Antti Hukka

Bio: Antti Hukka is an academic researcher from VTT Technical Research Centre of Finland. The author has contributed to research in topics: Relative humidity & Moisture. The author has an hindex of 3, co-authored 3 publications receiving 334 citations.

A mathematical model of mould growth on wooden material

Abstract: A mathematical model for the simulation of mould fungi growth on wooden material is presented, based on previous regression models for mould growth on sapwood of pine and spruce. Quantification of mould growth in the model is based on the mould index used in the experiments for visual inspection. The model consists of differential equations describing the growth rate of the mould index in different fluctuating conditions including the effect of exposure time, temperature, relative humidity and dry periods. Temperature and humidity conditions favourable for mould growth are presented as a mathematical model. The mould index has an upper limit which depends on temperature and relative humidity. This limiting value can also be interpreted as the critical relative humidity needed for mould growth depending also on the mould growth itself. The model enables to calculate the development of mould growth on the surface of small wooden samples exposed to arbitrary fluctuating temperature and humidity conditions including dry periods. The numerical values of the parameters included in the model are fitted for pine and spruce sapwood, but the functional form of the model can be reasoned to be valid also for other wood-based materials.

Puurakenteiden kosteustekninen toiminta

Abstract: In this research the moisture physical behaviour of wooden structures has been analysed and the interactions concerning humidity and carbon dioxide mass transfer between indoor air and structures has been studied. The aim of this research was to define exactly the moisture physical requirements and criteria for different layers in structures. A model and a solution method to simulate mold growth have been developed and a preliminary criteria for mold damages has been presented. For the hygrothermal analyses of structures the climatic data from all the important export countries of the Finnish construction industry have been collected and a dimensioning indoor climate for residential and office buildings has been created. This makes possible the hygrothermal analyses for export purposes. In the Finnish climate it is typical that mold growth can begin in the autumn on the wooden surfaces in contact with outdoor air, when the temperature and relative humidity are high enough. The results show that, in most buildings, minor mold growth can be found in cold parts of structures regardless of the materials used. No moisture physical defect or effect of indoor humidity is needed. As a result a realistic criteria for mold damage which accepts the above mentioned fact but not moisture damage is given. The water vapour resistance of the material layer on the warm side of a open porous thermal insulation layer must be five times higher than that on the cold side. It is necessary to have a genuine air barrier in the envelope in order to be able to control the pressure conditions in buildings and to avoid the harmful water vapour convection from indoor air to the envelope. Thermal insulation above the ground slab degrades the drying capability of the structure. Hygroscopic wooden material in interaction with indoor air will dampen the variation of indoor air humidity when moisture load is varying. This phenomenon can be significant in warm seasons, when the indoor relative humidity is high. Thermally massive wood dampens down the diurnal indoor temperature variation caused by the varying solar radiation load. These properties can be more important in Central Europe than in Finland.

WHO guidelines for indoor air quality : dampness and mould

Abstract: Microbial pollution is a key element of indoor air pollution. It is caused by hundreds of species of bacteria and fungi, in particular filamentous fungi (mould), growing indoors when sufficient moisture is available. This document provides a comprehensive review of the scientific evidence on health problems associated with building moisture and biological agents. The review concludes that the most important effects are increased prevalences of respiratory symptoms, allergies and asthma as well as perturbation of the immunological system. The document also summarizes the available information on the conditions that determine the presence of mould and measures to control their growth indoors. WHO guidelines for protecting public health are formulated on the basis of the review. The most important means for avoiding adverse health effects is the prevention (or minimization) of persistent dampness and microbial growth on interior surfaces and in building structures.

Moisture and Bio-deterioration Risk of Building Materials and Structures

Abstract: There are several biological processes causing aging and damage to buildings. This is partly due to natural aging of materials and excessive moisture. The demands on durability, energy balance, and...