When making new roofing and renovating the roof in non-ventilated roofs, due to the high diffusion resistance of heat-sealable roofing paper, it is very often necessary to ventilate the roofing. Effective venting is ensured by the use of perforated ventilation roofing felt and a fireplace in ventilation systems. This system allows moisture to accumulate under the cover to be drained away. In order to ensure effective venting, it is recommended to use one ventilation fireplace for an area of 40 - 60 m. Ventilation felt is laid without gluing onto a dry primed concrete surface or old roofing felt. The next layer of roofing felt is welded to the substrate through holes in the ventilation felt. Ventilation felt strips are laid on a 2-3 cm overlap. Ventilation roofing felt should not be placed in places particularly exposed to water penetration under roofing, i.e. in the drip strip, at roof outlets and drainage troughs, at building expansion joints, at chimneys and firewalls, etc. In these places, roofing felt 50 cm.