Suspended ceiling

[lyledunn]

I have a standard exposed grid 600x600 suspended ceiling below floor joists in a doctors surgery. The floor joists have no further protection and are exposed when you lift out a ceiling tile. They are 250x50 at 450mm centres with flooring grade chipboard over. The floor is really a roof space accessed via a trap door and loft ladders and is used for file storage. We have been asked to provide a staircase access. The only place to put the stairs results in travel distance being around 27m.
So this is a small single storey building and as I understand it we will need 60 min fire protection for the floor. The FRA has determined a current tolerable risk. L2 FA system in place.
We are not making the situation any worse than it currently is other than by perhaps increasing traffic flow to the floor by providing better access.
I can't see the ceiling grid providing the necessary 60 mins. Is there any way that this can be checked or can it be easily converted?

[kurnal]

Just for clarification is this in NI?

[lyledunn]

Yes, does that matter very much Kurnal?

[kurnal]

It is only of relevance in respect of the technical guidance to be applied but not specifically related to tests on ceiling tiles.

[wee brian]

In England, that would be building work and you would need building control approval.

[kurnal]

Is there any manufacturers information? Are the tiles clipped in place or just resting in the grid?

[Fishy]

A standard grid-type suspended ceiling will provide no appreciable contribution to fire resistance and there is no way you could practicably upgrade it to provide 60 (or even 30) minutes fire resistance.  If you really need 60 then a properly-specified ceiling would need to be installed (more likely you would remove it, fix an appropriate number of layers of plasterboard to the joists and re-install or replace - or make the new ceiling the finished surface).

[lyledunn]

We do our best to meet the requirements of 9999 which in turn helps demonstrate compliance with building regulations. We have noted recently that BC often give way to mitigating factors rather than insist on strict adherence to approved guidance. Not sure if this is a good thing for simple buildings as it tends to lead to a degree of inconsistency which is not always helpful to project managers like ourselves. So for example, in this simple case,  I am very confident that the appropriate requirements of neither 9999 or our Technical Booklet E are being met and would normally consider fire protecting the exposed joists. However, on previous jobs BC have allowed such a situation and allowed extended travel distance on the basis that a L2 system was installed. This is why I often turn to the expertease apparent on this forum, so I guess there is always an upside!

[col10]

Take a look at BRE Digest 208 for ways to upgrade from above, if you have L2, then what credibility does 60m have? why not 30m? but also speak to a structural engineer because you may be overloading the existing floor with all these files.

[kurnal]

Lyle you hit the nail on the head. A well considered and presented fire strategy document in cases such as the one you describe will often win the day and relaxations described within it accepted by the BCO or AI. This sort of work was my bread and butter before retirement. If however the inconsistency that inevitably arises is unhelpful then a fully code compliant solution is the reliable choice.
Remember the Building Regulations are solely to protect the H&S of persons in and around the building. Even an unprotected chipboard floor will offer some protection to occupiers, though not to firefighters. The old Building Regs 1976 gave some useful advice on this.  Additional detection may well make up the difference to ensure occupiers are able to evacuate safely and accepted response times and travel speeds, e.g. As suggested in the SFPE manual or even BS9999 may help. But always consider also access for firefighting on the mezzanine and potential for rescue below it.

In respect of your initial query ADB 3 gives some practical guidance in respect of the use of suspended ceilings as a component of a compartment floor.

[lyledunn]

Can you help me with interpretation of Table A3 in ADB3?  If I am reading it right it seems to indicate that providing SOF characteristics are met, the existing suspended ceiling in my case, if deemed to be W, X, Y or Z can contribute to 60min fire protection?

[Davo]

lyle

any pipes, wiring etc in the void?
If so, sparkies etc cannot be relied upon to re-clip the tiles.

Some excellent points listed!

davo

[lyledunn]

That's true Davo. In fact there are ASDs throughout the void formed by the ceiling. There is also a number of building services items that would need access for inspection and maintenance. It would be a hell of a job to provide fire resistance from below.  Perhaps it might be reasonable to suggest that the suspended ceiling will give some fire resistance to a floor that will be accessed by only one or two people on an infrequent basis and that the L2 system is at least some mitigation.

[wee brian]

Fire resisting suspended ceilings are a special system. Not in common use these days because of the maintenance issues.

You cant just plop different tiles in.

If it was me, I'd fix plasterboard or other system to the underside of the joists (in accordance with manufacturers spec). then put the false ceiling back again.

or you can blag you way out of having fire resistance but I don't think I'd be comfortable with that.

[kurnal]

You do need to know what you have got - one clue is that if the original tiles were not clipped in place then it is most unlikely to have been designed as a fire rated ceiling.

The other thing you might consider is whether the floor could be described as a raised storage area as described in B3?