I hope someone here can clear up some confusion in my mind. As you'll see, the question is whether it's worth the effort and expense to use ice melter pellets to keep an eavestrough clear of ice.

The roof on our house has a very shallow slope and the east side gets little sun. Last winter ice damming caused a fair bit of damage inside the house.

In late fall I installed a heater cable along the problematic side of the roof. Following the manual's instructions, I laid out triangles 15" wide at the roof edge with the point either 5 or 7 rows of shingles up -- I forget. Per the manual's instructions I then suspended the remaining cable about 1" inside the eavestrough.

I activated the cable during a light snowfall this week. I thought that warm melted water would flow from the roof into the eavestrough and then flow into the downspout and away from the house. Instead water flowed into the eavestrough and froze. The ice level is about 2-3" below the suspended cable. With more snowfalls, more ice will build up. When it reaches the cable, I assume/hope the cable will create a small channel to the downspout.

Sorry for the long-winded background. Here's my question:

It would not be too hard for me to climb up and put ice melter pellets into the eavestrough to keep it clear. Is that worth the effort and expense? Some of what I've read on the net suggests a frozen gutter is no problem as long as water from higher up on the roof -- over the house itself -- can flow down to the gutter and then over it. This, of course, would create big icicles, which I thought were supposed to be bad.

Thanks for any help.

 

Which side of the house (N,S,E or W)?

Do you have good sofit ventilation to keep the underside of the roof cold?

There must be some heat melting the snow.

Dick

 

The problem area is on the east side of the house. The house is built into a high, steep forested hill which blocks most of the morning sun. So that part of the roof is shaded for probably all but one hour.

Soffit ventilation should be OK. Every so often there are openings in the underside aluminum panels. We installed styrofoam soffit vent things between the roof joists inside the attic and also increased the attic ventilation.

I think most of the water now frozen in the eavestrough is snowmelt from when I turned on the cable, not natural melt. I neglected to mention that the eavestrough has a very long run -- about 40' -- and I doubt there's enough of a slope for water to flow well. When I installed the heater cable in good weather, I noticed quite a bit of rainwater just sitting in the gutter. I plan to redo it next summer, adding more downspouts so I can increase the slope of the gutter.

 

Even on a well pitched roof, ice can be a real problem. Since the area in question gets very little sun, one of the reasons for snow melt is gone, the sun. If we forget the hot wire , that leaves heat from your house as the only source. So the basics:

1. Air sealing, air leaks not only transport moisture, but heat into your attics. Neither is good. Energy star provides us with some of the air sealing details: Air Seal and Insulate with ENERGY STAR : ENERGY STAR
Since air can move easily through any wall cavity (behind the sheetrock) in your home, sealing all electrical outlets, and other penetrations are all beneficial.

Next is insulation. In Ontario, R=40 or more would be recommended. Where the roof rests on the outside walls, especially with a shallow pitch, there often isn't enough room to insulate as much as needed. That leaves the final detail:

Ventilation. Since some heat will always get through, your final option is to vent it out before it can warm the bottom of the foor deck. For a well air sealed and insulated ceiling, the recommended vent area is a combined inlet plus outlet area of one square foot for every 150 square feet of attic space. If all of the air sealing has not been done and the insulation is less than desired, then more vent area is needed. Remember, that those panels with little holes in them, you can only count the holes. They will have a rating that gives you the equivalent vent area, that will save you from counting the holes.

Valleys have an additional problem, the surface area of the roof increases as you move up the roof. In other words, the vents for the valley have to do more work than other vents.

I have never used the ice melt pellets, but would be concerned that if they were up there and a leak occurred, would the calcium or whatever they are made of create a bigger problem inside the house. Here is one more link to give you the technical side of the ice dams: http://www.crrel.usace.army.mil/libr.../MP02-5778.pdf

Bud

 

Thanks. I'll give the Army article a good read tomorrow with fresh eyes. My attic has a lot of ventilation. In addition to the soffit vents we put in large vents on each side of the roof so there's 4-way cross ventilation. I'll do the calculations in the Army article to make sure.

Last winter was the first in which we had an ice dam. Snowfall over the winter was unusually heavy and we had one or two sudden very warm spells. While the part of the roof right over the soffit gets little sun, the area just below the peak does. Based on what I've read so far, I suspect the snow in that area melted but the snow further down didn't. So the water had nowhere to go except into the attic.

If we get the same winter this year, I think I can manage that scenario with the heater cable and, as required, going up onto the roof and shovelling snow away from the peak area. My concern is how to get rid of the water at the roof's edge: Let it flow over an ice-filled eavestrough or keep the trough free of ice so the water flows into it and then to the downspout.

I wouldn't put ice melt pellets on the roof; only inside the aluminum eavestrough. And I'd use the organic pellets whose active ingredient is urea or beet sugar.

I found this page which indicates that simply letting the water flow over the eavestrough instead of into is OK. Right now I'm inclined to take that option.

One idea that occurred to me is to periodically use a hair dryer to heat the eavestrough from the underside, melting the ice from the bottom. Because the house is built into a hill, the eavestrough is easy to reach with a stepladder.

 

Canadianguy,

You need to run the heat cables along the bottom of the gutter and down the downspout in addition to what is on the roof. At least 3' below the ground line. Otherwise the water just freezes in the gutter.

 

That was one of three options illustrated in the manual:
-- Roof only
-- Roof + one strand suspended in gutter
-- Gutter only

I chose #2. I've since seen a roof rake on a 25' pole that would make it easy to clear snow from the roof area over the soffit. So after I re-do the eavestrough next summer, I'll use the gutter-only layout when I reinstall the cable. Can't remove and reinstall the cable now because the roof's too slippery, the shingles are too hard, and it's too damn cold.

That's exactly what has happened. So I'm now debating whether to:
-- periodically use pellets to thaw the gutter
-- periodically use a hair dryer to thaw the gutter from the underside
-- trust the suspended cable to maintain a channel in the gutter
-- do nothing and let snowmelt flow over the gutter

FWIW I live in the country so the downspout empties on top of the ground. The normal downspout has two 90-degree elbows and then runs down the wall of the house. For winter I replaced that with a straight vertical run secured to an iron T-bar driven into the ground. The downspout empties into a 4" plastic O-ring which carries water away from the house. I doubt there's much chance of the O-ring freezing solid or even substantially. But it's easy to check and, if required, I could easily remove it so water flowing into the downspout has a straight fall.

 

Some good reads: UMass Amherst: Building and Construction Technology Preventing Ice Dams Home Energy Magazine Online Second one is good.

Your intake soffit holes may not be giving you 1/150, or 1/300 with vapor barrier: Ventilation - Deer Park Roofing

The soffit vents may not get 9 sq.in. per ft. w.o. v.b.: http://www.fureyco.com/content/image...ng_The_Air.pdf Then with ANY heat loss from ceiling below, ice dams form above said loss.
Be safe, Gary

 

Thanks all for your help. Am now slogging through the reading material.

Let's say there are currently not enough soffit ventilation panels. ISTM the solution is simply to drill holes through the solid panels in between the perforated ones. They're aluminum. Yes? (I know there's no insulation right over the soffit panels. We had a handyman clear that area and install styrofoam channels -- a job he said he'd never do again!!!)

 

What are you coming up with for numbers? Can you replace the solid panels? Your handyman may never speak to you again if he gets that drilling job.

Bud

 

No numbers yet. I've just began reading (and converting into plain English!)

I'd do the drilling. From the outside. The house is built into a hill and the panels are easy to reach with a stepladder. I'll see about getting more perforated panels. The previous owners had Sears do the soffits and eavestroughs within the past 10 years, I think, so the panels might still be available.

(There was so little room inside the attic where the roof met the soffit that the handyman gave up on the idea of installing the channels from the inside, went outside, removed all the aluminum panels, cleared out some insulation from the soffit trough, shoved the channels into place and then reinstalled the panels. Still had to struggle inside the attic to do the west side of the roof because the soffit was too far off the ground. Fortunately, that side gets lot of sun and we haven't had any problems with ice damming.)