Vijay

Best way to hang posi joists into different materials

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Hi,

 

Head is a little done in with personal stuff at the moment, but I have to try and get my head around the best way to fit posi joists into different materials I have. I'm very keen to not have deflection/bounce, so the joists will be at 400 centres.

 

1. Into ICF. So I will be having a timber plate bolted into the ICF face/concrete core for the joists to fix to. Are there 2 options here - 1st is on hangers and the 2nd is on the top chord of the joist?

 

2. Into RSJ webs. Does the joist just simply sit into the RSJ web? I may have an option of changing the RSG for a posi joist, would that be better or worse?

 

3. Into load bearing 100mm block walls. Should I fix into the block work as it's built, or bolt a timber to the side of the blocks and fix the same as I would with the ICF walls?

 

Are all joist hangers made the same or do some makes fix better than others? I've also seen mention on a post about face fix and top fix hangers.

 

Any advice would be really appreciated :)

 

Cheers

 

Vijay

 

 

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Posted (edited)

Ask your joist designer for a maximum deflection of 12mm or 0.003 x span (whichever is least). That will resolve any bounce issues.

 

Actually just looked back at what we spec and it is the lesser of 8mm or span x 0.002, so a fair bit stiffer.

 

Timber plate attached to the wall is fine for 1.) and 3.) It is normally cheaper to top hang than use hangers. You will probably need blocking in between to stop twisting.

 

With 2.) you may be able to replace the steel with a glulam or posi which could make running services simpler.

 

Joist hangers are rated according to the loads and the floor designer should specify. Some are universal so can be faced fixed or wrapped over.

Edited by Mr Punter
Floor deflection limit wrong

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1 hour ago, Vijay said:

[...]

1. Into ICF. So I will be having a timber plate bolted into the ICF face/concrete core for the joists to fix to. Are there 2 options here - 1st is on hangers and the 2nd is on the top chord of the joist?

[...]

 

We have done both (into DURISOL) . I just followed the designer's instructions. Didn't have to think about it at all. 

Just make sure the dimensions sent to the designer are accurate to within 5mm or less.

 

Ask me how I know..... dare ya!

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5 hours ago, Mr Punter said:

Ask your joist designer for a maximum deflection of 12mm or 0.003 x span (whichever is least). That will resolve any bounce issues.

 

Timber plate attached to the wall is fine for 1.) and 3.) It is normally cheaper to top hang than use hangers. You will probably need blocking in between to stop twisting.

 

With 2.) you may be able to replace the steel with a glulam or posi which could make running services simpler.

 

Joist hangers are rated according to the loads and the floor designer should specify. Some are universal so can be faced fixed or wrapped over.

is that 12mm per certain span? 

 

I'm contacting a load of suppliers for the posi joists and finding a big difference in price, so that's why I asked if the hangers were made differently - as in are some better than others.

 

4 hours ago, recoveringacademic said:

 

We have done both (into DURISOL) . I just followed the designer's instructions. Didn't have to think about it at all. 

Just make sure the dimensions sent to the designer are accurate to within 5mm or less.

 

Ask me how I know..... dare ya!

 

Happy to do that, but is one way better than the other?

 

Wow, didn't realise they had to be that spot on lol I think I'm right in saying that they have ends that can be trimmed down?

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10 minutes ago, Vijay said:

is that 12mm per certain span? 

 

I'm contacting a load of suppliers for the posi joists and finding a big difference in price, so that's why I asked if the hangers were made differently - as in are some better than others.

 

Actually just looked back at what we spec and it is the lesser of 8mm or span x 0.002, so a fair bit stiffer.

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so 8mm of the overall span or per certain span?

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18 minutes ago, Vijay said:

so 8mm of the overall span or per certain span?

 

Overall

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When fixing joists to steel my builder insisted on filling in both sides of the web by shot nailing in some timber. Then used joist hangers with long tails. The tails were wrapped over the top of the steel and nailed into the timber infill on the back side. Where there were joists both sides they were staggered.

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5 hours ago, Vijay said:

think I'm right in saying that they have ends that can be trimmed down?

You can spec trimmable ends, and to varying amounts...i was able to take up to 100mm off each end of mine.

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Thanks guys :)

 

If a supplier offered a choice of hanging options, is there a proffered method or is it just do what's easiest for me?

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Seem to remember someone having problems in the past maybe on ebuild. It was to do with ledger plate and the joists not being tight which made them deflect more. Seem to remember @JSHarris giving advice?

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Top hanging would not require a joist hanger, so probably saving £2 -£4 per joist. 

Ive just had a box of 132 hangers turn up, it can add up. 

 

With the face fix hangers you do actually need to nail them on, which sounds simple and it is, but 132 hangers with 14 nails per hanger can take a while. 

Top hung you cut a spacer block and drop them on using the spacer to get the correct centres. Easy peasy. 

 

I think if it was me I would top hang onto all external walls, top hang on to all steels and use a built in masonry hanger into the block walls. 

If you download the Cullen timber hanger pdf it will show all the options. 

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I'm with Russell on this one; top hung, nailed. But get a quote for both designs, then you'll be able to make an informed decision. 

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Posted (edited)

Not sure how top hung will work too well with Polarwall ICF though, as I will be replacing part/all of and ICF panel with timber plank for a fixing plate, so I would have to notch out a space for the top chord to sit onto or add another timber plate onto the timber plank (that's replaced the ICF panel) and the joist sits onto that

Edited by Vijay

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40 minutes ago, Vijay said:

Not sure how top hung will work too well with Polarwall ICF though, as I will be replacing part/all of and ICF panel with timber plank for a fixing plate, so I would have to notch out a space for the top chord to sit onto or add another timber plate onto the timber plank (that's replaced the ICF panel) and the joist sits onto that

 

I have done this with Polarwall. We just fixed coach screws like these https://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-10-x-75mm-50-pack/9897g into the back of the timber plate at 400 ctrs so it is locked into the concrete. You could add another timber to the front if you want to hang the joists from the top flange, but joist hangers may work out cheaper.

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cheers :)

 

I'll contact the suppliers to look at what options they suggest :)

 

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05C0DEF8-EA2A-4517-8647-14F7F9D7BFA7.thumb.jpeg.6ebff65f5e26e1537f28c741e04cccef.jpeg

would it be easier to face fit the pole plate, instead of replacing the actual icf

the pic is for a roof but would be very similar except for more bolts and different spacing for a floor. 

If you remove the icf and replace with timber, do you not loose an insulation layer. 

@Vijay

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My inner leaf of ICF is 100mm, so I would need to get a good fixing through the timer plate, through the 100mm polystyrene and then into the concrete. My worry is the polystyrene could let the fixing bend downwards with weight.

 

I did mention losing the insulation to polarwall, but I intend to fit insulation back into between the joists (against the timber plate), so I'll only really be losing insulation where the joists sit against the timber plate

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Ours was less than 100mm insulation - it may have been 50mm.  Below ground we stuck an extra 100mm on the outside and we only did ICF for the basement with the rest in timber frame.  Here it is with the timber plate. It worked well with this brand of ICF as it fitted into the profiles just like the polystyrene.

 

P1040737.thumb.JPG.72b7e2550fbd69ba47026d5434932bfb.JPG

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A picture speaks a 1000 words :) That's exactly what I was trying to explain. Yes that's 50mm boards as it's the same as the rails

 

I'm so jealous of basements ;)

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@Vijay

all Icf are different obviously, but on a few of the makes I looked at that was not how it was done. 

I will try and find a vid after dinner to show you what I did. 

Worked a treat. 

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that polar wall method looks spot on with your system 

but if you fancy the rim board sitting on the face of the wall, look at the vid. This is what I did and it was straight forward. 

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Cheer bud. I saw that video in another post but think I prefer the normal Polarwall method. I think insulation wise, I lose exactly the same which ever way I go

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been in contact with a few suppliers and I've been quite shocked at the deflection's quoted. One told me 18 is normal and another has told me on my drawing, the max was 22mm with an average of 12-15mm. That's with 304mm joists at 400 centres. 

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What is the flange width they specified 

i had my i joists for my roof upgraded from 69mm to 96 mm as I asked for the deflection to be virtually eliminated. 

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