Level 3 Flashcards
Describe the property (Grove Road, Hertfordshire )?
Two storey concrete tiled, hipped roof with double bay windows. Multiple occupiers and many pets including fish tanks and vivariums.
What is mould growth?
Mould (sometimes referred to as mildew) is a fungal growth. Whilst mould itself is not toxic, some moulds can produce toxins that can have negative effects on human health, for example causing asthma
What four factors are required for mould growth?
Mould spores.
Food (anything with carbon atoms).
Appropriate temperature.
Moisture (70%-).
How does water enter buildings?
Condensation Penetrating dampness Rising dampness Leaks (e.g. from pipework) Trapped construction water (new builds)
Describe the main consequences caused by dampness within buildings.
Health hazard
Reduce strength of building materials
Cause movement in building elements
Lead to timber decay (dry and wet rot, insect attack)
Cause chemical reactions in building components
Reduce effectiveness of insulation
Damage decorations
How can you record damp in buildings?
Conductance Meter (aka Protimeter) Carbide Testing (aka Speedy Meter)
Explain how a conductance meter can be used to measure dampness.
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
Explain how carbide testing can be used to measure damp.
Used for masonry products (e.g. bricks, blocks, mortars etc.)
Material is drilled slowly to minimise heating (and thus drying) then weighed and placed in a container
Specific amount of calcium carbide is added and container is sealed
Container vigorously shaken so two materials mix
Moisture in sample reacts with calcium carbide to produce acetylene gas, causing pressure inside the container, which gives a reading on the pressure gauge.
Explain some of the limitations of carbide testing to measure damp.
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’
Destructive - requires several readings for accuracy
What guidance is available in relation to dampness in buildings?
BRE BR 466 - Understanding Dampness
Where was the mould growth found in the property?
The mould was identified behind furniture and on clothes within the cupboards. Water droplets were also found around the windows.
What is condensation and how is it caused?
Condensation - change of water vapour naturally present in air into liquid water
The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
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
What is meant by the terms ‘dew point’ and ‘relative humidity’?
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
What problems are associated with condensation?
Mould growth
Health risks
Timber decay
How would you identify condensation within a building?
1) Wall has a ‘misty’ surface or stains or streaks of water running down a wall (particularly in bathrooms, kitchens and below windows)
2) Damp patches with no definitive edges or mould growth
3) Dampness behind wall cupboards or inside wardrobes against external walls (areas where air circulation is restricted)
4) Localised dampness at potential ‘cold bridges’
5) Humidity (measured using a hygrometer), insulation and ventilation levels as well as heating and living patterns must also be taken into account
Did you consider any other means of investigating if water ingress was present?
I did consult with a thermographer, however it was not the right season to carry out the investigation (middle of Summer).
What steps would you recommend to eliminate condensation?
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:
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)
Increase ventilation to remove moisture-laden air (open trickle vents, open windows, mechanical ventilation)
Increase air temperature by heating - warmer air can hold more water vapour without condensing
Increase surface temperature by thermal insulation (external or internal)
What is interstitial condensation?
Occurs within the structure of an element, as opposed to on its surface.
How would you deal with interstitial condensation?
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 inuslation is added, a vapour barrier must be provided on the warm side of the insulation to act as a barrier to interstitial condensation
What guidance is available in relation to condensation in buildings?
BS 5250:2011 - Code of practice for control of condensation in buildings
What is condensation and how is it caused?
Condensation - change of water vapour naturally present in air into liquid water
The amount of water vapour the air can hold depends on its temperature (the warmer the air, the more water vapour it can hold)
If moist air comes into contact with a cold surface, the air will be cooled and its ability to hold water will reduce
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
How does modern living standards affect the occurrence of condensation within buildings?
Double-glazed windows can create a more ‘sealed’ building that lacks adequate ventilation
Trickle vents in windows (where present) are often kept closed
Balanced flue boilers (instead of open fires) reduce natural ventilation
Central heating systems are often used intermittently, meaning cold surfaces may coincide with high humidity levels
What are the different mechanisms of water ingress relating to penetrating dampness?
Gravity Capillary action Surface tension Kinetic energy (splashing) Wind force Differential air pressure (inside and out)
What are the common causes and routes of penetrating dampness?
Slipped roof tiles
Inadequate chimney/parapet flashing
Copings without drips or not bedded on DPCs
Leaking gutters (lack of correct support, damaged joints, lack of regular clearing)
Overflowing hopper heads
Leaking downpipes (broken joints, rusting cast iron downpipes to rear against wall)
Continuously running cistern overflows (not discharging water clear of wall)
Blocked gulleys (resulting in water splashing against wall)
Cracked render or movement cracks in brickwork
Defective pointing (recessed joints that could lead to frost action)
Cavity ties (upside down so drip ineffective, mortar droppings resting on ties, uneven courses resulting in ties sloping toward inner leaf)
Inadequately fixed cavity insulation boards causing bridging of the cavity from outer to inner leafy
Poorly fitted windows and doors
Sills without drips
Poorly designed thresholds
Missing vertical DPCs
Driving rain on solid walls in particularly exposed situations (on cliff sides/west side of the Pennines)
Vegetation growth to damp/shaded brickwork
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
Applying strong external renders (for the same reasons as using strong mortars)
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
How would you identify penetrating damp within a building?
Distinct damp patches with well-defined edges
Often in localised areas
Moisture readings show sharp change from wet to dry
Patches of efflorescence (crystallisation of sulphates and carbonates present in building materials)
Timber in area of damp has high moisture content
External inspection may reveal obvious defects (e.g. cracked render/brickwork, damaged downpipes etc.)
Deep wall probes indicate high readings in centre of wall
Line of dampness on internal plasterwork corresponding with mortar joints where cement mortar/dense wall materials have been used
Measure wall temperature, air temperature and RH to eliminate condensation
Salt analysis shows zero level of nitrates and chlorides, eliminating rising damp
What steps would you recommend to eliminate penetrating damp?
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
What is rising damp and how is it caused?
Ground water rising by capillary action through pores of the wall or floor material (Tide Line/1m)
Give some examples of how rising damp can be caused?
Causes:
Lack of/ inadequate lapping/failure of DPC/DPM
Bridging of an existing DPC/DPM (often by external rendered finishes or raised ground levels) or splashing from rain.
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.
What height can rising damp reach and what factors can affect this?
Rarely higher than 1.5m Depends on: Supply of water Pore structure of materials Rate of evaporation Heating within building Chemicals in ground and walls - efflorescence can block capillaries through which water evaporates, thus driving water further up the wall
What problems are associated with rising damp?
Lead to outbreaks of dry or wet rot under the right conditions
Reduce the strength of building materials, such as chipboard and plasterboard
Reduce the effectiveness of insulation
Damage decorations
How would you identify rising damp within a building?
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
What steps would you recommend to eliminate rising damp?
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
What different methods of installing/replacing DPCs are available?
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:
Physical replacement - more expensive, disruptive and can only be laid on horizontal course (not suitable for rubble walls)
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)
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)
What guidance is available for rising damp problems?
BRE Digest 245 (Rising Damp in Walls - Diagnosis and Treatment) - rising damp identification and remediation
BS 6576:2005 - Code of practice for diagnosis of rising damp in walls of buildings and installation of chemical DPCs
What methods can be used to minimise dampness within a basement?
Dense Monolithic Concrete
Tanking
Bund Wall System
Drained Cavity System
What are the disadvantages of using tanking as a method of waterproofing a basement?
Water is not drained, merely pushed to other areas around the structure, which could cause problems elsewhere
Only external tanking will protect the structure from aggressive sulphates that may be present in the surrounding soil, which is not always possible
What is a bund wall and how can it be used as a method of waterproofing a basement?
Construction of an inner non-load bearing wall to form a cavity joined to special triangular tiles laid to falls
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
Cavity should be ventilated
What is a drained cavity system and how can it be used as a method of waterproofing a basement?
Plastic membrane in an egg-crate type formation applied to the wall and floor with properly bonded overlap joints in one continuous system
Allows air and moisture to circulate and drains water into a sump, where it can be pumped into the surface water drainage system
What guidance is available for waterproofing basements?
BS 8102:2009 ‘Protection of Below Ground Structures against Water from the Ground’
How would you differentiate between rising damp and penetrating damp (RISING DAMP)?
For rising damp:
Positive salt analysis (containing nitrates and/or chlorides)
Visible tide mark to lower part of wall
Limit of dampness usually 1m-1.5m above ground
Moisture readings quickly drop above tide mark
Areas of dampness appear to get wetter in humid conditions (due to hygroscopic salts drawn up from the ground)
External inspection may indicate missing or bridged DPC
How would you differentiate between penetrating damp and condensation (PENETRATING DAMP)?
For penetrating damp:
Moisture content is usually localised/isolated
Moistures readings identify an epicentre of the water entry
High moisture content within fabric of element, not just on its surface
Evidence of an external defect (e.g. wall cracking, defective downpipe etc.)
Measure wall temperature, air temperature and RH to eliminate condensation
Mould growth unusual
How would you differentiate between rising damp and condensation (CONDENSATION)?
For condensation:
Water is usually on the wall face when wiped with hand
Negative salt analysis (no nitrates or chlorides)
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)
Moisture content of skirting normal but may contain staining due to water run-off
Deep wall probes indicate low readings in centre of wall
Mould growth likely
Surface temperature is below dew point temperature (established by measuring air temperature and RH)
