condensation on metal roof underside
I've got a problem that I'm not sure how to deal with.
150 year-old-house with a 100-year-old or so standing seam roof that is in good condition. The client has been chasing roof "leaks" for the 13 years she has had the house.
I've been in the attic during heavy rains and observed no leaks. But there is staining all over the attic floor. I went up on a cold day recently and saw wet marks on the floor. Sure enough, every exposed part of the metal roof had frost that was in the process of melting off.
The roof is over wide boards that have spaces of as much as a couple of inches between them (the original roof was cedar shingles. This appears to be the second roof).
I can't do much right now to reduce the humidity levels in the house. The house is on a stone foundation, full cellar under front half, inaccesible crawl under back half with dirt floors. It has bluestone slabs for a floor surface in the cellar half. I'll be able to remedy the crawlspace next year. I hate to cover the bluestone floor in the main cellar, and would like not to have to.
So my question is how best to keep the condensation from occuring on the underside of the roof? The thermal envelope is currently at the attic floor. I'm thinking that short of spraying the underside of the roof deck with foam, there is no good way to isolate the moisture from the metal.
What say the moisture-issue people out there?
Sorry about the long ramble, but wanted to give full info right off.