General Building Pathology

Question 1

What is the BRE?

Answer 1

Building Research Establishment, owned by charitable organisation the BRE Trust. BRE provides research, advice, training, testing, certification and standards for both public and private sector organisations in the UK and abroad.

Question 2

What are BRE Digests?

Answer 2

Summaries on specific topics in construction design and technology. They draw on BRE’s expertise in these areas and provide essential support for all involved in design, specification, construction and maintenance.

Question 3

can you give some examples of BRE digests you have used?

Answer 3

Timber Defect
BRE Digest 345 - Wet rots: recognition and control.
BRE Digest 299 - Dry rot- its recognition and control.

Cracking
BRE Digest 251 - Assessment of cracking in low rise buildings
BRE Digest 343 - simple measuring and monitoring in low rise buildings

Question 4

What is sick building sydrome?

Answer 4

Where people suffer illness from the poor design of building.

Question 5

What are the effects and what can cause it.

Answer 5

Contribution of factors within a building which may cause people to feel dizzy, sick, flu, stress, dry eyes etc

• Bacteria in air conditioning / ventilation
• Artificial lighting
• Heating provisions / humidity
• Noise levels

E.g. use natural ventilation where possible, correct lighting levels, place photocopiers in separate rooms to people

Question 6

What is a British Standard?

Answer 6

The British Standards Institution (BSI) is the UK National Standards Body (NSB). It publishes standards and provides a range of books, self-assessment tools, conferences and training services.

Question 7

Give an example of British Standards?

Answer 7

BS 9999: Code of practice for fire safety in the design, management and use of buildings.

Question 8

What does BS9999 set out to do?

Answer 8

A prescriptive code of practice for fire safety design beyond the limits of Approved Document B.
• It is NOT a fire engineering guide, although it uses fire engineering
• principles to formulate the guidance provided
• Conceived in 1997 to publish in 2002
• Sits between Approved Document B and Fire Safety Engineering
• Replaces/updates most of BS 5588: Fire precautions in the design, construction and use of buildings, except Part 1 for residential buildings

Question 9

What does BS9999 cover?

Answer 9

1 General
2 Risk profiles and assessing risk
3 Ensuring effective fire protection
4 Managing fire safety
5 Designing means of escape
6 Access and facilities for fire fighting
7 Designing the building structure: Load bearing and non load bearing elements
8 Special risk protection
9. Managing occupied buildings

Question 10

What is Approved Document B?

Answer 10

Approved Document B (Fire Safety) provides guidance about how the building regulations can be satisfied in common building situations, but these are not always applicable to more complex, larger building.

Question 11

What aspects of fire safety does Part B cover?

Answer 11

B1. To provide appropriate means of warning and escape.
B2. To adequately resist internal fire spread (linings).
B3. To adequately resist internal fire spread (structure).
B4. To adequately resist external fire spread.
B5. To provide reasonable access and facilities for the fire service.

Question 12

What is the difference between Approved Document B and BS9999?

Answer 12

BS 9999, is still prescriptive but it is a more flexible approach
Structured approach to risk based design based on FSE (Fire Safety Engineering)

Question 13

What is Fire Safety Engineering?

Answer 13

Fire Safety Engineering is the application of scientific and engineering principles based on the understanding of the effects of fire, the reaction and behaviour of people to fire and how to protect people, property and the environment.

Question 14

Flat roof construction defects

Answer 14

• Intersitial Condensation
• Missing termination bar
• Woodwall slab roof deck
• Rotten timber deck due to water ingress
• Lack of appropirate falls to drainage
• lack of insulation

Question 15

Flat roof covering defects

Answer 15

• Surface crazing – lack of solar protection
• Splites/tears/cracking
• Blistering
• Inadequate skirting, upstand height promoting water ingress
• Distortion

Question 16

Concrete defect

Alkali Silica Reaction

Answer 16

Alkali Silica Reaction (concrete cancer) BRE 330:
Defect: In certain situations the alkaline water can react with the silica in the aggregate to produce a gel. The gel takes in water, expands and can cause concrete to crack or disrupt.

Identification -
In unrestrained concrete, the cracks have a characteristic random distribution often referred to as ‘map cracking’.

In restrained concrete, the cracking tends to run parallel to the main reinforcing bars.

In particularly active situations, the cracks may be bordered by a colourless gel. This leads to surface pop-outs and spalling. Petrographic examination is the only sure way of identifying the attack.

Remedy - Three conditions are necessary for ASR to occur: certain silica in the aggregate, sufficient moisture, high alkalinity.

Removal of moisture by repairing damaged rain water goods is the first measure.

Removal of the delaminated concrete and an isolated patch repair may also be an alternative.

Secondary structural reinforcement can also be introduced.

Question 17

Sulphate Attack

Answer 17

Sulphate Attack

Cause: Reaction between sulphates, water and OPC or lime cement cause sulphates to expand

Source: Can be external or internal – due to penetration of sulphates in solution such as ground water, gypsum in the aggregate etc. Sulphates are found in soil, hardcore

Symptoms:

• Blowing concrete
• Expansions of concrete
• Horizontal cracking on inner face bonding, spalling at low level etc
• Rate of carbonation increases

Treatment: replace defective concrete, protect areas from sulphates
and water ingress – DPM to floor slab if replaced

Question 18

Chloride Attack

Answer 18

“calcium chloride additive used in 1960-70’s to speed up curing time,

banned in 1977.

OR Can be introduced via de-icing salts or unwashed marine aggregate (sea dredged aggregate. Coast areas are also affected from spray).

Chloride ions affect the natural passive protective film on reinforcing steel allowing it to corrode faster

Treatment:

"Cut out areas of affected concrete
Wire brush the affected areas
Apply corrosion inhibitor
Reinstate concrete
Continue to monitor

If included in the mixture

A longer term and more expensive solution is to induce cathodic protection. This is where an external anode is connected to the metal and the passage of an electric current is used to stop corrosions.

If risk of loss of structural integrity a replacement of the memeber maybe required.

”

Question 19

Chloride Identification

Answer 19

“Rust staining and delamination of concrete.

Examination of the re-enforcement bar will show signs of pitting where localized breakdown of the passive oxide layer has occurred.

Occasionally the rebar may be completely eaten away leading to obvious structural concerns.

”

Question 20

Name the famous case study associated with Chloride attack

Answer 20

Piper row car park (Collapsed in 1997-

Question 21

Name Typical Timber Defects

Answer 21

Insect Attack
Mould Growth
Wet Rot / Dry Rot

Question 22

What is wet rot?

Answer 22

• Rot that occurs in high moisture contents.
• Cause cuboidal cracking
• Dark timber

Question 23

What is the remedy for wet rot?

Answer 23

Cut out affected area and replace.

Question 24

Name some insects that might attack timber

Answer 24

Common furniture beatle
Death watch beatle
House longhorn

Question 25

How would you identify insect attack

Answer 25

Location
Time of Year
Bore Hole

Question 26

Can you tell me more about insect attack?

Answer 26

Size of bore hole. Common furniture beetle is 1-2mm redish and smaller
Deathwatch is 2-3mm brown with yellow hairs. Look at BRE number 453

Question 27

Name some typical brickwork defect.

Answer 27

Frost attack
Efflourescence
Sulphate attack
Lime run off
Lime blow in bricks
Wall Tie failure
Calcium silica bricks.

Question 28

What is Frost Attack?

Answer 28

Commonly seen in older bricks with higher porosity. Water penetrates brick and when freezes expands, blowing the face of the brick. Progressive defect which accelerates the worse it gets.

Commonly seen in exposed locations and at low level due to water splash back.

9% increase in volume when water freezes

Caused by underfired bricks, incorrect use of bricks, exposed location and poor detailing.

Question 29

What is Efflorescence?

Answer 29

Common sight in new brickwork. Casued by soluble salts in solution being brought to the surface as the wall dries out.
Usually harmless and temporary although unsightly

Question 30

What do the different types of cracks look like and associated causes?

Answer 30

Horizontal cracking to brick work/stone = 
wall tie failure  (cavity walls)
Regents street disease
Lack of latteral restrain
Roof Spread

Stepped cracking wider at top than the bottom =
Heave

Stepped cracking wider at the bottom than the top=
subsidence

Stepped cracking either side above a lintel/brick arch =
lintel failure

Hairline cracking at wall and ceiling joints =
Shrinkage
Settlement - usually of a new build

cracks between a house and an extention or a bay window =
Differential movement.

Vertical cracking on a steel framed structure or between two different materials =
thermal expansion

Large scale cracking and sudden damage.=
sink holes
mines.

Question 31

Tell me about some issues caused with asphalt roofs?

Answer 31

Blisters caused by entrapment of moisture;
Slumping at upstands;
Cracking and embrittlement of the asphalt upstands;
Plant installation damage;
Vegetation growth.

Question 32

Common defects associated with built-up flat roofs?

Answer 32

Ponding
Timber decay - no vapour check
Blistering - trapped moisture

Question 33

What about liquid plastic membranes?

Answer 33

Poor adhesion
Puncturing
Biological attack

Question 34

Single ply membranes?

Answer 34

Puncture damage
Embrittlement of flashings
Contamination - bitumen
seam defects
wrinkles in membrane