An arris rail has a triangular cross-section and is the standard choice for close-board fencing, where feather edge boards are nailed to the sloping face of the rail. A square-sawn rail has a rectangular profile and is typically used in post and rail fencing for paddocks, driveways, or open boundary lines. Both are widely available in pressure treated timber.
Timber Fence Rails for Post and Rail Fencing Projects
Fence rails are the horizontal backbone of most timber fencing systems. MacBlair stocks a range of pressure treated fence rails to suit closed board, post and rail, and arris-style builds, all treated to resist rot and insect attack. Lengths typically run to 3.0m, with profiles sized to handle the structural load of the fence above.
The range covers the main rail types used in domestic and agricultural fencing:
- Arris rails – triangular-section rails nailed directly to posts; the standard choice for supporting feather edge fence boards
- Capping rails – sit over the top of close-board fencing to protect end grain and give a tidy finish
- Square-sawn rails – used in post and rail fencing for paddocks, driveways, and open boundary work
Getting the spacing right matters. Most domestic fences use two or three rails per bay, fixed to timber fence posts set at roughly 1.8m centres. Use galvanised nails or screws throughout — they won't rust and stain the timber over time. Once rails are in place, a coat of wood preservative adds an extra layer of protection, particularly at cut ends exposed during installation.
All treated timber in the range meets BS 8417 guidelines for use in above-ground and ground-contact applications. Post holes should be a minimum of 600mm deep for standard bays, with postcrete used to set posts securely. For the full picture on completing a fence run, see the fencing range, which covers panels, posts, gates, and all associated hardware.
Fence Rail FAQ's
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For most garden fences up to 1.8m high, three arris rails per bay is the norm: one near the top, one near the bottom, and one in the middle. Shorter fences of around 1.2m can get away with two rails. For post and rail fencing used around paddocks or fields, three or four rails per bay are common to add strength and close the gaps between rails.
Most timber fence rails are sold in 3.0m lengths, which is the standard bay width for domestic fencing when posts are set at 1.8m centres with a slight overlap at each joint. Capping rails are also commonly available in 3.0m lengths. Always check the product listing for the exact length before ordering, particularly if your post spacing differs from standard.
Yes. Because fence rails are in constant contact with the elements and often close to ground level, untreated timber will deteriorate quickly. Pressure treated rails have preservative forced deep into the wood fibres, giving lasting protection against rot and insect damage. If you cut a rail to length on site, apply a brush-on wood preservative to the cut end to protect the exposed timber.
Arris rails are typically nailed through the face into the post using galvanised round wire nails, or secured with purpose-made arris rail brackets for a stronger fixing. Square rails can be nailed, screwed, or bolted depending on the load they need to carry. Always use galvanised or stainless steel fixings outdoors — plain steel will rust and can split the surrounding timber as it expands.