building paper v Polythene Vapour Barrier

[zaax]

Can I use Polythene Vapour Barrier

of building paper before I put down insulation in the loft (only has 5mm of foam beads at present and no ventilaton)

[Bob Martin]

[PeterC]

Site's frozen.

[NT]

very roughly equivalent to around 3mm solid insulation, which does make a useful difference. But nowhere remotely near enough by modern standards.

NT