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Damp and Condensation > Damp and Condensation > Flashcards

Damp and Condensation Flashcards

1
Q

What is water vapour?

A

Water in the form of a gas

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2
Q

How can water vapour be measured?

A

Dew point and Relative humidity

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3
Q

What is relative humidity expressed in?

A

A percentage

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4
Q

What are the factors of relative humidity?

A

temperature and water vapour/moisture

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5
Q

What does relative humidity measure

A

Relative humidity expresses the degree of saturation within the air.

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6
Q

Define capillary action

A

Capillary action is a function of the natural attraction between water and the capillaries found in concrete and masonry.

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7
Q

How does water rise?

A

water molecules stick to each other and to other substances such as glass. This creates surface tension. against the structure

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8
Q

How does rising damp occur?

A

• Capillary ‘suction’ of moisture from the ground into
porous masonry building materials.
• The moisture evaporates from either face of
the wall
• The moisture will rise is determined by the evaporation rate and the nature of the wall (usually 0.5-1.5m)

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9
Q

What are the faults of rising damp?

A
  • high tide like stains on may show on wallpaper and other interior finishes.
  • Blistering of paint /peeling of plaster
  • moulds
  • spalling of masonry
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10
Q

What are hygroscopic salts and where do they come from?

A
  • Ground water contains soluble salts (chlorides,nitrates and sulphates.
  • Hygroscopics are able to absorb moisture.
  • The salts are left on the walls when the water evaporates
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11
Q

How do salts impact the walls?

A
  • After many years, they form a salt band near the top of the damp.
  • Salts will continue to absorb moisture. This maintains a damp wall
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12
Q

Why is it important to omit the salts from the walls?

A
  • Even after a polythene sheet has been inserted, the salts can allow the wall to remain damp.
  • Salts like sulphates can damage the mortar therefore, they should be removed.
  • The salts left behind can often be seen as white efflorescence on the wall surface
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13
Q

How can damp rise even with dpm?

A

• Pierced polythene sheets
• Fractured slate
• No bridging between dpm and dpc
• flexible courses may become compressed and so
extrude from the joint
• Injected damp proof courses may be affected by ground water contaminants or fail to form a continuous band due to the construction of the wall

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14
Q

Does the absence of DPM always consequence in rising damp?

A

• Absence of DPC/Membrane does not always
mean that walls will be affected by rising
damp
• The presence of a DPC/Membrane does not
mean that such a problem cannot exist

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15
Q

When was DPM commonly used?

A

1960’s

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16
Q

How could you bridge DPC?

A
  • High ground level ( revamping driveway)
  • DPC placed at wrong height. (DPM should be atleast 160mm above ground)
  • Soil sloped against wall,above the dpc
  • Render of walls allow capillary action
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17
Q

What are thermal bridging?

A

Thermal bridges are sections through the fabric of significantly lower thermal resistance than the rest of the construction

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18
Q

Where does thermal bridging occur?

A

Occurs around openings and at junctions of walls/floors and walls/roofs. Concrete and steel framed buildings are particularly prone to cold-bridging unless these elements are individually insulated.

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19
Q

Why does thermal bridging occur?

A

Thermal bridging is the result of localised areas of low thermal resistance caused by the presence of elements with a high thermal conductivity

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20
Q

How does thermal bridging impact properties?

A

Condensation. Where thermal bridging occurs, the internal surface temperature will be lower than more thermally efficient surrounding surfaces. Condensation is highly likely to occur in these areas

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21
Q

Name 5 common areas of cold bridges?

A 
Window sills
Walls and Foundations 
Window Jamb
Window Head
Lintels
22
Q

What and how does penetrating damp occur?

A

Where water soaks through the building fabric of a building, either above or below ground level

23
Q

Give examples of penetrating damp

A
  • Defective rainwater downpipes and gutter
  • Exposed elevations to wind and progressive rain
  • Close proximity of trees and other vegetation
  • Lack of regular maintenance allowing materials to deteriorate
  • Poor workmanship – Lack of adequate weather sealing e.g. Bridging of Cavity Ties

These defects combined with deteriorating pointing, frost damaged bricks or faulty joints between window and walls, can allow damp to penetrate completely through the building fabric.

24
Q

What is condensation?

A

A reaction in which two molecules combine to form a larger molecule, producing a small molecule such as H₂O as a by-product. Condensation involves a gas changing to a liquid.

25
Q

How does condensation generally occur?

A

Generally the lifestyle of the occupants produce the majority of the water vapour however substances like air vents may be blocked which means less fresh air is egressing the property

26
Q

Name two types of condensation

A

Surface condensation

Interstitial condensation

27
Q

Where does condensation occur?

A

Condensation can occur anyway inside the property with kitchens and bathrooms in particular. When temperature is below dew point, water vapour forms.

28
Q

What can surface condensation cause?

A

Condensation can provide enough moisture to become a mechanism for decay such as damp

29
Q

Does condensation cause mould?

A

Water vapour in the atmosphere alone causes no problems. However, condensation and continuous high humidity will lead to mould growth

30
Q

What type of mould can form from condensation and high humidity?

A

The most common mould associated with condensation is the ‘black spot’ mould,
Aspergillus niger

31
Q

Can mould effect humans?

A

Where such conditions, occur it is mould spores in large numbers that may cause some to experience health problems.

32
Q

What are two of the signs of condensation

A

A ‘musty’ smell

Water moisture on ceilings and walls.

33
Q

Why are poorly heated and poorly insulated properties more prone to condensation?

A

Warmer air is able to hold more water vapour. This prevents condensation from forming. Colder air means there is less energy for the gas to stay in their state. Low energy makes gas turn into liquid.

34
Q

What does the surface temperature of internal walls will depend on?

A

The surface temperature of internal walls will depend
on the thermal efficiency of the wall and the external
temperature

35
Q

What are main factors of forming condensation?

A

If external walls are thermally inefficient, the property
is poorly heated and poorly ventilated and the external
temperature is low it is highly likely that condensation
will occur

36
Q

What would the Building Surveyor look for during an inspection?

A 
• Lack of ventilation
• Washing drying on radiators
• Tumble dryers venting into room
instead of outside
• Calor gas heaters
• Extractor fans not working or missing
• Window trickle vents closed or broken
• Covering of air bricks
• Contributing factors – Furniture such as beds, wardrobes and other belongings that are positioned against external walls cause cold spots, where warm air cannot circulate. Long curtains also below cill level restrict air flow.
37
Q

How would condensation form?

A
  • Surface condensation is formed when the moisture laden air comes into contact with suitably colder surfaces such as walls
  • As the moisture laden air gets close to the cold surface, the air starts to get cooled and the relative humidity (moisture) increases;
  • Against the cold surface, the temperature of the air now drops at or below the dew point temperature and liquid water drops out as condensation.
38
Q

What is interstitial condensation?

A

Occurs when warm, moist air from inside a building penetrates into a wall, roof or floor construction (the building fabric) and meets a cooler surface

This causes the air to cool, lowering its capacity to carry moisture, and resulting in condensation (dew point occurring) on the cold surface.

39
Q

How much impact can interstitial condensation cause?

A

Condensation can provide enough moisture to become a mechanism for decay such as rotting and corrosion of wall ties. This can cause major structural damage

40
Q

How could interstitial condensation be prevented?

A

interstitial condensation can be reduced with the incorporation of polythene vapour barriers or damp proof membranes into framed wall and roof constructions, on the inside of the insulating layer and framing

41
Q

What guidance do the Building Regulations give relating to condensation?

A

Building Regs Part C (resistance to contaminates and moisture)
• Part C2-The floors, walls and roof of the building shall adequately protect the building and its users from harmful effects caused by -
• Ground Moisture;
• Precipitation and wind-driven spray;
• Interstitial and surface condensation; and more

42
Q

What are the remedial works for condensation?

A

• Remove any damp affected plaster or other materials
• Consider dehumidifiers in excessively damp situations
• Insulate external envelope to remove
cold bridges
• Increase the thermal efficiency of external walls, therefore increasing the internal surface temperature
• Provide appropriate mechanical and background ventilation
• Provide an efficient heating system to maintain internal room temperatures
• Maintain external fabric - Mortar joints, decorations
• Repair any leaks which may cause penetrating damp, reducing internal surface temperatures in local area

43
Q

What are the remedial works for rising damp?

A
  • Remove any damp affected plaster or other materials
  • Consider dehumidifiers in excessively damp situations
  • Installation of new damp proof courses (possibly injected)
  • Reduce external ground levels
  • Replace solid ground floors with new insulated slab incorporating a Damp Proof Membrane
  • Re-plaster affected walls to a height of 1 metre using damp resistant renovating plaster
  • Consider increasing the thermal efficiency of external walls, therefore increasing the internal surface temperature
  • Provide appropriate mechanical and background ventilation
44
Q

What are the remedial works for penetrating damp?

A

Remove any damp affected plaster or other materials
• Consider dehumidifiers in excessively damp situations
• Remove the source, causing the persistent damp problems
• Carry out regular maintenance of external fabric, including:
• Unblocking of rainwater gutters
• Re-pointing of mortar joints
• Repairs to leaking plumbing. i.e overflows
• Repairs to damaged render which can hold water
Dealing with Damp
• Cut back any overhanging trees
• Remove any vegetation growth from the external fabric

45
Q

What equipment could you use to measure and establish the type of damp?

A
  • Moisture meters such as pin-type meters can be used for assessing the moisture condition in buildings
  • Calcium carbide samples- the only site instrument that will give an accurate moisture reading

Both deep wall probes and calcium carbide involve destructive testing. Deep wall probes can be used more discreetly if decoration rules out the use of the Speedy

46
Q

What do the numerical values on the moisture meter represent?

A

The numerical values represent the actual percent moisture content of wood (% MC) and the moisture equivalent (ME) of concrete, dry wall and other material

47
Q

What is the most common material in which moisture content can be measured using a moisture meter?

A

Timber

48
Q

What can the damp meter determine?

A
  • The damp meter can be used to determine if the fabric of a building is in a dry, borderline or in damp condition
  • A colour-coded scale enables the user to assess the moisture level of wood and dry wall at a glance
49
Q

How does the pin-type meter work?

A
  • These instruments work by reading across the two pins and detecting the change in resistance when they come into contact with the timber or other materials
  • All a pin type meter can indicate, at best, is whether moisture may be present
50
Q

Are damp meters accurate?

A
  • Pin meters should not be used to ‘measure’ moisture content in other materials such as masonry and plaster because there are major variances in masonry whereas with timber, there are less major variances.
  • Therefore no consistency between any two samples from different sites
51
Q

How does carbide testing work?

A

The test works by mixing an accurately weighed sample of mortar with a measured amount of calcium carbide within a specialist pressure vessel, following the test any moisture held within the mortar (from rising or penetrating damp) will react and cause a build up of pressure.

Damp and Condensation (1 decks)

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