Snow and ice on decks: when to clear it and how to avoid damage

Do you need to shovel snow off a deck?

Usually not for the weight. The American Wood Council's DCA 6, its prescriptive guide for residential wood decks, sizes structural members and connections for a 40 psf live load plus a 10 psf dead load. AWC says the same criteria can be applied to a deck carrying 40 psf of uniformly spread snow, as long as the deck is not prone to drifting or sliding snow.

For comparison, Michigan's residential code sets the design ground snow load at 25 psf for every community in Macomb County. A sound, code-built deck has room to spare in a normal winter.

Two caveats. That math assumes a deck built to code and still in good shape, with a solid connection to the house and no rot at the posts. And it assumes snow spread evenly, which is exactly what drifts and roof slide are not.

How heavy does snow on a deck get?

FEMA's snow load safety guide puts a foot of fresh snow at about 3 psf when it is light and dry, and up to 21 psf when it is wet and heavy. An inch of ice weighs a little under 5 psf. The water in the snow sets the weight, as heavy wet snow vs light snow explains.

Weights from FEMA P-957; deck rating from AWC's DCA 6. A deck in poor repair may hold less.

When should you clear a deck?

• Heavy, wet snow is piling past a foot. At that point the load is roughly half of what the deck is built for, and the next storm adds to it.
• Rain is forecast on deep snow. Snow soaks up rain, and FEMA notes that design snow loads account for light rain on snow but not heavy rainfall. Every inch of water the snow holds adds about 5.2 psf.
• A drift or roof slide has piled up. FEMA describes snow sliding off a higher roof and piling onto lower roofs and porches below it. A deck under the eave is in that fall zone. Clear the strip even when the rest of the deck is fine, and see roof snow load warning signs for the roof itself.
• The deck is a way out. Keep the path from the door to the stairs, and the stairs themselves, clear every storm. Stairs buried under a drift are not a weight problem; they are an exit problem.
• The deck shows distress. Sagging, a new gap where it meets the house, or posts that have shifted mean stay off it and have it inspected.

Macomb Lawn & Snow Solutions' residential visits cover the driveway, the front walk and a path to the mailbox. Decks are not included, so decide before the season who clears yours.

How do you shovel a deck without damaging it?

1. Use a plastic shovel, ideally one without a metal wear strip. Trex's care page says a plastic shovel may be used and warns never to use a metal one on Trex decking; shovel scratches are not covered by warranty. TimberTech says metal can damage both composite and wood decking.
2. Push along the boards, not across them, so the blade does not catch board edges.
3. Leave the last thin layer. Do not scrape for bare boards. A broom, the sun or a little ice melt finishes the job.
4. Throw snow off the open sides, away from the siding and door thresholds, where meltwater can work its way under the door.
5. Do not chip at ice. Melt it, or wait for it.

What ice melt is safe on composite and wood decks?

Composite makers disagree, so follow the brand on your boards:

From each manufacturer's winter care guidance. Check your own warranty documents.

Wood decks have no warranty to follow. TimberTech's advice is to skip rock salt on any deck, wood included. On wood, the careful approach is the same as on composite: plastic, along the boards, only as much ice melt as the steps and the exit path need, and a rinse once it thaws. For concrete steps and patios below the deck, see what ice melt is safe on concrete.