Digmixfill

Posi joists are trying to fit in with the surroundings by not being straight or square

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I have had mine sat loose in their hangers for a little while. This evening I've been measuring and cutting noggings for under the restraint straps and to my surprise the joists are anything but straight. I'd expect this kind of mayhem from timber joists, but engineered? One of the joists is trying for a corkscrew. Another is bowing upwards in the centre by a few mm. I don't think any of them have parallel sides (mostly this is because of lazy construction by the supplier)

 

Those of you who have fitted posi-joists, how have you found them when in situ? Wonderfully straight and true, or all over the shop?

 

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Normally pretty straight 

 I joists also 

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Everything has been stored inside, as instructed with the paperwork that came with the posis. They were trimmed, dropped in the hangers and left for a little while.

I didn't check the second room to see if they are behaving the same. I'll check tomorrow and take some pictures if I remember.

 

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Some of mine were a bit bowed, some a bit curved - I sent a few back to be re pressed as metal fixings were not all the way in.

 

 

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A pozi joist, truss, spine beam etc if supported on its bottom cord without restraint at the top will move and twist a bit. Nothing to worry about as the noggins will (should) put everything back straight.

We soon found out that pozi joist packs need to be left banded or stacked flat if not being fitted straight away or the packs would decide to fall over if left unrestrained as the joists moved and twisted.

Edited by markc

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Slightly more reassuring to hear that it's not just my set of posis that are cattywompous.

Is there a general rule of thumb for nogging placement when trying to straighten joists out? Start at either side of the room and work in, start in the centre and work out, etc?

 

Some of the fixings on my posis where not as affixed as I expected. When I questioned them with the maker, their production manager said they were ok and that it's really difficult to get things perfect on their machine. 😮

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 production manager said they were ok and that it's really difficult to get things perfect on their machine. Omg? the struts are either pressed in by a giant hydraulic G Clamp that swings around on a balanced beam, or they are tacked in place with a hammer and then the joist run through a big roller that squeezes them in.

I would aim to start in the middle, use temporary braces to get the middle straight and held in place, then work outwards. Ideally, leave the braces in until you have to remove them to lay the floor.

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46 minutes ago, Digmixfill said:

....

their production manager said they were ok and that it's really difficult to get things perfect on their machine. 

...

 

What did you both understand by perfect?

 

Wood is,  well, wood. It moves.  That's why I think that @nod uses metal frames. 

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11 minutes ago, ToughButterCup said:

 

What did you both understand by perfect?

 

Wood is,  well, wood. It moves.  That's why I think that @nod uses metal frames. 

Reasonably straight with a struts accurately positioned and squeezed in tight to form good connections. i took it that some of the struts were either not positioned correctly or pressed home.

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1 hour ago, ToughButterCup said:

What did you both understand by perfect?

I sent over pictures and simply asked if the fixings were ok. His reply was that it's really difficult to get things perfect on their machine. My understanding there was that he thought they weren't perfect.

 

Here are pictures showing the upward bow in joist 3. Joist 2 in these pictures is the corkscrew. I've numbered the joists in the pictures to indicate when I switched direction.

bow.1.thumb.jpg.64ee7dd153e183d45e2324c73657eb18.jpg

 

bow.2.thumb.jpg.119b97b92389e89f78f7046793c318f8.jpg

 

bow.3.thumb.jpg.2fac16f68fe65d6962e73f847414b4a8.jpg

 

Some pictures of the fixings shortly.

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I cant see anything wrong with them, as mentioned previously they are wood and wood moves. Once the noggins and floor are fixed it will all act as one unit instead of individual components.

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Here are a few examples of what I consider imperfections. The camera doesn't show them to be as stark as the eye.

 

 

chamfered.edge.missing.fixing.teeth.jpg

fixing.not.pressed.fully.home.2.jpg

fixing.not.pressed.fully.home.jpg

skewed.wood.fixing.not.pressed.fully.home.jpg

web.mashed.into.chord.buckling.edge.jpg

web.not.pressed.fully.home.jpg

wood.missing.edge.jpg

wood.not.square.metting.chord.jpg

wood.proud.pushing.out.fixing.2.jpg

wood.proud.pushing.out.fixing.3.jpg

wood.proud.pushing.out.fixing.4.jpg

wood.proud.pushing.out.fixing.jpg

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They don't look great.  I have never really thought about joist quality varying by manufacturer.  Is this Mitek?  Could you ask them to confirm that they are to standard?

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@Digmixfill that strongback hasn’t been correctly installed and nailed to all the joists by the looks of it - that needs resolving and then you need the floor noggins (use Z Clips) and then the boards glued and screwed.
 

Then decide how much deviation you have in the floor as it will be negligible. 

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2 hours ago, PeterW said:

that strongback hasn’t been correctly installed and nailed to all the joists by the looks of it

 

The strongback isn't nailed to anything at the moment.

I'm running noggings wall to wall at 1/3rd span. Then I'll add the end chord restraints with zclips. After that i'm going to place noggings in the lower chords to fix any joist twist. Finally I'll nail the strongback in place. Overkill I know.

 

Caberdek, screw and glue after that.

 

4 hours ago, Mr Punter said:

Is this Mitek?  Could you ask them to confirm that they are to standard?

 

Yes Mitek. Long before I ordered the posis I asked Mitek what their tolerances were. An engineer replied back to say +/- 1mm for length. Most of the posis here arrived as parallelograms, way out of tolerance. At the masonry end they are fixed with Simpson FMS straps, so even if Mitek offered to replace them all it would be a pain to remove them.

 

 

parallelogram.jpg

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8 hours ago, Digmixfill said:

Long before I ordered the posis I asked Mitek what their tolerances were. An engineer replied back to say +/- 1mm for length


The tolerance on a block is +/-6mm so why are you stressing about this ..?? Get the strong back in properly then do edge noggins and get the floor down and I reckon you will be +/-2mm across the floor. 

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12 hours ago, PeterW said:

why are you stressing about this ..??

I'm not stressing about this. I've squared them up, sorted for best match to length required and they're in place.

The individual chord lengths were within the +/- 1mm length, but top and bottom chord on some were offset by > 5mm.

 

Do you think it unreasonable for me to expect a joist to have at least on square end?

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