WBUR

FAQ: What To Do If You Worry About Roof Collapses, Ice Dams

BOSTON — We’ve been hearing this week about an unprecedented number of roof collapses in Massachusetts due to all the accumulation of snow. Most of the collapses have been flat-roofed industrial buildings, but that has many homeowners wondering if they should be concerned, as well.

To find out more about when a residential roof is at risk, and whether an ice dam may be developing on a house, WBUR’s All Things Considered host Sacha Pfeiffer spoke with Prof. Garrick Goldenberg, a registered structural engineer who teaches at the Wentworth Institute of Technology and is the chief structural engineer at Chappell Engineering Associates in Marlborough.

Sacha Pfeiffer: If you’re a homeowner with a house with a traditional pitched, angled roof, does that mean you shouldn’t be concerned?

Prof. Garrick Goldenberg: No, it doesn’t mean that just because you have a pitched roof, you’re OK. The steeper the roof, you probably are in better shape in terms of structural collapse.

The roof of the Quonset hut that housed Interstate Battery in Auburn Thursday (Fred Thys/WBUR)

The roof of the Quonset hut that housed Interstate Battery in Auburn Thursday (Fred Thys/WBUR)

So if you’re a homeowner with a roof that is an angled roof, how would you know whether you have a problem?

Try to get into your attic and see if your roof rafters are either deflecting, sagging, creaking or making any noise.

And if you have a sense that your roof might be compromised, what should you do to get the snow off your roof?

Unless you could reach it from the ground — say you have a ranch house or you could reach it with something with a long handle — I would strongly recommend getting a professional to do it. It makes no sense to risk your life for an unknown risk to your roof.

Boston has a lot of three-family houses that have flat roofs. Should people who live in or own three-deckers be concerned?

Anything that has a flat roof definitely requires a good look at it. Just to give you a number, fresh-fallen snow could weigh anything from 5-6 pounds per foot to 20 pounds per foot, depending on how compacted it gets. Ice would weigh 60 pounds per foot. Houses would have been designed for 30 pounds per foot of snow per square foot on the roof.

So if a homeowner is concerned that there may be so much snow on his or her roof that it’s at risk of collapsing, your advice is that if you can safely remove it, do it yourself. And if you can’t, hire someone.

If you can safely do it because you can reach your roof and you have a long-handled rake, how much snow do you need to get off? Just a little? Or just the edges? Or just enough to redistribute the load?

If you have more than a foot of snow, I would recommend trying to remove it.

The other big problem homeowners are having is ice dams. Give us a simple definition of an ice dam.

What happens in weather like this is that gutters fill with snow, the water builds up at that snow, and as the snow rises and ice is created at the edge of the roof, that water rises and gets under the shingles, and the water will start getting into insulation. And eventually — if there’s enough water — it will get into the attic and you will see it in your ceiling as a stain.

One roofer clears out an ice dam that has formed atop a home in Acton. (David Boeri/WBUR)

One roofer clears out an ice dam that has formed atop a home in Acton. (David Boeri/WBUR)

If a house doesn’t have gutters, can it not develop an ice dam?

Under normal circumstances, it should not.

If you have an ice dam developing in your gutter, is there a risk of the gutter being torn off by the weight?

Yes, there is.

I suspect I may have an ice dam at my house. There’s a giant mound of ice that’s formed in the gutter in front of my house. It’s going up and over the gutter, and there’s an enormous amount of icicles developing at our rim. Does that sound like an ice dam to you? And are those the typical signs: big mounds of ice in a gutter and lots of icicles?

Yes, that’s right.

So what is the short-term solution for removing ice dams?

I think you have to balance the safety. If that gutter falls off and doesn’t kill anybody it’s still better than you fall off the roof and have structural damage to your body.

If you suspect you have an ice dam or you know you have an ice damn and you don’t want to risk leaks to your roof and ceilings, whom should you contact to remove that ice if it’s not safe for you to do it by yourself?

You probably would contact a roofing company.

When we have sunny, thawing days, are those opportunities for homeowners to get snow off their roofs and ice out of their gutters before the next storm comes?

Absolutely, because these sunny days are also contributing to the build-up of ice.

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  • MB

    Prof. Garrick Goldenberg is wrong about gutters as the cause of ice dams.

    Gutters are NOT the cause of ice dams. The ice is caused by differential heating/cooling on the roof. Heat, travelling through the outer wall or rising through the attic onto the underside of the roof heats an area of the roof, the snow melts and the water travels down the shingles, then cools into ice in a lower, cold portion of the roof (perhaps the gutter, or a lower portion of the roof). This continues until a dam forms. Then, the water travels down the roof, cannot go past the ice, and slowly the water creeps under the shingles, then into the home via the ceiling or walls. A gutter full of ice is the effect of the roof warming snow to water, then re-freezing in the gutter and lower portions of the roof.

    If you see a well insulated home with a cold roof (little heat from the home affecting the underside of the roof) you’ll note that the gutters remain clear and clean of ice because there is little or no snow melt from the roof accumulating in the gutter that reforms in to ice.

    • http://www.wbur.org/people/spfeiffer Sacha Pfeiffer

      Mike: Professor Goldenberg does not say that gutters are the cause of ice dams — only that they can be a contributing cause of ice dams. As you correctly write, the underlying cause is the continual thawing and freezing of melting snow, resulting in a large mass of ice forming at a roof’s edge and/or in the gutter. Because that ice mass prevents melting snow from draining properly, the snowmelt can back up under the shingles and work its way into the house, causing water damage. But gutters are not required for ice dams to develop; ice dams can form when water builds up behind any kind of ice blockage.

    • Sacha Pfeiffer

      Mike: Professor Goldenberg does not say that gutters are the cause of ice dams — only that they can be a contributing cause of ice dams. As you correctly write, the underlying cause is the continual thawing and freezing of melting snow, resulting in a large mass of ice forming at a roof’s edge and/or in the gutter. Because that ice mass prevents melting snow from draining properly, the snowmelt can back up under the shingles and work its way into the house, causing water damage. But gutters are not required for ice dams to develop; ice dams can form when water builds up behind any kind of ice blockage.

    • orkid

      I have not, so far, seen any icicles forming along my roof drip line. Perhaps, because I have a well- insulated attic floor, a ridge vent the whole length of my roof, a wide overhang with 3- 4 inches wide vents the entire length of the soffits, and we keep the house temperature to 66-68 degrees F, there has not been much temperature differential to feed the melting/refreezing cycle. However, the snow accumulation on my ranch roof is considerable. Peter Hotton of the Boston Globe seems to indicate that having a sloped roof makes it less likely for a collapse. Nevertheless, I have used my snow rake to remove some of the accumulation.

  • MB

    Sorry, in this transcript, it does not read as such.

    In the Professor’s definition of ice dams, the process described begins with, and relies on a gutter being filled with snow that turns to ice with water that backs up the shingles. Then, after being asked, “If a house doesn’t have gutters, can it not develop an ice dam?” the Prof says, “Under normal circumstances, it should not.” He solely attributes the cause of ice dams to the gutters. This is not correct.

    Gutters can make an ice dam worse, but the ice dam cycle begins and continues elsewhere.

  • spotted salamander

    Have to agree with MB – when I read the transcript it seemed to me that the Prof was saying that if you don’t have gutters you “should be” alright. Neither I nor many of my neighbors have gutters — but most of us have ice dams.

  • Quark2610

    This is the best advice I’ve read that’s clear and does NOT leave us wondering too much more about structural issues.
    Given what we hear from local media up here in NH, every single homeowner needs to hire a professional TODAY to get the snow off his roof – which is ridiculous!

    STILL, I wish a structural engineer would come forward to tell us with just what kind of pitch we need to avoid worrying!

    Also, no mention, from any quarter, has been given concerning what to do about roofing companies’ price gouging!! I called a few roofing companies before our last storm, and was quoted $675 (!!) to shovel off snow from two 10 x 20 bump-outs on my house that get no sun. I was aghast at the quote and replied “OMG. You’re kidding, right?” Most rudely, he responded with “Don’t like it? Call someone else.” And he hung up. I did call someone else, but I know people who were coerced into truly unfair prices.

    In the end I remembered my contractor, who was kind enough to send two young men to roof rake these areas for $135 for 1 1/2 hours work. A real bargain~ but, frankly, between paying the plow guy for the driveway every time he plows (some storms he plows 2 or 3 times with his pick-up!) I’m thinking, one could go broke in a New England winter !

  • Rockijr

    Ice dams form from water hitting a cold surface and freezing and backing up. Removing gutters does not prevent ice dams. There are only 2 solutions to preventing ice dams and that is put plenty of insulation in that attic and insure you have adequate ventilation moving thru that attic. The attic temp should be no more then 5 degrees warmer then the outside air. If its impossible to add insulations, ( catheral ceilings) then puttin up the metal heating panels that go up 2 feet from drip edge will solve the problem of ice forming and freezing near the edges..

  • Anonymous

    Professor Goldenberg is a structural engineer and he is spot on in his explanation of the kinds of snow and ice loads that can cause a roof to seriously deflect (sag) and potentially collapse. However, he needs to discuss ice dam formation with his architect colleagues who will explain that ice dams form in sloped roofs when the upper part of the roof is warm enough to cause some melting and the bottom part is cold enough to cause the melt water to refreeze near the edge of the roof. As others commenting have pointed out, gutters are not a cause of ice dams even though they can contribute to the problem because they are beyond the envelope of the house and always cold.

    In designing sloped roofs, best practice is always to provide for air flow along the underside of the roof deck from bottom to top so that melting does not occur or, when it does, it occurs evenly. This is achieved by the proper placement of insulation and the accommodation of air flow from the underside of the eaves (soffit) up to an appropriate ridge vent.

    In the real world, this is not always possible and other workable but less reliable solutions such as electric heater tape, snow aprons made of metal, and/or impervious “ice and water shield” membrane under the bottom courses of roof shingles can mitigate the problem.

    Also, keep in mind that an ice dams from at the edge of a sloped roof, more or less above where the rafters are supported by the exterior wall. This is unlikely to cause a structural problem, but the weight of snow and ice further up the roof can be problematic for the rafters.

    It’s also worth noting that snow fences and other devices to keep snow from sliding off a sloped roof can contribute to the problem. Such devices should be limited to areas such as those above entrance doors where sliding snow could be hazardous. Otherwise, let the sloped roof do its job of shedding snow wherever possible.

    In summary, the best practice is to not let an ice dam form but to design so that, if one does form, water cannot find a path under the roofing materials into the house when it can damage interior walls and insulation.

    I still love living here in New England!

  • Goldilox

    Is that “ice damn” a Freudian slip? That’s when you say one thing, but you mean your mother. ;-)

  • Jkmacho

    Gutters??? NO, not always… A major cause not mentioned in the article is poor attic air sealing and poor insulation. That expensive heated warm leaking air into the attic and soffit area from the conditioned living area below causes the snow/ice melting at the shingles and roof decking. The freezing/thawing water backs up into the shingles causing both shingle damage and water leaking through the walls/ceilings.

    The solution as recommended by building shell experts is to seal off all attic perforations- pipes, electrical wiring, vents, parttion plates, etc. to prevent air air leakage into the attic and then insulate, being careful to allow some air ventilation from the soffits. Foam or dense-packed cellulose are the best insulation materials.

    Yes, you will get melting snow water runoff during the warm day that can back up from a clogged gutter, but any soffit ice dam formed with a properly insulated attic space will not back up through the shingles and cause any major problems.

  • Jkmacho

    Gutters??? NO, not always… A major cause not mentioned in the article is poor attic air sealing and poor insulation. That expensive heated warm leaking air into the attic and soffit area from the conditioned living area below causes the snow/ice melting at the shingles and roof decking. The freezing/thawing water backs up into the shingles causing both shingle damage and water leaking through the walls/ceilings.

    The solution as recommended by building shell experts is to seal off all attic perforations- pipes, electrical wiring, vents, parttion plates, etc. to prevent air air leakage into the attic and then insulate, being careful to allow some air ventilation from the soffits. Foam or dense-packed cellulose are the best insulation materials.

    Yes, you will get melting snow water runoff during the warm day that can back up from a clogged gutter, but any soffit ice dam formed with a properly insulated attic space will not back up through the shingles and cause any major problems.

  • http://www.hallettguttercover.com/ Hallett Gutter Cover

    The indoor furnace’s intense heat may just build up too much on the attic will melt snow right away and freeze up near the rood edge. Insulation and ventilation that’s properly planned will solve it. Exhaust vents will let warm air go through and get cool air in. The even distribution of temperatures will ensure that the melted snow won’t freeze instantaneously when it gets to the gutter. Have the vents installed at the soffits and eaves, and make sure it’s regularly checked.

  • http://www.hallettguttercover.com/ Hallett Gutter Cover

    The indoor furnace’s intense heat may just build up too much on the attic will melt snow right away and freeze up near the rood edge. Insulation and ventilation that’s properly planned will solve it. Exhaust vents will let warm air go through and get cool air in. The even distribution of temperatures will ensure that the melted snow won’t freeze instantaneously when it gets to the gutter. Have the vents installed at the soffits and eaves, and make sure it’s regularly checked.

  • http://www.ktmroofing.com Atlanta Gutters

    When winter comes, one main problem that every household does encounter is the piling of snows at the roof which is very risky for those who are living at the place. The roof area must be cleaned well to avoid collapsing.

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