This seems to be a common install in this area. Roofers are installing 15-20 year asphalt over 100+ year old slate.
I have spoke to slate roof specialists, Gerry Beaumont (Thanks mate) and now I am trying to call some roofers in the area to get there input.
If I see this I call it out as an improper install and recommend a specialist to evaluate. Today was an interlocking T asphalt shingle (Are these nailed or is there a different installation as they are interlocked)
As I looked down the street there where 1/3 with the slate in general servicable condition. 1/3 had asphalt over slate and 1/3 had asphalt tear offs.
Be carefull that you idenify the slate underneath or a very large lawsuit could be in the horizon.
My slate roof doesn’t have any decking, just strapping, and I am not at all sure that it would be sufficient to support the wieght of the slate PLUS the asphalt. Even if it is, how do they secure the shingles? Drive teh nails through the slate? They better be really good at knowing where the rafters are.
I’m lead to wonder about anyone who wants to cover a beautiful slate roof with generic shingles anyway…
David, I always remind myself that what may be permitted is not always best. Code, for instance, is usually the lowest permissiable standard. I will never approve of any layered roof, and can only imagine what might happen to a fastener when it hits a piece of slate. If it penetrates the slate, it will probably shatter it or, worse, richochet off. I begin my evaluation of all layered roofs, by editing, or adding to, this generaic narrative: “The roof has been layered, which is never sensibly recommended because it adds weight to the roof framing, and typically reduces the design life of the new roof by several years and requires a regular maintenance of its flashings.” Well, that’s my two-cents worth.