Wood joist spacing

[oemodm]

Hello everyone,

I'm an amateur builder. We have an outbuilding which I'd like to build a floating level for a little office space. Is it ok to build like this:

Could get some RSJ's but they are a hassle to get, handle, install. Wood's much easier. Span on 75 x 225 is around 5m

thanks / simon

 

[noseall]

A bit confused?

Are you looking at the floor joist supports or the joists themselves?

I doubt that you will find a timber deep enough to support an entire floor at that span. Steel would be more practical.

You floor joists (63mm x 175mm) may be ok though at 400mm c/c.

 

[RonnyRaygun]

Yeah, you won't get a standard size timber section to span 5m with that load on it.

A couple of steels would be the sensible option. You might get a couple of engineered joists that would be strong enough...
Or if possible put another post underneath and reduce the span.

The 63 x 175s would be OK though

 

[paulc2]

Read and thoroughly digest!

http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_2013.pdf

in particular, Section 2B.

 

[paulc2]

PS somewhere on the internet I found a table giving the various standard joist sizes and the appropriate max span for each, but I can't find it. I'll keep Googling a little to see if I can chance upon it again. (The building regs refer to the British Standards and equivalent, which are not freely available online).

 

[Alastairreid]

http://www.howarth-timber.co.uk/downloads/trada-span-tables-title-pages.pdf

 

[tony1851]

His floor joists are probably OK (assuming normal domestic-level loading). But he needs guidance on the main 5m - long support beams, and that won't be found in any of the usual tables.

As advised, timber would be impractical here, so steel would be required. For that he would need calcs from an SE.

 

[oemodm]

how utterly stupid of me.

If steel we're to be used (6m span), what cross section would be needed? (I or C section). This floating level is just for 3 or 4 people to be up there at any one time.

Perhaps I should pay an engineer to calculate this.

 

[noseall]

This floating level is just for 3 or 4 people to be up there at any one time.

What, in an empty room?

 

[oemodm]

This should be ok:

63 x 175's should be ok on 400 to 450 spacing http://www.jrpcad.co.uk/Pages/Timber_Span_Tables.aspx

although I would prefer this:

What do you guys think?

thanks again / simon

 

[noseall]

Surely those columns makes the room below rather unusable?

 

[oemodm]

room below will have 3 desks on each wall. will disguise the centre columns as a book case in the middle.

 

[noseall]

So, basically you are going to build a sleeper wall beneath in order to halve the span.

Sounds ok.

You may need to sheathe the wall in 18mm ply for stiffening.

 

[oemodm]

would the sleeper wall need a vertical support for each floor joist (10), or could get away with using 4 or 5 (as per last image).

 

[paulc2]

I think you need to firstly know the imposed load you're going to put on the floor. Then decide if you need/want an open span area underneath the floor of 5m+, or whether a wall there is going to be okay. Then do the necessary calculations to see what material, size and spacing works out most cost effective.

AIUI this construction will need to be inspected by building control? And they'll want to see detail calculations on how you arrived at the materials used?