Our 1915 home has a slate roof. When we bought the place, the home inspector did an inspection from the ground and told us that he thought the roof appeared to be well maintained and in decent shape. He said that a tell tale sign of poor maintenace was the use of roofing tar to fix leaks, etc., and he didn’t see any of that.
Another roofing contractor, supposedly someone who was an expert in slate, also did a from the ground inspection, and thought the roof appeared to be in good shape.
Now we’re being told by our GC that the roof is in fair condition at best. According to him, all the slate tiles have been sealed with silicone. He also said that if you look at the slate tiles (we pulled a bunch of them off for some construction work) that you can see holes in the slate.
I’m really in a quandry about what to do. I have different people telling me different things, and obviously, once you take off a slate roof it never goes back on again (at least in my budget). What is the best way to evaluate the condition of a slate roof?
Anyone have any recommendations on a knowledgeable person in the Boston area?
Replies
See if you could get slateman to come down. Offer to pay him as a consultant!
He also said that if you look at the slate tiles (we pulled a bunch of them off for some construction work) that you can see holes in the slate.
Slate are SUPPOSED to have holes in them - that's how they are attached to the roof.
I've never seen a slate with other holes - usually they crack or crumble when they fail, in my (admittedly limited) experience.
There is a good book called "The slate bible" or something close to that. Might help you figure out if your slate is really bad or not.
The whole thing sounds a little "off" to me, but it's hard to tell from a few lines on a bulletin board.
The better slate lasts about 100 years when looked after. Slate is many layers of slite and dust compressed. Its produced by splitting between layers.
Slate starts to fail when the layers start to separate. Sometimes a slate will crack and cause a leak. This where roofing muck gets used by the quick fix guys.
If you have clean and trim solid looking slates with next to no powdering, the roof should be good for a while. slate always needs some looking after with a replacement or two. Find the right guy or it can be a real mess.
"What is the best way to evaluate the condition of a slate roof?"
The type of slate, method of fastening, roof pitch, flashing and degree to which it is delaminating or turning into gypsum are all relevant. Think of your roof as an entire system, not just the slate itself. Is there felt under? Copper nails? Copper flashing? Condition? Copper *thins* with age due to acid rain - it may look OK but at that age it may have thinned to the point where you can poke your finger through it. Here is a good synopsis for evaluation written by your own state's government (Massachusetts) - http://www.mass.gov/cam/MAFMA/Tutorials/MAFMATutorial_SlateRoofs.pdf
The Slate Roof Bible - http://www.amazon.com/Slate-Roof-Bible-Understanding-Installing/dp/0964425815/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1212024631&sr=8-1 is a very good book, but is more oriented toward the history of slate than the on-line tutorial above. Here is another good site on condition evaluation - http://www.tileandslateroofs.com/heater2-H950.ivnu
At 93 years old, your slate is *likely* near the last part of its life, although if the fasteners and flashings are good and you don't plan to live in your house for more than 10 or 15 years you might get away with spot repairs. Vermont gray or black can certainly last 125 years or more, if it hasn't been messed with (a 'silicone coating' - maybe TWP or similar?? sounds like a bad idea). Take one of the slates that you took off the roof and see if it 'rings' like a bell or sounds more like wood - that's an indication of weathering.
Oh, and BTW I'd give more creedence to an up close inspection, and more to a roofer over a G.C. But don't let anyone on the roof without padded chicken ladders or similar protection.
Jeff
Edited 5/28/2008 9:53 pm ET by Jeff_Clarke
I took a look at the slates myself. They aren't crumbling at all. They certainly are weathered, that's for sure. But, I didn't see any evidence that they were falling apart - and I couldn't see any of the silicone sealing that the GC believes is there.
I'm going to get a slate person to look at it tomorrow. I believe the slate is PA slate, rather than VT slate. But, I'll find out tomorrow.
If it is PA soft vein slate like Bangor black then it should be delaminating badly by now with whitish deposits. If it is Peach Bottom then it is still 'new' ;o)
But PB is relatively much rarer so I would tend to suspect that it is VT or NY.
Jeff
The Slate Roof Bible is an excellent book. It's a joy to read and a very good "knowledge tool" for anyone with a slate roof.
The guy who wrote it has his own web site with "real"slate contractor references and slate roof advice. It may be worth calling him as well.
http://www.jenkinsslate.com/
It makes me cry when I see people tear off their slate roof that usually will last over 100 years (typically at the advice of a GC or asphalt roofer) and put on an asphalt roof that will come off in 15 years and doesn't look as good as the original!
Billy