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Attaching to the house
Should the deck be attached to the house or freestanding?
Almost every deck that falls down falls at the same place: the board bolted to the house. That one fact should shape how you think about this choice, and it does not mean the answer is always freestanding.
An attached deck hangs one edge on a ledger board fastened to the house, which means one row of posts and footings instead of two, and a deck that stays level with the house.
A freestanding or floating deck carries both edges on its own beams and posts. It avoids the connection entirely, which matters because inspection bodies attribute roughly nine in ten deck collapses to the deck separating from the house at the ledger.
The catch is that the Alberta code gives no specific direction on ledger fastening. Edmonton points builders at the International Residential Code for best practice instead. So if you attach, you are following a source your authority accepts, not a table in the Canadian code.
What a ledger has to do
A ledger carries half the weight of the deck, everything on it, and everyone on it, and it transfers that load into the rim board of the house floor. It also has to keep water out of the wall it is bolted to, for thirty years, through freeze and thaw.
The reason ledgers fail is almost never that the bolts were too small. It is that there were nails instead of bolts, or that there was no flashing, and the rim board the bolts were in had quietly rotted. The connection looks perfect from the deck right up until it is not there.
What good ledger practice looks like
- Bolts or lag screws, not nails. 1/2 in minimum, with washers under the head and under the nut on a through bolt.
- Staggered and set in. At least 2 in from the top and bottom edges of the ledger, and at least 5 in from the ends.
- Spacing from a written source. Ledger fastener spacing follows the joist span, and the numbers come from whichever source your authority accepts. Edmonton names the International Residential Code as the best practice reference because the Canadian code does not cover it.
- Flashing, every time. Even under a roof overhang. Not aluminum against treated wood or galvanized fasteners, because the two corrode each other.
- Into something structural. A rim joist or the framing, never into brick veneer, stucco, siding alone, or a rim you have not proven is sound.
When you may not attach at all
Do not hang a deck off a cantilevered floor, where the house floor overhangs the foundation wall, without an engineer stamped design. The one exception is where the original house builder installed a ledger there and it is marked on the engineered floor layout used to build the house. A cantilever was designed to carry the house, not a deck pulling down on its free end.
The same caution applies to a deck that extends past the end of an existing ledger. Putting a shallow foundation under the extension is not recommended: the deck will move differently along the ledger and along the free edge. Extend the ledger properly, or get the design done.
What freestanding costs and buys
Buys: no connection to fail, no holes in the house envelope, no flashing detail to get wrong, and freedom to build in front of a cantilever, a walkout, or a wall you do not want to touch.
Costs: a second row of posts and footings, so more digging and more concrete. A wider beam, because the middle beam of a freestanding deck often carries joists on both sides and lands in the two span table, which is heavier than the single span one. And more attention to levelling, because neither edge is tied to something that does not move. Edmonton is direct about that: a fully floating deck needs more initial and periodic levelling.
One more thing to plan: if the house has spread footings or weeping tile around the foundation, locate your piles so they do not interfere with either.
How to choose
| Your situation | Usually |
|---|---|
| Low deck, solid rim joist, straightforward wall | Attach, and flash it properly |
| House floor is cantilevered at the deck | Freestanding, or get an engineer |
| Brick, stone or stucco wall | Freestanding |
| Deck more than 1.8 m (5 ft 10 13/16 in) high | Either, but the foundation is engineered anyway |
| You will never be able to re-level it | Attach, so one edge stays put |
| Deck extends past an existing ledger | Extend the ledger, or get the design done |
Inspecting a ledger you did not install
- Look for the lip of flashing over the top of the ledger. No lip means no flashing, which means water has been running behind it for as long as the deck has stood.
- Count the bolt heads and look for washers. Nail heads mean the deck is nailed on.
- Push a screwdriver into the ledger near the bottom and near each end. Soft wood is a finding, not a maintenance note.
- Look inside the basement at the rim board behind the ledger if you can reach it. Staining there is the tell.
- Check whether the bolts land in a rim joist or in nothing. A bolt through sheathing into a cavity is holding air.
- City of Edmonton, Uncovered Deck Design Guide, Section 2, Beams, which states that the National Building Code (Alberta Edition) does not provide specific directions on ledger board fastening and points to the International Residential Code for best practice, and covers the cantilevered floor restriction, the fully floating deck and the ledger extension case.
- InterNACHI, Inspecting a Deck, and the How to Perform Deck Inspections course notes, for the share of collapses that begin at the ledger, the 1/2 in fastener and washer practice, the 2 in and 5 in edge distances, and the flashing material caution. These are inspection practice, and several of the numbers come from the International Residential Code, which is not in force in Canada.
Nothing on this page is an approval or a design. Code editions change and every authority having jurisdiction has the final word. Check your numbers with yours before you build.