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RICS APC Building Surveying (New Zealand) > 02 Dampness > Flashcards

02 Dampness Flashcards

1
Q

What is dampness?

A

The presence of unwanted moisture in the structure of a building, either the result of intrusion from the outside or condensation from within the structure.

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2
Q

What does dampness look like?

A
  • Visible wetting of walls, ceilings and floors
  • Blistering paint
  • Bulging plaster
  • Sulfate attack on brickwork
  • Mould on surfaces and fabrics
  • Musty smell
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3
Q

What are the forces that propel water from the outside into the interior of a building?

A
  • Capillary forces - water flowing through masonry or hairline cracks, usually by thermal catalysts.
  • Kinetic forces - wind-driven rain will force water into the depth of a wall.
  • Pressure differential - ventilation and air-conditioning systems may cause water to be sucked into the voids.
  • Gravity - water can drip in through imperfections in flashings, gutters, roofs, and parapet walls.
  • Surface tension - water will tend to follow a wet surface. It will flow around corners and edges.
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4
Q

What are the different ways moisture could enter the building?

A
  1. Rising damp
  2. Penetrating damp
  3. Condensation
  4. Weathering
  5. Trapped construction water (new builds)
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5
Q

What is rising damp?
- Identification
- Common Causes
- Controls
- Remedial Works

A

Moisture rising up from the ground through capillary action normally up to 1m high with tide marks. Usually from bridging of DPC or lack/failure of DPC.

(add more)

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6
Q

What is penetrating damp?
- Common failure of materials
- Location of water source
- Damage caused to materials or finishes
- Remedial works

A

Penetrating damp is when moisture from outside a building moves into the interior through the walls, roof, or ground.

Enters via a porous bridge transferring moisture through capillary action or there might be a hole in the building fabric.

Failures of materials - Roof leaks, internal leaks, blocked gutters, raised ground levels.

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7
Q

What are the different mechanisms of water ingress relating to penetrating dampness?

A

Luke Voce cards

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8
Q

What are the common causes and routes of penetrating damp?

A
  1. Cracks and defects: Water can enter through cracks in walls, roofs, window or door surrounds.
  2. Poorly installed insulation: Modern buildings can have water ingress if they have poorly installed cavity wall insulation.
  3. Degraded materials: Older buildings with porous bricks, degraded roof tiles, or defective masonry are more vulnerable.
  4. Faulty pipes, gutters, or roofs: Leaks from roofs, gutters, or pipes can cause penetrating damp

Luke Voce cards

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9
Q

What are the problems/effects associated with penetrating damp?

A
  1. Penetrating damp can damage plastering and wallpaper.
  2. It can cause toxic mold spores to grow.
  3. If left untreated, it can cause significant damage to the fabric of your home.

Luke Voce cards

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10
Q

What is Condensation?
- Common causes
- Interstitial
- Associated defects
- Mould
- Health risks
- Remedial works

A
  1. Condensation - change of water vapour naturally present in air into liquid water
  2. The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
  3. If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
  4. Once the air falls to a temperature where it can no longer hold the amount of water vapour present (i.e. it becomes saturated), liquid water will form on the cold surface
  • Warm moist air comes into contact with cold surfaces which releases the moisture. Generally at high level.

(add more)

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11
Q

What is meant by the terms ‘dew point’ and ‘relative humidity’?

A
  • Dew point - the temperature at which the air becomes saturated and will condense
  • Relative humidity - moisture content present within the air, referred to as a percentage of the amount of water vapour it can hold at that temperature. Warm air can hold more moisture than cold air, so as the air temperature falls, the maximum amount of water the air can hold also falls.
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12
Q

What is the acceptable RH in habitable spaces?

A

NZS 4303:1990 Ventilation for acceptable indoor air quality recommends relative humidity no greater than 60% in habitable spaces specifically to minimise the levels of allergenic or pathogenic organisms such as fungi and dust mites.

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13
Q

What causes condensation and high moisture levels?

A
  1. Moisture from leaks and damp ground
  2. Water released from household activities such as showering, washing, cooking and even breathing
  3. Moisture released from unflued gas heaters
  4. Inadequate heating and ventilation.
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14
Q

What problems are associated with condensation?

A
  1. Mould growth, particularly where RH remains above 70% for long periods (usually more than 12 hours)
  2. Health risks to the elderly, young children, asthmatics and those with weakened immune systems
  3. Can encourage timber decay where timbers are subject to prolonged moisture exposure
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15
Q

How would you identify condensation within a building?

A
  1. Wall has a ‘misty’ surface
  2. Stains or streaks of water runnin gdown a wall (particularly in bathrooms, kitchens and below windows)
  3. Damp patches with no definitive edges
  4. Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
  5. Localised dampness at potential ‘cold bridges’
  6. Patches of mould growth
  7. Humidity (measured using a hygrometer), insulation and ventilation levels as well as heating and living patterns must also be taken into account
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16
Q

How do you reduce the condensation and make houses warmer and drier?
What steps would you recommend to eliminate condensation?

A
  • Short term - mould-affected areas can be washed using a fungicidal or bleach solution - do not use water as this will just spread the mould
  • Long term
    Condensation can be controlled first, by reducing humidity, so that air is less likely to become saturated; second, by reducing the likelihood of warm air coming into contact with cold surfaces.

These improvements should be made in the following order:
1) Control moisture at source (remove unflued gas heater, add mechanical ventilation to kitchens and bathrooms)
2) Ventilate (openable windows, windows with ventilators)
3) Heat (raise the indoor temperature)
4) Insulate (raising the temperature of the windows and surface of exterior walls, thus lowering humidity)

17
Q

What is interstitial condensation, what are the signs, and how would you deal with it?

A

Interstitial condensation is condensation that occurs within the structure of an element, as opposed to on its surface. It is the formation of water droplets within a buildings walls, floors or roof.

If the internal surface temperature is above the dew point but the interior temperature of the element is below the dew point, water vapour will condense inside the element rather than on its surface

Signs
- Damp patches on walls or ceilings
- Hygroscopic salts on walls, which appear darker when damp
- Peeling wallpaper or rising paint
- Black mold

How to prevent it
- Ensure the building is well ventilated
- Use vapor control layers (VCLs) or membranes
- Position materials with low vapor resistance on the cooler side of the building
- Eliminate cold bridges
- Keep the internal temperature of the building even

If it occurs in a material such as timber, action will be needed to prevent risk of rot, usually by installing additional wall insulation
If internal insulation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation

18
Q

What is Weathering/?
- Life span of materials
- Degradation of materials due to location, exposure and vegetation
- Poor detailing

A

??

(add more)

19
Q

Why can dampness occur when water is trapped during construction?

A

Water can come from timber and concrete and can take a year or more to dry out.

(add more)

20
Q

Describe the main consequences caused by dampness within buildings.

A
  1. Health hazard
  2. Reduce strength of building materials
  3. Cause movement in building elements
  4. Lead to timber decay (dry and wet rot, insect attack)
  5. Cause chemical reactions in building components
  6. Reduce effectiveness of insulation
  7. Damage decorations
21
Q

What are the health risks associated with the presence of mould in buildings?

A
  1. Moulds produce allergens, irritants and sometimes toxic substances, so inhaling or touching mould spores can cause allergic reactions (e.g. sneezing, runny nose, red eyes, skin rash etc.) and respiratory problems (e.g. asthma attacks)
  2. There is contradicting research that certain toxigenic moulds can cause rare health conditions such as bleeding in the lungs - research is ongoing
  3. Who is at greatest risk? People with pre-existing asthma, People with weakened immune systems, Infants, and The elderly
22
Q

To avoid mould growth, what level should the relative humidity be kept under?

A

In New Zealand, the relative humidity (RH) in your home should be kept below 60% to avoid mold growth.

NZS 4303:1990 Ventilation for acceptable indoor air quality recommends relative humidity no greater than 60% in habitable spaces specifically to minimise the levels of allergenic or pathogenic organisms such as fungi and dust mites.

23
Q

What guidance is available in relation to condensation in buildings?

A

NZBC E3 Internal Moisture

This Building Code clause requires buildings to be constructed to avoid fungal growth and excessive moisture. Its provisions relate to habitable spaces, bathrooms, laundries and other spaces where moisture may be generated or accumulate.

24
Q

What are the tools for identifying different types of damp?

A
  • Conductance/Moisture meters (e.g. Protimeter)
  • Laboratory techniques (e.g. Carbide testing, Oven drying)
  • Temperature and humidity measurement
25
Q

What type of moisture meters are there?

A
  • Pinless mositure meter (uses radio frequencies that penetrate the material being tested within its depth of measurement).
  • Pin-type moisture meter (takes measurements by direct contact with the material)

Moisture meters must be calibrated at least every 6 months.

26
Q

Explain the process of using a pin-type conductance moisture meter.

A
  1. When materials absorb water, they can conduct electricity
  2. Conductance meters have two metal probes (electrodes) which are firmly pressed into the material being tested
  3. Electrical resistance between the two probes can then be measured
27
Q

Explain the process of using a pinless moisture meter.

A

To take a reading, place the meter to the surface of the area being tested and allow a few seconds for a reading.

Non-penetrating meter readings do not give 100% confirmation of moisture. Rather, they help you hone in on areas that should be investigated further.

28
Q

What are the limitations of a moisture meter?

A
  1. Calibrated for timber, so not accurate for other materials (only comparative readings)
  2. Readings may be higher if timber has been treated with water-based preservatives
  3. Electrical conductive surfaces (e.g. aluminium foil-backed wallpaper) may cause inaccurate readings
  4. Only surface readings can practically be taken (deep probes with insulated sides needed otherwise)
  5. Salts naturally present in walling materials conduct electricity and can be confused with damp problems
  6. Hygroscopic salts left by previous dampness may cause high reading, not necessarily ongoing damp problems
29
Q

What are hygroscopic salts?

A

Hygroscopic salts are water-soluble compounds that absorb moisture from the air. They can be found in building materials and are often associated with damp issues in homes.

  1. What are they made of?
    Composition - Hygroscopic salts are made up of nitrates and chloride, such as calcium chloride, calcium nitrate, magnesium chloride, and sodium chloride
  2. Where are they found?
    They are naturally present in the ground and are often found in building materials
  3. What do they do?
    - Absorb moisture - Hygroscopic salts attract and retain water molecules from the surrounding environment
    - Form white marks - When the water evaporates, the salts leave white marks on walls, which can look like tide marks
    - Cause damp issues - Hygroscopic salts can cause damp issues in homes, especially in older buildings
  4. How can they be prevented?
    - Damp-proofing: Install damp-proof courses or membranes to prevent moisture from moving up through walls
    - Salt-resistant plaster: Use salt-resistant plaster or render when replastering
  5. Other uses
    Hygroscopic salts are also used in dehumidifiers, desiccants, and in the preservation of food and pharmaceuticals
30
Q

What types of labrotary testing can be done to record damp in buildings?

A
  1. Oven drying (Gravimetric Testing)
  2. Carbide Testing (e.g. Speedy Meter)
31
Q

What is Carbide Testing?

A

It is a chemical test that measures the amount of moisture in a material.
Also known as speedy meters.

32
Q

Explain how carbide testing is used to measure damp

A
  1. Used for masonry products (e.g. bricks, blocks, mortars etc.)
  2. Material is drilled slowly to minimise heating (and thus drying) then weighed and placed in a container
  3. Specific amount of calcium carbide is added and container is sealed
  4. Container vigorously shaken so two materials mix
  5. Moisture in sample reacts with calcium carbide to produce acetylene gas, causing pressure inside the container, which gives a reading on the pressure gauge
  6. The amount of gas produced is udes to calculate the moisture content of the material.
33
Q

What are the limitations of carbide testing?

A
  1. Knowledge of material being tested is required as different materials will differ in the amount of moisture they can contain and still be regarded as ‘dry’
  2. Destructive - requires several readings for accuracy
  3. Cannot distinguish between free and hygroscopic moisture
  4. Can be misleading, especially when measuring moisture in flood-damaged buildings or a potential for hygroscopic salts
34
Q

What is Oven Drying?

A

Oven drying is a common method for measuring moisture content. It involves weighing a material, placing it in an oven, and weighing it again after it’s dry.

35
Q

Explain the process of oven drying to measure damp.

A
  1. Sample is weighed, dried in an oven and then weighed again
  2. Moisture content = (wet weight - dry weight x 100) / dry weight
36
Q

What are the limitations of over drying?

A
  1. Destructive
  2. Little practical use on site
  3. Over-drying can drive out volatile compounds from the material, which can lead to inaccurate measurements
37
Q

What guidance is available in relation to dampness in buildings?
(NZ only)

A
  • Building Code E3 Internal Moisture
  • Building Code E2 External Moisture
  • Building Code G4 Ventilation
  • New Zealand Standards - NZS 4303:1990 Ventilation for acceptable indoor air quality
38
Q

What guidance is available in relation to dampness in buildings?
(UK)

A
  • BRE BR 466 - Understanding Dampness
  • BS 5250:2011 - Code of practice for control of condensation in buildings
  • BRE Digest 245 - Rising Dampness in Walls: Diagnosis and Treatment
  • BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs

(check if still relevant)

RICS APC Building Surveying (New Zealand) (5 decks)

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