What different types of dampness are there?
- Penetrating damp
- Rising damp
- Condensation
What is the definition of rising damp?
Upward movement of water through a porous material due to capillary action
How do you identify rising damp?
BRE Digest 245 set out diagnosis method:
- Water approx. 1m high
- Salt deposits will be visible where water have evaporated and leave a tide mark
- Peeling of wall finishes
- Musty smell, rotting timbers (skirting)
- Usually where there is no DPC or where the DPC has been bridged
What causes rising damp?
- Lack of a DPC - only a requirement after 1875
- Damaged DPC - brittle slate, or penetration through a membrane
- Bridged DPC - external landscaping/ground level raising
Where should a DPC be located?
Should be 150mm above ground level
What materials would you expect a DPC to be constructed from?
- Pre 1900 - slate
- 1900s onwards - bitumen
- Modern - polymer materials
What are the treatment options for rising damp?
- Insert a DPC - either physically or chemically injected
- Hack off all blown plaster and replace with breathable/waterproof plaster or render
What is the process with physically retro-fitting a DPC?
- Cut out the brickwork and insert (access required from both sides)
- Can cause issues with services within wall
- Very costly and very disruptive
What is the process with chemically injecting a DPC?
- 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
What is the definition of penetrating damp?
Penetrating damp is caused by moisture passing through a building fabric
What is the cause of penetrating damp?
There are a number of possible causes, often due to construction, design or material failure:
- failed rain water goods
- failed roof coverings
- fixing penetrations in building fabric
- installation of services
- defective cavity tray
- burst water pipe
How would you identify penetrating damp?
If the profile of the dampness is consistent with whatever the suspected cause is. Thorough inspection required, and should be aware that moisture can track within buildings
What tests are available for penetrating damp?
A die test, when water with a die in it is applied to a suspected ingress point, and if the die comes through to where the damp is manifesting you can link the two
What is condensation?
Condensation is when moist air comes into contact with a surface with a lower temperature than the due point
What is the cause of condensation?
Condensation is caused by moisture in the air, from normal activities and cold surfaces
How would you identify condensation?
Condensation forms on cold surfaces, like windows and insulated areas - it will be visible on the surface
What are the consequences of condensation in a building?
Condensation can increase the moisture content of timber, which can in turn lead to rot/infestation
Condensation occurring on plaster walls can allow mould growth, with can be detrimental to health
What treatment is available for condensation?
- Increase natural ventilation (trickle vents, open windows)
- Install mechanical ventilation (extract in toilets and kitchens)
- Avoid drying clothes indoors
- Improve insulation and double glazing
- Ensure adequate heating
(Essentially, warm the surfaces to stop them achieving the dew point, and reduce the moisture content in the air)
What is interstitial condensation?
Interstitial condensation is condensation that occurs within a void or cavity where there is insufficient ventilation, insulation or absence of a vapour control layer
What is thermal bridging?
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
What tools would you sure to detect moisture?
- Speedy carbide meter
- Thermographic imaging
- Electrical resistance meter
- Capacitance meter
What is a Speedy Carbide Meter?
It’s used to test samples of material extracted, to establish the moisture content. It provides an accurate reading of the moisture content, but can require destructive testing and will most likely need to be sent away or brought back to the office etc. for definitive results
How is thermographic imaging used to detect moisture?
Moist areas will generally be a lower temperature. Can be used to detect cold bridging as well
What is an electrical resistance meter?
It measures moisture with a current that passes between two prongs. It is only calibrated for timber, though can be used as a comparison in other materials. Easy to use and causes minimal damage, can also react to salts so should be used with caution
