An A–Z of building pathology for APC

Achieving the Building pathology competency means you must prove you understand a range of building defects, their causes and remedies, as Built Environment Journal's second APC A–Z article shows


  • Jen Lemen FRICS

12 January 2023

Crack in a wall

The APC pathway guide for building surveying requires that candidates for the Building pathology technical competency must demonstrate 'an understanding of defects analysis, and the likely resultant defects from failures in building fabric'.

While all the following topics will be essential knowledge for the competency, this is not an exhaustive list, and you will need to ensure you read around the subject.

Advice: to demonstrate the competency to level 3, you are required to give reasoned advice and recommendations to clients on a range of defects, including those found in typical buildings in your locality as well as others encountered less frequently.

Bricks: a variety of defects can arise in brickwork, primarily resulting from poor design, materials, specification or detailing. Examples include frost damage, soluble salts on the building surface known as efflorescence, staining – for example, vanadium salts, iron or manganese – sulphate attack, and weathering of mortar joints. Being able to identify the defect and diagnose the cause is essential for surveyors, as is an ability to recommend practical and cost-effective remedial actions.

Cladding: significant defects can be found in the external wall systems of residential buildings, which include cladding. Recent concern has related to fire safety defects in particular, which were a primary factor in the Grenfell Tower fire. Surveyors need to be able to identify and advise on different types of cladding, including highly flammable products such as aluminium composite materials with polyethylene cores and certain high-pressure laminates.

Drainage: in a level 3 survey, surveyors will need to lift accessible inspection chambers for drains and septic tanks to observe normal operation. A drainage defect that surveyors may encounter is the deterioration of pitch-fibre pipes, which were commonly used from the 1940s to 1970s in certain areas of the UK.

Pitch fibre is made from wood cellulose impregnated with coal tar, which was originally specified to strengthen it. Drains made of the material were cheaper, more lightweight and easier to install than traditional clay pipes. However, pitch fibre reacts adversely to hot water, fat and oil, and this can lead to collapsed pipes and blocked drains, limiting their life expectancy.

Pitch fibre drains do not always need to be replaced if in good working order; however, they should be monitored if left in situ. If they are in very poor condition, drains will need to be repaired through re-rounding (using a tool to re-shape the pipe and remove any bubbling of the pitch fibre), or replaced entirely with modern plastic piping.

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Easi-Form: built from the 1920s to 1960s, the Laing Easi-Form is a house type categorised as non-traditional construction. The houses were designed to be quick and cheap to build, using concrete cast in situ or prefabricated concrete panels.

Such construction is not designated as defective under the Housing Act 1985. House construction types were designated as defective if there was a defect in their design and/or their value was significantly reduced as a result.

However, there are a number of typical defects that surveyors may encounter, which include poor thermal efficiency and levels of insulation, the presence of asbestos-containing materials, and condensation.

Foundations: to diagnose wider building defects successfully, it is essential to understand how foundations are constructed. These come in a variety of forms, including pad, raft and piled, depending on the load-bearing capacity of the underlying ground. Defects can result from sulphate attack, insufficient-load bearing capacity, drainage issues, insufficient width, and the effect of roots from nearby trees.

Hunting for leaks: a typical cause of damp in buildings is leaking pipework or water penetration through roofs, walls, floors and windows. Leaks can be a result of incorrect specification, detailing, designing or installation – for example, eroded mortar between external brickwork, slipped roof tiles or incorrectly installed plumbing pipework. Surveyors need to follow the trail to identify the potential causes of such defects, which may not be obvious on first inspection.

Insulation: cavity wall insulation can be retrofitted to buildings to improve their thermal performance. However, it is often installed incorrectly – for example, it may slump or block vents, while areas may be missed or cavities could be under- or overfilled. These can in turn lead to cold bridging, condensation, mould growth and damp.

With the insulation in the external wall cavities, it can be difficult to diagnose such issues without invasive investigation. A surveyor may recommend invasive investigation as an additional instruction, therefore, if this is the likely cause of an internal defect.

Joint position statement: RICS recently collaborated with Historic England and the Property Care Association to publish the joint position statement Investigation of moisture and its effect on traditional buildings: Principles and competencies. The document provides a detailed guide for all property professionals on how to detect and diagnose moisture defects in traditional buildings, the actions they should take, and how to take responsibility for the advice they provide.

K-value: this refers to the ability of a material to conduct heat. Materials that are good insulators typically have a low K-value. Related metrics include C-values, which relate to thermal conductance (how a material conducts heat), and R-values, which relate to thermal resistance (how a material resists heat transfer).

Large v Hart & Anor: Large v Hart & Anor [2021] EWCA Civ 24 related to a level 2 survey where the surveyor had only reported minor issues with drainage, gutters and pipework. On the strength of this the client subsequently purchased the property,  but experienced water ingress and damp after they moved in. This led to a successful negligence claim against the surveyor.

The court found the surveyor liable as his report failed to identify significant issues relating to damp and also had not advised obtaining a professional consultant's certificate before purchase. The case is a reminder of the importance of diligently diagnosing defects within the scope of the survey instructed, or at least highlighting where inspection and analysis have been limited.

Mortar: used to bind masonry together, mortar needs to be specified correctly to work effectively for a long period of time. The specification must include the strength of the mortar mix and the type of mortar used; for example, in traditional buildings constructed of stone, lime mortar should be used because it permits the building to breathe as well as some level of movement. The mortar is the sacrificial material in a wall construction and must always be weaker than the wall material.

Non-traditional construction: many types of non-traditional construction have been used in the UK, primarily between the late 1940s and the 1960s as a way of quickly building new houses after the Second World War. More modern methods of construction have also been used recently to address increasing awareness of the need for sustainability. Being able to recognise forms of non-traditional construction is essential, as well as typical defects associated with them, such as poor thermal performance and cracking.

Occupancy: the way a building is occupied and used may cause a variety of building defects. For instance, drying laundry without opening windows or intensive use of a bathroom without extraction can lead to condensation and mould growth. Another example is the storage of heavy items in loft space, which can crack the ceiling surfaces below.

Surveyors need to be able to factor the use of a building into their diagnosis of defects and recommended remedial actions. The latter may not always involve repair, but might entail advising how to use a building better.

'Being able to recognise forms of non-traditional construction is essential, as well as typical defects associated with them, such as poor thermal performance and cracking'

Period property: being able to identify the age of a building is key to diagnosing defects and their causes effectively. For example, Victorian houses are often constructed with solid masonry walls that are prone to rainwater penetration and internal dampness.

The presence of a damp-proof course (DPC) also needs to be considered as they are found in different forms in properties of different eras. For example, some old stone buildings may have no DPC, whereas slate or bitumen DPCs were used from around 1900s onwards, while since the mid to late 20th century modern polythene DPCs have been installed.

Quoin: this is simply the external angle or corner of a building;  knowing construction terminology of this kind is an essential part of the competency. Though remember, reports are to be in plain English for the layperson or client to understand.

Recording observations: surveyors need to be able to record an appropriate level of detail on building pathology in their reports, and this includes the use of sketches, drawings and photographs.

Standards: surveyors must be aware of relevant standards. In regulatory or disciplinary proceedings, RICS or any court or tribunal will take account of whether a surveyor followed the relevant standard, which would demonstrate the extent to which they had acted professionally and competently.

Structural movement: all buildings will experience movement; however, where this is substantial it will lead to a range of building defects, usually in the form of cracking. Causes of movement include subsidence, settlement and heave, among others. Surveyors need to be able to use BRE Digest 251 to diagnose cracking, including the category of crack and proposed remedial action.

Timber defects: a number of defects can occur in timber, such as wet rot, dry rot and insect infestation. A common example of the latter is infestation by wood-boring insects, which can be identified by the exit holes they leave in the timber as well as by larval excrement – frass – and wood dust. Such insects include the common furniture beetle, deathwatch beetle and house longhorn beetle, while termites are also a risk.

Underground rooms: a basement, cellar or other underground room is prone to a variety of building defects. These often arise where the water table is high but waterproofing – or tanking – is insufficient, leading to water ingress and damp-related issues.

Ventilation: ventilating buildings is essential to provide a healthy living environment, enabling fresh air to circulate and moderating internal temperature. Ventilation can be provided mechanically, using extractor fans for example, or naturally through building design and opening windows and doors.

Without sufficient ventilation, building defects such as condensation and mould can occur. One serious impact of poor ventilation among other contributory factors can be sick building syndrome, where occupants may suffer from symptoms such as a blocked nose, sore throat, cough or headaches.

Wall tie failure: in cavity wall construction, such ties are used to hold the internal and external leaves of the walls together. The cavity itself primarily helps to prevent water from entering the building and leaves space for insulation to be installed.

Wall ties are subject to corrosion, usually in older construction where milder steel ties were used; or they can fail as a result of poor construction detailing where they are not installed properly – or because there is a lack of galvanic corrosion protection, for example, as prior to 1982 galvanising standards for steel were lower than modern standards. Being able to identify cavity wall tie failure or replacement is an essential skill for surveyors.

X-ray imaging: where surveyors recommend further investigations into the condition of concrete in buildings, including floors and wall panels, digital X-ray imaging can offer a non-invasive alternative to cutting, coring or breaking concrete to take samples. This method can help diagnose concrete defects, such as corrosion in steel reinforcements.

Yield strength of steel: this refers to the maximum stress that can be applied to steel before it changes shape permanently. A related term is tensile strength, which concerns the resistance of steel to breaking under tension.

Zinc: more commonly found in European buildings, this metal is sometimes used as a roof covering or in gutters and downpipes. When specified and installed correctly, it can last for more than 100 years. Defects can occur due to thermal movement of expansion joints and the corrosion of other less resilient metals in contact with zinc.


Jen Lemen FRICS is a co-founder and partner at Property Elite
Contact Jen: Email

Related competencies include: Building pathology, Construction technology and environmental services, Inspection

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