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I purchased a house in the Metro Detroit area. 1943 built. Cape cod bungalow, pretty sure. Last winter, I had pretty bad ice dams and would like to re-insulate the knee walls before it gets too cold. I have one in the back and the front of the house. I've attached pictures of the roof / vents. I don't have an opportunity to add soffit vents with the gutters being right up against the house, but perhaps if we live here long enough, those smart vents or drip edge vents might be added.

So, without soffit vents, if I went up right against the inside of the house with insulation, that should be okay, as there's no air flow coming and I don't need to add baffles, correct? Additionally, the insulation as it exists is pretty old and I feel like pulling it all up, air sealing, and then putting new down might not be a bad idea. Please let me know what I'm incorrectly thinking about, and what might be the best way of preventing ice dams. I may do edge heating / coils and get a roof rake for the edges of the house.

https://imgur.com/a/3aWcoZI

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You would do well to adjust the insulation on the knee walls but you also have to place a decent amount of insulation in the ceiling joist area as it looks to be nearly non existent in the pictures. That could save you on your heating bills some but it is not likely to have a significant impact on ice dam formation.

The nature of ice dams forming is due to building heat passing through the roof and melting the snow. Water from the higher warmer parts of the roof runs down to eve area where the roof area is colder and allows the water to freeze. The fact that you have heated living space up to the roof peak (as evidenced by the gable end windows up near the peak) it is likely that the ceiling materials inside are nailed directly to the bottom of the rafters. This leads to minimal insulation in that area allowing the upper roof to be warmed by heat from the upper room.

You should definitely prepare, before snow flies, to invest in a roof rake. Plan to get it now before they get all sold out and are then not obtainable. These things help you to safely scrape the snow buildup off your roof before it has a chance to thaw/freeze and form ice dams. It does require some commitment to ensure that you rake the roof every time that snowfall occurs.

Note that it is best to remove all the snow from the roof to prevent the ice dams. If you just rake the lower edges of the roof and leave the snow up toward the peak that upper snow can still melt and the water run down the roof slope and freeze.

It can be valuable to watch the behavior of your roof after the first light snowfall in cold weather to note where it starts to clear first. If you have a lot of heat leakage on the upper roof it will be very obvious that that part of the roof clears first. Sometimes it is even possible to note where the space between the rafters is warmer.

(Note I used a conventional roof rake when I lived in snow country. I recommend the ones with the plastic rake blade because they are lighter and will potentially do less damage to your roof than a metal one. I have noticed in some Google picture searches that there are new types of roof clearing devices which consist of a long plastic sheet that is pushed up under the roof snow via a specially configured handle. The plastic sheet allows the snow to just slip down the roof. I have never used one of those so cannot vouch if the web site advertising is really as great as they make it sound).

  • And if I redo the insulation in the ceiling joists, I should remove the old and add some new? Because of the lack of soffit vents, can I just push them up to the rafters? Is there anything else I can try to do to stop heat transfer from the walls to the rafters? – Cyadd Sep 29 '18 at 20:27
  • @Cyadd - It is my guess that the biggest problem you are facing with regard to the ice dams is the heat loss through the ceiling that is nailed to the bottom of the rafters within the upstairs room. The area outside the knee walls under the lower part of the roof looks to me like it is already Ok from the standpoint of the roof. It is the ceiling joists in that area (floor joists from the perspective of the upstairs room) that could use good insulation to alleviate heat loss from the lower level of the house. – Michael Karas Sep 29 '18 at 22:33

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