A Simple Explanation of Where the Water Goes When Ice Dams Cause Leaks
Where the Water Travels:
Water hitting the Top Plate of the wall (A) spreads out across the top plate, travels downward with gravity, working behind the Siding (B) the Housewrap (C), the Insulation (D), the Vapor Barrier (E) and the Drywall (F). Water always seeks the path of least resistance and therefore frequently shows up through existing penetrations in the ceiling such as lights. Water leaks caused by ice dams can travel many feet from the source before manifesting inside the home. On homes built with vapor barriers on top of the ceiling finish, water will sit on top of the drywall and soak the insulation before leaking inside.
How to Figure Out if the Leak is from Ice Dams or from Something Else?
As discussed in Ice Dam Company Case Study #03, ice dams can form in many locations on the typical home. The eave (lowest edge of the roof) is the most common area for ice dams but we find them around other areas including skylights, in valleys and in low-pitch roof pans and saddles. Many times a winter we get calls from concerned property owners who are experiencing leaks – or at least that is what appears to be happening – because they see water, moisture or discoloration on the ceiling. It’s logical, after all, to assume the roof is leaking when one sees that sort of thing. But the fact of the matter is that winter roof leaks can be attributed to a few potential sources. Here are a few of the common sources:
Is the leak in close proximity to a plumbing fixture, water supply or drain line? The most common sources of plumbing related leaks in homes are associated with failing shower pans, over-flowed bathtubs and faulty caulking or bad wax rings around toilets. Water can travel many feet from the source before it finds the path of least resistance and shows up. It’s typical to see water coming through penetrations through the ceiling such as recessed lights and at sheetrock seams many feet from the leak source. Plumbing failures can occur at any time during the year. When they happen in the winter, homeowners often assume its an ice dam. Plumbing leaks can be tricky to find and fix. Our favorite tool to find this type of leak is the thermal imager. This is a special camera that sees through walls and ceilings to detect differences in temperatures.
Attic Frost and Attic Condensation
If possible, it can be tremendously helpful to peak into the attic. A healthy attic with good ventilation (Ice Dam Company Case Study #17) should not present moisture or frost on the framing members or roof decking. The photo, right, shows a poorly insulated, ventilated and air-sealed attic. Notice the frost on the underside of the roof decking? This is not good. Attic frost can cause tremendous damage and is most likely to accumulate when temps are quite low (below 10°F). Warm, moist air meets the ice-cold roof deck and freezes into frost. This cycle continues until as much as 1/8″ and 1/2″ of frost has built up. When outdoor temps rise above freezing, all of that frost melts and has nowhere else to go by the interior of the house. This type of ‘leak’ is tricky because it is actually not a leak. We have seen clients spend thousands of dollars trying to resolve a roof leak that was in fact nothing more than attic condensation. Future Ice Dam Company Case Studies will discuss how we fix this issue.
Exhaust Vent Condensation
This is a very popular source of the winter roof ‘leak’ phone call we receive. Similar to attic frost-related leaks, this problem is related to the accumulation of frost inside an exhaust vent, commonly a bath vent duct where it travels through an unheated attic. A quick review of the temperature variations from the previous week is a good clue that we may be dealing with an exhaust vent condensation issue. If we had a number of days with extreme cold (highs in the single digits) followed by a thaw (highs in the mid-high 30’s) our first guess without even visiting the home is that the source of the moisture is a condensation issue, not a roof leak. Of course, a thorough site inspection is essential in confirming our suspicions. In almost all cases when exhaust vents are the culprit the leak shows up in the bathroom. Future Ice Dam Company Case Studies will discuss how we fix this issue.
Last but Not Least…Ice Dams
Do you see icicles on the eave near the leaking area? Do you see an ice dam? While not always the case, ice dam causing leaks are usually plainly visible from the ground (See Ice Dam Company Case Study #20). The steeper your roof pitch, the more ice it takes to create interior leaking (See Ice Dam Case Study #09). If you have a low-slope roof area, accumulations as little as 1″ thick can cause problems. Likewise, a heavy blanket of snow can hide the significance of an ice dam, making it hard to ascertain it’s size. Ice Dam Company Case Study #01 and #02 describe some easy things to look for in determining if you have an existing ice dam issue. In our experience, it is unusual to get roof leaks cause by ice dams when no appreciable ice accumulations can be seen from the ground. It can happen, however. It is common to see water/ice coming through the soffit or down the exterior wall when ice dams have developed to the point where they are forcing water to back up into the roofing system.
We have spent a lot of time discussing the finer points about ice dams over the years. This Case Study is about pulling the focus back to the most global understanding of why ice dams happen.
What Causes Ice Dams
There are over a dozen factors that contribute to the formation of ice dams, all of which have been discussed in previous Case Studies. Fundamentally, only one condition MUST be met in order for ice dams to form: A temperature differential from one area of a roof assembly to another area, with the upper area being above 32° and the lower area being below 32°. See below.
How it Works
This diagram demonstrates the basic concept behind ice dam formation. Snow melts in the area above 32°, water runs down to the area below 32° and refreezes. This cycle continues until an accumulation of ice forms that is large enough to block water from flowing naturally off the roof. The resulting ‘ice dam’ forces water to back up under the roofing materials and into the structure. There are many intersecting variables that cause the phenomenon described here. See below.
List of 7 Contributing Factors to Ice Dam Formation
A period of outdoor temperatures ranging between 0°-10° at night followed by daytime temperatures between 10°-20°.
Repeated snow falls that keep the roof loaded with new snow resulting in at least 6″ of coverage at all times.
Thermal inefficiencies in the home that allow warmth to heat up the roof deck from the underside.
Homeowner lifestyle that results in excessively heated spaces (More heat equals more roof snow melting).
Roof pitch: Flatter roof pitches tend to be more affected by problematic ice dams.
Eave depth: Smaller eaves tend to be more affected by problematic ice dams than deeper eaves.
Age and construction style of home: Older homes tend to be more affected than newer homes.
How the Distribution of Snow Can Affect the Formation of Ice Dams
Snow and Ice Dams
There is a complex relationship between snow and ice dams. Yes, you need snow to get ice dams. Snow is, after all, the fuel that feeds the formation and growth of ice dams. Furthermore, it is unlikely to get ice dams unless there is an ongoing layer of snow on your roof over a period of time (normally at least 7-10 days). But it takes more than just having snow on your roof to get ice dams. See Ice Dam Company Case Study #23 for a list of contributing factors. One factor that seldom gets discussed is the affect of wind on the formation and severity of ice dams. While this is not a primary factor, it is something worth exploring. This Ice Dam Case Study looks at the affect a thinning snow cover has when seen on a roof slope that also faces the sun. The affect described below is exacerbated by the presence of darker roofing materials as they absorb more solar energy than lighter materials.
Mountains and Roofs Share Something in Common
Any skiers out there? Wind speeds increase near the ridge of a roof just like the top of a mountain. Snow on one side of the ridge is often swept away while remaining in place just on the other side of the peak. This phenomenon can affect both sides of a roof if wind direction changes from day to day, leaving the snow coverage thin or non-existent on the upper few feet of the roof below the ridge.
Condensation, The Silent Killer
The lack of an insulating snow blanket can allow heat from the inside of the home to meet cold exterior air in a thinner ‘conduction plane’. When heat hits a thin surface such as a roof decking, where there is a great temperature differential from one side to the other, condensation is also likely. Think of frost on old, single paned windows. The more space there is between the heat and cold, the more room there is for this interaction, greatly reducing the likelihood of condensation. A thick blanket of snow is a perfect insulator for this purpose. It creates more separation between the warmth being lost from the home and the frigid exterior air. Homes with thick snow coverage on their roofs generally seen as more efficient because heat is not escaping through the roofline to reduce the snow through melting.
The Truth About Gutters and their Relationship with Ice Dams
In 2011, Ice Dam Company owner Steve Kuhl wrote a nationally published article about ice dams for the Journal of Light Construction. One of the topics that receieved the most attention was the notion that gutters have nothing to do with ice dams. Here is a deeper look at that assertion.
There is a great deal of confusion and misinformation about the relationship between gutters and ice dams. Many people are under the misconception that gutters cause ice dams or that gutters filled with ice can cause water to back up into homes. Not true. We repeat. Gutters have nothing to do with ice dam formation or severity. For this reason, buying systems that heat gutters in order to prevent ice dams is a total and complete waste of money.
We know that ice dams occure when:
Escaped heat from the inside of the home warms the roof deck.
Melting snow results in water that runs down to a cold, unheated area of the roof (frequently the eave, as shown below).
That water freezes, forming ice. After many of these cycles, that ice piles up to form an ice dam.
Study the illustrations below. These are identical eave designs, one with gutters, the other without. The Area B in the diagrams below is referred to as the ‘cold edge’ of the eave because heat from the interior of the home doesn’t travel that far. Fact One: Whether or not a home has gutters, a cold edge will still exist and this is where ice dams form. Fact Two: leaks from ice dams occur in Area A, at the leading, top edge of the ice dam where water–with nowhere else to go–is forced up under the roofing material and into the home. Put another way, if the home in Figure 2 had bad leaks inside, those leaks would not be eliminated whatsoever if we took a chainsaw and cut off the gutters along the red dashed line (C). Moreover, if we heated the gutters using a fancy electrical system, the likelihood of ice dams and the subsequent leaking would NOT be affected. Spend money on heat cables for the lower edge of your roof, not on heating the gutters only. High quality heat cables can be quite effective in preventing ice dams.
Figure 1: Ice Dam Without Gutters; Figure 2: Ice Dam With Gutters
None of this is to suggest that ice in gutters are harmless. We have seen many gutters damaged or destroyed by ice dams and that is a problem most homeowners would like to avoid. The point here is that, all else held equal, if a home is likely to get ice dams the addition or deletion of gutters will be of no consequence to the formation or severity of said ice dams. Likewise, for this reason, installing heated gutters or adding heating systems to existing gutters will have no affect whatsoever on the occurrence or severity of ice dams. To read more Case Studies click here.
I’ve been working on a new graphic to describe the basics for homeowners in Minneapolis to identify a problematic ice dam. It’s true that some ice dams cause no problems. The key consideration in determining whether or not an ice dam is a current problem is all about where you see ice. Study this drawing closely and you will see that any ice behind the facia is a bad sign. Ice through the soffit, down the exterior wall or through the window frame is very bad thing. Leaks caused by ice dams minneapolis
Removing Ice Dams in Minnesota: We Serve Many Areas in the Minneapolis Metro
The Ice Dam company based out of Hopkins, Minnesota, about 5 miles west of Minneapolis. We've done gutter ice removal, roof ice removal and ice dam removal all over the Twin Cities, on new houses and old ones.
Some of the more frequent places we've done ice dam services are: