Abstract: A method for preventing and combating attacks of fungus and of other harmful living organisms, such as longicorn beetles and wood worm in existing building structures, by heating the attacked areas to temperatures lethal to living organisms by means of electromagnetic energy. A HF generator comprising a balanced output communicating with a plurality of electrodes is arranged relative to the attacked area of the building in such a manner that the electrodes in combination form a capacitor, wherein at least a part of the attacked area completely or partially constitutes the dielectric of the capacitor, whereafter the HF generator is activated, said generator operating at a frequency within in a frequency range from 3 to 20 MHz, in particular from 10 to 15 MHz, and more preferred from 13 to 14 MHz, most preferred 13.56 MHz to provide a HF power heating the area between the electrodes to a temperature lethal to living organisms.