Damp

Question 1

What different types of damp are you aware of?

Answer 1

• Penetrating damp
• Rising damp
• Condensation damp
• Hygroscopic damp

Question 2

What is rising damp?

Answer 2

• Rising damp refers to the upwards movement of moisture through a permeable wall structure whereby the moisture is derived from groundwater. The moisture rises through pores in the masonry by capillary action.
• Rising damp can transport hygroscopic salts into the building fabric from the groundwater. Hygroscopic salts attract moisture from the air and so can lead to hygroscopic dampness even if the rising damp has been rectified.

Question 3

What is the cause of rising damp?

Answer 3

• Rising damp is caused by a lack of DPC (such as in buildings built prior to 1875).
• Failed DPC
• Bridged DPC (caused by factors such as external render or ground level).

Question 4

How would identify rising damp?

Answer 4

• Increased moisture content in the wall which decreases with height up to around 1m in height (this can be checked by using a protimeter to take readings at 100mm intervals vertically to establish a moisture pattern or by using the speedy carbide test).
• Visible tide mark which may be as high as 1.5m whereby the moisture has evaporated before it can rise further through the masonry.
• Decorative spoiling such as wallpaper peeling, plaster deterioration and paint blistering.
• Timber decay in skirting boards, floor joists embedded in the masonry wall and other timbers.
• Mould growth.
• Efflorescence.
• Erosion of building fabric due to salt expansion during crystallisation.

Question 5

How would you rectify rising damp?

Answer 5

• Removal of any external structures / materials (such as piled earth or render) which may be bridging the damp proof course.
• Insertion of a new chemical (such as damp-proofing rods or cream) or physical (damp-proofing membranes) DPC at least 150mm above external ground level (to minimise the risk of rain splash-back bridging the DPC).
• Removal of damaged or salt-contaminated plaster, drying of the wall and replacement with salt-resistant plaster to prevent hygroscopic damp.

Question 6

What is penetrating damp?

Answer 6

• Penetrating damp is moisture that penetrates laterally through the fabric of the building from sources such as rain and leaking pipes.

Question 7

What are the causes of penetrating damp?

Answer 7

• Solid masonry walls such as those built before 1920 are at high risk of penetrating damp from driving rain.
• Leaking or blocked rainwater goods.
• Spalled or cracked brickwork.
• Blocked wall ties (normally with mortar).
• Failed or blocked cavity trays.
• Render to external walls which traps moisture and prevents evaporation.

Question 8

How would you identify penetrating damp?

Answer 8

• Investigate externally for evidence of damaged brickwork, mortar or rainwater goods.
• Internal damp patches which occurs in an isolated area (this can be checked using a protimeter to establish a moisture pattern or by using the speedy carbide test).
• Any damp patches may appear darker following a period of heavier rain.
• Borescope can be used to investigate wall cavities and determine if wall ties are blocked.

Question 9

How would you rectify penetrating damp?

Answer 9

• Remedy leaking or blocking rainwater goods.
• Replace all spalled brickwork and repoint degraded mortar joints.
• Replace all blocked or failed cavity wall ties or cavity trays.
• Repair cracked render or remove render completely to allow evaporation from the masonry.

Question 10

During a building survey, you identify damp spots and decorative damage at roughly 450mm x 900mm centres. What would your recommendations be?

Answer 10

• The standard spacing for cavity brickwork wall ties is 900mm x 450mm centres which suggests the damp spots may be caused by penetrating damp due to blocked or defective wall ties.
• I would recommend a borescope inspection to determine the condition of the wall ties.
• Remove mortar or debris from wall ties or replace if wall ties have been installed to an incorrect fall or the drip mechanism has failed.

Question 11

What is condensation damp?

Answer 11

• Moisture contained within the air will condense when the relative humidity reaches 100%.
• Relative humidity increases as temperature decreases and so moisture will often condense when it contacts a cold surface.
• Surface condensation occurs when the moisture condenses on an exposed surface such as a wall or window.
• Interstitial condensation occurs when the moisture condenses within the fabric of an element such as the internal leaf of a cavity wall.

Question 12

What causes condensation damp?

Answer 12

• Lack of ventilation. (loft space)
• Lack of insulation causing lower temperatures.
• Cold bridges.
• Life-style activities such as cooking, drying clothes internally and showering.
• Low temperatures or intermittent heating. or heating some rooms more than others (problem in low income households - fuel poverty or elderly where they only use and heat a few rooms)

Question 13

What is a cold bridge?

Answer 13

• An area of a building construction which has a significantly higher heat transfer than the surrounding materials which can lead to additional heat loss in this area.
• Cold bridges can occur where a material is a poor insulator or where there is a break in the insulation caused by elements such as wall ties, balconies and wall-ceiling junctions.
• The temperature is lower as a result of the higher heat transfer meaning higher risk of moisture condensing when contacting the material.

Question 14

How would you identify condensation damp?

Answer 14

• Damp patches and black mould growth especially on cold surfaces such as external walls or ceiling-wall junctions.
• Damp patches and black mould growth in poorly ventilated areas such as behind furniture.
• Decorative damage.
• Normally more prominent in winter months when the temperature falls.
• High relative humidity.

Question 15

How would you identify areas of cold bridging/damp?

Answer 15

Thermal imaging cameras can help pinpoint colder and damper areas, which are indicative of thermal bridging.

Question 16

How would you remedy condensation damp?

Answer 16

• Remove excessive sources of moisture (such as drying clothes externally or ensuring extraction fans are used when cooking or showering).
• Increase ventilation by opening windows or installing trickle vents.
• Maintain internal heating systems on a constant level as opposing to intermittent operation which can lead to a decrease in internal temperature.
• Install insulation to external walls or thermal breaks to cold bridges.