Following up on a short article about local
ice dams and related fun
during Boston's endless winter of 2015, I've decided to
proactively attack the huge load of snow on the back roof and take
some of the weight off before, say, it gets rained into and becomes
even heavier. No ice-dam or water problems because of the
superinsulation, but none of this pack is about to slide off by
itself due to the sturdy snow-rail underneath holding it back.
The pink box highlights where the siding had shrunk enough in the cold to gap open at an insufficiently overlapped joint. |
There doesn't seem to be any weight on the gutter, which is a relief. Still nice and level. It helps that it's not holding up 200 pounds of icicles, as many other gutters all over Massachusetts are. |
There's also no sign of panel attachment compromise or sliding. If anything, the ends are snugged up against the drip edge tighter than usual due to shrinking in the cold. |
This makes sense, though, and it's not because there's something wrong
with the insulation. Snow has some R-value, nominally about 1
per inch, although probably a little less as density goes up.
So two feet of variably-compressed pack adds R-20 or more to the roof
assembly, which itself is about R-26 through the foam and sheathing
to begin with. So the roof panels themselves are now maybe 60% of
the way through the thermal gradient between the 60F-ish of the attic
and the 15F daily averages we've been having outdoors, putting it
around 33F and perhaps more on a sunny day.
Which is exactly why more houses get ice dam problems under heavier snow accumulations, especially if things like ridge vents get blocked. Even with good attic-floor insulation in a typical vented setup, enough heat can leak up to accumulate more under that big blanket and start melting what's on the roofing layer itself. Now that I think about it, that's probably the main reason this place never really had any ice dam problems pre-retrofit. It had gable vents instead of a ridge vent, which would remain open under snow cover, and I usually let the whole upstairs run cold over winter anyway. It also had very small eaves and no gutters back then, which would give water far less opportunity to refreeze and accumulate on its way off the roof. It sported a few small icicles now and again, nothing major. Some element of dumb luck, perhaps, but nice to be able to explain. |
About half finished at this point. Looks ugly, but most of that oppressive weight is going to be safely on the ground soon enough. |
Done! Or done enough, at least. I've left anywhere from one
to five or six inches in place, partially to facilitate walking around
on and partially to keep a little of that free extra R-value and mitigate
the night-sky radiation issue. It's also not worth trying to dig
down completely flush with the panels; even though I've got a plastic
shovel it's not worth banging up the finish on the metal any more than
necessary.
It does seem prudent, however, to completely clear the panel above the stink-pipe to minimize what comes down against it during melt. Which we're still convinced is never going to happen. In the meantime, development of a better solution can proceed. |
Okay, now it's time to have some fun. This picture links to a
short video of pushing part of the front-side pack off and having it
go most of the way down. This only works near the right and
left ends of the roof, and not so much in the middle -- could be related
to that mild heating effect from inside, hard to say. But having
seen part of this avalanche off earlier, I decide that I have to try and
snag some video of what it looks like.
I suppose I'm hoping for something
more spectacular,
but I guess I get what I get. What I can't push off with
an extended-handle broom will simply continue to sit there until it
warms up enough to slide off on its own, but this nonetheless helps
take some of the load off this part of the roof too.
The mound in the front yard is taller than I am by now, and it won't be a surprise if some of that water winds up in the basement once the ground underneath gets totally saturated. At this rate I'll probably still have snow on the north side in July. |