Fixing Internal Insulation

[PeterW]

I've got a question on the addition of IWI to an existing structure.

 

We have an existing building that is remaining, and I've discovered that the cavity is insulated (unusual for a double garage !) and therefore the plan to add blown bead to the cavity has now gone out of the window.

 

So I have 65mm cavity that appears full filled with fibre so we will need to add 70mm of PIR to the inside rather than the 50mm we were expecting. That now adds a question as to how to achieve this..?

 

I had considered using a 50mm layer which is secured back with low expansion foam and then 50x25mm battens screwed to the wall to mechanically secure it, filling the 25mm gap with a second layer of PIR between the battens. This allows me to also include a service void if needed in the 25mm insulation layer.

 

Have I missed a better way that doesn't need battens and lots of ling fixings...??

[Nickfromwales]

If you just foam or dab EPS onto the wall you'll be surprised at how well it adheres and how rigid it goes. Just done the attic pine end ( stone ) walls this way and it's rock solid. I then foamed / dabbed PB straight on top of the EPS and skimmed. 

Fixing anything to the wall is a pita but I overcame that with BFO concrete screws ( 43" tv on tight with no movement ). 

Dont underestimate just how well EPS bonds without mechanical fixing, but I dabbed the shit out of mine so next to no voids . 

Whack one on and see for yourself.   

These are all 30mm EPS PB's stuck with dab and foamed all around. They're going nowhere. 

 

[bassanclan]

To meet building regs I'm pretty sure the insulation needs mechanical fixings, the fear/theory being that a fire would melt the foam fixing causing 8'x4' sheets of molten insulation falling over, which would otherwise stay in position if mechanically fixed.

 

[Crofter]

I fixed my IWI using big plastic insulation washers- £12 per hundred off Amazon.

I was originally just going to use the battens to hold the insulation in place, but I've fitted a separate VCB over the insulation so the washers hold the insulation in place whilst I am getting the battens finished.

 

Tbh on a masonry construction dot/dab would probably work, I was fixing to studs though.

[ADLIan]

+1 on mech fixings & fire issue when using D&D/foam. See plasterboard manufacturers instructions.