Building pathology

Question 1

What are the causes and remedies for flat roof defects?

Answer 1

Surface crazing - solar damage. Small areas can be patched but significant damage would require replacement, solar protection should be added.

Ponding - inadequate falls increases risk of frost damage and reduces the lifespan of the roof covering. Adjust falls to provide a suitable gradient of 1:40

Blistering - caused by water vapour pressure below the roof covering, blisters should be cut out and re-bonded allowing trapped moisture to escape first.

Thermal movement - cracks and splits occur when there is thermal or moisture movement between the roof substrate and membrane. In an extreme case re-roofing will be required using a high-performance felt

Loose flashings or upstands - poor workmanship of weather damage

Damage by tradesman or falling debris

Question 2

What is a method of assessing flat roof defects?

Answer 2

Electronic leak detection

Question 3

What should be considered when deciding whether to replace or repair a roof?

Answer 3

Its age, life expectancy, and condition.

Question 4

Explain damp?

Answer 4

Moisture in a building causing decay, staining, mould, frost damage or wet patches

Question 5

What is a speedy carbide meter?

Answer 5

A device to measure moisture in masonry, drilling into wall to obtain dust and put in sealed container with calcium carbide

Question 6

What causes rising damp?

Answer 6

Lack of, failure, or bridging of damp proof course. Treatment would be removal of any thing bridging the damp proof course, injecting a damper of course if necessary, using lime plaster and wash to minimise damage to internal finishes if no DPC

Question 7

How would you rectify a cold bridge?

Answer 7

Possibly by introducing insulation we are missing, in an extreme case it may need to be rebuilt with better insulating materials or a thermal break

Question 8

If you saw a number of cracks on an external wall what would you consider?

Answer 8

I would know the type of material, form of construction, and soil. Consider trees or stance, alterations, drainage, structural alterations

Question 9

Explain different causes of cracks?

Answer 9

Subsidence, Heath, differential settlement, lintel failure, corroded lintel

Question 10

How do you assess cracks?

Answer 10

Using BRE Digest 251 and monitoring:
<2mm very slight
2mm-5mm - slight or aesthetic
5mm - 15mm - moderate concern
15mm - 25mm - severe
>25mm - very severe possible unstable

Question 11

What could cause stepped cracking on the corner of a building?

Answer 11

Settlement, subsidence, heave

Question 12

What causes cracking in concrete?

Answer 12

Carbonation, chloride attack, silica reaction as well as structural movement and poor design

Question 13

Explain heave

Answer 13

Upward movement of the ground in cohesive soils such as clay, caused by removal of trees or changes in the water table. Can also be caused by leaking drains or inadequate foundations built within movement zones.

Question 14

What are the main timber defects?

Answer 14

wet rot, dry rot, insect attack

Question 15

How do you identify Dry rot?

Answer 15

Shrinkage and warping of timber caused by the removal of moisture. Splits into cuboidal cracking. Wood becomes light and crumbles when touched. Greyish funghi when wet or yellow or purple when dry. From 20% moisture. More serious than wet rot as continues to grow when dry.

Question 16

How do you identify wet rot?

Answer 16

Darker appearance, crumbles to the touch appears flaky and spongy. Funghi can be white, brown, Amber, green or black with flexible strands when dry. Fruiting bodies can be a number of different colours. Occurs 30-50% moisture

Question 17

How do you rectify dry or wet rot?

Answer 17

Remove the source of moisture, promote rapid drying, apply fungicidal treatment, and replace affected timbers.

Question 18

How would you identify and resolve dry rot in floor joists?

Answer 18

Would shrinkage and cuboidal cracking. Grey or yellow fungi. Cotton wool type funghi if humid. Affected timbers removed and replaced with pre-treated timber and remaining timbers treated with fungicide. Affected masonry should be sterilised. Cut back approx 1m from affected areas.

Question 19

How would you identify and resolve wet rot in floor joists?

Answer 19

High moisture content of around 50%. In areas where there is significant dampness following a leak of building failure. Surface cracking along the grain. Affected timber is dark brown. Remove the source of dampness, remove affected timbers and treat or timbers with a preservative. Additional ventilation may be required.

Question 20

What are common insects that attack Timber?

Answer 20

Common furniture beetle, deathwatch beetle. Study boreholes to identify if the infestation is active or dormant. Apply a suitable treatment overlapping at least 300 mm onto sound timber. Holes are typically 1 mm to 1.5 mm in diameter, frass dust if active

Question 21

How does woodworm affect timber?

Answer 21

The adult beetle lays eggs on or under the surface of the timber, results in Gladstan feed on the timber is causing structural and cosmetic damage before hatching as Beatles which then repeats the cycle. It is treated with insecticides but the type of beetle must be identified first.

Question 22

What could cause a deflected timber floor and how could it be rectified?

Answer 22

Notching, what, insufficient size joist, overloading, deterioration of sleeper walls. Carry out repairs as applicable, over cloud, remove and replace, install a solid floor.

Question 23

What causes crazing and cracking on the surface of a new reinforced slab?

Answer 23

Poor or inadequate curing caused by environmental conditions. Poor mix.

Question 24

You are asked to inspect a leak on the first floor of a two story cavity wall building what would you do and what are potential causes?

Answer 24

Firstly I look at any building information available and consider the type of construction and materials. I would ask the building owner or occupier when it started and if it changes in location/appearance. I will inspect the property externally to look for any damage to the roof coverings or flashings I would also look in the loft for any leaking pipes or other leaks.

Question 25

How would you identify cavity wall tire failure?

Answer 25

Horizontal cracking every 450 mm or so. Corrosion of old wall ties or movement of the wall is a ball scope to confirm the defect and then locally replace ties. I would recommend using stainless steel fixed ties secured with an epoxy resin.

Question 26

What is nail fatigue?

Answer 26

Corrosion of iron slate fixings in old roof - slates will fall and will usually affect the whole roof

Question 27

What is JKW?

Answer 27

It is a large perennial plant that has hollow stems and distinct give it a bamboo appearance, grows in zigzags. Leaves are like shields. Can grow through cracks in walls or foundations. Flowers are small and cream or white.

Grows in dense colonies that crowd out other spaces can grow up to 7 m high and 3 m deep making removal difficult and is resiliency cutting. Will re-sprout from boots. Most effective method of control is herbicide application via injection around the flowering stage in late summer or autumn.

Question 28

Why is Japanese knotweed a problem for buildings and construction sites?

Answer 28

The invasive root system and strong growth can cause damage to foundations and structures. There are legal restrictions on its removal and disposal. Cutting can result in it spreading around the site. Must be disposed in license landfill sites and can be expensive.

Question 29

What are the legal restrictions with Japanese knotweed?

Answer 29

An offence under the wildlife and countryside act to plant or otherwise cause it to grow in the wild. Illegal to spread Japanese knotweed and is classed as controlled waste.

Question 30

What are the four main types of treatment for Japanese knotweed?

Answer 30

Excavation, mechanical disturbance, route barriers, herbicide. Timescales for treatment vary from eight weeks for excavation, 2 to 5 growing seasons for herbicide treatment, 3 to 4 years for some herbicide treatments. Refer to a specialist Japanese knotweed surveyor to identify, and provide advice on its treatment or management. Discuss with legal advisor on implications for a mortgage. Follow RICS professional standard of Japanese knotweed and residential property 1st Ed 2022 and decision tree.