Help with max span of ceiling joists

13 Mar 2014
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United Kingdom
Hi all,

Could really do with some sound advice on the configuration of a timber-framed film studio - especially how to tackle the ceiling.

It's basically going to be a large wooden box inside a warehouse - 9.7M wide x 6.8M deep x 3.5M high. Stud walls and ceiling will be clad with 2 layers of acoustic plasterboard on the inside (19mm and 12.5mm) and OSB (18mm) on the outside.

The ceiling only has to support its own weight plus some light rigging and cameras and a small air con unit.

The plan was to run a triple bean (3 x 250mmx50mm bolted together) over the depth of the structure (so a spam of 6.8M) roughly in the middle... and then hang single joists (250mx50mm) at right angles off the triple beam. These would span about 5.4M on one side and 4.2M on the other. All timber would be C16 graded, rough sawn carcassing timber.

Having looked at various tables, it seems like 250mm has a max span of 5M. This is probably for external applications, maybe load bearing etc.

Would we be better off just running joists the depth (6.8M) of the structure every 400mm instead of using a triple?

Would 250mm cut it for out application? Could we bolt 2 together if not?

Or are we looking at RSJs?

Any advice would be very much appreciated.
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Your triple beam spanning 6.8m would be well over-stressed - you need to consider steel.
The joists spanning on to it would be OK.

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