Steel Posts / Retaining Wall Advice

100PFC vs 150PFC C-Channel Steel Posts: Sizes & Specifications

Choosing the right steel post starts with two questions: which series suits your wall, and which profile you need at each position along it. This guide covers the second question for C-channel (PFC) posts specifically — the exact specifications for 100PFC and 150PFC, how they compare to each other, and which one fits your sleeper thickness.

For the broader decision between C-channel and H-beam posts, see our H-Beam vs C-Channel guide. This article stays focused on the PFC dimensions themselves.

What C-Channel (PFC) Means

PFC stands for Parallel Flange Channel — a C-shaped steel section with one open side. You'll also see it called a C-channel post or, less formally, a C-beam. All three names describe the same profile.

The "parallel flange" part of the name matters more than it looks. Older channel sections (sometimes called taper flange channels) have flanges that get thinner toward the tip, which made them harder to bolt through consistently. PFC sections are hot-rolled with flanges of constant thickness from web to tip, which is what makes them practical for bolted connections, brackets and post caps — you're not guessing at a tapering surface when you drill or fit hardware.

In Australia, PFC sections are manufactured to AS/NZS 3679.1 (Hot-rolled bars and sections), the same standard that defines UB, UC and other rolled structural shapes. That's why a 100PFC or 150PFC bought from any compliant Australian steel supplier will match the same depth, flange and web dimensions — the section is defined by the standard, not by an individual retailer.

Because the channel is open on one side, a PFC post accepts a sleeper from one direction only. That makes it the correct choice for:

• Wall ends and starts
• Steps and level changes
• Any point where the wall terminates cleanly rather than continuing

Mid-run positions along a straight wall use H-beam (UC) posts instead, since a UC post accepts sleepers from both sides through its symmetrical flange profile. Retaining Walls Direct stocks PFC posts in two sizes — 100PFC and 150PFC — matching the 100 Series and 150 Series post ranges.

100PFC vs 150PFC at a Glance

Feature	100PFC	150PFC
Series	100 Series	150 Series
Sleeper fit	75mm & 80mm sleepers	75mm & 100mm sleepers
Steel thickness	5mm	Heavier section — see full spec guide
Length range stocked	400mm–3600mm (10 lengths)	2000mm–5800mm (11 lengths)
Typical role	Low garden walls, boundary edges	Taller walls needing heavier posts
Galvanising	Hot-dip to AS/NZS 4680	Hot-dip to AS/NZS 4680

For the exact depth, flange width, web thickness and weight per metre of each section, see the dedicated 100 PFC dimensions guide and 150 PFC dimensions guide.

100PFC Specifications and Use Case

The 100PFC C-channel end post closes off 100 Series walls with a clean, finished face at each end. It's paired with 100UC H-beam posts along the straight run.

Section	100PFC (Parallel Flange Channel), C-channel
Role	End / start post — accepts sleepers from one side
Steel thickness	5mm
Fits	75mm & 80mm concrete and timber sleepers
Lengths available	10 lengths, from 400mm to 3600mm
Galvanising	Hot-dip galvanised to AS/NZS 4680
Compliance	AS 4678-2002 Earth-retaining structures

Typical use: low garden walls and boundary edges built with 75–80mm sleepers, where 100PFC finishes each end and 100UC H-beams carry the sleepers in between. As a general guide, RWD positions the 100 Series for walls up to around 800mm, though this depends heavily on soil type, spacing and surcharge — always confirm against the sizing guide or an engineer for anything approaching that upper range.

150PFC Specifications and Use Case

The 150PFC C-channel post is the heavier-duty equivalent, used to terminate taller 150 Series walls cleanly at ends and starts, alongside 150 Series H-beam and corner posts along the run.

Section	150PFC (Parallel Flange Channel), C-channel
Role	Heavy-duty end / start post — sleepers one side
Lengths available	11 lengths, from 2000mm to 5800mm
Galvanising	Hot-dip galvanised to AS/NZS 4680
Compliance	AS 4678-2002 Earth-retaining structures

Typical use: taller 150 Series walls, where the longer lengths give the extra embedment a bigger wall needs. As a general guide, RWD positions the 150 Series for walls up to around 1.2–1.5m, though again this depends on soil, spacing and surcharge. For the full run-down of exact depth, flange and web dimensions on the 150PFC section, see our dedicated 150 PFC dimensions guide.

Choosing Between 100PFC and 150PFC

In practice, the choice between 100PFC and 150PFC rarely gets made on its own — it follows from whichever series you've already chosen for the rest of the wall. A few pointers to sanity-check that decision:

• Match the series, not just the post. If you're building with 75mm sleepers on a low wall, 100PFC end posts paired with 100UC mid-run posts is the standard combination. Don't mix a 150PFC end post into a 100 Series wall — the sleeper fit and post depth won't line up.
• Consider what's either side of the end post. A wall that steps down, turns a corner, or meets a different wall height at its termination often needs closer engineering attention than a straight run, regardless of which PFC size you're using.
• When in doubt, go up a series. An oversized end post rarely causes a problem. An undersized one, on a wall that ends up taller or more exposed than planned, is a much harder mistake to fix after the concrete has gone in.

Installation Considerations for PFC End Posts

End posts carry the same general installation rules as any other steel retaining wall post, with one added wrinkle: because they only take a sleeper from one side, they're often subject to a slightly different load pattern than a mid-run post, particularly where the wall turns or terminates against a slope.

As a general starting point, RWD's published guidance is:

• Standard post spacing of around 1.8–2.0m centres for residential walls, reducing to 1.5m or less on reactive clay, sandy soils, or where surcharge loads apply.
• Embedment of roughly one-third of total post length below ground, with a practical minimum of around 600mm regardless of wall height.
• A concrete footing rather than compacted soil alone, with reactive clay or loose sandy sites typically needing 20–30% more embedment than the baseline.

These are general starting figures, not a substitute for site-specific advice. For the detailed embedment table by post series and soil class, see the steel post sizing guide, and for anything approaching the upper end of what 100 or 150 Series posts are typically used for, involve a structural engineer before you dig.

Which Suits Your Sleeper Thickness

Post series and sleeper thickness go together — matching them correctly keeps the sleeper seated properly in the channel.

• 100 Series (100PFC) — fits 75mm and 80mm concrete or timber sleepers.
• 150 Series (150PFC) — built to work with both 75mm and 100mm concrete sleepers.

If you're not sure what thickness your sleepers are, check against our concrete sleeper range before ordering posts — the two are sold as a matched system, and a post with the wrong channel width will leave the sleeper loose or unable to seat fully.

Compliance

Both 100PFC and 150PFC are:

• Manufactured from hot-rolled structural steel sections to AS/NZS 3679.1
• Hot-dip galvanised to AS/NZS 4680 — the correct specification for in-ground steel in Australian conditions, not a painted or zinc-plated substitute
• Supplied to comply with AS 4678-2002 Earth-retaining structures

Compliant materials are one part of a compliant wall. Post size, spacing, embedment and footing still need to be confirmed against your specific wall height, soil type and any surcharge load — use the steel post sizing guide as a starting point, and involve a structural engineer for walls over 1.0m, near boundaries, on reactive clay, or carrying vehicle or building loads.

Maintenance and Lifespan

Hot-dip galvanising is a sacrificial zinc coating — it protects the underlying steel by corroding preferentially, and in typical residential ground conditions across Australia it's designed to provide decades of protection with no maintenance required. A few points worth knowing:

• Any on-site cutting, drilling or welding removes the galvanised layer at that point and creates a local corrosion risk unless treated with a compatible cold-galvanising compound.
• In extreme coastal conditions — roughly within 100–200m of breaking surf — additional protective coatings may be worth considering on top of standard hot-dip galvanising.
• A light white, powdery surface bloom (zinc oxide) on new galvanised steel is normal weathering, not a defect, and will settle within the first year or two.

Common Mistakes When Specifying PFC Posts

Most problems with PFC end posts trace back to a handful of avoidable mix-ups rather than the steel itself:

• Ordering the wrong series for the sleeper on hand. A 100PFC won't seat a 100mm sleeper properly — that thickness belongs to the 150 Series. Check your sleeper thickness before you order posts, not after delivery.
• Using a C-channel post where an H-beam was needed. Because PFC posts only take a sleeper from one side, using one in a mid-run position (rather than at an end or start) leaves the sleeper unsupported on the open side. Reserve PFC for genuine termination points.
• Under-ordering post length. Post length needs to cover embedment plus the full height of sleeper stack above ground, plus a small margin. It's a common mistake to size the post to the wall height alone and forget the in-ground portion.
• Skipping the footing. Even a correctly sized and correctly specified post underperforms if it's set in compacted soil rather than a proper concrete footing — the standard applies to the material, not the installation, so getting one right doesn't guarantee the other.

Corner, Joiner and Other End Post Options

Standard PFC posts assume a straight termination — a wall that simply stops. Not every end condition is that simple. Where a wall turns a corner, joins another wall, or needs to change direction, a straight C-channel post isn't always the right fit, and RWD's Corner / L-Post / Joiner range covers those cases specifically, including 45° and 90° angle options.

As a rule of thumb:

• A wall that simply ends, with nothing continuing beyond it, uses a standard 100PFC or 150PFC end post.
• A wall that turns a corner and continues in a new direction uses a corner post, sized to the same series as the rest of the wall.
• A wall that joins or steps against an existing structure may need a joiner post or site-specific engineering advice, particularly where the two sections carry different loads.

 

Mixing up these roles — using a standard end post where a corner post was needed, for instance — is one of the more common sources of a wall that looks fine on installation day but develops problems at the joint over time.

FAQs

Ordering PFC Posts With the Rest of Your Wall

Because PFC end posts are only one part of a wall system, it's worth working out your full materials list before placing an order rather than ordering posts in isolation. For a straight wall, that typically means: two end posts (100PFC or 150PFC, one at each termination), H-beam (UC) posts at regular centres along the run, matching concrete sleepers, and drainage materials behind the wall.

A few practical notes that make ordering smoother:

• Order posts and sleepers from the same series together, rather than sourcing them separately, to avoid a mismatch turning up on delivery day.
• Round post length up rather than down — a longer post can be trimmed on site if needed (with a touch-up to the cut edge), but a short post can't be extended.
• If you're not confident on quantities, RWD's retaining wall material estimator will work out posts, sleepers, concrete and drainage from your wall length and height, and a free quote can confirm final numbers before you order.