After a slight cock up (not mine thankfully) we have one external wall that will have to be narrower than the rest (long story...)

Original proposal from outside was: render, 100mm block, 240mm EPS blown bead, 100mm block, plaster.

For this one wall it will have to be narrower, so builder is suggesting: render, 100mm block, 115mm Kingspan K106, 100mm light weight block, plaster.

 

From Kingspan brochure:

 

Both are around about 0.13 W/mK. Just wondering if there are any clever ideas for alternatives that result in the same or better u value and no thicker? 

 

 

 

For me,that system requires such attention to detail & supervision during the install that you don’t actually achieve the u-value they claim. Think about a bricky on the scaffold cutting those sheets at a tray damp detail,or around a lintol,or even just up to a cavity closer on a reveal. Trust me,there’ll be gaps galore. 
 

You could upgrade to the silver/graphite? blown in beads to get a better u value

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For me,that system requires such attention to detail & supervision during the install that you don’t actually achieve the u-value they claim. Think about a bricky on the scaffold cutting those sheets at a tray damp detail,or around a lintol,or even just up to a cavity closer on a reveal. Trust me,there’ll be gaps galore. 

 

Yes indeed, that was a large factor in the decision to go with the blown bead.

 

 

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You could upgrade to the silver/graphite? blown in beads to get a better u value

 

Already using silver...

What about insulated plasterboard? Basically another 50mm of PIR, and reduces any cold ridges through the cavity.