"Todd" wrote in message
oups.com...
5 years ago we had our original slate roof replaced on our house built
in 1915 with 30 year Elk asphalt architectural shingles. The roofers
did not have to replace any woof as it was all solid and in good shape.
The wood beams on the roof are butted close to each other with little
to no space between them.

It's a pity you got rid of your slate roof. Our old neighborhood in
Pittsburgh consisted of houses built between 1910 and 1935, nearly all were
stone & brick houses and many of them had their original slate roofs. It's
hard to find a competent person to work on them but by golly they last.

I'm currently in Ithaca, working at Cornell University in the civil
engineering department. I was doing some archival work and found a campus
wide roof inventory and a subsequent study about roof maintenance procedures
done in the 1980s. Many of the older buildings on campus were built with
slate roofs and in the 1970, campus maintenance started to replace those
roofs with asphalt shingles (it was the modern thing to do). However the
conclusion of the study was that it was, by far, more cost effective to keep
the slate roofs. While a slate roof does need individual slates replaced
every so often and maintenance (regular attention to flashing & leaks before
they become a problem), overall they last pretty much forever. OTOH, asphalt
roofs need to be completely replaced every 10-20 years.

Chris