Unlike a lattice truss, a girder gives birds something a truss does not: a wide, flat, continuous ledge running the length of the building. That makes it harder to ignore and — usefully — much easier to fix. This is a spike surface, and a straightforward one.
At a Glance
An I-beam or plate girder has a bottom flange that is typically 100 to 300 mm wide and runs unbroken for the whole span. To a pigeon that is a road: level, wide enough to turn around on, covered by the beam web above and the roof above that. Birds line up along it the same way they line up on a parapet.
The difference from a truss is that there is only one surface per beam, and it is flat. That is why the answer here is spikes and the answer on a lattice truss is netting.
| Flange width | What is needed | Why |
|---|---|---|
| Up to about 100 mm | One row, centred | Nothing usable left either side |
| About 100–200 mm | One wide row, or one row offset outward | A pigeon needs roughly a palm's width to settle |
| Over 200 mm | Two parallel rows | A single central row leaves a usable strip on both sides |
The half-covered flange is the commonest failure
Somebody fits a single narrow row down the centre of a 250 mm flange, and the birds simply stand on the outer edge with their tails over the drop. From the floor it looks like the spikes are not working. They are working, on the 60 mm they cover.
Measure the flange before ordering. On anything over roughly 200 mm, budget for two rows — which means twice the running metres.
Clearance to the moving crane
On a gantry or crane girder, anything you fit has to sit entirely outside the clearance envelope of the crane, its trolley and its festoon cabling. A spike strip in that path will be sheared off on the first pass — and dropped onto the floor below.
Before ordering, confirm with your maintenance team which face of the girder is clear through the full travel. Often the inner face is out of bounds and the outer flange is free, which changes where the strips go. This is worth ten minutes and it is the one constraint unique to gantry girders.
| Location | Used for | Fix |
|---|---|---|
| Bottom flange | The main perch, whole length | Spikes, one or two rows by width |
| Top flange where exposed | Perch, if reachable and uncovered | Spikes |
| Web stiffener pockets | Nesting — sheltered three sides | Spikes in the pocket, or fill it |
| Gusset and cleat plates | Flat platforms at connections | Small spike sections |
| Bearing and end plates | Wide flat area at the support | Spikes |
| Services on the beam | Trays and conduit clipped to it | See cable trays |
Connections and stiffener pockets are where nests appear first. If the run is long and the budget is finite, protect those before the plain flange.
For narrower flanges, cleats, gussets and stiffener pockets. Long straight runs are quick per metre once access is set up.
Fits: flanges to about 100 mm, connection plates, stiffener pockets
For wide flanges. Broader coverage per row means one row may do what would otherwise need two, which on a long span is a real saving.
Fits: flanges roughly 100–200 mm, bearing plates, wide cleats
Where the girders sit within a roof structure that is being used generally — trusses, purlins and light fittings all in play — netting the void covers everything at once.
Exposed steel in stilt parking, canopies and open ground floors — short runs, but directly above parked vehicles.
Atriums, malls, stations and covered markets, where the beam is visible and the installation has to look deliberate.
The main case. Crane gantries, plant structures and long-span beams, usually specified with the rest of the roof.
Fit spikes along the bottom flange, and use two rows on anything wider than about 200 mm. Cover the stiffener pockets and connection plates as well — those are where the nests are.
Because a girder is one wide flat ledge per beam and a truss is hundreds of angled members. Spikes suit a ledge. Nothing practical suits a lattice at height, so you separate the void instead.
Measure the flange. Up to about 100 mm, one row. Over roughly 200 mm, two rows — otherwise the birds stand on the uncovered edge and it looks as though the spikes have failed.
Yes, but only outside the crane's clearance envelope. Confirm with maintenance which face stays clear through the full travel before ordering — anything in the path will be sheared off and dropped.
It should not, because nothing is drilled or welded. Adhesive or clamp fixing only, and the surface needs proper preparation on galvanised or painted steel.
The access is the expensive part, so plan to clean, fix and inspect in one visit rather than three. If several surfaces up there are in use, price netting the bay against spiking the beams before deciding.
Industrial scale. Give us the total beam length, the flange width and the number of bays, and we will work out the running metres including the second row where it is needed.
Send a photograph along the length of the beam and one measurement — the flange width. That tells us whether it is one row or two, which is the number that decides the quantity and the cost.