Down in Canberra, the Australian equivalent of Washington, we are wondering
about the life expectancy of the sulfur-crested white cockatoos (quite large
raucous birds that look wonderful flying past, but destroy your sleeping
patterns if they roost nearby) ... we've found that they have a taste for
ripping up (and eating by the lack of evidence remaining) "Nuralite" which
was the proprietary system of asbestos filled bituminous sheet membrane
installed here through the '60s and '70s.  Quite large areas seem to be
consumed in relatively short periods - but they seem to leave the gravel
surfaced modern replacements alone so far!

Roof membranes, like so much else, are a workmanship issue and a detailing
issue as much as a materials issue.  Many of the older bituminous systems
have worked not because the materials are great but because they were
installed by people that knew what they were doing (or were lucky).  Good
details and good work practices were more likely to be known when there were
apprenticeship programmes and young people were able to learn trades.   I
also feel that performance specification has much to blame in this area,
because anybody can say that they will be installing something that will meet
your spec ... but if it doesn't, then it must be somebody else's fault!

Cheers

david

PS  Will be off list for a while during a change of ISP.  Back soon with yet
another address!