While driving through town yesterday, I took a few pictures (see below) which prompted me to write this post.  We have been hit hard here in the midwest with cold temperatures and snow.  This sets up a perfect storm to develop Ice Dams.

Ice dams are caused by heat escaping at the intersection of the exterior wall and roof.  Older homes are the most susceptible because of the way they used to be built.  Typically, 2×4 or 2×6 rafters were set right on the top of the exterior wall framing.  This only allows for a minimal amount of insulation at this point.  The escaping heat melts the snow that has gathered on the roof and refreezes when it hits the overhang -causing an ‘ice dam’.  This can cause major damage to the roof, gutters and siding as well as lead to potential leaks, creating more problems.

You probably have seen the zig-zag heating element wires used to melt the dams at the roofs edge.  Ideally, you want to get more insulation at this point so you are not losing heat (thus energy).  One option is to put vent chutes in the rafter space, to keep air circulating in the attic, and then use a foam insualtion that has a better R-value at the roof/wall location.  Another option,when you next replace the roofing material, is to install furring strips to create venting right under the finished roof.  The goal is to keep this material cold so there is no melting.

New construction uses an Energy Heel truss which raises the height of the ‘attic’ area at the exterior wall.  This allows for more insulation to be installed at that vulnerable location.

To remove ice dams, the best way is to use steam.  There are many services that are equipped for this and it is important to have them removed before more damage is done.

Click on the images below to enlarge.

Written by Michael Huber AIA LEED AP
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