A steel beam needs galvanizing when it lives outside or in a wet location: deck and porch beams, carport and canopy frames, exterior posts, balcony framing, and lintels in walls that stay damp. Inside a dry, heated house, a shop primer is usually enough. The cost of a galvanized beam is driven by its weight and size, the fabrication details galvanizing requires, handling to and from the galvanizer, and any paint over the zinc. We don't publish prices, but we can prime or galvanize to suit your drawings and quote the beam as it will actually be made.
This guide covers where galvanized beams and posts earn their keep, how galvanizing changes the way a beam is fabricated, and what goes into the price.
Do steel beams need to be galvanized?
Most don't. The 2024 Ontario Building Code sets only minimums for houses and small buildings:
- Exterior steel beams must be shop primed with rust-inhibitive paint (Article 9.23.8.2).
- Exterior steel columns susceptible to corrosion must have at least one coat of rust-inhibitive paint on the outside surface (Article 9.17.3.3).
Galvanizing goes beyond that minimum. It is chosen by the designer or owner when a painted finish would need frequent maintenance or would be hard to reach later. For engineered buildings, the specification says which steel is galvanized. Our post on whether structural steel needs paint or galvanizing covers the full range of finishes, and galvanized vs painted structural steel compares the two head to head.
Where galvanized beams and posts make sense
Galvanizing earns its cost where steel stays wet, sees salt, or is hard to repaint:
- Deck and porch framing. Steel beams and posts under decks sit in the weather, collect snow and get splashed from below. See steel beams and posts for decks.
- Carports, canopies and pergolas. Exposed on all sides, often near driveways where de-icing salt gets tracked and sprayed.
- Exterior posts at grade. Posts on or in concrete corrode fastest at the base where water collects. See embedding steel posts in concrete vs base plates.
- Balcony and walkway framing. Hard to reach once finished, and exposed to water from above.
- Lintels in wet walls. Angles carrying brick in exposed walls, especially where flashing is poor. See do steel lintels rust.
- Garages, wash bays and unheated buildings. Interior steel that stays damp or sees salt from vehicles.
A beam inside a heated basement, or one fully encased in concrete, rarely benefits from galvanizing.
Appearance is worth a thought too. A fresh galvanized finish is bright or matte grey and can look uneven from piece to piece, and it weathers to a dull grey over time. If the beam is on show and colour matters, plan for a duplex system (paint over the galvanizing) from the start rather than painting it later.
How galvanizing changes the way a beam is made
Hot-dip galvanizing coats the steel by dipping the finished piece in a bath of molten zinc after it has been cleaned and fluxed. The zinc bonds to the steel, covering every surface the zinc can reach, inside and out. Common specifications for fabricated steel are ASTM A123 and CSA G164, the Canadian standard for hot-dip galvanizing of irregularly shaped articles; bolts and small hardware are usually galvanized to ASTM A153 or a similar fastener specification.
Because the beam goes into the bath as a finished piece, galvanizing has to be designed in from the start:
- All fabrication first. Every cut, hole, cope, slot and welded attachment (cap plates, base plates, clips, tabs) must be done before galvanizing.
- Vent and drain holes. HSS posts, tubes and any enclosed space need holes so cleaning solutions, zinc and air can flow in and out. Sealed sections are a safety hazard in the bath. The holes go on the shop drawings.
- Size and shape. The piece has to fit the galvanizer's bath. Long beams may be dipped one end at a time where the galvanizer allows it, or detailed with a bolted splice.
- Distortion. Thin, long or asymmetric pieces can warp from the heat. Heavier, symmetrical sections behave better.
- Clean welds. Weld slag and some anti-spatter products won't come off in the galvanizer's cleaning and leave bare spots, so welds are cleaned in the shop.
- Tight overlaps. Plates lapped tightly over each other can trap cleaning solution and weep rust later. Overlaps are either seal welded with venting or avoided.
- Threads and fits. Zinc adds thickness, so tight fits, threaded parts and bolt holes need allowances.
What drives the cost of a galvanized beam
Here are the main factors that move the price, and why:
- Weight. Galvanizing is commonly priced by the weight of steel processed, so heavier beams and posts cost more to galvanize.
- Size and shape. Pieces that fit the bath easily are simpler to handle than long beams that need special handling or a splice.
- Fabrication for galvanizing. Vent and drain holes, cleaned welds, sealed or vented overlaps and splices add shop time.
- Surface condition. Paint, markings, grease or heavy rust have to be removed before dipping.
- Handling and transport. The steel travels from the fabrication shop to the galvanizer and back, or to site, with protection against damage to the coating.
- Hardware. Galvanized bolts, nuts, washers and anchors to match.
- Paint over the zinc. A duplex system (galvanizing plus paint) needs surface preparation and a compatible coating system. It is chosen for colour or extra life in harsh exposure.
- Schedule. Galvanizing adds a step and time to delivery.
It is worth comparing on life-cycle, not just the first invoice. A primed and painted exterior beam costs less up front but needs inspection and repainting over its life. A galvanized beam costs more to start and typically needs little attention for many years in ordinary exposure. Where the steel is hard to reach once the deck or porch is finished, that difference matters.
Installing galvanized beams and posts
A galvanized beam is only as good as the coating that survives installation:
- Avoid site cuts and holes. Every field cut or hole is bare steel. If one is unavoidable, clean it and touch it up with a zinc-rich coating.
- Don't weld on site without a plan. Welding burns off the zinc and creates zinc fumes. If site welding is in the design, it needs proper ventilation and protection, and the area has to be repaired afterwards.
- Use compatible fasteners. Galvanized or stainless fasteners, as the designer specifies, so connections don't become the weak point.
- Detail the base. Keep post bases above grade and above standing water, and don't bury steel in soil unless it is designed for it.
The beam itself is still a structural member: size, bearing and connections come from the designer or engineer, and a building permit is normally needed for structural work on decks, porches and additions.
Ordering galvanized beams and posts
Tell us at the quote stage that the steel will be galvanized, and give us the member sizes, lengths, plates and holes from your drawings, plus where each piece will be installed. We fabricate beams, posts, lintels and plates in our CWB certified shop, detail the venting and connections for galvanizing on the shop drawings, and can prime or galvanize to suit, with delivery across the GTA and Ontario.
Send your drawings for a quote, or see our steel products.
Frequently asked questions
Do steel beams need to be galvanized?
Not inside a dry, heated building, where a shop primer is usually enough. The Ontario Building Code requires exterior steel beams in houses to be shop primed with rust-inhibitive paint. Galvanizing is a specification choice for steel exposed to weather, moisture or salt, such as deck beams, porch posts and carport frames.
How much does it cost to galvanize a steel beam?
It depends on the weight and size of the piece, the fabrication needed to galvanize it properly, handling and transport to the galvanizer, surface preparation, and any paint over the zinc. Because these vary so much, the reliable way to price it is a quote on the actual beam or post.
Can you weld or cut a galvanized beam on site?
It is best avoided. Cutting and drilling expose bare steel that then needs touching up with a zinc-rich coating, and welding burns off the zinc and produces zinc fumes that need proper ventilation and protection. Plan all cuts, holes and welded attachments before the beam is galvanized.
Are galvanized steel posts good for decks?
Yes. Galvanized HSS or other steel posts are a common choice for decks, porches and carports because the zinc protects the inside and outside of the tube. The posts must be detailed with vent and drain holes and connected to the footing in a way that keeps water from sitting against the steel.
