For most roofs in St. Louis, never — let nature handle it. The reason for that is that most roofs are built to handle the snow that is piled up on it, removing snow is dangerous to you and often the process of snow removal causes more damage to the roof than the snow would.
Removing snow is not only dangerous for your house. It is more dangerous than you might think. Do not work alone. If you can’t see where you are throwing snow, like over the edge of a high flat roof, have a spotter below who will keep pedestrians away and who can communicate with you by cell phone. Remember that clumps of hard snow or ice thrown from a third story flat roof in St. Louis can do serious damage to a car or person below.
If you do clear a roof, do not try to remove the last layer of ice or snow that is attached to the roof. Remove the weight above it but leave that layer to protect the roof membrane or shingles. Trying to go right down to the roof will most likely cause the roof to leak when things begin to thaw.
Also be aware that any guide-line that simply says remove snow after 6 or 12 inches of accumulation is not taking into account the actual weight of the snow. If you think about shoveling snow you know that there is light snow and there is heavy snow — in fact snow weight varies from fluffy flakes to heavy water soaked snow to solid ice, and even ice can be light and heavy depending on how much it is made up of air bubbles.
WHEN IS SNOW ON THE ROOF TOO MUCH SNOW?
So, when is snow too much snow? The easiest indicator, that professionals and homeowners alike can use, is to keep an eye on center-of-the-house doors, like the door to the bedroom upstairs. If it does not stick or jam at all before the snow (except perhaps seasonally in the humidity of the summer) and it does begin to stick as the snow accumulates, that is like a thermometer that says your house has a fever, there is a problem. You should also keep an eye open for new cracks in the plaster or drywall, usually near corners of those inside doorways.
FLAT RESIDENTIAL ROOFS
If it is a flat basin roof (slopes to a central drain) it is “relatively” safe to work on the roof as you can fall over the edge but you won’t just slide off the edge. If it is a flat roof that slopes to an edge you should take the same type of precautions that you should take on a steeper slopped roof — either work from the edge and don’t get on the roof at all or use a safety rope attached to a solid tree on the opposite side of the house. You should buy or rent a harness, a strapping arrangement that you see mountain climbers and construction workers wearing that allows for a good attachment of a safety rope — one rope for your ladder, another rope for you.
By the way, the technique for throwing a rope over the roof is to use a fishing rod and reel to cast over the roof and then draw the rope back.
REMOVING THE SNOW
Snow can be drawn down the roof, a little at a time working from the bottom edge towards the top. Ice however should be removed working from the top of the roof down so that the released ice can slide off the roof sliding on ice, not sliding on exposed shingles — a big lesson from the ice storm. Rarely should we ever remove ice right down to the shingles or membranes but leave a bit of a protective ice layer. That last little bit of ice is stuck to the roof covering and you will probably create water leaks trying to remove it.
Removal of ice from the edge of the roof is best done with non-salt chemical de-icers or electrical de-icing cables — not with hatchets or hammers. Chopping and cutting caused more roof problems than all the ice during that big ice storm. Any ladders should be tied down on both sides to prevent slipping sideways and even tied to a line over the house so it can’t be pushed backwards by sliding snow — and never work alone.