February 21,2015; 6:30AM,EST
Determining how much snow is too much snow, depends on the shape and age of the rooftop.
If a roof is pitched or slanted, and in fairly good condition, heavier snow may be less of a problem. However, older and more flat roofs could easily succumb to the weight of the snow and fail.
Mark
Settlemyer, left, gets help clearing snow from the roof of his mother's
house from Ken Wesley on Wednesday, Nov. 19, 2014, in Lancaster, N.Y.
Lake-effect snow pummeled areas around Buffalo for a second straight
day, leaving residents stuck in their homes as officials tried to clear
massive snow mounds with another storm looming. (AP Photo/Mike Groll)"As snow sits on roofs, especially flat ones, it compacts and becomes more dense," AccuWeather Meteorologist Mark Paquette said. "When snow and ice falls on it, it becomes heavier."
A cold rain can also lead to heavier snow and more weight on a rooftop because when the rain falls it is then absorbed by snow already on the rooftop. As a result, the snow becomes even heavier than it was before the rain.
If the snow becomes too heavy, it can weaken the internal structure of a roof and cause damage or even cause the roof to completely collapse.
The type of snow that falls can also contribute to the likeliness of a roof collapse.
"There are different types of snow as well that can cause various damage," Paquette said. "A lighter, fluffier snow that falls with cold temperatures is a much different story than a wet, heavy snow with sleet and rain."
The more dangerous type of snow is the wetter, heavier snow due to its increased water content. This type of snow is most common around areas in southern New England.
To prevent a roof collapse or damage due to snowfall, keep tools handy that allow for timely and easy snow removal after a storm.
- Bob DesRochers · Top CommenterI've lived in New England for almost 70 years and I've never heard of a roof collapse on a residential house other than a flat roof. Your article is alarmist and full of errors.
Tom Eddy · Top CommenterIf you look at some old barns, you will notice a "bulge" at the barn center. Basically, the snow load is pushing the walls out. As you know, most NE barns have 6/12 or greater pitch. No matter the slope, enough snow on the roof will cause some damage.
I have a full log home with a 4/12 pitch. The roof supports have been doubled over the architects recommendation. With a snow load of 36 inches(20lbs/foot), I still get about a 1/8 inch spread.
David Wade · Top Commenter
- Tom Eddy · Top CommenterThe diagram above is misleading. From a pure pressure standpoint, walls are pushed out but not down. The push out causes the roof to collapse. A couple simple vertical 2/4's on center can hold up an entire snow loaded roof as long as they have strong base supports.
K.r. Qunynghamm · Top CommenterPay no attention to Bob DesRochers as he probably lives in a fortress, and pays little or no attention to reports of roofs collapsing from heavy snow. It happens, believe me. It can happen to pitched roofs, but just at a much lower rate than flat ones. He also didn't point out the so called 'errors' either as there is only one, and it's more misleading than an 'error', and the 'tools' needed 'that allow for timely and easy snow removal after a storm' aren't things most of us have or can control: A backhoe with a 36' bucket to pull the snow off and a 70 degree day with plenty of sunshine. Oh, don't agree with me? Don't care one ioto.
Bob Adams · Top Commenter · Winter Haven, FloridaThe roof collapsing is usually only a problem for flat roof tops. The danger for pitched roof tops is usually caused from water that inters into the fascia area and runs down the soffit and into the home along the wall or ceiling, causing water damage. This happens from the buildup of ice that expands and gets past the flashing that is installed at the edge of the fascia and roofing material. It happened to many homes in my home town of Klamath Falls Oregon in the winter of 1992-1993. That is why many home owners went to metal roofs that shed snow better than composition roof shingles.
Song Butcher · Kazoo Player at Professional MusicianNot such an Alarmist point. Yes houses made of sticks and paper can lose walls to roof weight. Regardless of pitch and also from Chilly bowled Foundations in drought regions. Bob's comment , in 70 years. Not many people hear of roof collapse with the exception of Roofers and we've seen many over the years. More important is if your going to get on the roof in snow be very weary of the ground below and what or where you will land. Holy bushes are not your friend. Sure feet and good times. Good luck.
Sandi Zeese · Albany High School (Albany, Georgia)This was very timely! I have a flat roof over my porch and we are getting sleet and freezing rain that will soak right into the snow...Time to go out the window with a shovel! Thanks!
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