Cable railing installation

Laying out, anchoring and tensioning a CR Fence & Rail cable system — top mount and side mount, on wood and on concrete, level runs and stairs. Cable behaves differently from a picket guard in almost every step, so read this rather than adapting the guard rail guide.

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 building official has the final say.

The four numbers that govern every cable job

• Post spacing: 4 ft maximum, centre to centre — level and stairs alike.
• Cable spacing: 3⅛ in (3.125 in) centre to centre.
• Cable tension: 225 lb per cable.
• Run length: 50 ft maximum for a straight continuous run; less with corners.

1. Why cable lays out differently
2. What the code requires
3. Divide the run — equally
4. Terminal posts carry everything
5. Anchoring — top and side mount
6. Running and tensioning the cable
7. Stairs
8. Final checks

Step 01 Why cable lays out differently

With a picket guard rail, each bay is a rigid factory-made panel and the posts land wherever the panels end. Cable is the opposite. The cable runs continuously from one terminal post, through every post in between, to the terminal at the far end. An intermediate post is not a termination — it is a support, and a support can go anywhere you like.

The two families, side by side

	Picket guard rail	Cable railing
Infill	Rigid panel, picket spacing fixed at the factory	Continuous cable, spacing set by the post holes
Dividing a run	Full panels, cut the last one	Divide equally
Max post spacing	6 ft	4 ft
What sets that maximum	Top rail bending	Cable sag against the 4 in sphere
Intermediate post	Panel joint	Cable support — place it where you like
Run length limit	None	50 ft straight

The 4 ft limit is about sag, not about strength

A tensioned cable is not rigid. Push on it between two supports and it deflects — and the code does not ask how strong it is, it asks whether a 4 in sphere can pass through. That is what caps the span. Industry testing of a 316 stainless cable at 3⅛ in spacing and 225 lb tension puts the maximum unsupported cable span at 48 in, and that is where our number comes from.

The practical consequence: widening a bay defeats the sphere rule long before anything bends. If you cannot make 4 ft work, add a post. Do not stretch the bay.

Step 02 What the code requires

The requirements, and the clause each comes from

Requirement	Level	Stairs	Clause
Guard height — from the walking surface; on stairs from the nosing line	36 in min	34 in min	IRC R312.1.2 + exc. 1
Where the guard top is also the handrail	—	34–38 in	IRC R312.1.2 exc. 2
Commercial / IBC	42 in min	42 in	IBC 1015.3
Opening — measured against the cable under load, not at rest	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, any direction	200 lb	200 lb	IRC R301.5 · IBC 1607.9.1.1
Infill load on one square foot	50 lb	50 lb	IBC 1607.9.1.2

The sphere test on a cable system is a loaded test, not a resting one. An inspector will push the cables apart. That is the correct test, and it is why post spacing and cable tension both matter — they are the two things that decide how far the cables move when someone leans on them.

Step 03 Divide the run — equally

The layout rule

1. Divide the run length in feet by four.
2. If that lands on a whole number, subtract one. If it does not, round down.
3. That is your line post count.
4. Add two terminal posts, one at each end.
5. Space them all evenly across the run.

Worked examples

Run	÷ 4	Line posts	Terminals	Total posts	Bays	Each bay
12 ft	3.0	2	2	4	3	4.00 ft
16 ft	4.0	3	2	5	4	4.00 ft
20 ft	5.0	4	2	6	5	4.00 ft
22 ft	5.5	5	2	7	6	3.67 ft
30 ft	7.5	7	2	9	8	3.75 ft

Equal bays are not a code requirement — they are what the arithmetic gives you, and they look better. Unequal bays are perfectly acceptable as long as no single bay exceeds 4 ft. The maximum is per bay, not an average across the run. If an obstruction forces one short bay and one long one, the short one is fine and the long one must still be under 4 ft.

Run-length ceilings — a separate limit, and it is not about spacing

Friction through the intermediate posts caps how long one continuous cable can be, no matter how the posts are spaced:

• 50 ft maximum for a straight continuous run.
• Runs with corners: shorter, and no more than two bends. Past that, terminate and start a new run.
• Under 25 ft you may tension from one end only. Longer runs want a tensioner at both ends.

Exceed these and you cannot get even tension along the run — the far end stays slack however hard you pull at the near end.

Corners

Where a run turns, you have a choice. A double corner post lets the cable run continuously around the corner without terminating, which is cheaper and keeps the run as one tensioned system. Terminating at the corner is also valid but turns one run into two, each needing its own terminals and tensioners.

Step 04 Terminal posts carry everything

A terminal post is not a line post with extra fittings

Every cable in the run pulls on the terminal post at once, and they all pull the same way. Ten cables at 225 lb each is 2,250 lb of steady horizontal load on a 36 in guard — and about 2,700 lb on a 42 in guard, which carries twelve cables.

That load is permanent. It is there on a calm day with nobody touching the railing. A line post never sees it — the cable simply passes through. This is why terminal posts, their anchors and their blocking are specified differently, and why you must not substitute a line post at the end of a run.

• End posts take the termination and tensioning hardware at one or both ends of a run.
• Corner posts take the turn. If cable terminates at the corner, it carries the terminal load on both faces.
• Line posts are drilled pass-throughs. The cable slides through; no fitting, no load.

Line post holes should be deburred or fitted with the supplied grommets. A raw drilled edge abrades the cable every time it moves, and it also cuts the coating at the one place water sits.

Step 05 Anchoring — top and side mount

The anchoring schedule is the same as for our guard rail, with the spacing changed and one addition for terminals.

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	15.875 mm	5/8 in

Fastener schedule by substrate

Substrate	Schedule
Wood, top mount	4 × 3/8 in through-bolts where both faces are reachable; otherwise 4 × 3/8 in structural lags with 80 mm minimum thread penetration into solid lumber (112 mm commercial). Decking and composite thickness do not count. Solid blocking under every post, minimum 2-ply, screwed to adjacent joists.
Wood, side mount	4 × 3/8 in through-bolts with nut, washer and a 50 mm diameter washer on the back face. Do not lag a side mount — see the warning below. Blocking mandatory.
Concrete	4 × 3/8 in wedge anchors, 3.5 in minimum embedment, concrete ≥ 3,000 psi, slab edge depth ≥ 200 mm, anchors ≥ 64 mm from top and bottom faces. Adhesive anchors equivalent at the same embedment. On CoastLine (aluminium): stainless anchors PLUS the supplied isolating washers — aluminium against stainless in salt air is a galvanic cell, and the isolators are what prevent it.
Hollow block	Not permitted without project-specific engineering.
Steel	By the project engineer.

Through-bolt a side mount. Do not lag it.

A side-mounted post's top fastener is loaded in withdrawal — pulled straight out — the weakest way to load a fastener. A 3/8 in lag at 3 in penetration in common framing is worth about 729 lb against roughly 2,400 lb of demand. That is a 3.3× shortfall. On a cable terminal post, which also carries the permanent cable tension, it is worse still.

Two derates for side mount

• Post spacing drops to 48 in — which for cable it already is, so no change to your layout. This is the one place cable is easier than guard rail.
• The post gets longer. A 42 in guard needs roughly a 49 in post. Order the side-mount part; do not adapt a top-mount post.

Blocking behind a terminal post is not the same job as blocking behind a line post. The terminal carries a permanent 2,250 lb pull toward the middle of the run, in addition to the code load. Block generously and tie the blocking into more than one joist.

Step 06 Running and tensioning the cable

Finish the frame completely before you tension anything

All posts anchored. Top rail on and fixed. Every fitting in place. Only then tension.

Tensioning an incomplete frame will deflect the posts beyond allowable limits — and because the load is steady, they do not spring back. You will have bent the guard before you have finished building it. This is the single most common way a cable install is ruined.

Running the cable

1. Fit the termination hardware at the first terminal post.
2. Feed the free end through every intermediate post in turn, all the way to the far terminal. One continuous length — do not cut and join at intermediate posts.
3. Fit the tensioner at the far terminal and take up the slack by hand.
4. Repeat for every cable before tensioning any of them.

Tensioning sequence

Start at the centre and alternate outward — like the lug nuts on a wheel

1. Begin with the middle cable of the run.
2. Work alternately above and below it, outward toward the top and bottom cables.
3. Take several passes. Bring everything up gradually rather than pulling any one cable to full tension first.
4. Target 225 lb per cable.
5. Go round again after all cables are tensioned — earlier ones will have relaxed as later ones came up.

Tensioning from one end of the stack to the other twists the posts progressively and leaves the frame racked. Alternating from the centre keeps the load on each post balanced at every stage.

The sphere check, done properly

Once tensioned, push the cables apart at the middle of the longest bay and try to pass a 4 in sphere. If it passes, either tension is low or the bay is too wide — and the fix for a wide bay is another post, never more tension. Over-tensioning to close a gap loads the terminal posts beyond what they were anchored for.

About mid-span cable stabilisers

A stabiliser holds cable spacing at mid-bay. It is not a structural component and it is not a substitute for a post — it is bolted to the cables, not to the structure, so it does nothing for the top rail or the frame. Our systems are designed at 4 ft post spacing and do not require one. If anyone offers you a stabiliser as a way to stretch a bay past its rated span, the frame still has to be rated for that span without it.

Step 07 Stairs

Measure the 4 ft maximum ALONG THE SLOPE

Run your tape parallel to the angle of the stairs, nosing to nosing. Do not measure horizontally. If you set posts at the horizontal spacing, the sloped distance between them exceeds 4 ft and your cables sag past the sphere limit.

At a typical 7 in rise and 11 in run the slope is about 13 in per tread, so 4 ft along the slope is a little under four treads. Expect a post roughly every three to four steps. That is normal for cable on a stair and every maker in this category is in the same range.

Setting stair posts

• Surface-mount on the treads, set back from the nosing — no more than about 2 in.
• Same setback on every post, including the level posts at the top and bottom, or they will not line up when you sight down the flight.
• Keep the post far enough back that the cable does not touch the tread nosing as it passes — about an inch of clearance.
• Blocking under every stair post.

Cable on a rake

• Terminal fittings at the top and bottom of the flight must swivel or be set in angled holes to match the stair pitch. Use the stair fittings, not the level ones — a level fitting forced to an angle bends the cable at the termination and that is where it will fail.
• Beveled washers go under any fitting seated in an angled hole.
• Pre-bend the cable to roughly the stair angle before tensioning. It self-aligns as tension comes up.
• Tensioning sequence and target are unchanged — centre outward, 225 lb.

Height and openings on a stair — both more forgiving

• Guard height 34 in minimum from the line connecting the nosings, not from a single tread. A 36 in post serves the stair without a different part.
• 34–38 in if the guard top is grasped as the handrail.
• Sphere opens to 4⅜ in on the open side of a stair.
• The triangular opening at riser, tread and bottom rail may pass up to 6 in.
• Loads are unchanged. Same 200 lb, same 50 lb.

Step 08 Final checks

1. Loaded sphere test at the middle of every bay, top to bottom, level runs and stairs. Push the cables apart as an inspector will.
2. Check tension on every cable after the full run is up, and again after a week. New cable and new fittings both settle.
3. Push the top rail outward and downward at the middle of the longest bay. Movement at a base plate means a short fastener, an oversized hole, or missing blocking.
4. Inspect the terminal posts. They carry a permanent load; any lean or any gap opening at the base plate is a defect to fix now, not to watch.
5. Check guard height at both ends of every run and at both ends of every stair flight.
6. CoastLine, coastal sites: rinse with fresh water on a regular schedule. Salt that is rinsed off does nothing; salt left to concentrate in a drilled hole is what causes pitting.

What voids the product

• Tensioning before the frame is complete. The most common and least recoverable error.
• Post spacing over 4 ft, or measured horizontally on a stair.
• Substituting a line post for a terminal post. It is not anchored for the cable tension.
• Over-tensioning past 225 lb to close a gap that needs another post instead.
• 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, or running cable through a raw un-deburred hole.
• Omitting blocking, anywhere.
• Running cable through a CoastLine post without its isolating bushing. The cable is stainless and the post is aluminium; the drilled hole is where the coating is cut, water sits and salt concentrates. The bushing is the part that makes coastal aluminium work, and leaving it out is the one mistake that will show up as pitting.

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.