Any SE's help with joist strap detail. (Includes drawing).

[Watshot]

Part of my loft conversion has a joist span of just under 4m. The steels which will support the roof via the stud walls run at 90 degrees about mid way across the joists. The engineer has included a 'flexible galvanised strap' to give additional support to the joists at this mid point. See drawing below.

This looks like a jiffy type hanger to me but I could not find anything off the shelf to suit. So I placed an order with Simpson through my usual builders merchant based on the drawing. Unfortunately they supplied restraint straps that had been bent and twisted to suit, although they were twisted above floor level and cut too short so I have rejected them (which they have accepted as their mistake).

So can anyone confirm from the drawing before they have another go, whether this is a jiffy/joist hanger type design, or are they right to use restraint strap material?

The clues I am using are (besides the look of the drawing itself) that the detail specifies nailing, wheras restraint strap would be screwed due to it's extra thickness; the detail says "wound under joist", this would be too hard with thicker material (although impossible either way as the ceilings are in the way! What's that about?).

I assumed that this would be obvious stuff for the manufacturer, surely this is a fairly common application in loft conversions? All the dimensions are on the drawing.

Only other thing is they seemed very expensive, but I thought for bespoke items, low volume, I'd take it on the chin. They are now offering the first lot at half price if I can use them, but to be honest I just think they are all wrong, my plasterboard has to sit flush against these and they are too thick. I am worried that they will try and recoup some of their loss on the new (correct) version. I have seen the cost of this type of metalwork from various outlets for off the shelf items, but I was charged over £9 a piece before vat etc, for 46 pieces.

Can anyone confirm what they should be making and maybe a ballpark figure?

I will ring my engineer if necessary but he has retired and 5 years have passed.......so this is easier.

In case it's not clear, the load is just for the floor, the steel takes the roof load.

Greatful for any help, as always.

Untitled

• Watshot
• 25 Sep 2010
• 2

 

[^woody^]

Those are normal speedy long leg hangers

The problem with using straps to make them is one of bending them precisely and nice and square to hold the joist properly.

 

[Watshot]

Thanks for replying Woody.

So what I'm actually looking at then is a pair of long leg hangers, one on either side of the steel? Would they overlap across the top plate and try to nail through matching sets of holes, or would you aim to finish halfway, butted up together? Is that enough 50mm across the top? I'm guessing you would normally only use one so get 100mm across the top.

Bit of a bugger as the joists are in already, but you would have thought that Simpson Strong Tie and the builders merchant would have been able to correctly identify a standard fitment like this. And a lot cheaper too.

My overall depth there is about 400mm, joist width 50mm. Should I be buying 450x50? Can't see any longer ones at the moment.

Many thanks.

 

[geraint]

Thanks for replying Woody.

So what I'm actually looking at then is a pair of long leg hangers, one on either side of the steel? Would they overlap across the top plate and try to nail through matching sets of holes, or would you aim to finish halfway, butted up together? Is that enough 50mm across the top? I'm guessing you would normally only use one so get 100mm across the top.

Bit of a b*****r as the joists are in already, but you would have thought that Simpson Strong Tie and the builders merchant would have been able to correctly identify a standard fitment like this. And a lot cheaper too.

My overall depth there is about 400mm, joist width 50mm. Should I be buying 450x50? Can't see any longer ones at the moment.


if icould read it it would help

Many thanks.

 

[geraint]

Those are normal speedy long leg hangers

The problem with using straps to make them is one of bending them precisely and nice and square to hold the joist properly.

so why are the straps below the timbers....

 

[Watshot]

if icould read it it would help

Maybe it's a trait like doctors handwriting.....

The relevant text by the red lines reads:

Flexible galvanised straps wound under joists and nailed through packers + top plate of beam

I guess the straps are below the timbers if they are speedy hangers like Woody says.

 

[^woody^]

so why are the straps below the timbers....

Because that's what joist hangers do?

 

[noseall]

so why are the straps below the timbers....

Because that's what joist hangers do?

I think Grrrrraint is what is known as a troll and that you should not trust advice given over an Internet forum (no kidding Sherlock) and that we should all stop posting immediately for fear that someone may use the advice and do summat daft.

 

[Watshot]

so why are the straps below the timbers....

Because that's what joist hangers do?

I think Grrrrraint is what is known as a troll and that you should not trust advice given over an Internet forum (no kidding Sherlock) and that we should all stop posting immediately for fear that someone may use the advice and do summat daft.

Point taken, don't want to encourage any more falling out, seen it all before.

So can anyone confirm that they are two speedy hangers back to back? Would they overlap at the top? Seems a bit overkill for less than 2m each way. But makes more sense than the rubbish Simpson's came back with.

Noseall? Woody? Always value your input......cheers guys.

 

[^woody^]

The only reason I can see for having a hanger each side of the beam is for even loading with no potential for twisting of the beam, but having said that its not clear whether this potential would apply in this case

But the drawing seems to be misleading. It shows the original ceiling joists below the new ones, and it shows those hangers going down below the existing ceiling joists (and plasterboard!) - but he has drawn it wrong as it implies that the hangers are fixed to the new joists but extend further down past them to support the existing joists too

The doddery old engineer must have done this at 4:55 on the Friday when he retired, so he could get away on time

 

[Static]

Looks more like a couple of ms galv 30x5 twisted straps each side of the beam to resist torsion in the beam or reduce the joists effective length, rather than support the joists.. could be wrong tho the image is pretty poor quality..
Course could always be a belt and braces attempt at uplift resistance.. if the roof isnt strapped down elsewhere.. actually the more i look at it the more likely i see this as the reason..

Theres a 3mm thick strap that can be bent on site..

 

[Watshot]

Well I've just bought 92 long leg jiffy hangers (450mm) so they should just about meet across the top. Whether it's support or lift or whatever I hope that should suffice. Saved a fortune as well.

Building control passed the drawings/detail so I don't know what they are expecting. If I ask them they always refer you back to the engineer, makes you wonder if they know what they are looking for when they do inspect.

I spoke to the engineer's son who works at the practise who confirmed hangers or banding was adequate, but wasn't really familiar with my job.

Thanks to all, I shall plod on...