Best practice for installing Cellox insulation boards

[markf]

I need to place Cellox insulation between the joists of my flat roof. 120mm depth has been specified, but as Cellox does not come in this thickness I am making it up with two layers of 60mm.

Now as I understand it these sheets come foil covered on one side? If this is the case is there any sort of recommendation as to which way the foil faces (into the house or into the roof) for each sheet?

Thanks

 

[JerryD]

All the cellotex I've ever used has foil on both sides. Make sure you are using the right cellotex, they make dozens of different types, all for different purposes.

One point about your insulation, it is good practice to use 70mm between the joists and then 25mm under the joists (covering the joist timbers). This stops cold bridging from the timbers as this can cause marking on the inner decoration after a while. It's probably regs to do it like this as it's always specified like this on drawings we get.

 

[Jasonb]

Jerry D's method also creates an airspace which will stop the buildup of moisture on the underside of the roof deck if you have not got enough joist depth.

Jason