A wall or roofing construction(10) includes a thermal insulation layer. The insulation layer comprises a plurality of insulating boards (11) laid to abut edge to edge. The insulating boards are substantially water vapour impermeable. The joints (12, 14) between adjacent boards (11) are sealed by a self-adhesive, air barrier, water vapour permeable tape (1). A self-adhesive, air barrier, water vapour permeable tape (1) is provided. Also provided are methods for sealing joints or gaps in ducts (19) or pipes and methods for allowing moisture diffusion.