What wood to use for external steps on a metal box-section frame?

Question

We've got some rotting wooden outside steps that I want to replace. They're just seven 1 metre-long planks screwed to a metal framework from the underside.

I'd planned to use scaffold boards as once cut to length the size is good, and I figured they'd take a lot of abuse. Also there quite rough so no need to add chicken wire or gripper pads for traction in the wet, maybe.

Lining up in the shop to buy them though I realise that they're not treated, like a lot of external wood tends to be.

How long would they last if I used them in their natural untreated state? I live in the UK so we have plenty of rain!

Alternatively I could treat/paint them with something? What products would be recommended? I'd like them to have a dark stain, rather than paint, if possible.

Or should I be looking at different wood completely?

Part of the appeal of scaffold boards is that they're relatively cheap, of course.

Answer 1

I assume that the scaffold boards are SPF (spruce, pine, or fir). If so, they'll gray out and start to rot within a year, mostly at the contact points with the supports. If you were to seal them well before installation they'd do a bit better, but only by a few years.

Some wood naturally resists rot, such as cedar, redwood, and teak. They should still be sealed, though, to preserve appearance.

Otherwise, treated lumber is generally the most cost-effective. Since you don't need it rated for ground contact, almost any will do. It'll last 10-20 years, depending on various factors relating to moisture.