Fire Stop Locations for Timber frame with external cladding

[HanleeHouse]

Hi All, 

 

I'm about to start the external of my timber frame build which is a mix of Stone and render. Stone sections on 38mm battens, and render on 38mm cross battens. All then covered in 12mm cement board to apply the final finish. 

 

I've been racking my brain regarding the fire stops. I'm aware that the 38mm / 76mm timber around openings is sufficient. However, it's the horizontal fire stops that I'm questioning. I've seen some have used intumescent strips top and bottom of the cavity, others one strip between floors. 

Please could I ask what you have done on your builds? Also, do I need them on the single story side sections, or just the two story?

I've attached my elevations for reference. 

Many thanks appreciate your help. 

David 

PL-003 Proposed Elevations.pdf

[Great_scot_selfbuild]

@HanleeHouse did you ever get any resolution to this (from elsewhere) I'm just about to post on the same topic and was doing my due diligence of seeing what other threads had been started - very surprised to see so few threads on this topic. I like the design btw!

[Dunc]

I ended up just putting a proposal to my BCO and asking if they were happy.

They required horizontal fire stops (intumescent strips) between floors (though couldn't specify if this should be at ceiling plasterboard level, or at upper floor level), at the eaves, and above/below windows/doors

[Great_scot_selfbuild]

9 minutes ago, Dunc said:

I ended up just putting a proposal to my BCO and asking if they were happy.

They required horizontal fire stops (intumescent strips) between floors (though couldn't specify if this should be at ceiling plasterboard level, or at upper floor level), at the eaves, and above/below windows/doors

I could write you the response I'd get from my BCO:

It's for your Principal Designer to define where it goes, I just check it's where they say it needs to be.

 

(I'm assuming this is now the common approach to all BC questions?)

[Dunc]

I just said: This is my proposal for fire stopping. Are you happy?

They said "nearly" just don't forget the eaves.

simples.

[Great_scot_selfbuild]

Just now, Dunc said:

I just said: This is my proposal for fire stopping. Are you happy?

I like it. This matches my preference for always offering a solution to a design that I can make work, rather than someone else coming to me with an unworkable one.

 

Do you have any recommendation on product? I need it to fit behind the counter battens (I have a 25mm gap)

[saveasteading]

4 hours ago, Great_scot_selfbuild said:

any recommendation on product

It doesn't have to be fancy special stuff. It is stopping fire from spreading through a cavity so even wood will usually be suitable.

[trialuser]

1 hour ago, saveasteading said:

It doesn't have to be fancy special stuff. It is stopping fire from spreading through a cavity so even wood will usually be suitable.

? Unless the cavity also needs to be ventilated?

I had to use intumescent stuff, cant remember what it was but cost a fortune.

I could use wood fo vertically aligned stops.

[Great_scot_selfbuild]

7 hours ago, saveasteading said:

It doesn't have to be fancy special stuff. It is stopping fire from spreading through a cavity so even wood will usually be suitable.

@saveasteading this is helpful. I’d been so focussed on my arch tech’s previous reference to intumescent material I was overlooking this. However, as @trialuser says, the horizontal one will need to be ventilated.

[Nickfromwales]

42 minutes ago, Great_scot_selfbuild said:

@saveasteading this is helpful. I’d been so focussed on my arch tech’s previous reference to intumescent material I was overlooking this. However, as @trialuser says, the horizontal one will need to be ventilated.

Yup. No getting away from intumescent strips here I’m afraid. Wouldn’t pass muster with BCO but will also be in your b regs spec. 

[Dunc]

Timber for vertical.

CV strip was the least expensive intumescent that I found for horizontal.

Good service from lifeline fire protection who advised on which size product to use. 

[Big Jimbo]

I expect, but dont know, if the area behind the cladding will need to be ventilated, but i expect it will. So you will need to find something that leaves the gap free, usually 25mm, but expands to fill that gap in the event of a fire.

Also, my own thoughts are that any cladding on the outside, should be ventilated, at the top, and the bottom, together with gaps in any battens that allow airflow into areas, such as under windows etc.

Think of it as a roof that needs full ventilation. You could achieve full ventilation by using a cross batten system. Don't forget to mesh the top, and bottom to prevent, wasps, bees, mice etc, making a nice home behind your cladding. As for fire stops, in my opinion, don't be tempted to fully block the cavity, with fire socks, or you wont have any ventilation. I was pondering the same problem on a house that i didnt build in the end. Sorry, i could not find any products that would leave enough of the ventilation gap, and expand enough to close it, in the event of a fire.

[G and J]

We've had good service, price and fast delivery from envirogaf directly...you tell them the size of the cavity and they specify the cv size you need.

[Great_scot_selfbuild]

16 minutes ago, Big Jimbo said:

Don't forget to mesh the top

Yes, it'll need to be ventilated.

 

No matter how many times I mention that we need a mesh installed, this seems to be something that is actively ignored and it looks like I'm going to have to go and add this to the list of stuff I need to do myself!

 

(has anyone got any recommendations for mesh they've actually used? I'm sure I can find some, but no doubt some products will be easier to use and handle than others, so I'd like to hear some first-hand experience)

[Dunc]

I have plastic eaves vents to go ontop of the fascia board.

At cladding voids (bottom of the cladding, top & bottom of windows, verges, anywhere a mouse could think looks interesting) I'm using stainless steel woven mesh, 8 count. 150mm x15m rolls from Robinson Wire Cloth were the cheapest I could find, even with a surcharge for delivery to Scotland. Listed as "rodent mesh". Wear gloves, cut to size with tin snips, bend to shape by hand no problem, fix with button head stainless screws or just trap behind battens, as appropriate. I must have got through 150m of the stuff and I'm still not done.

 

You definitely need mesh!

How this partridge thought it would squeeze up a 50mm gap is beyond me....I shall be re-prioritizing getting the eves vents sorted 🙄

 

[Nestor]

1 hour ago, Great_scot_selfbuild said:

(has anyone got any recommendations for mesh they've actually used? I'm sure I can find some, but no doubt some products will be easier to use and handle than others, so I'd like to hear some first-hand experience)

I fixed this mesh at the top and bottom of the battens behind the Cedar cladding.

https://www.robinsonwirecloth.co.uk/online-shop/Soffit-insect-mesh-stainless-steel-30m-roll-p49612077

[saveasteading]

We had wasps somehow getting through a 2mm local gap between overlapping weatherboards. They then chewed the stud behind to make paper for a nest. 

So mesh needs to be very small. Someone will have studied this I hope.

Overlapping messages. That mesh looks fine.

Edited 5 hours ago by saveasteading
Overlapping messages

[Nestor]

6 minutes ago, saveasteading said:

We had wasps somehow getting through a 2mm local gap between overlapping weatherboards. They then chewed the stud behind to make paper for a nest. 

So mesh needs to be very small. Someone will have studied this I hope.

Overlapping messages. That mesh looks fine.

The mesh is fine, how effective it is, down to whoever fits it.

[G and J]

28 minutes ago, Dunc said:

150mm x15m rolls from Robinson Wire Cloth

Snap......is working well, again fast delivery good price

[Dunc]

Worrying on the wasps @saveasteading. The plastic eaves vents I have are about a 3-4mm gap. Given they're sold as eaves vents I'd rather hoped they were fit for purpose in keeping unwanted beasties out. Now feeling paranoid that they may not do the job! Having said that, round here I'm much more concerned about rodents and weasels which we know nest in the neigbours' lofts than insects: not much will keep out the midgies 🤣.

 

Problem is as the weave of the mesh reduces so does the air flow.

Edited 4 hours ago by Dunc