Fire protection

[A_Novice]

Hi guys,

Quick and easy. For a timber frame first floor we need 6mm fire resistant board like Supalux to provide 30 mins protection.

Does this board just go on the outside or does it also need to provide internal protection as well so used on the inside also?

Our design at the moment looks like this.

12.5mm plasterboard
25mm insulation board
150 x 47 studs with 90mm insulation between studs
9mm osb
6mm fire resistant board
Breather membrane
Battens
Tiles

Anything wrong with any of that?



Thanks

 

[^woody^]

The idea is to protect from external fire spread - this must be close to or on a boundary? The plasterboard provides the internal protection.

I'd put the fire board on after the membrane, and ensure its a breathable board, I'm not sure if Supalux is. Or use the fire board as the sheathing instead of OSB and membrane

Any why are you specifying a 150mm frame and only using 90mm of insulation? That air void is a risk. You can use a 89mm CLS for that insulation, or 150 Rockwool for a 150 frame.

 

[A_Novice]

Thank you Woody.

Yes it is within 1m of the boundary unfortunately

The building notes I have specify 90mm celotex between the 150 studs.

The builder starts in two weeks but I have found quite a few inconsistencies with the drawings and the building notes and also what the building inspector advises.

E.g. drawings show 100mm studs for external timber, notes say 150mm. Building inspector approved the plans but later told me it must be 150mm studs and will tell the plan checkers to be more thorough next time.

Building regs say CELOTEXFR for external walls. Building inspector says no it doesn't have to be after I told him it doesn't exist anymore.

It all seems very wooly.

I trust the builder I have chosen but can't help but feel nervous about all this.

 

[Notch7]

6mm fire resistant board like Supalux

Thats seems expensive at close to £100 / sheet.

 

[A_Novice]

Thats seems expensive at close to £100 / sheet.

Have read enviroboards are a cheaper alternative. No idea how true that is though.

 

[John D v2.0]

edit: half hour protection from each side of the wall is alright, although after grenfell, you'd have thought they would tighten up the regs on that!

 

[A_Novice]

half hour fire protection isn't enough for an external wall within 1m of a boundary, when I looked it up it was more like triple boarding on either side of the timber frame.

Can you provide a link?

Who regulates private building inspectors?

 

[John D v2.0]

Can you provide a link?

Who regulates private building inspectors?

ah you replied while I was looking it up, when I found it, the current regs do indeed say 30 minutes each side as long as window sizes are basically kept down, max 1m2. Perhaps the triple boarding was from a party wall. Anyway just disregard my comment!

 

[A_Novice]

ah you replied while I was looking it up, when I found it, the current regs do indeed say 30 minutes each side as long as window sizes are basically kept down, max 1m2. Perhaps the triple boarding was from a party wall. Anyway just disregard my comment!

No probs. What provides the fire resistance on the inside? Or does one board like 6mm supalux provide enough.

Just reread Woody's post and yes plasterboard from the inside

 

[John D v2.0]

inside would be plasterboard plus skim. You would only have to look closely at any windows and doors you fitted in that elevation.

 

[Leofric]

A vapour barrier on the warm side of the insulation is required and counterbattens under the horizontal battens . I would get whoever drew the plans to pull all this together now and co ordinate the drawings and building construction notes to Building Control's satisfaction before you start work on site.

 

[A_Novice]

Thanks. Going to chase up the architect today.

Having read a few bits over the weekend and taking on board the comments here what would be wrong with this.

12.5mm plasterboard (foiled backed and taped to provide VCL)
150 x 47 studs with 150mm rockwool insulation between studs
fire resistant board (replacing OSB)
Breather membrane
Battens
Tiles

This way saves having the 25mm insulation boards and also combines the sheathing and fire resistant board into one.

Does it provide enough insulation?

Obviously there are a number of ways to do this.
Read more: https://www.diynot.com/diy/threads/fire-protection.521660/#ixzz5ltoujUkx

 

[^woody^]

Why isn't your designer doing all this instead of you having to alter the design?

 

[A_Novice]

All sorted I hope.

Building control are happy with

Tiles
Battens
Membrane
Fire resistant board
OSB
150 studs with 100mm insulation
25mm insulation backed plasterboard taped at joints

The builder and architect are happy with this. I did ask BC about not having OSB and just using the fire board as the sheathing but he wouldn't allow it as it is too brittle. (no doubt there is a product that combines the two)

I also mentioned about the 50mm of cavity between the studs. All 3 said a small air gap is needed.

I thought there were a few ways to skin this but it seems there are hundreds ha ha.

 

[^woody^]

So, it seems you have a building inspector who is actually qualified in timber frame design and condensation risk analysis, and a designer who is not. I don't know if your builder should be happy or worried.