Building Pathology Flashcards
Tell us about the methods of assessing flat roof defects you have learned about?
Electronic leak detection is possible through a weak electrical field directed on to the dampened surface and any current that ‘earths’ into the building changes the nature of the field locally.
This should pinpoint the penetration or just as importantly show when water penetration is not caused by a roof leak.
Also a thermographic examination could be carried out to identify the areas of the leaks.
The thermographic image will highlight areas of moisture retained within the roof in order to pinpoint the location of the leak.
What are the common defects associated with flat roofs?
The common defects associated with flat roofs include:-
Blistering.
Splitting of coverings.
Sagging due to failure of the decking between joists.
Ponding due to insufficient falls.
Damages to flashings.
What are the causes and remedies for some of the defects associated with Flat Roofs?
Crazing - Surface crazing is caused where there is a lack of adequate protection from the harmful effects of exposure to the sun or, in rare occasions, chemical attack. If this is only in small localised patches no treatment is necessary but should be regularly rechecked. If the crazing is more widespread the areas will have to be re-roofed and specialist protection introduced.
Ponding - A minimum gradient of 1:40 is required for a flat roof to shed water effectively. Where the
appropriate fall has not been built in or has been altered by structural movement ponding is likely to occur. Where water is allowed to sit on the surface of a felt roof for an extended period its lifespan will
be drastically reduced. An increase in the gradient of the roof will need to be achieved through structural alteration and re-covering.
Thermal Movement – Cracks and splits can occur when there is thermal or moisture movement between the roof substrate and membrane. It is likely that localised re-roofing will be necessary to address this issue using a high performance felt.
Blistering - Blisters can be caused by water vapour pressure occurring below the roof covering. The blister should be cut and then re-bonded to the underlay allowing any trapped moisture to escape first. The source of the moisture should also be traced and rectified.
Flashings and Falls Around Openings Defects - Poor workmanship or deterioration of the flashing details around openings can lead to water ingress. Also 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. They should be repaired using localised patch repairs.
What should you take into account when deciding whether to repair or
replace a flat roof?
Its age, life expectancy and overall condition.
Surveyors also need to consider whether the defects are localised or effecting the whole of the roof and if the defect is effecting the surface layer or the roof structure.
A client’s intentions for the building also need to be established including their budget, the building’s use, any disruption caused through repair and possible phasing requirements.
You are asked to inspect a flat roof take us through the
inspection process?
Firstly I would gather historical building information and details of any current or previous issues with the roof.
I would then make arrangements for access and prepare necessary RAMS to establish the roof’s:
o Age.
o Previous repairs undertaken.
o When and where the roof leaks.
o Ponding issues.
o Use of the rooms below.
o Whether the roof is used as a balcony or terrace.
o Access arrangements.
What is damp?
A building is only considered to be damp if the 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?
The use of a protimeter can establish the prevalence of damp in buildings.
Moisture meters or a Speedy Carbide Meter can also be used to determine the moisture content of walls, and the level of 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.
By drilling into masonry and putting the 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.
Describe three issues and remedies for rising damp.
Rising damp is caused either by lack of a damp proof course, a defective damp proof course or external features bridging the damp proof course.
The remedy therefore involves removing the external feature causing bridging, the
injection of water repellent chemicals into the brick work or the fitting of a new physical damp proof membrane.
Where a damp proof course is not suitable, lime plaster and wash can be used to minimise the damage caused to the internal finishes.
How would you identify penetration damp, what are the
causes and how would you remedy it?
Penetration damp can be identified through the appearance of damp patches on walls, ceilings or floors.
These patches tend to grow or darken after periods of heavy or prolonged rain.
Causation can be due to rain driving through exposed masonry walls that have insufficient thickness, problems with cavity trays, cracked or detached rendering, defects to window cills and blocked cavity ties.
Remedies for penetrating damp include the repointing of defective mortar joints, application of masonry water repellent, making good defective joint details, inspection of cavity trays and cavity ties to address any blockages and the inspection of areas of roofs such as chimneys, parapets and thresholds to address any defects in these elements.
What is a cold bridge?
A cold bridge is created when materials that are poor thermal insulators come into
contact, allowing heat to flow through the path created.
Insulation around a bridge is of little help in preventing heat loss or gain due to thermal bridging.
The bridging has to be eliminated, rebuilt with a reduced cross-section or with materials that have better insulating properties, or with an additional insulating component, called a thermal break
What are the causes of condensation and how would you remedy it?
Hot air is able to carry moisture and when this hot 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.
Causes of condensation include a lack of insulation, lack of ventilation and unheated areas of the building.
Remedies of condensation include a reduction in moisture generation, providing adequate ventilation, provide adequate heating and improving the building insulation.
How long would you leave the brick & plaster to dry out before commencing work?
You need to allow time for the brick to dry out before commencing works.
A de-humidifer can speed up the process, however a minimum of 3-4 months is recommended.
What ways could moisture enter the building and how would you differentiate between the different types?
Penetrating damp — moisture gets into the building because there is a porous bridge transferring moisture by capillary action from the external face of the walls to the internal face of the walls. This could be due to a single skin of masonry, water trapped behind render and mortar snots on cavity ties. There may also be a hole in the roof which allows moisture in and gets into the ceiling due to the force of gravity.
Rising damp — moisture rises up the wall from the ground due to capillary action normally up to a maximum of 1m high tide marks. This is identified through a visual inspection of its location and extent and also use of a moisture meter. If there is a DPC, this may be failing with something bridging the DPC however one would need to ensure
there are no other possible causes.
Condensation — hot moist air hits a cold surface and condenses causing the surface to absorb the moisture which encourages staining and mildew growth. This is identified through the distinctive mildew, the location of poorly ventilated areas with high humidity, kitchens, bathrooms, bedrooms and rooms used for drying clothes.
You are inspecting a building and identify a number of cracks in the external wall take me through your thought process?
I would firstly note the material the wall is constructed from and what form of construction the building is.
I would also consider any local factors which could be causing the cracking such as:-
o Trees.
o Stumps.
o Alterations to the building.
o Drains in the vicinity of the crack.
o If there have been any alterations to the building such as extensions, rooms in the roof or internal layout alterations.
What other sorts of cracks would you expect to see on a brick building and what might have caused them?
Subsidence — A movement down in the ground level. In clay soil, the growth of large trees which remove water from the ground can cause this. This leads can lead to 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 top and thinner at the bottom.
Heave — A movement upwards 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. This leads to 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.
Settlement — A movement down 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.
Differential Settlement — If two sections of a building are constructed off different foundations or the ground is made up of different soil types or strata then one may settle more than another causing cracking between the two sections of the building. This issue is
most common with extensions.
Lintel failure — 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.
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.
What size cracks are of concern?
Up to 2mm — very slight concern.
2mm-5mm — slight or aesthetic concern.
5mm-15mm — moderate concern.
15mm-25mm — severe.
Over 25mm — very severe with stability concerns.
If there was stepped cracking on the corner of a building,
what might have caused it?
Settlement.
Subsidence.
Heave
What if the cracks were present on concrete?
I would consider the common concrete defects such as Carbonation, Chloride attack and silica reaction as well as issues relating to structural movement and poor design and construction.
What type of soil is susceptible to heave and what are the possible causes?
Cohesive soils such as clay.
Possible causes include removal of trees and changes in the water table.
Leaking drains or inadequate foundations that are built within the movement zones.
What types of timber defects are there?
The main timber defects are:-
Dry rot.
Wet rot.
Insect attack
Dry rot with shrinking and warping timber caused by removal of moisture from the wood.
Wet rot with darker or white appearance that crumbles to the touch, it appears flaky and is a soft spongy texture.
Describe the different types of rot and how you would
recognise them.
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.
Wet Rot — 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 are the remedial measures to dry & wet rot?
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 required.
The ends of the joists in a timber floor built in an external wall have been seriously affected by dry rot. How will you recognise this type of rot and what action would you take to resolve the problem?
Typical indications of dry rot include:
Wood shrinkage and dark cracks of a ‘cuboidal’ manner.
A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow which often develops under less humid conditions.
This ‘skin’ can be peeled like a mushroom.
White, fluffy ‘cottonwool’ 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 the masonry, it should be isolated using physical containment and/or masonry sterilisation.
The ends of the joists in a timber floor built in an external wall have been seriously affected by wet rot. How will you recognise this type of rot and what action would you take to resolve the problem?
Wet Rot results in a 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:
o Surface cracking where cracks follow the timber grain.
o Hyphae strands which are light brown & yellow (a key difference from dry rot).
o Infected timber turns dark brown in colour.
The first step to remedy wet rot is to find and eliminate the source of dampness to prevent the timbers becoming damp.
All infected and/or damaged timber should be removed, as these may be structurally impaired due 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 to improve the ventilation.
What are the remedial measures for Dry Rot?
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, similar to wet rot needs to be cut out and replaced, including those within approximately 300mm-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 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.
Explain the life cycle of dry rot?
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.
Hyphae – where timber and moisture are present the spore will produces very fine white 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.
Mycelium - the resulting hyphae mass is known 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.
Fruiting Body - to 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.
Name some common insects that are known to attack timber and explain what remedial methods are available?
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 weevils.
Category C – where no treatment is needed for bark borers.
Remedial measures for these insects include:-
o Studying flight holes to identify the type of beetle and determine if the infestation is still active or dormant.
o Apply two coats of boron based treatment to all affected areas overlapping at least 300mm onto the sound timber.
o In the case of a severe attack, replacement timber with pre-treated wood is required.
How do you identify the presence of woodworm?
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 1mm 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.
How do woodworms affect timber in buildings?
Typically the adult beetles lays eggs on, or just under the surface of the wood members in question.
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.
What is a woodworm infestation likely to indicate?
Most species of woodworm require that the wooden item contain a higher 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.
How is a woodworm infestation treated?
Woodworm infestation is generally controlled with chemical insecticides.
However it is also advisable to investigate and solve possible damp issues as dry wood is not usually affected and wood that remains damp may be re-infected at a later date.
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?
Confirm the cause of the deflection whether this is due to:-
- Notching.
- Rot.
- Insufficiently sized joists.
- Insufficient centres.
- Overloading.
- Deterioration of sleeper walls.
Confirm if the issue can be remedied and whether the timber floor can be retained.
There may be a potential to:-
-Supplement the timber joists.
- To overboard.
- Remove and replace with suspended timber floor.
- Install an alternative solid floor.
A newly cast reinforced concrete slab is exhibiting crazing and cracking on its surface, what are the possible causes?
Poor or inadequate curing which are 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 coarse 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.
What are Nickel Sulfide Inclusions?
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 remains in a high-temperature form.
Over several years, the 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.
What else may have caused glazing to crack if it wasn’t Nickel Sulphide Inclusions?
Structural movement around the window opening could have put pressure on the glazing and caused the crack.
You find a leak at a high level on the first floor of a 2 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 such a defect?
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 roof coverings and defective or missing flashings around roof penetrations.
When in the roof space I would also look for evidence of leaking pipes.
How does cavity wall tie failure present itself and how would you fix it?
Cavity wall tie failure can be identified when horizontal cracking appears in every 5 or so brick courses or in render.
It is due to the corrosion of old steel ties such as large fishtail ties.
To remediate this issue I would firstly use a boroscope 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 utilised to remedy this issue.
What is nail fatigue?
This is a common problem for pitched roofs with slates or tiles.
The nails have rusted through allowing the slates or tiles 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 foam spray solution, but as it sets hard it prevents the roof from moving and also impedes the ventilation.
What is Japanese knotweed?
Japanese knotweed is a large, herbaceous perennial plant.
What does it look like?
Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo.
While stems may reach a maximum height of 3-4 m each growing season, it is typical to see much
smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down.
The leaves are broad oval.
The flowers are small, cream or white
Why is it an issue?
It forms thick, dense colonies that completely crowd out any other herbaceous species.
It can extend 7 metres (23 ft) horizontally and 3 metres (9.8 ft) 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.
Why is it an issue for buildings and construction sites?
It is listed by the World Conservation Union as one of the world’s 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 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 it?
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.
It is also classed as “controlled waste” in Britain under part 2 of the Environmental Protection Act 1990 which requires disposal at licensed landfill sites.
How should it be dealt with?
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
What is the treatment of Japanese Knotweed?
Typically, there are 4 methods:
Excavation
Which involves digging out and removing all knotweed material.
Once the knotweed has been fully excavated, there are a number of options available:-
* The traditional method has been to dispose of it as landfill.
* This is considered unsustainable and expensive and was regarded by the Environment Agency in their 2006 Knotweed Code of Practice as a last resort.
* On-site treatments of excavated material can include burying it in a cell burial (enveloped in root barrier and with the top of the cell no less than 2 meters below finished ground level).
Mechanical disturbance
This is not an eradication method in itself but involves weakening the rhizome of the plant by cutting it up into smaller pieces and pulling some of the deeper rhizomes closer to the surface. This makes the knotweed more susceptible to other forms of treatment.
Root barriers
Barriers are used to contain knotweed that, for one reason or another, cannot practically be excavated (e.g. rhizomes that spread across boundaries or are in 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.
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 for months or even years after initial application.
However, residual herbicides increase the risk of dormancy occurring and most residual products have now been withdrawn for 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.
What are the timescales for treatment of Japanese Knotweed?
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:
o Excavation and removal to landfill – 8 weeks.
o Excavation and burial on site – 8 weeks.
o Excavation and relocation - 8 weeks.
o Herbicidal treatment of relocated knotweed - 2–5 growing seasons.
o Cultivation and herbicidal treatment - 2–5 growing seasons.
o Herbicidal treatment programme – 3–4 years (less than 20m2).
