On Sun, 23 Jun 2019 08:53:42 +0100, Tim Lamb wrote:

Dry blowing snow for example.
We once had 2" of snow in an unfelted (Edwardian built) loft.

Argh, I'd forgotten about dry powder snow! ******* stuff follows the
air flow and is capable of doing so through door jams, ie around 2 x
90 degree bends. We've had the roofs stripped, breathable membrane
laid and reslated powder snow is no longer a problem in the lofts,
even with the "Beast from the East". Same can't be said for a couple
of the older doors and windows though.

--
Cheers
Dave.