Metal joists??

[daddyfreddy]

I'm reconstructing some stairs over 2 floors and need to provide support for them as well as provide support for a section of the landings. To go the traditional route would involve wooden joists and brick wall supports. The major draw back being the waste of space and also lack of light in an already very dark house. Full size wooden joists would also seriously restrict the head height between uppper landing and the first stretch of stairs.

Rather than use this is there an alternative metal frame which can be custom fabricated or bolted together and save the hassle? I'm sure there must be something from the commercial side of building which has gone into residential construction. Anyone know or can suggest a company. Or at least suggest where I could get metal floor joists that would be half the height of traditional wooden ones.

Thanks!

[Rick]

I guess you would need an engineer to design/size the frame so building regs don't complain, then you can look up "steel fabricators" in Yell.

All the comercial floors I have seen use small joists, but thick heavy RSJ's at frequent intervals, but then again all the ones I have seen are in warehouses and hold up tonnes of stuff.

a 127x76 RSJ will take a 24.8 Kn load (2.48 metric tonnes) evenly distributed on a 4.0 m span.

From the tables I have you need to get to a 305x102 RSJ to span 6m, unless you have an engineer to some extra checks.

Now some "watch outs", - all steel has to be boxed in in fireproofing, normally plasterboard. - You will need to rest eash steel on a 7N block, or something similar, the engineer will work out what exactly uou need.

- Steel is hard to work with, I got a 7m 254x102 on my roof, but it took me days of jacking it up 3 inches at a time to do it.

You may also find that an engineer can solve your problem in a way you have not thought of.

Rick

[daddyfreddy]

Thanks, Rick. Seems I'm going to have grab a structural engineer somewhere!

[Christian McArdle]

I'm considering such a solution for my loft conversion. Some points I've found:

1. Steel itself really isn't particularly expensive. It may be several times the cost of wood, but wood is so cheap anyway.
2. Fire proofing is the main concern. The metal framework needs to be protected against fire. It should be supplied with a fire resistant coating (which you must specify as an optional extra). This coating then needs to be repaired after installation.
3. Finding someone willing to design and install the system will be difficult.
4. Obtaining the steel is very easy. Find a local steel stockholder, who will happily supply any section in any length with a few days notice.
5. The steel can be very, very thin compared to wood. (I think a 90mm SHS would be enough to span 4m for a habitable room).
6. Steel bends much less than wood. The steel design is limited by deformation after a few mm in the middle, whilst the wood design is limited simply by keeping the bend down to an acceptable level to prevent cracks and a spongy feeling, which is usually about 10 times the bend allowed in the steel.

Christian.

[Mike]

One point to consider with steel though is that BCOs don't have the same 'feel' for it as wood so you may have to provide more detailed calculations whereas for wood they can usually look at it and agree that it's strong enough.

[Rick]

I think you find the regs contain more tables for working out the size of wood you need, than they do for steel. The BCO simply has ro remember the tables, or have a handy sheet sheet in his car.

[Christian McArdle]

The regs no longer contain the tables. They just refer to tables published elsewhere (probably costing several hundred pounds to purchase).

On the plus side for steel, it is actually quite difficult to make a floor that isn't strong enough unless you're being silly.

Christian.

[Tony Bryer]

[Christian McArdle]

more expensive than having them in the regs, though, available free of charge.

Christian.