In this article we’re going to discuss how to prevent ice dams forming on your roof in snow states like Michigan. Use the links in the Table of Contents below to jump to individual points of interest or when you’re re-reading.
Ice Dams
The beautiful icicles hanging from roofs all over Michigan in our Winter Wonderland are testimony to the fact that many homes experience ice dams. Snow accumulates on roofs and remains there when the outside temperature and the attic temperature are below freezing. The required water for ice dam formation comes from snow melt on the roof. Heat leaking upwards from the home warms the attic space and the underside of the roof. The snow layer in contact with the roof surface melts because the outer layers of the snow pack insulate it from the wind and cold despite temperatures being well below freezing. If you ice fish or snow mobile, it’s the same mechanism that generates deep slush on a lake even when it’s 10° below. Insulation in the attic is never 100% effective. The higher its “R” number, the more effective it is, but some energy will always leak out and potentially heat the attic space, providing the energy that heats the underside of the roof.
Ice Dam Formation
Initially the water produced travels down the roof to the gutter and away from the home via the downpipe. Water formed at the point furthest away from the downpipe has the greatest distance to travel on the metal gutter. There’s of course no insulation from the elements on the gutter so on cold days the water progressively turns to ice at the furthest point from the downpipe. If the cold continues long enough, ice works its way along and may even cover the top of the downpipe itself.
Once there’s nowhere for melted snow to go, it simply fills, then runs over the gutter forming icicles. At the same time, the ice formed in the gutter gradually builds, eventually creating a dam all future snow melt can’t overcome.
Roof Leaks Caused by Ice Dams
Figure 3 shows the structure of an ice dam as revealed during the spring melt. Once the ice dam is formed, any water formed behind it will stay on the roof surface. That’s usually not a problem for the small amounts of water formed by heat from the home, but once the warm, late winter sun begins to melt the roof snow, it’s a different story. Now many gallons of water are possible and just like a stream dammed in a valley will form a lake, a small, slushy lake will form behind the ice dam. As water piles further up the roof it penetrates the shingles which are not designed to guard against standing water. The water is now against the underlay materials. Any holes, missed spots, or failure to properly overlap these in construction will allow water to penetrate through to the wooden roof surface with disastrous consequences if not detected and treated early. Once roof leaks caused by ice dams and springtime rain find their way to the wooden structure of the roof, some very expensive repairs will be needed unless treated right away.
Prevent Ice Dams by Design
If you live in snow country, the cynics say move to Arizona if you want to prevent ice dams, but home owners and construction engineers have a few ways to help minimize their effect. We should perhaps have titled this section How to Live with Ice Dams since the vast majority of homes don’t suffer damage even after winters where extensive roof ice has formed. We just need to learn how to prevent ice dam problems.
One of the more obvious construction options that generates ice dams in snowy winters is the use of vaulted ceilings. We all love those gorgeous high ceilings but it’s important to take some time to think about what goes on in the rooms below before adding them into the house plan.
A vaulted ceiling by definition is directly below the roof, that means the attic space, the square footage between the base of the roof and the top of the insulation in the attic, is much smaller than in conventional flat ceiling rooms. Any heat generated in that room will heat the underside of the roof more than other spaces in the attic and has the potential to cause an ice dam. For that reason, it’s great to have vaulted ceilings in bedrooms, studies and sitting rooms, but not such a good idea on family rooms or kitchens where cooking and gas or log fireplaces heat these rooms tremendously.
Often chimneys from log stoves in cabins and lake homes extend through vaulted ceilings and inevitably apply high levels of heat to the underside of the roof.
The rule here should be think where most energy from the home will leak into the attic. Try to avoid vaulted ceilings in these areas whenever possible or take countermeasures to protect against the effects of ice dams if you can’t.
Using Roof Rakes
Using roof rakes to prevent ice dams forming seems like a great idea. If ice formation is caused by snow on the roof, why not simply remove it with a telescopic roof rake? The answer to that question is largely down to how the roof rake is used. It’s a great idea to reduce the amount of snow on the roof, but unless the operator is familiar with roof structures and construction methods it is very common for home owners to do more damage with a roof rake than they risk with ice dams.
A roof rake is a flat metal blade designed to be gently dropped into the snow five or six feet above the gutter. A gentle pull takes the snow down one to two foot in width at a time depending on the size of the rake. Unfortunately, most home owners seem to attack the snow aggressively, scraping it down to the roof surface and catching structures like siding, gutters, shingles and flashing in the process. If you must rake your roof, don’t try and remove all the snow and don’t scrape it down to the shingles. Look on the ground for granules from your roof shingles for excellent feedback on your raking style. If you can see lots of them, you are being too aggressive, likely damaging the roof and shortening its life accordingly.
Our advice is to get some instruction from the many excellent videos and articles online showing how it’s done before you rake your roof for the very first time. Better still, ask your friendly roofing pro how they do it.
Ice & Water Shields
Ice and Water, as most roofers refer to this 3-foot wide waterproof membrane, seals directly to the wooden base of the roof. It forms a seal around shingle nails as they penetrate into the roof base and is the best defense available today against standing water penetration from ice dams. It is designed to be placed first on the roof and is typically placed above the gutters and along the edges and valleys created in the roof structure. In most cases a single 3-foot membrane is sufficient, but in states like Michigan where ice dams are common it is worth installing a second layer to provide six feet of static water protection above the gutter line. Tresnak Roofing always installs six feet of Ice and Water. The extra layer is a smart defense against water build up and is great for homes with wood stove chimneys and vaulted ceilings. It’s also much, much cheaper than the water penetration repair you’ll get if your home produces ice dams and you haven’t prepared the roof structure for them.
Attic Ventilation
Some amateur roofers might suggest laying Ice and Water over the entire roof. That will certainly protect the roof from incoming moisture, but since it forms a very tight seal it will act as a moisture barrier causing condensation build up inside the attic.
The 2015 update to Michigan Residential Code prevents the situation above by requiring ventilation air intake and ventilation exhaust be balanced. The common ‘bumps’ seen on modern roofs are vent structures that do just that. Tresnak Roofing uses the Lomanco DeckAir product to help balance ventilation, keep the attic space cold and prevent the formation of major ice dams.
Don’t swap ice dams and water penetration for fungus, mold and wood rot. Always ask a roofing pro to install the underlayment on your roof or you might prevent one problem and end up causing another.
Roof Repair or Replacement Decisions
Contact Tresnak Roofing for all your roofing needs. We’d love to welcome you to our family of hundreds of happy customers in the Detroit area and would be delighted to offer advice on preventing ice dams or any other roofing topic you’re concerned about.
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