The ledger board is the structural piece attaching a deck to a house's rim joist. It carries half the deck's load — every joist hangs off it. Improper ledger installation is the single most common cause of deck failure: pulling away from the house, water infiltration causing rot, undersized fasteners. Done correctly, a ledger lasts the life of the deck.
This guide covers proper ledger installation per current Ontario Building Code: lag bolts or structural screws into rim joist, flashing, proper fasteners, and required inspection.
Before you start
Three things to settle:
1. Connect to rim joist, not band board. Ledger MUST attach to the rim joist of the house — the structural framing element. NOT to siding, not to brick veneer, not to band board (cosmetic). Failure to identify the rim joist correctly is the #1 deck failure cause.
2. Flashing is mandatory. Without flashing, water gets between ledger and rim joist, causing rot. Z-flashing or specifically designed deck flashing required. Continuous; no gaps.
3. Fastener spec is structural. Code-specified: 1/2 inch × 5+ inch lag bolts OR Simpson SDWS structural screws (2 fasteners per joist bay, staggered). NOT regular deck screws. Wrong fasteners = wrong load capacity.
What you'll need
Tools
- Drill with 1/2 inch wood bit
- Impact driver
- Level (4-foot)
- Tape measure
- Pencil
- Clamps (for holding ledger during install)
Materials
- Pressure-treated 2× lumber for ledger (sized to deck — typically 2×8 or 2×10)
- Lag bolts (1/2 inch × 5-6 inch) OR Simpson SDWS structural screws
- Z-flashing or deck flashing
- Aluminum or stainless steel washers
- Construction adhesive (PL Premium)
- Caulk (high-quality polyurethane)
Two fasteners per joist bay, staggered
Code requires lag bolts or structural screws every 16 inches OC (matching joist spacing).
Two fasteners per joist bay, staggered top/bottom for load distribution.
12 ft of ledger = 18-24 fasteners minimum.
Step-by-step instructions
Identify the rim joist
Inside the house, look at where main floor meets exterior wall.
Rim joist: 2× lumber running parallel to floor joists, at the perimeter.
Don't attach ledger to: drywall, siding, fascia, band board.
If unsure, expose framing in basement to verify.
Mark ledger height on house
Deck top surface = inside floor surface (matches with door threshold).
Ledger top edge = deck surface − decking thickness (typically 1 inch) − joist depth.
Mark on house at planned ledger location.
Cut ledger to length
Pressure-treated 2× lumber sized per deck (typically 2×8 or 2×10).
Length: deck width minus 1.5 inches (the rim joist width on each end).
Cut clean square ends.
Position and clamp ledger
Ledger against house at marked height.
Verify level (front edge of ledger sits at uniform height across length).
Clamp in position.
Drill pilot holes through ledger and rim joist
1/2 inch wood drill bit (for 1/2 inch lag bolts).
Through ledger AND through siding (or sheathing) AND into rim joist.
Two holes per joist bay (16 inches OC), staggered top and bottom of ledger.
Insert lag bolts and washers
Slide bolt through hole.
Stainless or galvanized washer behind nut.
Or: Simpson SDWS structural screws drive directly without pilot drill (verify with manufacturer).
Hand-thread first, then tighten with impact.
Tighten to spec
Tighten lag bolts firmly, but don't over-tighten (compresses wood, bolts can't reach proper torque).
Test fit — ledger should be snug against rim joist.
If gap exists: shim between ledger and house (carefully, with code-rated shims).
Install flashing above ledger
Z-flashing or deck flashing OVER the top edge of ledger.
Flashing tucks under siding above (siding lifts to install).
Bend flashing's bottom edge so it laps over the front face of ledger.
Continuous around entire ledger length.
Caulk the top edge of flashing
Where flashing meets siding above: polyurethane caulk bead.
Prevents water from getting behind flashing.
All gaps and seams sealed.
Inspection by building inspector
Permit-required inspection before deck framing continues.
Inspector verifies fasteners, ledger sizing, flashing.
Pass: continue with deck.
Fail: fix issues before framing.
Common mistakes that cost you
- Ledger to siding/band board not rim joist. Ledger pulls out under load, deck collapses. ALWAYS rim joist.
- Standard deck screws instead of lag bolts. Insufficient strength. Code-spec fasteners only.
- No flashing. Water rots ledger and rim joist. Flashing mandatory.
- Too few fasteners. Code requires 2 per joist bay. Skipping = under-strength.
- Skipping permit/inspection. Deck not legal for use. Insurance won't cover failure.
Frequently asked questions
Can I attach to brick veneer?
No — brick veneer is non-structural. Bolts pull through brick.
Through brick into rim joist behind: requires 6-8 inch lag bolts.
Or: free-standing deck (independent of house) avoids ledger attachment entirely.
How many fasteners do I need?
16 ft ledger × 2 fasteners per 16 inch bay = 24 fasteners minimum.
Lag bolt size 1/2 inch × 5+ inch (or Simpson SDWS structural screws).
Code-required spacing varies; Ottawa typically 16 inches OC.
Do I need a permit?
Decks over 2 ft above grade: permit required in Ottawa.
Below 2 ft: typically no permit but verify.
Permit ensures code compliance and inspection.
A City of Ottawa building permit fee applies; confirm the current deck permit fee on the MyServiceOttawa portal.
When to call us instead
Deck ledger work is structural and code-bound. Our team handles deck design, permits, and structural framing as part of outdoor projects.
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