Posi joist spans

[flanagaj]

Can anyone advise here regarding how they would arrange the joists for the below floor plan.  Would you simply lay n joists across the 6.4m span across the whole length of the house?

We are using sleeper walls, so could also have the joists orientated across the sleeper walls, this would mean that the widest span would be the width of the kitchen at 5.7m.   But if you do that, I assume that you will need to add batten to the top or the bottom of the joists to ensure that the finished floor level and also the ceiling levels are the same?

I did ask our technical architect who is doing the drawings whether we will have a steel and he replied

"I haven’t designed any steels or structural elements.  The structural engineer will do this. Do you have an engineer in mind?"

Which did concern me a little.

I just had a quick look and a steel spanning 5.7m will be 300mm deep, where as a Posi Joist is only 254mm (600mm centres) or 219mm (400m centres)  we are already quite restricted on height and a 300mm steel would eat into this height and also make any duct / pipe routing slightly trickier and require a bit more though.  That being said, bouncy floors is definitely something that I would rather avoid.

[ToughButterCup]

2 minutes ago, flanagaj said:

...
"I haven’t designed any steels or structural elements.  The structural engineer will do this. Do you have an engineer in mind?"

Which did concern me a little.

 

Don't be. - concerned that is. Its normal.

Get your preferred supplier to provide a design for both the steel and the POSIs.

[ProDave]

Run joists end to end of the house, supported on sleeper walls aligning with each of the internal walls.

 

Repeat for upstairs (so internal walls made structural) with stair hole.

 

Your widest span will be the kitchen / diner, the joist supplier will size them for that span.

 

I am surprised at the posi joist sizes you quoted. My longest span id 5M and my joists are 300mm deep.  The narrow joists you quote won't leave much room for 110mm waste pipes for instance.

[JohnMo]

Either your structural engineer, you must have one?, or the structural engineer of the posi joist supplier/manufacturer should be supplying full set of drawings with all supporting calcs, These should be reviewed and approved by your structural engineer.

 

What I like about the Scottish system, is you cannot get to this point, no structural design drawings, no building warrant, no warrant, no build.

[saveasteading]

If you go on the James Jones website there is an interactive joist span table.

 

You have a wide span and must accept deep joists. 

 

From it you can see different joist specs at different centres.

At some stage they can end up so close together with such wide flanges that it is nearly a solid floor.

 

Or use a steel, and hang the joists in the same zone.

[Nickfromwales]

1 hour ago, flanagaj said:

Can anyone advise here regarding how they would arrange the joists for the below floor plan.  Would you simply lay n joists across the 6.4m span across the whole length of the house?

We are using sleeper walls, so could also have the joists orientated across the sleeper walls, this would mean that the widest span would be the width of the kitchen at 5.7m.   But if you do that, I assume that you will need to add batten to the top or the bottom of the joists to ensure that the finished floor level and also the ceiling levels are the same?

I did ask our technical architect who is doing the drawings whether we will have a steel and he replied

"I haven’t designed any steels or structural elements.  The structural engineer will do this. Do you have an engineer in mind?"

Which did concern me a little.

I just had a quick look and a steel spanning 5.7m will be 300mm deep, where as a Posi Joist is only 254mm (600mm centres) or 219mm (400m centres)  we are already quite restricted on height and a 300mm steel would eat into this height and also make any duct / pipe routing slightly trickier and require a bit more though.  That being said, bouncy floors is definitely something that I would rather avoid.

You can have the steels modified before installation, to create holes and/or letterboxes for MVHR and small bore services to go through.

 

You can do a surprising amount of this, as a good SE will specify welded plating to fortify if needed, to put the strength back in. 
 

You can also strategise how the steel is installed, eg by having a 100x100mm or even just a 75x75mm box section post somewhere alone it’s span, going down through a GF wall to founds, you can further expand your options for chopping into the steel.

 

Plenty of options here, if you get a professional who finds solutions vs problems. 

[Stratman]

@flanagaj I used this online calculator to size psijoists roughly before getting the TF engineer to specify exactly: https://www.mitek.co.uk/span-calculator/span-calculator-uk/ 

 

If you are having MVHR then Total Homes specify an absolute minimum open web joist of 254mm to get 150 dia. rigid ducts through. 

 

[Mr Punter]

If you have MVHR ducting, bear in mind that to feed in the ducts one end of the run must be clear of walls, so they sometimes need to be fed in before the walls progress.  Strongboys and steels can get in the way as well, as can solid timber beams and flitch beams.

[Nickfromwales]

2 hours ago, Stratman said:

If you are having MVHR then Total Homes specify an absolute minimum open web joist of 254mm to get 150 dia. rigid ducts through. 

Which is a bit daft tbh. I wouldn’t entertain building my house to take a service duct, a good M&E designer / consultant should work the system designs to suit what was cost effective and practical to build. Also, if you’ve gone turnkey then a lot of floor and roof sections will be delivered as cassettes, so that’s out the window completely then. 

 

The radial installs I always go with only need semi-rigid at 92mm or less, and zero need to sequence installing long lengths of spiral galv ducts in at the construction phase.
 

That also doesn’t allow for any alterations on the fly.

 

The other issue with large bore galv systems is the need for multiples of satellite anti cross-talk and acoustic attenuators which have to live in areas you’ll never get to ever again.

 

The valves closer to the unit usually need choking, closing them up, to allow the ones furthest away to get the flow they need (balancing) so that can make the closets ones quite notable, acoustically.

 

Not a ‘fan’, lol. 

[flanagaj]

4 hours ago, ProDave said:

I am surprised at the posi joist sizes you quoted. My longest span id 5M and my joists are 300mm deep.  The narrow joists you quote won't leave much room for 110mm waste pipes for instance.

I pulled the sizes from this page.

Specifier - Wolf System Easi Joists