the area should be kept dry and heated, to ensure all timbers are fully dried out to prevent or reduce the likelihood of further outbreaks.

Question 27

Explain the lifecycle of a rot.

Answer 27

The four main dry rot lifecycle stages are as follows:
1 - Spore - Spores are omnipresent and in very large numbers. Dry rot spores appear as a fine orange brown dust. the spores are activated when combined with timber and moisture.
2 - Hyphae - Where timber and moisture are present the spore will produce very fine 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 know 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 - Tp perpetuate itself, the fungus will create a fruiting body (sporophore). This mushroom like form is a function 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 28

name some common insects that are known to attack timber and explain what remedial methods are available.

Answer 28

Category A - Where insecticidal treatment is required for the Common Furniture beetle, Death Watch beetle, and House Longhorn beetle.
Category B - Where treatment is only necessary for associated rot due to Wood Boring Weevil.
Category C - Where no treatment is needed for Bark Borers.
Remedial measures for there insects include:-
- Studying flight holes to identify the type of beetle and determine if the infestation is still active or dormant.
- Apply two coats of Boron based treatment to all affected areas, overlapping at least 300mm onto the sound timber.
- In the case of a severe attack, replacement timber with pre-treated wood is required.

Question 29

How do you identify the presence of woodworm?

Answer 29

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

Question 30

How to woodworms affect timber in buildings?

Answer 30

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

Question 31

What is woodworm infestation likely to indicate?

Answer 31

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

Question 32

How is a woodworm infestation treated?

Answer 32

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

Question 33

You are surveying a deflected timber floor in an early 19th Century building. What are the causes and methods available to deal with this if the Client requires a level floor?

Answer 33

1 - Confirm the cause of the deflection, whether this be due to:
- Notching
- Rot
- Insufficiently sized joists
- Insufficient centres
- Overloading
- Deterioration of sleeper walls.
2 - Confirm the issue can be remedied and whether the timber floor can be retained.
3 - There may be potential to:
- Supplement the timber joists
- To overboard
- Remove and replace with suspended timber floor
- Install an alternative solid floor.

Question 34

A newly cast reinforced concrete slab is exhibiting crazing and cracking on its surface, what are the possible causes?

Answer 34

• Poor inadequate curing caused by environmental conditions being conducive to high evaporation rates and a lack of adequate protection.
• Too wet of a mix, excessive floating or use of a jitterbug that will depress the course aggregate may have been undertaken resulting in an excessive concentration of cement paste and fines at the surface.
• Finishing operations performed while bleed water remains at the surface and other finishing procedures that produce a high water cement ratio at the surface.
• Sprinkling cement on the surface to dry up the bleed water.

Question 35

What are Nickel Sulfide Inclusions?

Answer 35

• They are inherent in the glass production process and are microscopic imperfections in the glass, known as inclusions.
• Most of these are completely harmless, but Nickel Sulfide inclusions have been shown to cause disastrous failure of tempered glass.
• When glass is rapidly cooled to achieve the properties of tempered glass, the Nickel Sulfide inclusions remain in a high temperature form.
• Over several years Nickel Sulfide will return to its low temperature state, and in the process will increase in volume. This can cause cracking and additional tensile stresses which, in tempered glass, can lead to spectacular failures with no visible cause.
  This phenomenon has also been referred to as “Spontaneous Glass Failure.

Question 36

What else may have caused glazing to crack if it wasn’t Nickel Sulfide Inclusions?

Answer 36

Structural movements around the window opening could have put pressure on the glazing and caused the crack.

Question 37

You find a leak at a high level on the first floor of a two-storey building constructed with a 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 the defect?

Answer 37

• 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 to assess whether there had been any alterations to the building.
• It is also prudent to speak to the building owner or occupier to enquire whether they can advise the location of the source of the leak and when it is most prevalent.
• My first thought would be to suspect a roof leak so I would assess the roof both externally and internally for signs of defective or missing flashings around roof penetrations.
• When in the roof space I would also look for evidence of leaking pipes.

Question 38

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

Answer 38

• Cavity wall tie failure can be identified when horizontal cracking appears every 5 courses or so of brickwork or in render.
• It is due to corrosion of old steel ties such as large fishtail ties.
• To remediate this issue I would firstly use a borescope to confirm the defect is wall tie failure.
• I would then look to locate wall ties and isolate or remove them to ensure no further damage is caused.
• Installing replacement stainless steel mechanically fixed ties secured with an epoxy resin can be utilized to remedy this issue.

Question 39

What is nail fatigue?

Answer 39

This is a common problem for pitched roofs with slates or tiles. The nails have rusted through allowing the slates to fall. If one nail corrodes this could be a sign that large sections are at risk.
The remedial measure would be to strip the roof and secure the tiles or slates with new nails.
Some roofers advocate a spray foam solution, but as it sets hard it prevents the roof from moving and also impedes ventilation.

Question 40

What is Japanese Knotweed?

Answer 40

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

Question 41

Why is Japanese Knotweed an issue?

Answer 41

• It forms thick, dense colonies that completely crowd out any other herbaceous species.
• It can extend 7 metres horizontally and 3 metres 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.

Question 42

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

Answer 42

• It is listed by the World Conservation Union as being one of the worlds 100 worst invasive species.
• The invasive root system and strong growth can cause 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 eradication will take several attempts with herbicide injections which is tome consuming.
• It can also be disposed of in licensed landfill sites, however this is a costly process.

Question 43

What legal restrictions are there in dealing with Japanese Knotweed?

Answer 43

• In the UK, it is an offence under Section 14(2) of the Wildlife and Countryside Act 1981 to “plant or otherwise cause it to grow in the wild”. By default this meant it was also made illegal to spread it in the UK.
• It is also classed as “controlled waste” in the UK under Part 2 of the Environmental Protection Act 1990 which requires disposal at licensed landfill sites.

Question 44

How should Japanese Knotweed be dealt with?

Answer 44

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 45

Japanese Knotweed - Treatments

Answer 45

Typically there are four methods:
1 - Excavation - Involves digging out and removing all Knotweed material. One the knotweed has been removed there are a number of options available.
- Dispose of in landfill - Last resort method (Environment Agency Knotweed CoP)
- On-site treatments - Can include burying it in a cell burial (enveloped in root barrier with top of cell no less than 2 metres below ground level).
2 - Mechanical Disturbance - Involves weakening the rhizome of the plant by cutting it up into smaller pieces and putting some of the deeper rhizomes closer to the surface. This makes the knotweed more susceptible to other forms of treatment.
3 - Root Barriers - Barriers are used to contain Knotweed that, for one reason or another, cannot practically be excavated (eg. rhizomes that spread across boundaries or close proximity to structures). You must use specialist root barrier membranes for this as standard plastic sheets are not strong enough to prevent Knotweed growth.
4 - Herbicide Control - This involves the regular use of herbicides, usually over a few growing seasons, to gradually kill off the plant. There was a time when residual herbicides were the preferred choice of contractors, since they are stronger and keep working in the soil or even years after initial application. However, residual herbicides increase the risk of dormancy occurring and most residual products have now been withdrawn from use in the UK.
The most commonly used herbicide is non-residual and contains the active ingredient glyphosate. This chemical takes longer to stop the emergence of any new growth (usually 3-4 years for a standard domestic infestation) but is more likely to have a lasting result.

Question 46

What are the timescales for treating Japanese Knotweed?

Answer 46

• Timescales vary according to the control method chosen. generally speaking, the more time available for treatment the more options there are and the less it will cost.
  The average timescales are:
• Excavation and removal to landfill, or burial on site - 8 weeks
• Herbicidal treatment - 2-5 growing seasons.