Illinois Deck Railing Code: Heights, Baluster Spacing and Handrails
What this comes down to
- A flat 2x6 cap on a stair guard is not a handrail. A stair with four or more risers needs a rail a hand can grip.
- No opening in a deck guard may pass a 4 inch sphere, and that includes the gap under the bottom rail.
- Stair guards get slightly more room: 4 3/8 inches between balusters and 6 inches at the triangle by each tread.
- Under the IRC a guard is needed once the drop passes 30 inches, and it stands at least 36 inches on the deck.
- The top of a guard must resist a 200 pound push outward, which is a question about the post connection, not height.
- Illinois sets a floor, not a ceiling. Some villages ask for more, such as guards at 24 inches or closed stair risers.
Most deck railings that fail inspection are tall enough. They fail on a gap, a grip or a push. The Illinois deck railing code is the IRC as each town adopted it. Its railing rules are mostly about children and hands.
This guide takes those rules one at a time. It covers baluster spacing, stair guards and handrails. It then covers the load a guard must carry and the extra rules some villages add.
What does the Illinois deck railing code require?
Whatever the local permit office adopted, on top of a state floor. Illinois has no railing code of its own. Since 2025, every local code must be at least as strict as the IRC on structure.
Under that baseline a guard is needed once a deck is more than 30 inches above grade. It must stand at least 36 inches tall. Footings, ledgers and stairs are covered in the guide to the state deck code.
The code calls the railing around a deck a guard. A handrail is the rail a hand holds on a stair. One rail can do both jobs, but each has its own rules. Most failures sit where the two get confused.
How far apart can deck balusters be?
Close enough that a 4 inch sphere cannot pass between them. The International Code Council publishes the opening limits in section R312.1.3. The rule runs from the deck surface up.
That makes the gap under the bottom rail part of the test. A bottom rail set 5 inches above the boards fails, however tight the balusters are. So does a wide gap at the house wall.
The 4 inch figure is about the size of a small child's head. Wood moves, so a gap built at 3 7/8 inches can open past 4 as balusters dry and twist. Careful carpenters space wood balusters tighter for that reason.
Are stair railings held to different spacing?
Slightly, yes. Balusters along the open side of a stair may leave gaps up to 4 3/8 inches. The triangle under the bottom rail, at each riser and tread, may pass up to a 6 inch sphere.
The stair guard height changes too. It is at least 34 inches, measured straight up from a line joining the tread nosings. Measuring from the back of a tread reads high, and hides a short guard.
Does a deck stair need a handrail as well as a guard?
Yes, once the stair has four or more risers. The IRC wants a handrail on at least one side, 34 to 38 inches above the nosings. A guard only counts if its top is shaped to be gripped.
That is where the flat 2x6 cap fails. A round handrail must be 1 1/4 to 2 inches across. Any other shape needs a perimeter of 4 to 6 1/4 inches. A 2x6 measures about 14 inches around.
The handrail has to run unbroken from above the top riser to above the bottom one. Its ends return to a post or the wall so a sleeve cannot catch. Most decks use a round rail on brackets.
How strong does a deck railing have to be?
Strong enough for 200 pounds at any point along the top. Table R301.5 of the IRC sets that figure in the design load table. Balusters must resist 50 pounds over a square foot.
On a guard that is not also a handrail, the 200 pounds pushes outward and downward. A handrail must resist it in any direction. Glass panels carry a load factor of 4 on top of that.
Simpson Strong-Tie's engineering blog describes the guard post testing behind the rule. Virginia Tech researchers pushed guard posts outward, the critical direction. The work led to a tie anchoring the top bolt.
A post can pass every height and gap rule and still fail the push. The usual fault is a 4x4 bolted to a thin rim with nothing behind it. The guide to a wobbly railing covers the fix.
Can a DuPage village ask for more than the IRC?
Yes. The state sets a minimum, and villages amend upward. Lombard requires guards on any deck surface 24 inches above grade. That is six inches below the IRC trigger, so a deck legal in one village can fail in the next.
The Village of Schaumburg publishes one village's deck guide in plain terms. It requires closed stair risers once a deck is over 30 inches high. Open risers are common on older decks.
That guide lists a handrail grip of 1 1/4 to 2 5/8 inches. The 2021 IRC caps a round rail at 2 inches. Handouts can lag the adopted edition, so the ordinance decides. The guide to a permit application covers who to ask.
Are cable, glass and horizontal railings allowed?
Yes, if they meet the same sphere and load rules. Cables flex, so a run with 3 inch gaps at rest can open past 4 inches when pushed. Post spacing and cable tension are what stop that.
The IRC does not ban horizontal rails that a child could climb like a ladder. Some builders avoid them on high decks anyway, and a local amendment can rule them out. Glass needs a rating sheet for the inspector.
How do the railing numbers compare side by side?
The table sets the IRC baseline for a deck guard, a stair guard and a handrail side by side. Local amendments can move any of these numbers. The permit office for the address has the final word.
| Requirement | Deck guard | Stair guard | Stair handrail |
|---|---|---|---|
| Required when | Drop over 30 inches within 36 inches of the edge | Open side over 30 inches above grade | Four or more risers |
| Height | 36 inches minimum | 34 inches minimum from the nosing line | 34 to 38 inches from the nosing line |
| Largest opening | Under a 4 inch sphere | Under 4 3/8 inches, 6 at the tread triangle | Not limited |
| Load at the top | 200 pounds outward and down | 200 pounds outward and down | 200 pounds in any direction |
| Grip | No rule | No rule unless it is the handrail | 1 1/4 to 2 inches round |
What does it cost to bring a railing up to code?
Railing replacement starts at $35 per linear foot. A stair repair starts at $225 and a full stair rebuild at $795. What moves each number is mostly what turns up once the old railing comes off.
| The work | Starting price | Wider market | What moves it |
|---|---|---|---|
| Railing replacement | From $35 per linear ft | $40 to $100 per linear ft | Material, stair runs, and whether posts need new blocking |
| Deck stair repair | From $225 | $250 to $750 | Adding a graspable handrail, or closing open risers |
| Full stair rebuild | From $795 | $900 to $2,500 | Number of risers, a landing, and new footings |
What cannot be determined from the deck surface?
Whether the posts will hold 200 pounds. The bolts, blocking and ties sit behind the rim or under the boards. A post can feel firm to a hand and still hang on two bolts into rotted wood.
Which code edition and amendments apply. A railing built to an older edition may have been legal then and can often stay. Only the adopting ordinance, or the local code official, settles that.
And whether the post bases are sound. Rot at the foot of a post weakens the guard from below. That is a structural repair, covered in the guide to rotted deck posts.
Deck railing code questions
How high does a deck railing have to be in Illinois?
Under the IRC, at least 36 inches on the deck. Along a stair it is 34 inches, measured from the nosing line. A guard is required once the drop is over 30 inches within 36 inches of the edge. Some villages are stricter, so the local code for the address decides.
How does Perfect Work check a deck railing against the code?
Perfect Work Remodeling & Repairs measures every guard and stair with a tape and a 4 inch gauge. Each post is pushed outward to feel for movement. It is then checked from below for bolts and blocking. Every shortfall goes on a written list with its fix and price.
Is a 2x6 on top of the railing enough as a stair handrail?
No. A flat 2x6 measures about 14 inches around. The IRC limit is 6 1/4 inches for a rail without a finger recess. A stair with four or more risers needs a graspable rail, usually round, on brackets by the guard.
Do I need a permit to replace my deck railing?
In many DuPage towns, yes, because guards are treated as structural safety items. Swapping a few balusters in kind often is not. The permit office for the address gives the definitive answer. It is worth asking before any posts come out.
What does a railing estimate from Perfect Work include?
An estimate from Perfect Work Remodeling & Repairs prices the guard by the linear foot. Posts, stair guards and handrails are separate lines. Any rotted post or rim found during the check is listed on its own. A permit fee, where one applies, is its own line too.
Can my old railing stay if it was legal when it was built?
Usually, unless it is unsafe. An existing guard is generally judged by the code it was built under. Anything replaced is built to the code in force now. A new run of railing has to meet today's gap, height and load rules.
A railing that passes the tape and the push
The Illinois deck railing code comes down to three tests. A tape checks height, a 4 inch ball checks gaps, and a hard push checks the posts. Most railings that fail do so on the last two.
A visit from Perfect Work Remodeling & Repairs runs all three tests on every guard and stair. The posts are then checked from underneath. Railing and stair work fall under deck repair and replacement.
Call Perfect Work at 630-297-7888 · Book a railing check