Health & well-being for occupants: Ventilation, Condensation & Internal Air Quality Indoor Air Quality Relative Humidity In Dwellings Mike Davies University College London
Today The move to tighter dwellings - why is control of moisture important? (Surface) Relative Humidity - a key parameter How can surface RH be controlled? Development of guidelines Building Regulations Summary
The health benefits of tackling climate change Household energy use is an important target for actions to tackle climate change Properly designed and implemented, such actions could have major co-benefits for public health To investigate, we examined the effect of strategies to improve energy efficiency in UK housing stock 3
Why is control of moisture important? Moisture gives rise to two types of problems: condensation on internal surfaces accumulation of moisture within a structure in areas where it may cause corrosion of metal components, decay of timber based components or reduction of the performance of insulants I will focus today on the first of these two issues
Why is control of moisture important? Persistent dampness and microbial growth on interior surfaces and in building structures should be avoided or minimized, as they may lead to adverse health effects. Indicators of dampness and microbial growth include the presence of condensation on surfaces or in structures, visible mould [and] perceived mouldy odour.
Why is control of moisture important? There are many potential moisture related problems e.g: Mould Bacteria Dust mites However ADF refers to mould so I ll focus on mould today. The ADF performance criterion for moisture is as follows: There should be no visible mould on external walls in a properly heated dwelling with typical moisture generation.
Terminology Water vapour Saturation Dewpoint Vapour pressure Saturated vapour pressure Relative humidity (RH)
The RH of the ambient air determines how much moisture will be absorbed by hygroscopic materials This in turn determines the risk of mould growth on surfaces and the decay of materials Note that RH close to the surface of a material is the same as water activity which is often used to describe mould growth conditions
CIBSE
How can surface RH be controlled? To control RH, it is necessary to: limit moisture input to the building achieve high surface temperatures by providing more insulation limiting thermal bridges if necessary, increasing the heat input provide effective ventilation
How can surface RH be controlled? The following factors should be taken into account in design: Occupant activity and heating/ventilation regime Built-in water
How can surface RH be controlled? Thermal insulation Thermal bridging Thermal response
How can surface RH be controlled? Ventilation Low energy design we must ensure that adequate ventilation remains
Under what conditions will mould grow? RH Temperature Time Nutrients ph value Substrate salt content Light Oxygen content
Under what conditions will mould grow? You do not need to have condensation for mould growth to occur
Under what conditions will mould grow? Clarke
Under what conditions will mould grow? The challenge is to devise guidance that captures enough of the science but yet is straightforward enough to be implemented That was our task for ADF 2010
Development of guidance Analysis of field data Laboratory work
Laboratory work
Mould species in study Ulocladium consortiale Penicillium chrysogenum Aspergillus repens Aspergillus versicolor Cladosporium sphaerospermum Aspergillus niger
Building Regulations So, what did we recommend for ADF 2010? We gave recommendations for RH limits in order to meet the primary criterion of no mould on external walls The guidance for the ventilation systems given in ADF is intended to ensure that these (and other) limits were met
Building Regulations For all dwellings (existing and new) the moisture criterion is likely to be met if the average surface water activity of the internal surfaces of external walls is less than the values noted in table 1 during the heating season Table 1. Surface Water Activity
Building Regulations However, as a guide, for new dwellings, the moisture criteria in table 1 are likely to be met if the average relative humidity in a room is less than the values noted in table 2 during the heating season Table 2. Room Air Relative Humidity
Summary (1) Moisture related problems are important With reduced infiltration we need to be careful to control moisture carefully
Summary (2) However.it is not just moisture related issues that we have to worry about - e.g: PM 2.5 Combustion products (e.g. CO and NO 2 ) Radon ETS VOCs Temperature - increased exposure to heat?
End michael.davies@ucl.ac.uk