Can you cut 20mm PIR into spacers to maintain void between 50mm PIR & shed wall?

[aguyinbath]

I'm insulating my shed to use as office. It's quite thick and sturdy, like a log cabin in construction. I'm planning to attached 70mm deep (finished size) stud frame to wall, fit 50mm cellotex (leaving 20mm air gap behind it), then tape and plasterboard. Battens seem to be either 19mm or 25mm (not 20mm) and wood seems to have tolerance so it might be out by 20% anyway. As the battens are just to space the 50mm PIR and maintain void behind - would it be ok to use 20mm PIR cut into small squares and glued to the corner of each void (60mm centres)? That seems cheaper, easy to cut and a reliable depth. What am I missing?

Thanks!

 

[phatboy]

Just bang a line of nails in (Stainless if you wish), and push the insulation against them. Quick and easy.