Jump to content

Best way to hang posi joists into different materials


Vijay

Recommended Posts

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

 

 

Link to comment
Share on other sites

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
Link to comment
Share on other sites

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!

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

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
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...