*Dampness

Question 1

How does water enter buildings?

Answer 1

1. Condensation
2. Penetrating dampness
3. Rising dampness
4. Leaks (e.g. from pipework)
5. Trapped construction water (new builds)

Question 2

Describe the main consequences caused by dampness within buildings.

Answer 2

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

Question 3

How can you record damp in buildings?

Answer 3

1. Oven Drying (Gravimetric Testing)
2. Conductance Meter (aka Protimeter)
3. Carbide Testing (aka Speedy Meter)

Question 4

Explain the process of oven drying to measure damp.

Answer 4

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

Question 5

Explain how a conductance meter can be used to measure dampness.

Answer 5

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

Question 6

Explain how carbide testing can be used to measure damp.

Answer 6

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

Question 7

Explain some of the limitations of oven drying to measure damp.

Answer 7

1. Destructive
2. Little practical use on site

Question 8

Explain some of the limitations of using a conductance meter to measure damp.

Answer 8

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

Question 9

Explain some of the limitations of carbide testing to measure damp.

Answer 9

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

Question 10

What guidance is available in relation to dampness in buildings?

Answer 10

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

Question 11

What is condensation and how is it caused?

Answer 11

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

Question 12

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

Answer 12

• 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

Question 13

How does modern living standards affect the occurrence of condensation within buildings?

Answer 13

1. Double-glazed windows can create a more ‘sealed’ building that lacks adequate ventilation
2. Trickle vents in windows (where present) are often kept closed
3. Balanced flue boilers (instead of open fires) reduce natural ventilation
4. Central heating systems are often used intermittently, meaning cold surfaces may coincide with high humidity levels

Question 14

What problems are associated with condensation?

Answer 14

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 sublect to prolonger moisture exposure

Question 15

How would you identify condensation within a building?

Answer 15

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

Question 16

What steps would you recommend to eliminate condensation?

Answer 16

• 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 - combination of the following:
  
  1. Reduce moisture generation (lids on pans, dry clothes outside, vent tumble dryers externally, do not use paraffin or bottled gas heaters, put cold water in bath before hot)
  2. Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)
  3. Increase air temperature by heating - warmer air can hold more water vapour without condensing
  4. Increase surface temperature by thermal insulation (external or internal)

Question 17

What is interstitial condensation and how would you deal with it?

Answer 17

1. Interstitial condensation is condensation that occurs within the structure of an element, as opposed to on its surface
2. 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
3. If it occurs in a material such as timber, action will be needed to prevent risk of rot, usually by installing additional wall insulation
4. If internal inuslation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation

Question 18

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

Answer 18

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

Question 19

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

Answer 19

70%

Question 20

What guidance is available in relation to condensation in buildings?

Answer 20

BS 5250:2011 - Code of practice for control of condensation in buildings

Question 21

What is penetrating damp?

Answer 21

Water that ingresses through the structure of a building

Question 22

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

Answer 22

1. Gravity
2. Capillary action
3. Surface tension
4. Kinetic energy (splashing)
5. Wind force
6. Differential air pressure (inside and out)

Question 23

What are the common causes and routes of penetrating dampness?

Answer 23

1. Slipped roof tiles
2. Inadequate chimney/parapet flashing
3. Copings without drips or not bedded on DPCs
4. Leaking gutters (lack of correct support, damaged joints, lack of regular clearing)
5. Overflowing hopper heads
6. Leaking downpipes (broken joints, rusting cast iron downpipes to rear against wall)
7. Continuously running cistern overflows (not discharging water clear of wall)
8. Blocked gulleys (resulting in water splashing against wall)
9. Cracked render or movement cracks in brickwork
10. Defective pointing (recessed joints that could lead to frost action)
11. Cavity ties (upside down so drip ineffective, mortar droppings resting on ties, uneven courses resulting in ties sloping toward inner leaf)
12. Inadequately fixed cavity insulation boards causing bridging of the cavity from outer to inner leafy
13. Poorly fitted windows and doors
14. Sills without drips
15. Poorly designed thresholds
16. Missing vertical DPCs
17. Driving rain on solid walls in particularly exposed situations (on cliff sides/west side of the Pennines)
18. Vegetation growth to damp/shaded brickwork
19. Repointing older buildings with cement mortar - stronger but less breathable than lime mortar, reducing the rate of evaporation. Also not as flexible so more likely to crack through drying shrinkage, thus allowing water ingress
20. Applying strong external renders (for the same reasons as using strong mortars)
21. Walls built in denser materials (e.g. granite or engineering bricks) - lack the ability to absorb water so most water runs down the face, which makes minor cracks more critical in allowing moisture ingress. Evaporation is also restricted

Question 24

What problems are associated with penetrating damp?

Answer 24

1. Lead to outbreaks of dry or wet rot under the right conditions
2. Reduce the strength of building materials, such as chipboard and plasterboard
3. Cause chemical reactions in building components (e.g. sulphate attack)
4. Reduce the effectiveness of insulation
5. Damage decorations

Question 25

How would you identify penetrating damp within a building?

Answer 25

1. Distinct damp patches with well-defined edges
2. Often in localised areas
3. Moisture readings show sharp change from wet to dry
4. Patches of efflorescence (crystallisation of sulphates and carbonates present in building materials)
5. Timber in area of damp has high moisture content
6. External inspection may reveal obvious defects (e.g. cracked render/brickwork, damaged downpipes etc.)
7. Deep wall probes indicate high readings in centre of wall
8. Line of dampness on internal plasterwork corresponding with mortar joints where cement mortar/dense wall materials have been used
9. Measure wall temperature, air temperature and RH to eliminate condensation
10. Salt analysis shows zero level of nitrates and chlorides, eliminating rising damp

Question 26

What steps would you recommend to eliminate penetrating damp?

Answer 26

• Identify the source of penetrating damp and remove or provide a barrier, for example:
  
  • Replace defective rainwater goods
  • Introduce DPCs beneath copings or vertical DPCs around openings
  • Repair cracked render/brickwork
  • Unblock gulleys/rainwater goods
  • Replace poorly installed cavity ties
• Application of a hydrophobic masonry paint (repels water but still allows the wall to breathe) may also be beneficial for solid walls that experience excessive rain penetration

Question 27

What is rising damp and how is it caused?

Answer 27

• Ground water rising by capillary action through pores of the wall or floor material
• Causes:
  
  1. Lack of DPC/DPM
  2. Inadequate lapping of DPC/DPM
  3. Bridging of an existing DPC/DPM (often by external rendered finishes or raised ground levels)
  4. DPC/DPM failure through natural deterioration or damage caused by building movement
  5. Splashing from rain or downpipes where DPC is less than the recommended 150mm above ground (Approved Document C)
  6. Increase in ground water levels (e.g. man-induced changes to the water table, leaking drains, blocked land drainage systems, leaking water mains and springs) - likely if rising damp occurs fairly suddenly

Question 28

What height can rising damp reach and what factors can affect this?

Answer 28

• Rarely higher than 1.5m
• Depends on:
  
  1. Supply of water
  2. Pore structure of materials
  3. Rate of evaporation
  4. Heating within building
  5. Chemicals in ground and walls - efflorescence can block capillaries through which water evaporates, thus driving water further up the wall

Question 29

What problems are associated with rising damp?

Answer 29

1. Lead to outbreaks of dry or wet rot under the right conditions
2. Reduce the strength of building materials, such as chipboard and plasterboard
3. Reduce the effectiveness of insulation
4. Damage decorations

Question 30

How would you identify rising damp within a building?

Answer 30

1. Visual inspection of possible causes (lack of / bridging of DPC/DPM etc.)
2. Characteristic tide mark that does not extend beyond the lower part of the wall
3. Damp contours can be pinpointed with a moisture meter
4. Damp limited to usually 1m-1.5m above ground and readings above peak will drop quickly
5. High percentage of moisture content in timber skirtings
6. Salt analysis using a calcium carbide meter determines a high level of nitrates and chlorides, which are contained naturally in the subsoil
7. Areas of dampness appear to get wetter in humid conditions due to hygroscopic salts (nitrates and chlorides) brought up from the ground, which attract water in from the atmosphere
8. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) contains detailed guidance on rising damp identification and remediation

Question 31

What steps would you recommend to eliminate rising damp?

Answer 31

• Identify the source of rising damp and remove or provide a barrier, for example:
  
  • Lower the ground level (where DPC is breached or ground level is not 150mm below DPC)
  • Repair leaking drains/water mains
  • Unblock land drainage systems
  • Replace DPC or provide new where non-existent
• Replace plaster/finishes where hygroscopic salts may still be present
  
  • Renew to height 300mm above level of rising damp
  • Re-plaster with a cement-based plaster (not gypsum plaster as most of these cannot prevent the passage of hygroscopic salts and quickly breakdown in wet conditions), preferably containing a waterproofer or salt inhibitor

Question 32

What different methods of installing/replacing DPCs are available?

Answer 32

Installation of any type of DPC must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works:

1. Physical replacement - more expensive, disruptive and can only be laid on horizontal course (not suitable for rubble walls)
2. Chemical injection - cheaper, lines the pores with a water-repellent solution (usually silicone/latex) however effectiveness depends on its successful penetration of the wall and lack of ‘viscous fingering’ (chemical spreads out and does not form a continuous barrier)
3. Electro Osmotic DPC - a titanium wire (anode) is secured around the wall at DPC level and connected to a small power supply, which causes moisture molecules to repel down the wall back into the ground (not supported by the BRE)

Question 33

What guidance is available for rising damp problems?

Answer 33

1. BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) - rising damp identification and remediation
2. BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs

Question 34

What methods can be used to minimise dampness within a basement?

Answer 34

1. Dense Monolithic Concrete
2. Cementitious Tanking
3. Mastic Asphalt Tanking
4. Bund Wall System
5. Drained Cavity System

Question 35

How is dense monolithic concrete used to waterproof a basement and what are its main disadvantages?

Answer 35

1. Walls and floor are constructed from high quality dense monolithic concrete to form a watertight barrier
2. May not always be water vapour proof so some form of lining (tanking) may be required
3. Only applies to new-builds

Question 36

What is the difference between cementitious tanking and mastic asphalt tanking?

Answer 36

Cementitious Tanking:

1. Certain additives are added to a cement based medium and applied to the base slab and walls
2. Not very good at withstanding substantial levels of hydrostatic pressure

Mastic Asphalt Tanking:

1. Provides a continuous waterproof membrane applied to the base slab and walls
2. Can be applied internally or externally depending on the circumstances on site (i.e. external may not be possible in existing buildings)
3. Membrane needs additional protection by building an inner skin wall backfilled to keep the membrane adhered to the earth-retaining wall

Question 37

What are the disadvantages of using tanking as a method of waterproofing a basement?

Answer 37

1. Water is not drained, merely pushed to other areas around the structure, which could cause problems elsewhere
2. Only external tanking will protect the structure from aggressive sulphates that may be present in the surrounding soil, which is not always possible

Question 38

What is a bund wall and how can it be used as a method of waterproofing a basement?

Answer 38

1. Construction of an inner non-load bearing wall to form a cavity joined to special triangular tiles laid to falls
2. This enables moisture to collect in the cavity and drain away into a sump, where it can be pumped into the surface water drainage system
3. Cavity should be ventilated

Question 39

What is a drained cavity system and how can it be used as a method of waterproofing a basement?

Answer 39

1. Plastic membrane in an egg-crate type formation applied to the wall and floor with properly bonded overlap joints in one continuous system
2. Allows air and moisture to circulate and drains water into a sump, where it can be pumped into the surface water drainage system

Question 40

What guidance is available for waterproofing basements?

Answer 40

BS 8102:2009 ‘Protection of Below Ground Structures against Water from the Ground’

Question 41

How would you differentiate between rising damp and penetrating damp?

Answer 41

For rising damp:

1. Positive salt analysis (containing nitrates and/or chlorides)
2. Visible tide mark to lower part of wall
3. Limit of dampness usually 1m-1.5m above ground
4. Moisture readings quickly drop above tide mark
5. Areas of dampness appear to get wetter in humid conditions (due to hygroscopic salts drawn up from the ground)
6. External inspection may indicate missing or bridged DPC

Question 42

How would you differentiate between penetrating damp and condensation?

Answer 42

For penetrating damp:

1. Moisture content is usually localised/isolated
2. Moistures readings identify an epicentre of the water entry
3. High moisture content within fabric of element, not just on its surface
4. Evidence of an external defect (e.g. wall cracking, defective downpipe etc.)
5. Measure wall temperature, air temperature and RH to eliminate condensation
6. Mould growth unusual

Question 43

How would you differentiate between rising damp and condensation?

Answer 43

For condensation:

1. Water is usually on the wall face when wiped with hand
2. Negative salt analysis (no nitrates or chlorides)
3. Moisture readings may occur across the full height of a wall (although higher readings at lower levels as warm air rises so less chance of condensation)
4. Moisture content of skirting normal but may contain staining due to water run-off
5. Deep wall probes indicate low readings in centre of wall
6. Mould growth likely
7. Surface temperature is below dew point temperature (established by measuring air temperature and RH)

Question 44

What are hygroscopic salts and are they problematic?

Answer 44

1. Salts that absorb moisture in from the air
2. As they absorb water, they continually re-dissolve, which prevents any crystallisation
3. Often associated with rising damp, as nitrates and chlorides (both of which are hygroscopic) naturally present in sub-soil are drawn up through the wall with water and are left behind on the surface once the water evaporates, causing surfaces to become wetter from moisture in the air as well

Question 45

What is efflorescence and is it problematic?

Answer 45

1. Temporary white powdery substance often seen on the face of new brickwork and in cases of rising damp
2. Caused by sulphates and carbonates naturally present in building materials crystallising as water evaporates, due to their relatively insoluble nature
3. These salts are not hygroscopic and merely indicate that moisture is evaporating from the structure
4. They may only be problematic in cases of rising damp, as the crystals can sometimes block pores in brickwork, thus preventing evaporation and driving damp higher up the wall
5. Can be brushed off if appearance is causing a concern

Question 46

What is cryptoflorescence and is it problematic?

Answer 46

1. Crystallisation of salts (often magnesium) below the surface of the brick
2. Can cause spalling where old, relatively weak bricks are re-used inappropriately, particularly in areas of excessive dampness
3. Can also occur through salts deposited by the run-off from limestone or from air pollution
4. Damage can also occur where bricks are covered by a surface treatment (as salts may crystallise behind it)
5. The effect on the bricks is similar to that caused by frost attack

Question 47

How do you test to establish if service pipes are leaking?

Answer 47

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Question 48

What is the adverse effect of well-insulated buildings?

Answer 48

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Question 49

When carrying out a survey of a Victorian house, what potential pathology issues could lead to damp problems in the building?

Answer 49

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Question 50

What problems are associated with vegetation growth to damp/shaded brickwork?

Answer 50

Can retain moisture and cause pentrating dampness

Question 51

What measures should be adopted to repair a property affected by flooding?

Answer 51

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Question 52

What would be required from a damp specialist before you recommended them?

Answer 52

Must be by a reputable company and members of the British Wood Preserving and Damp-Proofing Association (BWPDA) offering an insurance backed guarantee for the works

Question 53

Where should a DPC be located?

Answer 53

Should be 150mm above ground level

Question 54

What materials would you expect a DPC to be constructed from?

Answer 54

• Pre 1900 - slate
• 1900s onwards - bitumen
• Modern - polymer materials

Question 55

What is the process with physically retro-fitting a DPC?

Answer 55

• Cut out the brickwork and insert (access required from both sides)
• Can cause issues with services within wall
• Very costly and very disruptive

Question 56

What is the process with chemically injecting a DPC?

Answer 56

• Holes are drilled in brickwork at 120mm centre
• Chemical cream is injected at low pressure
• External holes should then be plugged
• Must be allow to dry before plastering
• Can be difficult to ascertain the quality, best to ensure a guarantee for the work is provided

Question 57

What is thermal bridging?

Answer 57

Thermal bridging, often known as cold bridging, is caused where there is direct contact between internal and external faces of a building due to thermal properties of the fabric being poorer than that around the area. Will often cause localised condensation and therefore mould growth