BEYOND DEW POINT:
Surface Mould Risk Calculator

Dew point (Td) isn't the metric you want to watch when it comes to mould germination and growth. Mould does not need liquid water to grow.

The below interactive graph lets you map surface temperatures that results in localised RH that risks germination and growth of primary, secondary and tertiary colonising moulds. We call those growth points Tg1, Tg2 and Tg3.

Enter room air conditions (°C and %RH) to see the risk temperature of any surface in that room. Edit the input boxes or drag the cursor around.

These growth conditions need to remain stable for long enough for each category of colonisation. This is species dependent and other variables will apply.

Surface Mould Germination Risk
°C
%

Calculated Properties

Humidity Ratio:
(g/kg) --
Vapour Pressure:
(mmHg) --
(kPa) --

Surface Conditions

Tg1, Primary coloniser risk:
-- °C
Tg2, Secondary coloniser risk:
-- °C
Tg3, Tertiary coloniser risk:
-- °C
Td, Dew Point (100% RH):
-- °C

Note: Calculations assume standard sea level pressure (101.325 kPa).

Tg1

Germination/Growth point 1
66%+ for 12-24 hrs+
Primary colonising moulds germinate & grow
aw 0.66+

Tg2

Germination/Growth point 2
80%+ for 48-72 hrs+
Secondary colonising moulds germinate & grow
aw 0.80+

Tg3

Germination/Growth point 3
90%+ for 7-14 days+
Tertiary colonising moulds germinate & grow
aw 0.9+

Td

Dew point
100%RH
Condensation forms and
bacteria multiply
aw 1
Empty space, drag to resize
The above thresholds are broadly accepted generalisations. There is considerable biological variation between mould species and some can germinate and grow at lower levels of water activity / humidity and required times vary greatly depending on environmental considerations.

Tg1, Tg2 and Tg3 are notations original to The Restoration Academy UK Limited, used to describe surface growth conditions.
The UK Centre for Mould Safety's training provision is delivered by The Restoration Academy Ltd
The UK Centre for Mould Safety is managed by Indoor Air Aware Community Interest Company
Company registration: 16821411
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