Which joists for new build Posi vs I joist?

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Are any of these joists preferred over the other for different situations in a new build.
Posi - Metal webbing, I joist the solid chipboard type.

Looking to build a 2 storey detached home with MVHR using semi rigid or galvanised ducting (Not spec'd yet) along with the usual services.

What's the pro's and cons over each other?
Is either one better for preventing sound from TV or music travelling to rooms below or next to?
Best for securing pipes or cables to prevent future creaks and noises?

Interested to hear opinions from anyone who have used these.
 
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There is no difference to the end user. Except higher cost.

Advantage to the designer is longer spans for smaller depths.

Advantage to the builder is lighter weight for lifting. That's it.
 
I thought the pozi joists were meant to be miles better for acoustic? Might have got that totally wrong tho
 
I'll be doing a lot of the installation work myself or with friends in trades, it's nice to have whatever is easiest but as installation is a one time event, I'd rather choose the strongest or the best for sound and acoustics. At a glance, if both are the same strength, the metal webbing webbing Posi joists look 10 x easier to run pipes and services through with no holes to drill. The only thing I can imagine maybe causing an issue, the space between webbing is fixed and might be less than the largest hole you can drill in an I beam.

I think I'm looking at 250mm deep but not had a final design yet.
 
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Cost-wise they're both expensive. Can't remember the hole-drilling rules for the JJ I beams but I don't think they were generous so if you're using hot air ducts the Posi joists would be easier. Of course easier still is to design your vent terminals and ducting runs so they run parallel to the joists.....unless you've got some massive spans traditional timber will give you much better price performance, if you have got massive spans then consider some midspan steels and smaller section joists (though midspan steels would give you issues with services unless you utilise the false ceiling sketch below)

Acoustically you'll get far better performance by separating the ceiling from the floor (so false ceilings not connected to the floors above). Pipes don't creak if the system has been properly designed and installed.
 
Except an absolute boon in time saving for the plumbers and electricians. Positively orgasmic if the mad homeowner is going the whole hog with home security, home cinema, disco lighting and automation.
Not really that much of a boon considering it's a new house when access will be easy and the designer should be sorting out the services layout, and smart home infrastructure in accordance with Part R and current guidance.
 
My plumber and sparks disagree. Access is always easy when installing new joists Woods - what's your point there?
They are old fashioned. Upgrade them to Plumber 2.0 and Sparks 1.5.

The point is, the modern way is to have service ducts and accessibility. Not just running stuff wherever it's easiest. And how long does it take to drink or notch a joist anyway. It's a new build don't forget, with a free reign with access and layout.
 
the modern way is to have service ducts and accessibility.
Nonsense. Accessibility is another moot point. Anywhere where there are new joists being fitted - there is unlimited access to those spaces.

The argument here is about the benefits of hollow web joists verses solid web. To dismiss the benefits of hollow web in preference of 'service ducts' is creating a time consuming problem that is already solved. You need to get with it Woods.
 
Cost-wise they're both expensive. Can't remember the hole-drilling rules for the JJ I beams but I don't think they were generous so if you're using hot air ducts the Posi joists would be easier. Of course easier still is to design your vent terminals and ducting runs so they run parallel to the joists.....unless you've got some massive spans traditional timber will give you much better price performance, if you have got massive spans then consider some midspan steels and smaller section joists (though midspan steels would give you issues with services unless you utilise the false ceiling sketch below)

Acoustically you'll get far better performance by separating the ceiling from the floor (so false ceilings not connected to the floors above). Pipes don't creak if the system has been properly designed and installed.

Looking at an estimate I received for Posi joists, they came in at £3600 inc VAT. The MVHR ducting shouldn't need passed through any joists because they all drop vertically down from the loft space and others run parallel to the joists. I'm not sure I can have standard joists as some of my spans are to span a 5m wide room and a 4.8m room. Quite a few people are saying 400mm centres are also better than 600mm on wider spans to stop them moving as much and for plaster boarding needing lots of noggins.

Do building regs now require a wall plate bolted around the perimeter of a room then the joists attached via metal joists hangers?
 
I built them in last time but heard a while ago that they had stopped letting you build them into the inner leaf and you now have to support them via joist hangers.

I'll get a price for 9 x 3's and see how they compare, The £3600 Posi joist quote says it's for 600mm centres but they vary throughout when i looked at the floor plan 450 to 580. Having read up on res bar for attaching plasterboards to help reduce sound transfer, I think Posi will be better for acoustics than the I joists. Just need to check strength comparison. There has to be a reason the local company offers both.
 
I built them in last time but heard a while ago that they had stopped letting you build them into the inner leaf and you now have to support them via joist hangers.
That's not mandatory - you are allowed to build them in, which is better structurally. The slight downside is that you can get air leakage to the cavity resulting in heat loss, but to my mind that should not take precedence over structural stability.
 

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