How long fire protection around internal steel RSJ

[paulandfrodo]

I have had a look in Part B Volume 1 and cannot see the answer, it could be that I'm in a fuss and not looking hard enough.

I have cased a 152x89x16UB on THREE sides with 12.5mm Gyproc Fireline. Well, the steel is actually encased in 25mm ply ( for some other reasons ) and then the fireline is clad onto that.

The steel is spanning 2m on an internal wall.

I suppose the issue lays around should is be providing 30 or 60 mins protection. Gyproc's documents say this provides 30mins protections ( White Paper - section C02.S03.P05 ). With
another 2.5mm making it upto 60mins.

Would the addition of the 25mm ply help - I've emailed Gyproc's tech department to see if that reveals anything.

Any comments ( within reason ) would be appreciated.

 

[Notch7]

structural steel needs 60 min protection for buildings under 18 metre high.

I think you might be right that 15mm fireline plasterboard is needed.

im not sure if 12.5 will be enough -although I have a feeling thats what Ive done in the past -I vaguely remember its 2 layers of normal or 1 of fireline.

I have read 12.5mm fireline needs a 2nd layer of normal 12.5mm tacked over.

mechanical fixings are required as well -adhesive is not accepted.

 

[paulandfrodo]

If it's 60 mins, then you are right, the white paper shows 15mm thickness. I just was not sure if it was 60 or 30 mins.

I can still do additional mechanical fixings over.

I suppose my only potential get-out would be that it supports the floor upstairs and a timber wall above that! It's in an old victorian property and the floor joists above are 3" by 6" or 7". I'll measure up and look at my span tables to see if that floor would actually stay up if the wall was not present !

Might just be easier to crack another layer on, well, if I can get hold of any - this virus thing is making ordering more, err,

 

[Mr Chibs]

I was told either 15mm fireproof or two 12.5mm layers of plaster board.

 

[^woody^]

30 minutes for domestic. The 25mm ply and 12.5mm P/B and skim will be adequate.

 

[paulandfrodo]

Hey woody. I normally use an independent inspector, however this time I've used a local one.

Historically I have always done 12.5mm fireboard and things have been signed off.

So I am slightly confused as to his insistence or how to deal with it. Whilst we could put another layer on, it will screw up some other dimensions in the room we have. As you can see, we lined the steel before building our stud under to ensure full protection.

How would you suggest we progress this ? Anything easy I can read in Part B that I can wave at him ? Or even better a layman's interpretation ?

Pic's attached so you can see what's been done.

 

[^woody^]

12.5mm standard plasterboard and 3mm skim will give 30 minutes protection, the issue is the joints - which in theory could allow heat though. Thist tends to be concept behind double boarding - to cover the joints, and not necessarily to give thicker cover. But as long as there is something substantial behind the joints to protect from heat entering then it should be fine.

Some manufacturers show a strip of plasterboard or something like thin Supalux to back up the joint, but others show timber behind all joints, so this should be fine too.

The fire protection of the steel is 30 minutes just like that of the ceiling and floor it is holding up. So logically, if you consider the ceiling, that will have 12.5mm board and skim and joints beneath a joist just the same, so if that's acceptable then the same thing .... the same protection in the same way should be acceptable for a steel beam.

The issue with your 25mm ply, is that it will rely on some common sense from the inspector to acknowledge that it is substantial enough to cover a 0.5mm joint for 30 minutes. If he can't get his head around that, perhaps suggest that you will add a bead of intumescent mastic to every joint too.

I don't know if I still have any guides, as its such a common acceptable thing that it does not crop up nowadays. I'll have a quick look, but I don't think I have. You may hae to rely on reasoning with the inspector on what the actual problem is.

 

[paulandfrodo]

Thanks woody, I've approached the inspector with suggested solutions.

I've also said that if I have to, I will just crack on and double board everything. I will grumble and scuff my feet. I will just plan all future steels with this provisio. or, perhaps more grown up, get a verbal ok before I do it. Which, at the moment is hard.

I can see if I used the suggested Gyproc Clips it would have satisfied the requirements, but not timber. I have also emailed Gyproc's Tech team for comment.

Sometimes when dealing with building or planning inspectors you need to agree that, at worst you will follow the strict letter of the law and then, when they see willing they will sometimes allow a little mercy.

Let's see if reasoning and common sense prevail.

I shall now get on with my challenge of getting some door linings. Bought everything I thought I needed for a full refurb before lock down... Forgot the bloody door linings... Kitchen, Bathroom, Plasterboard, Plaster, Steel, Timber... Check... Door lining... Nop !

 

[paulandfrodo]

Got the reply from BC.

I'll put some intumescent on the joins and he's asked we put the skim on to 5mm rather than 3mm. Seeing the he also knows the plaster, who also lives on the same street as the job he's happy he will do that right.

Thanks woody, good course of action. Appreciated.