ligthing in rsj cavity

[pbarrett]

has anyone done this,

got a customer who wants a t8 batten in one with a sandblasted glass cover, will be double boarded inside it then fitting and wiring on to then blasted cover to conceal, but will it need venting for heat etc, any opinions gratefull, can show drawings too

 

[Knobhead]

A lot depends on the size of the RSJ, I've done the same in the past but the RSJ's 12" deep.

 

[pbarrett]

its a massive steel I beam, supporting 3 upper floors, around 12-14" deep

 

[Richard Burns]

The manufacturers instructions normally state minimum clearances from surrounding surfaces (10 to 50mm) but with that size RSJ I think you would be fine.

 

[imago]

The calculations could be done to prove it for certain, but I would think an RSJ of that size would act as a huge heatsink so wouldn't be an issue.

You have the fire protection for the RSJ covered with double boarding, but you can single board it if you use fireboard instead. That'd give you a little more depth to work with. BC here only require single thickness boarding on RSJ's now as that gives half hour protection, but as fireboard is only maginally dearer it's belt and braces and customers often appreciate the thought.

 

[Knobhead]

Why are you boarding the JSJ web? What is the board going to protect? It's a light fitting not a oxy-propane cutting torch!
The web will be 15mm thick solid steel!

 

[imago]

Because the building regs require it.

Part B Volume 1 4.2
"Elements of structure such as structural frames, beams, columns, load bearing walls (internal and external) floor structures and gallery structures should have at least the fire resistance given in Appendix A, Table A1." This relates to the tests in BS476-21.

If you cut through all the "blah, blah" there needs to be sufficient fire protection to prevent a steel support (RSJ) reaching 550 deg c within half an hour. There are a number of way to do this, sprays, coatings etc etc. |The cheapest and easiest is to 'wrap' the beam in 12.5mm plasterboard which is deemed to have fire break through resistance of 30 minutes.

 

[Knobhead]

Madness!

 

[imago]

Madness!

No arguement from me. Can you imagine that state of the rest of a building if the RSJ's had reached 550 degrees? Still, I suppose it means the demolition company can 'recycle' the steel more easily.

 

[Knobhead]

Makes me wonder how the steelwork around this ever held together!
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