Joist hangers and steel beams...

[HammieUK]

I'm currently planning out a loft conversion, and I'm after some advice on how best to support the joists. My structural engineer has spec'd 152 x 152 x 30 UC beams for the floor, one of which runs through the middle of the room, these support 47 x 147 (regularised 50 x 150) joists, my problem is how ensure the joists will be proud of the steels so that it does not contact the flooring. I can think of 3 options:

- Fit larger 47 x 170 joists into the web of the beams (would require some notching and maybe structural calcs)

- Bolt timber into the web of the beam, use face fix hangers to support the joists, might require larger 47 x 170 joists to ensure the hangers can be fully nailed while still leaving the joists proud of the beams

- Bolt timber into the web of the beam, shot fire timber to the top of the beam, use jiffy hangers and 47 x 147 joists

Any advice on what's best? As always, I'd like to minimise cost and floor height. Thanks for any help

 

[noseall]

We usually have some holes drilled into the web then bolt timbers into the beam.

TIP: When fitting the joists you are sometimes better off temporarily fixing the joist to the web timber at the desired height with a couple of screws prior to fitting the hanger. Then fit the jiffy hanger after, thus securing the desired joist height position first rather than trying to get the hangers spot on.

 

[HammieUK]

Do you use face fix or jiffy/speedy hangers?

Thanks for the tip, it's one of those things that's probably really obvious once you've finished the job

 

[^woody^]

So your paid for an engineer, paid for the loft plans, had a floor designed that is not as deep as the beams within it , and to top it all no-one has bothered to design how it all goes together so you need to sort this out yourself?

You need to be asking for someone to do their job or give you a refund

You wont need any calcs if you upgrade the joist sizes

Any of your options will do, and will be just as good as each other

 

[HammieUK]

The structural engineer actually specified the jiffy hanger method, I was just considering other options, I wouldn't expect a structural engineer to go into every detail and dimension anyway. This is the kind of question that a builder would be more qualified to answer, since they've actually done this kind of thing before and understand the difficulties involved.

Calcs would only be needed if I had a particularly anal building inspector, since I'd have to notch it below the spec'd joist size.

 

[noseall]

Do you use face fix or jiffy/speedy hangers?

jiff-speed fellas.

 

[^woody^]

I wouldn't expect a structural engineer to go into every detail and dimension

Well you should

Part of designing a beam, is working out how the loads are going to be applied to the beam and transferred along it

Of course a builder may have some experience and preferred method, but it is for the designer to design the method and specify how it all goes together

Noses advice is sound though, but you need to confirm it with the designer and bco if you are altering the design

 

[HammieUK]

I disagree that they should be detailing everything, for example the joists hangers have been specified as 'jiffy/speedy hangers, of suitable size, grade and fixing to support 2kN sustained load'. They could have said 'use joist hangers model xxx nailed with xx twist nails xxmm long, fixed to timbers in steel webs xxmm by xxmm....etc', which would have been excessive detail and not what I would expect (or want).

Nothing wrong with challenging a design anyway, any changes would be confirmed bco and structural engineer first as you say.

 

[^woody^]

the joists hangers have been specified as 'jiffy/speedy hangers, of suitable size, grade and fixing to support 2kN sustained load'.

And that is my point, it is inadequate or just plain lazy specifying

How are you supposed to fix these hangers to a steel beam when the hangers are designed for timber fixing?

So in specifying these hangers then there must [presumably] be some timber involved to fix them to. So then that begs the question what size timber, where, and how is that fixed?

Do you put a bit of 25mm timber in the web an partially notch the joists or something thicker? Do you wedge it in for a friction fit or glue or bolt it. If bolts how many, and will they affect the web?

You either know what he may be thinking, or you end up guessing. But whatever, its a poor designer who does not bother with the detail that actually matters - ie how things are all fitted together

I see these drawings and 'specifications' daily, and all they do is pass on the thinking and the risk to the builder or others. And many times extra cost to the client too

In your case, by virtue of posting the question, then there must be some doubt. And doubt is not something which should never be present with construction drawing or design.

A client should have confidence that the designer has done his job, and that the design is the best and is the easiest or most economical, and that that such basic things are not left to chance or the guesswork of others