Tread boards in external stairs for houses

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Greendrake

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#236145 19-May-2018 20:23

I am about to build a small (3-riser) entrance stairway for my house guided by this how-to:

This question is about the treads which appear to be consisting of three separate boards each. The text even specifies a gap between them:

Treads spanning 900–1000 mm between strings should be nominal 50 mm thick minimum and grooved or have a slip-resistant finish. Boards should have 5 mm gaps between them.

Am I understanding it right that the treads are indeed to be of three separate boards each? Or are they just grooves in a single-piece tread?
Why so? Is it so that water could drain in the 5-mm gaps? Or is it for better slip resistance? Or both?

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Ge0rge

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#2019160 19-May-2018 20:26

Yup - three separate boards. It's for cost for one thing - try pricing up a 300mm wide x 50mm thick piece of timber - it'll make your wallet snap shut so fast your eyes will water!

Bung

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#2019189 20-May-2018 00:09

I read it as treads 50mm nominal but they don't have to be made up as boards. I've seen treads as a single plank or built up with 2 x150mm boards. Any gap should be wide enough to not trap water or debris. Your example has chosen 3 x 100mm assuming that this would be available as griptred decking. I'd be a bit cautious there and check. Most decking dimensions have shrunk relying on joists closer together. I don't think that stringer spacing would work with skinny 90 x 40mm (or 30) decking. You can put grip strips onto treads instead of having grooved timber.