White powder off sarking?

reeac

My garage had a pitched roof of rafters, sarking felt, battens and tiles. In the past couple of months I've noticed deposits of fine white powder on the car that lives in the garage. It's soft in texture and initially I thought that it was fine sawdust maybe from woodworm activity but closer inspection of the rafters reveals no sign of worm activity and now I wonder if it's some anti-stick powder applied to the sarking felt during manufacture which is now being shed after about 18 years of service. Maybe the felt flaps a bit in windy weather. Has anyone encountered such a phenomenon?

London50

Hi

Just did a quick online check ..see link below {the final answer} I think you may be correct with your thoughts :0)

http://www.dampdecay.co.uk/index.php/your-questions-answered/48-dry-rot/454-white-powder-on-roof-timbers-is-it-dry-rot

reeac

Thanks....it seems to be a well known effect. Although I'm a great Googler I hadn't thought of looking there.