Shallow depth joists?

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rossyl

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Hi

I am aware that joist depth depends on span, as well as, thickness of joist.

I have a low ceiling that I'd like to increase the height of. Before going to a structural engineer, I'd appreciate a rough idea of what I can achieve, by removing it all, moving the joists up, and replace the joists. However, joist depth will have an impact on that.

Happy to use Metal Open Web Joists, I-beam Joists or normal timber joists.

From what I've read, nearly all joists no matter type are at minimum 200mm deep.

Is that correct, or, can you get shallower depth joists?

As an FYI, the area is approx 3m x 4.5m.

Thanks
 
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Floor-joist depth can start as small as 100mm if you only had a short span.

The size of joist required depends on the span, spacing and grade of timber.

Open-web and pozi joists will give you no advantage as they are usually used on longer spans and are therefore deeper.
 
Thanks. Approx 3.5 span, so I think (subject calcs) 75 x 147mm is the best I can get depth wise.

That sound about right?
 
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rossyl said:
Thanks.

I had hoped there was some "super slim" solution, closer to 100mm.

But, looks like I'm dreaming :)
Click to expand...

Actually, you might not be dreaming and could be on to something.

If you could get 100 x 100 C16 timbers and put them at 150 centres (ie only a 50mm gap between them!) it would actually work. The critical issue with timber floor joists is almost always deflection and, although unusually slim, a floor like this would still be within the specified limit for deflection.

Also, if you could firmly screw 18mm plywood down as a floor finish upstairs, with plenty of screws and some glue, that will also strengthen the floor.
 

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Thanks, that's interesting. The rooms above are a bathroom and also a "plant" room (boiler and invented cylinder). Might having such tightly fitted joists make it very difficult to plumb?
 
Oh...........
So not just a bedroom then?

cap floor.PNG
 
If there's a wall between the 2 rooms above and it runs the right way you could possibly hide a timber beam in it to split the span, otherwise you could split the span with a small steel if a 100mm one was up to the job.
 
tony1851 said:
The size of joist required depends on the span, spacing and grade of timber.
Click to expand...

Tony, would the maximum span size alter if the joists were for a loft floor? For example if the span was 4.0mtrs but you could never actually walk on 1.5mtrs of it due to a pitched roof?
 
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