How to prevent snow loading

By Chris KnowlesChris Knowles


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“Cottage country got socked in with another big dump of snow last night,” reports the radio weatherperson as you sip coffee in your city kitchen and watch a bleak rain decorate the window. “That’s two straight days of record snowfall.”

Oh boy! Say the kids.

Uh-oh, say you.

You’re worried, of course, about a weight of snow on your cottage roof. The kids, on the other hand, know that a trip north to shovel the shingles means tobogganing, snowmobiling, eating white snow instead of brown…

First thing Saturday, you load up the family trickster and wobble north with all the other anxious cottage owners and their eager offspring.

But should you bother? If inspecting the roof is mainly an excuse for a wintertime respite, then by all means, pack up and get going. If, on the other hand, the sole purpose really is to shovel the roof, and your cottage is well built, you can probably save yourself the gas.

What can take the weight

A cottage roof built to building-code specifications and properly maintained will — freak exception aside — stand up to the worst winter can throw on it. “More people are injured or killed every year trying to shovel roofs than from roofs falling on them,” notes Adaire Chown, technical adviser to the National Building Code at the Institute for Research in Construction in Ottawa. “Particularly if your cottage was built to code in the last 10 years, you can be pretty sure it’s not going to collapse.”

But what about an older cottage? Again, if it has lasted this long and has been properly maintained (no leaky shingles or dry-rotted rafters), odds are you’ll do more damage shoveling it than leaving it alone. Says Gord Allison, chief building official for the City of Barrie, Ont.: “Older roofs may have a longer span than the code now allows and may have deteriorated from dry rot or insect damage, so that’s a concern. But then again, many people overbuilt their cottages in past years because materials were readily available and economical, so some are even sturdier than they need to be.”

Barrie, as you know, has a peculiar affinity for snow, which prompted Allison to do an informal snow-load study last winter. He started by referring to the National Building Code Supplement, which gives the average pressure exerted on a roof by “new” freshly fallen snow as about 6.4lbs. per cu. ft., and the weight of “old” snow that has been compressed as double that. The code also includes a lengthy list of snow-accumulation data for determining how a roof should be built based in part on that data. In Barrie, the code requires that a roof be capable of supporting a minimum snow load of 37lbs. per sq. ft. (White River, Ont. tops the chart with a 60-lb. minimum, while Toronto is down near the bottom of the pile at 18lbs.)

“Using those numbers,” says Allison,” there would have to be 5’9” of new snow or 2’10” of old snow on a roof to reach even the minimum code requirement. As we looked around, we saw no circumstances where there was that type of buildup. Eventually, the wind and sun compress it, but a lot is blown or melted away, too”

This survey aside, were there any actual cases of roof collapse in Barrie last winter? “No,” answers Allison,” except for a greenhouse, but its roof had too long a span.”

To shovel or not to shovel

His reassuring words are echoed by cottage builder Wayne Judges, proprietor of Judges Contracting in Walker’s Point. “If you can avoid it, you’re far further ahead not to shovel the roof,” says Judges, who keeps an eye on a number of local cottages over the winter — sometimes shovelling them if the snow is deep enough and the roofs are suspect. “Just walking on a roof in winter can cause the shingles to crack — you can hear the cracking sound up there.” Shovelling can also shave off shingles, lop off roof vents, or worse… “Yeah, at least once or twice a winter I fall off a roof, though usually snow breaks my fall.”

Judges says he generally doesn’t get concerned about snow load until depth on a roof reaches 5’ or 6’. “If the cottage is built with trusses or is post-and-beam, there shouldn’t ever be a problem, so I won’t worry about it. Otherwise, the first thing I’ll do is take a look at the roof from the outside. If there’s a sag in it — either midway between the eave and the ridge or along the ridge itself — that’s a good indication that something’s going wrong.

“Once I’ve looked at it from outside,” he continues, “the next thing I might do is go inside and take a look. Often a rafter has actually split, which can be caused by weight on the roof or if the building has shifted. Water stains, though not necessarily a sign of structural damage, can mean that some rafters may have rotted out. If I spot a problem, then I’ll shovel.”

Signs of trouble

Most contractors will inspect a cottage roof for damage and assess its snow-load risk at no charge. However, nearly all the obvious signs of trouble — including water stains, dry rot, insect infestation, split or sagging rafters, cracked drywall where the walls meet the ceiling, or sticky doors or windows caused by a shifting roof — will be readily apparent from a cursory look around the cottage and in the attic. You can also make note of the materials used in the roof and then check them with your local building department. If the rafters are 2” x 4”s and the code requires 2” x 6”s, for example, you may not have a roof over your head for long.

And don’t forget about the roofs over additions or above closed-in porches or outbuildings such as sheds and bunkies. These may have a different construction or a shallower slope that puts them at greater risk of collapse.

Also, the roof of a newly closed-in verandah or recently insulated cottage that previously had only summertime visitors might be susceptible to problems if the cottage now gets wintertime company. “The advent of the snowmobile has opened up cottages that may not have proper roof ventilation,” notes Doug Head, chief building official for Smith Township. “Warm air gets up into the attic and can’t get out, which causes wood rot from condensation and ice damming around the eaves.” Head also points out that the more layers of heavy shingles on a roof, the less additional weight from snow it can hold.

Make long term repairs, not quick fixes

Replacement or permanent repair is, of course, the sensible way to fix a roof made rickety by age or damage. But as a temporary solution — or merely for winter peace of mind — many cottagers fashion makeshift reinforcements for a little extra structural support. It’s the old post in the centre of the cottage trick, which, like shovelling, can sometimes be more harmful than helpful.

“You have to pick strategic points at which to put the posts,” cautions David Gillett, an Orillia cottage designer. “Make sure they rest against something solid or you’ll come back in the spring and find a big depression in the floor or a hole in the ceiling.” Use at least 4” x 4” lumber for the supports, and place them squarely over a floor joist (preferably one that’s supported by a beam or a pier, or both) and directly under a ceiling joist.

Wet snow weighs a lot more than fluffy, dry snow, a steep steel roof sheds snow better than a flat asphalt-shingled one, and a roof with jutting dormers and valleys can create deep drifts better than one that’s smooth and windblown. Put another way, there are as many snow-load variables as there are snowflakes in a blizzard. So if you’re concerned about the amount of snow on your cottage roof, sure, check it out. Just be careful up there.

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Lora Kee

Lora Kee

Mar. 6, 2013

2:13 pm

Great tips!

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