Fixing POSIs to a wall plate (rim joist)

[ToughButterCup]

Reading this thread and all the dire warnings written there sent me scurrying off into Tinternet to look and see what I can find.

Well, the only method of fixing them I haven't found was by using bubblegum.

 

There's oodles of guidance and I have read a good deal of it. MiTek say that the fixing method rests with the designer.

So I had a little phone chat with two or three companies and they all said that 'we' could discuss how I wanted them to be fixed.

And anyone who knows me, knows that that is going to be a one-sided conversation.

 

So, come on BH, help me out here. help make me sound as if I know just a leeeetle  bit about metal web joists rather than sound more of a complete plonker than I already am.

 

I know what to avoid: floor bounce - because of @readiescards 's thread (thanks)

• not installing them back to front (PeterW here ) [What the Hell is back to front on a POSI fgs?]
• make sure the trimmer is correctly seated (Jamie same thread)
• make sure the chords of the joists (flange, web ?) are wide enough (Peter Stark same thread)
• use 400 centers (already knew that - by accident)
• make sure the bottom chord is supported correctly (PetereW same thread)
• AlexPHD (same thread ) tightly pack between the bottom chord and the wall (what with Alex?)
• Peter Starks are hung from the top chord on a ledger plate (Whassat fgs ?) and he uses a strong back  (should I consider one?)
• PeterW's helpfully annotated image of where the problem lies (same thread)
• @JSHarris seems to argue against hangers (same thread)
• Try pre-cambering a little bit ( @JSHarris same thread)
• @CC45 has strengthened his POSIs (same thread)

That's a good start....

 

Do people use hangers because they are easy, and becuase they are easy to use, they don't pay attention to detail (present company excepted)?

 

My spec is for the POSIs to be hung on a wall plate (rim joist) Knowing all of the above, how would you make sure the problem didn't occur in the first place?

 

[Alexphd1]

First off who ever is designing your joists make sure they are designing for minimum bounce and not just a floor to pass building regs. 

We just shaved down wood for packers between bottom chord and timber rim board. 

I am not a fan of joist hangers, I see them as just another place for movement but they do make the job slightly more easy. 

Edited July 24, 2018 by Alexphd1

[joe90]

Our floor was designed for 600mm spacings but we put them at 400mm as both my builder and I hate floor bounce. We used finnjoists buried in the walls so I am not familiar with pozi joists.

[Russell griffiths]

Off topic slightly but still relevant 

 

if you say your wall is a bit wibbly wobbly, I would do as much as I can to level it out before fitting your rim joist

 

 temporarily fit your rim joist, scribe all around it, remove rim joist, grind hack chip wall until rim joist sits nice and flush, a thin skim of render in the low spots, re fit rim joist

this will ensure better fitting of posi joists and you should be able to get them all the same length 

 

dont forget to air seal behind rim joist. 

[ToughButterCup]

17 minutes ago, Russell griffiths said:

Off topic slightly but still relevant 

if you say your wall is a bit wibbly wobbly, I would do as much as I can to level it out before fitting your rim joist

[...]

dont forget to air seal behind rim joist. 

 

Damn. You are right. Phhhhhhhhhhhh.  Damn.

[CC45]

I would put them at 400mm centres now - mate has done that and his floor is solid BUT if you use copper for plumbing you will find it a pain.

[nod]

3 hours ago, recoveringacademic said:

Reading this thread and all the dire warnings written there sent me scurrying off into Tinternet to look and see what I can find.

Well, the only method of fixing them I haven't found was by using bubblegum.

 

There's oodles of guidance and I have read a good deal of it. MiTek say that the fixing method rests with the designer.

So I had a little phone chat with two or three companies and they all said that 'we' could discuss how I wanted them to be fixed.

And anyone who knows me, knows that that is going to be a one-sided conversation.

 

So, come on BH, help me out here. help make me sound as if I know just a leeeetle  bit about metal web joists rather than sound more of a complete plonker than I already am.

 

I know what to avoid: floor bounce - because of @readiescards 's thread (thanks)

• not installing them back to front (PeterW here ) [What the Hell is back to front on a POSI fgs?]
• make sure the trimmer is correctly seated (Jamie same thread)
• make sure the chords of the joists (flange, web ?) are wide enough (Peter Stark same thread)
• use 400 centers (already knew that - by accident)
• make sure the bottom chord is supported correctly (PetereW same thread)
• AlexPHD (same thread ) tightly pack between the bottom chord and the wall (what with Alex?)
• Peter Starks are hung from the top chord on a ledger plate (Whassat fgs ?) and he uses a strong back  (should I consider one?)
• PeterW's helpfully annotated image of where the problem lies (same thread)
• @JSHarris seems to argue against hangers (same thread)
• Try pre-cambering a little bit ( @JSHarris same thread)
• @CC45 has strengthened his POSIs (same thread)

That's a good start....

 

Do people use hangers because they are easy, and becuase they are easy to use, they don't pay attention to detail (present company excepted)?

 

My spec is for the POSIs to be hung on a wall plate (rim joist) Knowing all of the above, how would you make sure the problem didn't occur in the first place?

 

Counter battening makes a massive difference An afternoons work and £100

[CC45]

@nod- like additional strongbacks - could be worth putting these in as joists get installed - if possible.  I've added extra screws to all my strongbacks and it did make a difference.

[ToughButterCup]

9 hours ago, CC45 said:

@nod- like additional strongbacks - could be worth putting these in as joists get installed - if possible.  I've added extra screws to all my strongbacks and it did make a difference.

 

Strongbacks: my design doesn't require them, and battening and counter battening hasn't been mentioned up to now.

Is this (are they) something I can choose to add?  - I'm thinking of my BR submission here.

[PeterW]

You can add strong backs if you want - pretty easy to do. 

[CC45]

They need to go in first I guess then you will need to slide the joists along unless the split  the distance in half and use two overlapping strong backs.  Not a lot of extra cost or time really.

[ToughButterCup]

Thanks to you all I'm feeling almost confident about fitting these POSIs.  Thanks very much everyone.

 

By the way: I often cite the facts, or techniques or options contained in posts made on BH . Most often I get 

 

" T'aint dun like vat rewn 'ere "

Tickety Boo, I say.

 

[HerbJ]

Review your floor joist locations and clash check against various penetrations and interfaces, such as

 

• MVHR ducts
• shower traps, especially if you have a wet room or low profile trays
• 110mm sewage piping
• etc

We had to move some joists, not much but  some at standard 400mm centres would have clashed ......... Even though I thought ahead and had the joist layout revised, I still had to check and check again, as the TF erectors didn't pay sufficient attention to this detail.

 

You;'re doing great! Keep going.....

[mvincentd]

...if youre not using the smaller flexi ducting for mvhr remember to put the rigid stuff in simultaneous to the posi's or you'll be cutting lots of very short lengths later on!