Is my Timber Frame as Fire Resistant as it could be?

[Triassic]

This left me wondering,  what is current best practice when constructing a Timber Framed house, with regard to the Fire Resistance?

 

1 hour ago, Dudda said:

If it's timber frame you really should be using 15mm and have to by law in Ireland. See attached guidance note recently issued to all architects in Ireland in relation to fire safety in timber frame houses.

BCMS Information Note 1-2018 Guidance on Timber Frame Walls.pdf

 

edit to clarify: published by the Building Standards, Department of Housing, Planning and Local Government in Ireland. Not relevant to building regulations in the UK but it would be good practice to follow the best guidelines in relation to fire.
 

 

Edited October 5, 2018 by Triassic

[Jeremy Harris]

We used 12.5mm with a 3mm plaster skim, but building control were happy with just 12.5mm plasterboard.  A lot depends on the insulation used, I think.  We have blown-in cellulose, behind a 12mm vapour-tight board, and that's almost non-flammable.  I tested some of the cellulose and it's very reluctant to burn, even in the open, it tends to just char and only keep burning when a flame is pointed at it. 

 

Supposedly, when packed into the frame, there isn't enough air available to maintain combustion, at least during the early stages of a fire.  Coupled with the 30 minute protection of the plasterboard and the fact that we have no combustion devices in the house, I suspect that the fire risk is pretty low, and really only in the kitchen.  If the price of the retrofit kitchen fire suppressing mist systems comes down I might look at fitting one.

[Triassic]

It was this bit of the document that caught my eye ..

 

"In constructions where the internal plasterboard slabs are not fixed directly to the timber frame stud, i.e. where insulation is fitted on the face of the stud, then the construction is not in compliance with I.S. 440:2009 Timber Frame Construction, Dwellings and Other Buildings and cannot be assumed as having a given fire resistance.   "

 

My bolding

 

In my build, I have an internal service void, as do many other people.

[Jeremy Harris]

I believe they are referring to insulation directly behind the plasterboard, which might well cause the plasterboard to heat up far more quickly and fail, when compared with plasterboard fitted to a timber frame stud with a void.  We have a service void, but the counter battens are 50 x 50 and fitted to the timber frame, and the timber frame has a 12mm thick vapour-tight board, so I would guess that would meet or exceed the 30 minute fire resistance time.  Not sure about internal stud walls, though, as although the plasterboard is screwed directly to the studs, there is dense insulation packed in them to reduce noise transmission.

[dpmiller]

Fig 1 in the document has a layer of PIR over the studs and is agreed?

[lizzie]

omg.....remember my hairdryer escapade, that still gives me nightmares!

[Dudda]

2 hours ago, JSHarris said:

We used 12.5mm with a 3mm plaster skim, but building control were happy with just 12.5mm plasterboard.  A lot depends on the insulation used, I think.  We have blown-in cellulose, behind a 12mm vapour-tight board, and that's almost non-flammable.  I tested some of the cellulose and it's very reluctant to burn, even in the open, it tends to just char and only keep burning when a flame is pointed at it. 

 

Supposedly, when packed into the frame, there isn't enough air available to maintain combustion, at least during the early stages of a fire.  Coupled with the 30 minute protection of the plasterboard and the fact that we have no combustion devices in the house, I suspect that the fire risk is pretty low, and really only in the kitchen.  If the price of the retrofit kitchen fire suppressing mist systems comes down I might look at fitting one. 

That build up would not now be allowed in Ireland.

 

Just to clarify. Insulated plasterboard slabs (where insulation is fixed to the back of plasterboard in a factory) are not allowed anywhere in timber frame houses.

 

The plasterboard has to be 15mm (12.5mm isn't good enough) and has to continue around all reveals. It has to be mechanically fixed and it doesn't matter what the insulation is. You can see in fig 2 it's wool (which is natural and non flammable) and fig 3 it's PIR which is flammable.

 

These are new guidelines. In Ireland we don't have building inspectors like the UK and the architect has to sign off on the project. I've signed off on several houses in the past with only 12.5mm plasterboard in timber frame houses but won't with these new guidelines.

[Jeremy Harris]

What's the difference between taped and filled 15mm plasterboard and 3mm plaster skimmed 12.5mm plasterboard?  Both have ~15mm of gypsum plaster, so I'm struggling to see why there is a problem, but I'll try and see if I can find any fire test data later. 

 

If I had to make a guess, I'd say that a plaster skim possibly provides better fire protection than taped and filled boards, but that is just a guess, based on the fact that I believe that the critical factors are the heat capacity of the plasterboard, the thermal conductivity and the effectiveness with which it provides a flame seal for the 30 minutes resistance that's required.

[Dudda]

23 minutes ago, JSHarris said:

What's the difference between taped and filled 15mm plasterboard and 3mm plaster skimmed 12.5mm plasterboard?  Both have ~15mm of gypsum plaster, so I'm struggling to see why there is a problem, but I'll try and see if I can find any fire test data later. 

 

If I had to make a guess, I'd say that a plaster skim possibly provides better fire protection than taped and filled boards, but that is just a guess, based on the fact that I believe that the critical factors are the heat capacity of the plasterboard, the thermal conductivity and the effectiveness with which it provides a flame seal for the 30 minutes resistance that's required.

In Ireland during the ceitic tiger we had a lot of poor quality built houses which are informing a lot of new regulations. You can get a factory certified 15mm plasterboard slab to perform. Its of a high quality produced in a controlled environment. If it's 12.5mm plasterboard and 3mm skim applied on site then who's going to certify that? How can you verify with certainty that it's 3mm and not 1mm everywhere? How can you be sure it was mixed correctly, the water wasn't contaminated or that the plasterboard surface was clean and dry before it was plastered? Yes you can get good plasterers and I'm sure yours were but we all know a lot of cowboy plasterers are around. Remember your house was a self build one off. In a large estate with 100 timber frame houses it's hard to oversee everything.

 

It's all about quality and accountability.... or in reality who you can sue if something goes wrong.