Ok, my logical mind says "this house has been here for over 180 years, and snowfall totals are less now than they used to be"...but then the OTHER voice is having a mini-fit over the 28" of snow and ice we've gotten in the last 24 hours. I'm shuddering to think what that clinging mess must weigh, and perhaps more important...does modern insulation reducing heat loss, cause increase in snowload that could be dangerous to an old slate roof? I'm worrying over the idea that, prior to modern insulation, the heat escaping thru the roof would likely have caused faster melt & faster shedding. It's all nice and wonderful to see that my heating dollars are not making an immediate exit, but it's making me wonder: at what price? Input & discussion as always, greatly appreciated!
Well, it's not really answering the questions in my head, but last night, in a cataclysmic roar, about 10" of snow, on a sled of 8" of ice, slid off the roof in one screaming chunk. That entire side of the roof shed all at once, all the way to the peak. There's a 4' high pile of snow & ice on the ground now, totally blocking both exterior back patio doors. This, from the part of the house with the most insulation, which had shed almost NONE of the fallen snow. It redoubles my curiosity about how well a very old slate roof is going to fare under such conditions.
Is your slate roof original to your house, or a recent improvement? Our slate roof was installed seven years ago, and we have had sudden downslides of snow and ice this past week because of all the bad winter weather. I immediately went outside and photographed the roof with a telephoto lens to see if there was any damage. None. No damage. Just piles of snow and ice on the ground. The downslides sound terrible from within the house, but the house has fared far worse.
I believe it's original, or at least pre-1900 because all town records were lost to fire in about 1898. It's in super condition, with only minimal sway-backing of the ridgeline. I'm so relieved to hear from your experience that a spectacular shedding like that, left no damage. I'd much rather discover I've worried over nothing, than the alternative!! THANK YOU!!
I honestly think this is a case of obsessive overthinking. I am prone to this as well. Your overly analytic mind entertains a very large number of permutations of possible events, stringing together "what ifs" which is more or less a part of the obsessive-perfectionist personality that home restorers tend to have.
Relax. Your roof has seen much heavier in the past. Its way overbuilt.
No doubt Stu, I'm the "overthinking queen"!! I'm now just living in deep admiration of the engineering and materials of that time, because you are ABSOLUTELY right...It's WAY overbuilt!
I was just up in the attic today...hand hewn timbers, 8"x10" (roughly...only planed on 3 sides, so are mostly the size of the tree they came from), with decking made from wide (up to 28"!!!) plank pine, 2" thick. Overbuilt, might be an understatement! THANK YOU for giving me the green light to relax about this!!
There are brackets sometimes called "Snow Eagles" that are designed to hold snow in place on slate roofs, and allow the snow to melt slowly, and not come crashing down all at once, causing problems. Google "Snow Eagles" and you should get some results.
Lack of insulation will cause ice dams and other problems. Again, Google "cold roof" and you should find some solutions.
I used to have tremendous loads of snow come crashing down too. My young neighbors' daughter (before I bought the property) said that on occasion she heard thunderous & earth shaking crashes! She lives a good ways down the block too. Now, with synth. slate there is little for the snow to grab onto and it comes down in metered amounts. Additionally, I got snow guards attached to the new roof for the 'what if" situations where there might be a person, pet or property parked under the eaves. So far, I haven't really needed them. They weren't too costly, however they aren't inexpensive either.
As per the load limit - my old roof did well with the full slate / full snow load and seems just as happy with the reduced weight of the synthetics. There is no bowing on this 140 + year old roof. So, I do think the carpenters of the time overbuilt for those harsh New England winters.
p.s. I've attached a picture of snow guards made by Carlisle. I wanted some cool snow eagles, but the warranty for the roof didn't allow for decorative snow guards. :(
That said, well hung gutters should be able to survive snow slides. I think that the heyday of snow guards probably was a time when many houses didn't have gutters anyway. (That I am not sure of: does anyone know when gutters became standard?) Aluminum gutters can't handle it well (I speak from experience), but after switching to copper half-round gutters hung off of cast copper hangers, I have not had even a hint of issues.