Fire barriers required behind cladding.

[Big Jimbo]

Just a heads up. I'm planning on building in Block and Block rendered on the external bottom half, and clad in Hardi plank on the top half.  Now the medium density blocks are not flamable, and neither is the cladding. However, the cladding will be mounted on timber battens and will therefore have a ventilated cavity behind it.  My understanding of the current building regs is that i am going to have to have a fire stop in this cavity.  Because the cavity has to remain open, i am going to have to get something like Tenmat FF102/50.  For me to put a band around the bottom of the cladding, and a band around the top, i'm  going to need about 150m of the stuff It's blinking £25 a meter ! That's about £3750.......Yikes, that is going to be painfull on the budget.

Can anybody tell me i dont need it ?

As a second question. Do i now need to close off the top of my cavity ? I'm having a cold roof, and have read that moist air in the cavity can rise into the roof, and cause damp/condensation.Is this the case even though i am having a full fill cavity ?

Thanks for all your help as usual.

[Temp]

Google found..

 

https://www.labcwarranty.co.uk/technical-blog/cavity-barriers-behind-decorative-cladding

 

 

Quote

 

Therefore, to satisfy Building Regulations there should be cavity barriers installed in the cavity formed behind a ‘decorative cladding’ (such as timber boarding, hung slates or tiles etc. or any other finish) which is constructed onto the outside of an external wall masonry wall.  

 

This will include concealed spaces behind cladding on detached houses as well as semi-detached and apartments/flats.

 

 

I have a small area of vertical hung tiles on battens so my house built in 2007 would no longer comply.

 

[Temp]

1 hour ago, Big Jimbo said:

i am going to have to get something like Tenmat FF102/50.  For me to put a band around the bottom of the cladding, and a band around the top

 

And something similar where the cladding has a window in it?

[eandg]

Treated 2*2s wrapped in DPC around your windows. 

 

Envirograf does the same but for about two-thirds of the cost of Tenmat. 

[Big Jimbo]

Thanks @eandg i will check that out.

[Big Jimbo]

Anybody got any idea if i will have to close off the top of my masonary, full fill cavity wall, before it enters the cold roof ? I would have liked to have ran the insulation through to join up with the loft insulation.

[markharro]

I have just managed to persuade our BCO that cavity barriers pointless and not needed behind our open timber cladding for what it is worth. We are in Scotland.

[TonyT]

Have a look at the technical standards for cavity closers and speak to your local building control.

 

I would see more cold bridging if the cavity insulation didn’t extend into the roof void