Risk factors for thermal cracks




Factors which influence
thermal cracks

Advice on how the risk of
thermal cracks can be reduced

sun rays Frame

The increased risk depends on:

  1. Frame material
    1. wood or PVC;
    2. dark aluminium with thermal division;
    3. dark heavy metal;
    4. light aluminium with thermal division;
    5. light aluminium;
    6. concrete.
  2. Type of frame
    1. fixed light, without pressure gaskets;
    2. fastenable, openable air vents;
    3. horizontal panel frames;
    4. sliding;
    5. fixed and openable frame with pressure gaskets.
  • Insulate frame from brick.
  • Use similar edge covering on the sides or not bigger than 45 mm.
Shadows of facade elements from the outside

The increased risk of thermal crack, if:

  1. vertical projection;
  2. horizontal projection;
  3. outside blinds.
Keep the distance of at least 2 cm from the blind at their entire hight for natural ventilation. No contact of the blinds and glass may exist in any circumstances.
Paint on glass (inside or outside) The risk of thermal crack increases significantly. Try to avoid.
Paper or plastic screens (inside or outside) The risk of thermal crack increases significantly. Try to avoid.
Interior curtains The risk of thermal crack increases significantly if curtains are non-transparent and if there is no ventilation. Gap between the glass and the curtains inside the building must be ventilated.
Leaning of objects against the glass The risk of thermal crack increases significantly. Try to avoid.
Heating and conditioning devices Radiators The risk increases by putting a radiator closer to the glass or increasing the temperature of the radiator. Radiators and heating pipes must be not closer than 20 cm from the glass. The temperature of heating liquid may not exceed 65°C.
Air circulation equipment Real danger is created if the air flow is directed to the glass. The risk increases if the gap between the circulating air flow and glass is small (even if the air is parallel to the glass). The flow must be parallel to the glass, preferably in the distant place of the premises. The intake gate must be located not closer than at 20 cm from the glass.
Stoves, mobile refrigerators Real danger of thermal crack. The equipment must be located at the distance of 30 cm and more from the glass, depending on the power of equipment.
Fireplaces Real danger of thermal crack. Install a protective screen between fire and glass.


Solution: when the risk of thermal crack is high, glass must be thermically hardended or tempered (depending on the level of risk of thermal crack).