That's the way we refer to soemthing (GB) that really works; often, it is used as a noun 'a practical'; or it is used as an adjective to qualify some other noun describing the specific item: 'a practical staircase'.

It's harder when you want a general term like 'décor', since we can't say 'a practical scenery' — and a 'practical set' would be a bit silly, really.

So you might be stuck with saying something like 'a practical scenic element' etc. — it really all depends on the specific context in which it is used.

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Note added at 22 mins (2013-05-28 18:35:07 GMT)
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The problem is, an entire stage set is by its very nature 'practical' — actors must be able to enter it and walk around; so at that level, it is taken for granted and wouldn't really be described as 'practical'; hence if used in this way, it would tend to be read with the other meaning of 'practical' — i.e. that it is functional, sensible, handy, ... For example, we might say that of a set that comes apart easily for striking, with easily-handled, not-too-heavy sections...

One can have a 'practical ladder' (one you can actually climb up), a 'practical door' (one that actually opens), a 'practical telephone' (it rings) 'a practical lamp' (it lights); one might have a 'practical bridge' — high up between two parts of the set, which actors can walk across (like for a battlement scene)

But for an entire set, I think you'll need to re-phrase it a bit to make it sound like natural technical jargon in EN.

For example "A set composed entirely of practicals" (or: 'practical elements')

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Note added at 57 mins (2013-05-28 19:10:50 GMT)
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I remember one memorable occasion when former Coronation Street star Pat Phoenix was in a touring play that came to our theatre, and she had to descend from the (pretend) first floor landing of the set down the supposedly practical staircase; only it was fixed very well, and she came a mighty cropper! Like the true old trooper she was, she played out the rest of the show with what turned out to be a badly sprained ankle!

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Note added at 1 hr (2013-05-28 19:24:16 GMT)
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See this rather helpful stage glossary:

http://www.theatrecrafts.com/results.php

PRACTICAL
Any object which appears to do onstage the same job it would do in life, or any working apparatus (eg light switch or tap). Light fittings which have to light up on the set are called Practicals.



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Note added at 3 hrs (2013-05-28 21:28:38 GMT)
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For the sake of completeness, let me repeat here what I said above in answer to Daryo's discussion comment: a 'praticable' as a specific type of scenic element is generically referred to in EN (GB) as a 'riser' — some kind of dais or platform.

However, I repeat my reservations that this is the intended meaning here.