How damned is this ice?

January 11, 2021 9:38 AM

We moved to a 1950s-era house that has a not-very-steep roof, deep eaves, no gutters. There's ice buildup on the roof in a spot where two parts of the house intersect, a v-shaped area that gets little sun. Should we try to remove that ice (with one of those socks or something) or is it okay to leave it there so long as the eaves below that spot are clear?

The ice is a foot or two in from the edge of the roof but it's a good 3-4" thick. No leaks (yet?) It's a single-story so it's not hard to rake some of the snow off and we can get on a ladder to knock icicles down from above, which is less likely to harm the shingles I gather than just going off on them from below, tempting though it may be. Part of me says "this house has been fine since the fifties, and there have been much worse winters, so why worry?" but then the anxious part says "yeah, but that garage that creates the shade was added only a few years ago so don't relax." (And then there's the part that says "at least you don't have that horrible landlord anymore, suck it up" which, curiously enough, doesn't really help.) I've read previous ice damnation posts here, and ... maybe I'm overthinking this.

posted by zenzenobia to Home & Garden (5 answers total)

What's happening is that heat is getting to the underside of your roof, up above that ice buildup. It is melting the snow, then the water runs down to that area where there is no heat under it, so it refreezes and builds up. The heat is just from normal transmission up through your ceiling insulation. Unless there's missing insulation, you can't stop it. But once it gets up into your attic, there should be sufficient ventilation to remove it so that it doesn't melt the snow. Ideally, this is done through soffit vents (which run the length of the roof, they should be visible under the overhang), combined with a ridge vent (all along the top of your roof). This results in air flowing up from the soffits, out through the ridge, keeping the underside of your entire roof as cold as the outside, thus preventing melting and ice buildup. (This kind of ventilation can be messed up by improper insulation — insulation that covers up the soffit vent, so look for that.) But in an older house, you might only have vents in the eaves at both ends of the house. Those are OK but not as good. AND, if the garage was added a few years ago, the way it was built may have blocked air flow from one eave vent to the other. Ergo, heat buildup, melting, freezing. Bottom line: rather than focus on removing the ice (which risks damaging the shingles and doesn't address the root cause), get up into your attic, even if you have to crawl around up there, and figure out whether the ventilation is adequate.
posted by beagle at 9:54 AM on January 11, 2021 [5 favorites]

Response by poster: Thanks, it’s really hard to get up in there, but that’s likely the problem. There seem to be only ridge vents and no telling what shape they’re in.
posted by zenzenobia at 10:42 AM on January 11, 2021

Don’t have a ton to add except to link my favorite explainer on ice dams (warning- Instagram) and to mention that improving your interior air barrier, by making sure there’s a firm seal from the wall to ceiling, can also help, as it keeps warm air from leaking into the wall cavity.

This isn’t an issue now but when the ice starts to thaw you will probably get more water in your framing than you want- maybe not a ton, maybe it’ll dry out, but I wouldn’t let that keep you from fixing it. Better attic ventilation will also keep your house cooler in the summer, it’s generally a good idea.
posted by q*ben at 10:12 PM on January 11, 2021 [1 favorite]

A 50s house is likely (around here anyways, conventions differ by area) to have birds mouth rafters which are funtionally quite a bit different than the high rise truss pictured in q*ben's link. If you do there is minimal if any insulation between the top of the wall and the roof deck and no space really to add any. Valleys which handle a disproportionate amount of water compared to the rest of the roof and are more shady are usually the first places dams occur.

At this time I wouldn't mess with the ice on the roof. Damage to the roofing is likely and it's dangerous to be messing with it. Though it might be a good idea to get a roof rake and remove any snow that is above the dam.

However going forward next summer/fall you should install heat tracing on your eaves in the problem areas. The heat tracing cable will both melt the ice so it doesn't form a huge mass that can damage your roof all by itself and provide a channel for melt water to reach the edge of the roof. The channel will prevent water backing up under shingles and thereby damaging roof decking and wall framing/cladding.

There are DIY kits available if you are handy and don't mind working on a ladder. The process for a shingled roof is pretty straight forward if the roof is in good shape. If the shingles are crumbly then the clips will just tear the shingles. The tracing is a permanent install; you leave it in place year round.

In the winter you turn the heat tracing on when it is snowing and if there is an ice build up in the channels. A count down timer is useful so that you can turn it on for a couple hours and then have it shut off and remain off until you trigger the timer again. They sell them with remote controls which is handy if you are lucky enough to have eave receptacles. Be aware of the amp draw of your heat cable and the rating of the timer. Though at the typical consumer 5W/foot you need over a 100ft of cable before that is usually an issue. Make sure to use a winter rated extension cord if you require one.

It is a good idea to test it every fall to make sure it is still working.
posted by Mitheral at 6:33 AM on January 12, 2021 [1 favorite]

Response by poster: Thanks, all. This was my first time of Asking, and this is all really helpful. Looks like we need to fix the ventilation in the attic and should look into heat tracing, at least in the area that's a problem. And stop bashing at the ice on the roof!

And good timing - expecting a big snowfall later today and tomorrow. We'll be definitely using the roof rake.
posted by zenzenobia at 8:57 AM on January 14, 2021