Deck railing is a code-required safety feature on any deck more than 24 inches above grade in Ontario. The railing must withstand 200 lbs of horizontal force at any point — engineered specifications that aren't optional. The install includes posts attached securely to the deck structure, top and bottom rails between posts, and balusters spaced no more than 4 inches apart.

This guide covers wood railing installation. Composite, aluminum, and glass railings have similar structural requirements with different installation hardware.

Before you start

Three things to settle:

1. Code requirements. Ontario Building Code: railing required at any deck over 24 inches above grade. Minimum height 36 inches (1070mm) for guards above 1.8m grade, 42 inches (1070mm) for guards above 1.8m. Baluster spacing: maximum 4 inches (100mm) between balusters. These are minimums — your home insurance and resale demand compliance.

2. Post anchoring is critical. Posts must be anchored to deck framing (joists or rim board), not just to deck boards. Use through-bolts (carriage bolts) through the rim/joist with washers and nuts. Lag screws into the side of a joist are insufficient for code load.

3. Permit may be required. Adding new deck railings (especially as part of larger deck construction) requires building permit in Ottawa. Replacing existing for like-for-like: usually no permit. Confirm before starting major work.

What you'll need

Tools

Cordless drill with bits
Drill bits and pilot bits
Mitre saw or circular saw
Tape measure and level
Speed square
Wrench (for through-bolts)
Pencil

Materials

Pressure-treated 4×4 posts (or 6×6 for larger spans)
Pressure-treated 2×4 top and bottom rails
Pressure-treated 2×2 balusters (or commercial baluster sets)
5/8 inch through-bolts (carriage bolts) with washers and nuts
3-inch deck screws (galvanized or stainless)
Construction adhesive (PL Premium)

Through-bolt the posts

Lag screws into deck joists from the side fail under code loading. Posts must be through-bolted: 5/8 inch carriage bolt drilled completely through the rim joist, with a washer and nut on the inside.

This is the only mounting method that meets the 200-lb horizontal load requirement. Skipping through-bolts is a code violation and dangerous.

Step-by-step instructions

Plan post locations

Posts at every corner and 6 feet on centre maximum along straight runs.

Plan post locations relative to deck framing — posts must align with rim joists or solid blocking.

Install posts at corners

Position post at the corner, with bottom even with the underside of deck framing.

Drill two through-holes (5/8 inch) horizontally through the post AND the rim joist behind. Holes should be staggered (not on same vertical line).

Drive carriage bolts through the post and joist. Tighten with washer and nut on the inside.

Install intermediate posts

Same process for posts along straight runs — through-bolt into the rim joist or solid blocking.

Maximum 6 feet between posts.

Install top rail

Cut top rail (2×4 or commercial top rail) to fit between posts.

Position with top edge at desired height (36 inches for standard residential deck).

Drive 3-inch deck screws from the inside of the post into the rail end. 2-3 screws per joint.

Install bottom rail

Bottom rail typically 4-6 inches above deck surface. Allows water drainage; cleanable.

Same installation: cut to length, screw through post into rail end.

Install balusters

Cut balusters to length (top rail to bottom rail).

Space 4 inches maximum between balusters (code requirement). Use a 4-inch spacer block to ensure consistent spacing.

Drive screws through top and bottom rails into baluster ends.

Verify code compliance

Test at multiple points: push horizontally with 200 lbs of force (your full body weight if you weigh 200 lbs).

Railing should not flex visibly or move at any point. Posts should not pivot.

If anything moves, add additional through-bolts or blocking.

Apply finish

Pressure-treated wood: clean and let weather a few months before applying stain or sealer.

Apply deck stain or sealer to protect from weather. Re-apply every 2-3 years for outdoor longevity.

Common mistakes that cost you

Lag screws instead of through-bolts. Code violation. Always through-bolt posts.
Baluster spacing over 4 inches. Children can fit through. Code violation; safety hazard. Maximum 4 inches.
Posts too far apart. Maximum 6 feet between posts. Wider spans flex under load.
Skipping the permit. Major railing work requires permit in Ottawa. Working without voids insurance.
Using regular nails or screws into pressure-treated wood. Corrodes the fasteners. Use galvanized or stainless steel only.

Frequently asked questions

What's the minimum railing height?

Ontario Building Code: 36 inches (914mm) for residential decks under 1.8m above grade. Higher decks require 42 inches.

Many homeowners go 42 inches across the board for consistency and safety.

Why are through-bolts required?

Through-bolts pass completely through the post and rim joist, with a washer and nut on the inside. Distributes load across both pieces.

Lag screws pull out under sustained horizontal force; through-bolts can't pull free without breaking the wood.

Can I use composite or aluminum railings?

Yes — composite (Trex, TimberTech) and aluminum railings install with kit-provided hardware. The structural requirements are the same as wood.

Modular kits often pre-engineered to meet code. Verify Ontario code compliance before purchase.

When to call us instead

Deck railings are safety-critical. Failed railings cause serious injuries. Professional installation ensures code compliance and structural integrity. We do deck work as part of exterior renovations.

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