washington state home inspection

Ice Damming In Pullman

After skating for most of the season, Old Man Winter showed up with a shovel and has proceeded to bury us. So far, several areas have reported record snow falls including my home town of Asotin. For those of you that scoffed when my sweetie bought me a snow-blower, HAH! The Snow Joe has earned its keep this month.

The view from the roof at an inspection in Pullman.

The view from the roof at an inspection in Pullman.

Also happening this month - business is picking up. This time of year gets pretty treacherous for walking roofs, though sometimes it can be done. It requires a careful consideration of the underlying structure of the snow and of the point of access, but snow by itself is not a primary limiting factor.

What is a primary limiting factor is ice. And, by golly, we are seeing a lot of ice on the edges of roofs lately due to ice damming.

What Is Ice Damming?

In its simplest form, ice damming is a build up of ice on the eave of a roof. The formation is from snow melting at a higher point on the roof, typically over the heated portions of the home, and flowing down the roof slope to the eave. The eave is at nearly the same temperature as the air outside. As the water hits this frigid zone, it re-freezes.

In the process, the dam blocks more water from flowing freely off the roof deck, thus extending the ice dam. Because the velocity of water drainage plays a part in the process of re-freezing, lower slope roofs are more susceptible to ice damming.

On a low enough slope, the ice can build up many feet along the roof deck. That is what I found with the roof in the second picture. My best estimate is that the ice extended 8-10 feet up the roof from the edge.

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Damaged Caused By Ice Damming

The presence of the ice is not the major cause of damage to the home. While the accumulation can cause problems, it is the water behind the dam that causes the most concern. Our roofs are not designed to act as pools and are not water-proof. They are water shedding. That is a huge difference. Obstructed water will not drain down the roof. Water being water, it will try to find a way to flow with gravity. This means flowing under the shingles, finding gaps in the underlayment, and getting into the ceilings and walls of the home.

It is not just a matter of getting a roof stain on your ceiling, though. This moisture in your attic can be a major contributor to the growth of mold and wood destroying fungus.

How To Recognize an Ice Dam

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Ever drive by a house and admire the long glittering icicles hanging from the roof? Well, admire those from a distance. If you see those on your house, you likely have an ice damming issue.

Likewise, if there is a four inch iceberg on the edge of your roof, you’ve got a problem.

Also, a couple people a year get killed by falling ice or icicles from a roof.Do not walk right under the icy spears admiring them. If you are walking around a house with ice on the roof, stay near the wall under the eave or well clear of the fall zone to the perimeter.

Just a heads-up - if there is ice at the edge like this, I’m not getting on the roof.

How To Fix Ice Damming


The first thing to do is figure out where the heat is coming from to allow for the excessive snow melt. Usually, the first and best answer is that you do not have nearly enough insulation in your attic. You don’t even need to go into your attic to figure this out - if your roof is the first in the neighborhood to lose snow cover, you probably need more insulation. (I take perverse pride in having snow on my 1910 built home long after everyone else has exposed their shingles.. It a great sign that I did a solid job of insulating the home. Lower energy bills are nice, too.)

There are other factors that come into play. If you have canned ceiling lights, they can create enough heat to cause problems. Have a contractor insulate the boxes.

Check to make sure that you have enough effective attic ventilation. If you do not, the attic will retain warm air and lead to ice damming. Also, to mold growth.

If you have a furnace in the attic, make sure all the joints in your duct work are tight. Leaky ducts will cost you in more than dollars.

Insulate all your ventilation fan ducts. Bathroom fans and dryers move warm air to the outside. If they pass through the attic on the way, they will transfer much of their heat to the attic space. Insulate them and limit that possibility.

If these steps do not work to control your issue, it is time to call in a quality contractor to perform a thorough analysis of the heat transfer taking place, including thermal transfer through air exfiltration from ceiling penetrations or up the wall cavities.

Good luck! As always, if you have questions, feel free to call. I may have a tidbit of information that can help.

I’ll leave you with one more scary picture . . .

Water is actively leaking and two different fungi are growing.

Water is actively leaking and two different fungi are growing.

Raised-Heel Trusses

Since the late 1960s, most houses have been built with engineered trusses (click on the link for more information than you need) instead of traditional rafters. Trusses offer greater spans to open up our interiors with great rooms, require less time and labor to erect, and provides a more uniform pitch to the roof, which may not seem important to you, but your roofer loves it.

Early truss systems resembled a triangle with a bunch of triangles inside the outside one. The problem that we ran into, from an energy usage standpoint, were those skinny angles at the ends of the truss. Often, there was not sufficient room to get an adequate amount of insulation into the space. I see a fair number of homes with shadowing on the ceiling at the outside edges of the rooms from precisely this.

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A 1970s Engineered Truss

Note how skinny it is at the low edge. Not much room for insulation.

When energy was really cheap (raise your hand if you can remember $.25 gasoline!), this was not a big priority. Today, with more expensive energy and an improved awareness on how to heat and cool our homes efficiently, what happens on that edge is important. One solution was to re-design the truss. Meet the raised-heel truss.

The raised-heel truss

Raised-heel trusses are engineered to provide enough space for the insulation. By design, they are taller than older truss designs at the point where they cross the wall. This section, called the heel, intersects at the perimeter wall and lifts the top chord of the truss. From my research, it looks like the energy-saving qualities of the raised-heel were not the primary reason they were developed, though. Initially, the were built to match roof lines and increase curb appeal. Go figure . . .

Even though the cost for these trusses are not substantially higher than with other truss systems, I still don’t see that many of them. When I do, it’s good news for my clients!

(A quick note on the video - I shot it in an attic while hanging from the framing - it might not sound smooth and polished.)