24/7 use, attic temp, ice dams- wife's theory

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scajjr2

scajjr2

Feeling the Heat
Dec 9, 2010
305
Kingston, NH
A little background- wife and I been together for 8 years. She built house (saltbox) back in 1983, remodeled in 2005 so it is now more of a small cape style. 1600 sq ft.
It is a center chimney, house is electric baseboard, she had a wood/coal stove for occasional (usually weekends) use. No basement, slab, well insulated attic, house as well.

Now for the past 3 winters we have had a pellet fire running 24/7 from late Nov thru April first with a basket insert in the wood stove for 2012-13, Harman P43 last 2 winters. Have had ice dam issues all 3 of those winters, even with me raking as much as I can off the (now) 2 roofs on the back (north) side.

Now Lori's theory is that with heat in the chimney 24/7 it is raising the attic temp just enough to promote the ice dams. We have 3 foot foam soffit vents along the north side which I would think would let enough cold air in.
Lori wonders if wrapping the chimney in insulation in the attic would help.
I haven't heard of this being done, what's the opinion of you folks?

Sam
 
I would be surprised unless the dams are very near the chimney that wrapping the chimney would have a impact. Not sure if its allowed either someone else may know better.

You may have ice dams because your house is warmer now on a consistent basis. It may also be warmer near the ceilings then before.
 
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How is the chimney constructed?
Are there ridge and/or gable vents too?
Does the snow melt around the chimney? A lot?
 
Squirrel said:
If you have no ventilation at the peak of the roof heat will be trapped there. Adding a ridge vent or venting at the top of any gables should fix it.
Click to expand...
I have lots of ventilation on my roof. My stove is direct vent out a wall. Still have ice dam issues. Insulation is blown in in attic, seems fluffy enough. Had New roof in 2011, ice and water shield etc. I have a whole house fan that I cover with a roll of insulation in the fall. That is the only thing I can think of that lets heat into attic. I'm going to try covering it better this year and see if that helps. I do notice that the snow melts around my chimney first, thou I can't imagine it gets warm in my situation.
 
When I bought my present house I was glad to see large vents in each gable. In summer the bedrooms got really hot. On investigating I found the "vents" had been screwed onto a solid wall. Ten minutes with a hole saw in the attic solved the problem.
 
I have owned two cape style homes and they both had ice damn issues. Here is what I have learned:
  1. Ridge vents are much more effective than gable vents.
  2. Typically there is no air barrier around the chimney and the ceiling joists. This needs to be sealed with flashing and high temperature silicone.
  3. Any knee walls are typically not insulated correctly. There needs to be an air barrier otherwise air from the first floor will go into the knee wall area and then along your rafters into the attic. Fiberglass or blown-in insulation does not stop air currents. This is known as the devil's triangle by insulators.
  4. A metal roof will solve the problem.
 
The attic isnt properly vented is what it boils down to. Cold air outside needs to be able to be drawn into the attic from overhangs and travel unobstructed along roof to the peak. Insulating the chimney is not likely a good idea. Perhaps adding a small fan to promote air flow through attic, though counter-intuitive, may be best bet. I fought with a poorly insulated house for 6 years. My new modular has 4x the R rating and after one nasty winter, no ice dams to be seen.
 
Most ice damming I have seen is due to inadequate soffit venting. As mentioned above, you really need the flow from under the soffits, up to the peak. And a lot of the time, it is due to a quick insulation job. Someone comes in and blows in a lot of nice fluffy looking insulation, but in doing so they also blocked the airflow from the soffit area. If the soffit venting area was adequate to start with. That can be compounded if the attic space wasn't properly airsealed before all that new insulation was added - stack effect will still pull warm air up through all that nice insulation if the holes aren't airsealed first. A chimney should have very little effect on the warmth of an attic.
 
maple1 said:
Most ice damming I have seen is due to inadequate soffit venting. As mentioned above, you really need the flow from under the soffits, up to the peak. And a lot of the time, it is due to a quick insulation job. Someone comes in and blows in a lot of nice fluffy looking insulation, but in doing so they also blocked the airflow from the soffit area. If the soffit venting area was adequate to start with. That can be compounded if the attic space wasn't properly airsealed before all that new insulation was added - stack effect will still pull warm air up through all that nice insulation if the holes aren't airsealed first. A chimney should have very little effect on the warmth of an attic.
Click to expand...
Sounds like I need to call an insulation contractor. I have sofit, ridge, and one gable(no plywood behind it!) Vent. I will have to inquire about the rest of your post for my situation. Thanks, all, for the advice, though I'm not the original poster!!
 
Much good advice above. Ice dams result from inadequate venting of attic and, to some degree, inadequate insulation in some cases. Sounds like an airflow issue here. Correct now before winter.
 
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