Abstract: A roof vent ingress prevention device includes a generally tubular base having a circumferential side wall, a lower pipe-engaging section and an upper section having at least two side vents formed therein, the side vents extending through the side wall for venting of gas from within the generally tubular base. A base slippage prevention device such as a circumferential bead or outward slant to the wall means is mounted on an outer face of the circumferential side wall intermediate the lower pipe-engaging section and the upper section of the generally tubular base and is operative to prevent the generally tubular base from slipping downwards into a roof vent on which it is mounted. Finally, a vent cap is mounted on the upper section of the generally tubular base, the vent cap including a plurality of vent openings formed therein for venting of gas from within the generally tubular base.