Home-made Insulated Plasterboard (less than HALF PRICE)

[John D v2.0]

If it's a low volume item then it will always have a premium, but then you're getting a manufactured item with a known quality standard so for builders there's an advantage of less chance of needing expensive labour to rework the situation later.
For DIY it's often better to do the labour yourself and take your time.
You need mechanical fixings even for the manufactured one as far as I know, so once it's up it's up anyway!

I would avoid polystyrene if it's a wall with sockets or switches on it as it's a pain to add conduit or similar to protect the PVC.

 

[mrrusty]

With 62.5 PIR insulated PB under £50 ex I couldn't be bothered trying to make my own - all that glueing, lining up. keeping flat while it dried. The bought stuff goes up quickly like lego. Depends how you value your time. https://www.cwberry.com/xtratherm-thermal-laminate-board-2400mm-x-1200mm

 

[robinbanks]

Depends how you value your time

Indeed, and a DIYer with more time than money may well opt for that-saving a tenner a board, how many boards an hour could you make?

 

[DaveFix]

The thought of gluing baking foil to a wall with generous overlaps, then covering with PIR board which has been cut so that the joints are staggered with the joints of the plasterboard being placed on top. Sounds like it could be more moisture and thermally efficient than the manufactured boards.

 

[Mr Chibs]

Perhaps you could melt bones down to make the glue too.

 

[robinbanks]

Not sure about the baking foil bit; Tyvek and others make aluminised vapour impermeable aluminised felts for that purpose. Google Tyvek AirGuard