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 recognise 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 coloured 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 ‘cottonwool’ 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 sterilisation.