Abstract: An axially slidable pipe boot provides a substantially gas-tight seal between a gas vent pipe and a flexible barrier sheet surrounding the pipe. In a first preferred embodiment, the slidable pipe boot comprises a tubular sealing member having an internal O-ring seal. The tubular member is dimensioned to fit around the exterior of the pipe with a compression fit of the O-ring providing a sealing engagement with the pipe. An annular flange on the lower end of the tubular member is sealingly attached to the barrier sheet. In a second preferred embodiment, upper and lower tubular sealing members are axially joined together by a hollow tubular sleeve that fits around the pipe. Each of the tubular members has an internal O-ring seal that engages the exterior of the pipe with a substantially gas-tight compression fit. The lower tubular member has an annular flange that is sealingly attached to the flexible sheet.