Ceiling joist sizes...

Ive just checked joist sizes and spans for no load ceilings and am sure this can't be right.
( I'm referring to www.salford.gov.uk/ceilings-and-flat-roofs.pdf )
97x50 on 600 centres = max span of 1890mm
Surely a 4x2 can span greater than that? I need 3.6m so according to this table I'm looking at using 170x50 on 600 centres to achieve this, is this right?
I'd hoped to use CLS and not sawn :-(
Tony
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If you read it again it states clear span between binders so your 100x50 nominal size timbers would be fine at 3.6 span between walls with a single binder spiked down the middle. This is assuming that it is a ceiling under a pitched roof and not a flat roof construction using the ceiling joists as any support for the roof
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message

Mike
Did see that but unfortunately I'm dropping an existing ceiling from 3.6m to 2.4 so I would be using an existing ceiling joist as support.
Tony
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I think I have missunderstood the idea of a binder. I shall investigate further...
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snip...
I've had another look and there are two tables. The first is entitled "MAXIMUM CLEAR SPAN OF CEILING JOISTS IN METRES" and states a maximum span of 1.89m for 97x50mm on 600m centres.
The second table is entitled "MAXIMUM CLEAR SPANS FOR CEILING BINDERS IN METRES" and shows the maximum binder span based on its dimensions and centres.
Appreciating that a binder ties the joists together and helps support them my problem is that the main ceiling area is 3.6m x 5.6m. The intention being that joists run across the 3.6m width on 600mm centres so any binders would be 5.6m long which in turn would need supporting!
Maybe I've just got the wrong end of the stick?
Tony
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Now I understand... duh!
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What is the problem here?
Is it that you want, or have to use 100 x 50 joists, or just a query on the span?
You can space them closer together, use SC4 timber, use a binder or double up a few to get this span if necessary.
Yes a 4 x 2 can span a greater width, but it will start to bow under self and imposed loads, which while may not fall down, would cause unacceptable cracks to the ceiling.
The spans in the approved documents are just a convenient reference. They include a good margin for safety, but if you could do the calculations then you may be able to prove that the 4x2 was good for a wider span.
dg

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On Sun, 7 Dec 2003 12:54:36 -0000, a particular chimpanzee named

The thing with ceiling joist sizes is that "ceilings" with a void over tend to be loaded almost as heavily as floors. They may have to withstand the weight of a water tank and a point load of 0.9kN (about the weight of a plump plumber). Not to mention all the old toys, books, LPs, etc that are no longer needed but can't be thrown out just in case.
The span tables are at www.odpm.gov.uk/stellent/groups/odpm_buildreg/documents/page/odpm_breg_600462.pdf. You may be able to downsize if you use C24 (SC4) timber at 400mm centres rather than SC3 (which is what I suspect the Salford table shows) at 600mm.
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Hugo Nebula
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