Guard rail installation

Measuring, laying out and anchoring a CR Fence & Rail picket guard rail — top mount and side mount, on wood and on concrete, level runs and stairs. Written against the 2021 IRC and IBC, with the clause behind every requirement named so you can show your inspector.

What we can and cannot tell you

CR Fence & Rail does not hold an ICC-ES evaluation report or an Intertek code compliance research report for this system. Everything below describes what the code requires and how our parts are designed and dimensioned to meet it. It is not a third-party rating, and we will not present it as one.

Your local building official has the final say, and amendments vary by jurisdiction. If your project needs a stamped evaluation report, tell us before you order and we will tell you honestly where we stand.

1. Choose the right line first
2. What the code actually requires
3. Measure and lay out the run
4. Counting posts
5. Top mount — wood and concrete
6. Side mount — the harder one
7. Stairs
8. Final checks

Step 01 Choose the right line first

Three lines share the same look and the same install method. They do not share the same steel, and the difference matters most exactly where it is least visible.

The three lines, honestly

Line	Post	Built for	Not for
EdgeLine	40 × 40 mm, 1.5 mm wall, Q355D steel	Ground-level decks, patios, porches and garden runs at 36 in. Clean lines at the lowest cost.	Elevated decks and anything at 42 in. See the note below.
ProGuard	50 × 50 mm, 2.0 mm wall, galvanised Q355D steel	The general-purpose structural guard — raised decks, balconies, 36 in and 42 in.	Salt air within about a mile of the coast.
CoastLine	50 × 50 mm, 3.0 mm wall, 6061-T6 aluminium	Coastal and marine exposure, pool surrounds, anywhere chloride reaches the metal. Half the weight of the steel lines.	Nothing structural — same 1.97 in post as ProGuard, in a material that does not rust.

EdgeLine is not a height product, and we would rather say so than sell you one

A guard's job is to take a 200 lb concentrated load in any direction without failing. That load arrives at the top of the post and the post has to carry it as a cantilever, so almost all of the work is done by the post wall and the base plate — the parts nobody looks at.

EdgeLine's post is a 40 × 40 mm tube with a 1.5 mm wall on an 80 × 80 mm plate. That is a sound guard on a low deck at 36 in, where a fall is short and the code applies the residential load case. It is not what we would put on a second-storey balcony, and it is not what we would put at 42 in under the commercial load case. For those, ProGuard's 50 × 50 mm post at a 2.0 mm wall on a 115 × 115 × 10 mm plate is the product, and the price difference is small next to the consequence.

If a supplier tells you their entry-level rail is fine at any height, ask them for the post wall thickness and the base plate size. Those two numbers are the answer.

Step 02 What the code actually requires

Four things get checked. Know them before you set a single post, because two of them are decided by where you put the posts and cannot be fixed afterwards.

The requirements, and the clause each comes from

Requirement	Level	Stairs	Clause
Guard height — measured vertically from the walking surface; on stairs from the line connecting the tread nosings	36 in min	34 in min	IRC R312.1.2 + exc. 1
Where the top of the guard also serves as the handrail	—	34–38 in	IRC R312.1.2 exc. 2
Commercial / IBC occupancies	42 in min	42 in	IBC 1015.3
Opening — no sphere of this size may pass anywhere in the guard	4 in	4⅜ in	IRC R312.1.3 + exc. 2
Triangular opening at riser, tread and bottom rail	—	6 in	IRC R312.1.3 exc. 1
Concentrated load, applied in any direction at the top	200 lb	200 lb	IRC R301.5 · IBC 1607.9.1.1
Infill load on any one square foot	50 lb	50 lb	IBC 1607.9.1.2
Uniform load along the top, commercial only	50 lb/ft	50 lb/ft	IBC 1607.9.1

Two of these are settled at layout, not at assembly

The 4 in sphere is decided by where the last picket sits relative to the post — so it is decided when you cut the final panel, and step 03 exists to get that right.

The 200 lb load is carried by the post and its anchorage, so it is decided by your fastener schedule in steps 05 and 06. No amount of good assembly rescues an under-anchored post.

"In any direction" is the phrase that does the work. It includes straight down — someone sitting on the rail — and for a rectangular top rail the downward case is the harder one, because the section is shallower in that direction than it is horizontally. Our rail sections are sized against the downward case for exactly this reason.

Step 03 Measure and lay out the run

A picket panel is rigid, with the picket spacing set at the factory. You cannot stretch it to fit an opening. So the rule is the one every manufacturer in this category uses:

Use full panels, and cut only the last one

Work along the run in full 6 ft panels. Only the final panel in each run gets cut. Do not try to divide the run into equal shorter bays — that wastes material, adds posts, and gains nothing.

Cut the last panel from BOTH ends, not one

This is the step that gets missed, and it is the one that fails inspection. If you take the whole cut off one end, the gap between the post and the first picket is doubled on that side — and that gap is exactly what the 4 in sphere is measured through.

1. Measure the remaining opening, inside face of post to inside face of post.
2. Divide that measurement in half.
3. Find and mark the centre of the panel.
4. From that centre mark, measure out the half-length in each direction, and cut at both marks.
5. Never cut through a picket hole.

The acceptance test

The gap between the post and the first picket must be equal at both ends, and less than 4 in. If it is equal and under 4 in, the panel is right. If it is unequal, you cut from one end — take the panel down and redo it. Assembling a cut panel from the centre outward makes this self-correcting.

Corners

Treat each straight leg as its own run. A corner post serves both legs and is a different part from a line post or an end post — it takes rail connections on two faces at 90°.

Step 04 Counting posts

The arithmetic is short and people get it wrong in the same direction every time.

A run of N sections needs N + 1 posts

Four sections need five posts. Eight sections need nine. There is always one more post than section, because the run has to be closed at both ends.

Of those N + 1 posts: 2 are terminals (end posts, or corner posts where a leg turns), and the remaining N − 1 are line posts.

Worked examples at a 6 ft section

Run	Full panels	Cut panel	Sections	Posts	Terminals	Line posts
12 ft	2	—	2	3	2	1
16 ft	2	1 at 4 ft	3	4	2	2
20 ft	3	1 at 2 ft	4	5	2	3
24 ft	4	—	4	5	2	3
30 ft	5	—	5	6	2	4

Step 05 Top mount — wood and concrete

The post stands on the surface and bolts down through a welded base plate. This is the stronger and simpler of the two mounts, and the one we recommend wherever the structure allows it.

Base plate — ProGuard and CoastLine

Dimension	Metric	Imperial
Plate size	115 × 115 mm	4.53 in
Plate thickness	10 mm	0.394 in
Holes	4 × Ø11 mm	for 3/8 in bolts
Hole spacing, centre to centre	82.55 mm	3.25 in
Edge distance, hole to plate edge	15.875 mm	5/8 in

Why the holes are 11 mm and not 10 mm. A 3/8 in bolt is 9.525 mm. A 10 mm hole leaves 0.475 mm of clearance — about 30% of what the steel code treats as standard for a bolted connection. These plates drop over anchors that were drilled by hand, where real position error is several millimetres. 11 mm gives 1.48 mm of clearance and makes the plate fit the hole pattern you actually drilled.

On wood

• Solid blocking under every post is mandatory. A base plate lagged into decking alone has nothing to hold: the 200 lb load arrives as a prying couple and pulls the fasteners straight out. Block between joists, minimum 2-ply, screwed to the adjacent joists.
• 4 × 3/8 in structural lag screws, hot-dip galvanised or stainless, with a minimum 80 mm (3¼ in) of thread penetration into solid lumber — 112 mm for commercial work.
• Decking and composite thickness do not count toward penetration. Measure from where the thread first enters solid framing.
• Through-bolt instead wherever you can reach both faces. It is always the stronger connection.

On concrete

• 4 × 3/8 in wedge anchors, minimum 3.5 in embedment, into concrete of at least 3,000 psi. Adhesive anchors at the same embedment are an equivalent alternative.
• Slab edge depth at least 200 mm, and keep anchors at least 64 mm from the top and bottom faces of the slab edge. Anchors set too near an edge break out a cone of concrete well below their rated load.
• On CoastLine, use stainless anchors AND the isolating washers supplied with the post. Aluminium and stainless in contact in salt air is a galvanic cell; the isolators are what stop it, and they are not optional.

Two substrates we will not give you a schedule for

Hollow block: not permitted without project-specific engineering. No manufacturer in this market publishes a schedule for it, and we are not going to invent one.

Steel: by the project engineer. There is no published schedule anywhere, ours included.

Step 06 Side mount — the harder one

The post bolts to the face of the rim joist or fascia and rises past the deck surface. It buys you deck area and a cleaner edge. It also changes the mechanics completely, and two things must change with it.

Through-bolt. Do not lag.

In a side mount the top fastener is loaded in withdrawal — pulled straight out of the wood — which is the weakest way a fastener can be loaded. A 3/8 in lag at 3 in penetration in common framing is worth roughly 729 lb. The top fastener on a two-bolt mount needs about 2,400 lb. That is a 3.3× shortfall, and it is why every manufacturer that publishes a fascia schedule either through-bolts or demands four deep lags.

Side-mount fastener schedule by substrate

Substrate	Schedule
Wood rim default	4 × 3/8 in through-bolts, hot-dip galvanised or stainless, with nut and washer, plus a 50 mm diameter washer on the back face to spread the load. Solid blocking behind the rim is mandatory — minimum 2-ply, screwed to adjacent joists.
Wood, lag alternative retrofit only	4 × 3/8 in structural lags, 80 mm minimum thread penetration into solid lumber (112 mm commercial). Decking and composite fascia thickness do not count toward penetration.
Concrete	4 × 3/8 in wedge anchors, 3.5 in minimum embedment, concrete ≥ 3,000 psi, edge depth ≥ 200 mm, anchors ≥ 64 mm from top and bottom faces. Stainless on CoastLine.
Hollow block	Not permitted without project-specific engineering.
Steel	By the project engineer.

Blocking is not optional, and here is the part people miss

Fasteners into the face of a rim joist are in side grain, which is normal and fine. The real hazard is a post landing at a point where a joist end butts the rim — end grain holds a fastener very poorly. That is precisely what the blocking requirement converts back into solid material. Block first, then locate the post.

Two derates you must apply when you side mount

• Post spacing drops to 48 in, against 6 ft top-mounted. Side mount is a weaker connection and the layout has to respect that.
• The post gets longer. It reaches down the rim face, so a 42 in guard needs roughly a 49 in post — about 178 mm more than the top-mount version. Order the side-mount post; do not try to make a top-mount post reach.

Measure the guard height from the walking surface, independently of the bracket. If you set the bracket first and measure the rail from the bracket, the two datums drift apart along the run and you finish with a guard that is short at one end.

Step 07 Stairs

Measure the 4 ft maximum ALONG THE SLOPE, not horizontally

Run your tape parallel to the angle of the stairs, nosing to nosing — or lay a straight board on the tread noses and measure along that. Do not measure the horizontal distance. If you set stair posts at the horizontal spacing, your rail sections come out too short and will not reach.

At a typical 7 in rise and 11 in run, the slope distance is about 13 in per tread, so 4 ft along the slope covers a little under four treads. A one-storey stair is usually three posts; a second-storey stair, four or five.

Setting the posts

• Posts surface-mount on the treads, set back from the nosing — no more than about 2 in from the nosing edge.
• Use the same setback on every post, including the level posts adjacent to the stair. If the setbacks differ, the posts will not line up when you sight down the flight, and the amount you have to trim off each post base will differ too.
• Blocking under each stair post, same rule as a level deck.

Height and openings change on a stair — both in your favour

• Guard height is 34 in minimum on the open side of a stair, measured vertically from the line connecting the tread nosings — not from any single tread. That is 2 in lower than the level requirement, so a 36 in post serves the stair without a different part.
• If the top of the guard is also being grasped as the handrail, it must land in the 34–38 in band.
• The sphere allowance opens to 4⅜ in on the open side of a stair.
• The triangular opening formed by riser, tread and bottom rail may pass up to a 6 in sphere.

The loads do not change on a stair. Same 200 lb concentrated, same 50 lb infill. Only the geometry allowances move.

Step 08 Final checks

1. Sphere test every opening. A 4 in ball must not pass anywhere on a level run — including between the post and the first picket at both ends of every cut panel, and under the bottom rail.
2. Push the top rail hard, outward and downward, at the midpoint of the longest bay. Any movement at a base plate means a fastener is short, a hole is oversized, or the blocking is missing.
3. Check guard height at both ends of every run and at the top and bottom of every stair flight, measured from the walking surface or the nosing line.
4. Re-check every base plate fastener after the first season. Timber shrinks; this is normal and it is why the check exists.

What voids the product, and why

• Drilling a CoastLine post on site. Every hole is machined, deburred and radiused BEFORE the post is coated. A hole drilled afterwards is bare aluminium at the one place salt collects — if it is genuinely unavoidable, seal the exposed metal back to the coating with the approved touch-up before installing.
• Cutting or drilling a post. The post is the structural member; a hole in it is a hinge.
• Omitting blocking. Every load path in this document assumes solid material behind the fastener.
• Omitting the isolators on CoastLine, or substituting plain stainless fasteners for the supplied isolated ones. Aluminium against stainless in salt air corrodes at exactly the point where water sits.
• Using EdgeLine above a single storey or at 42 in. Covered above, and worth repeating here.

Related

Railing specifications & documentation — the hub, with every page in this set.

Specifications by line: EdgeLine · ProGuard · CoastLine

Guides: Guard rail installation · Cable railing installation · Engineering & code compliance

Full product specifications · All instruction guides

Questions an installer or an inspector needs answered that these pages do not cover? Contact us — we would rather answer it than have you guess.