Dear Estimable Folks,

We're on our third strawbale building at our place, a very small round house to be my therapy/writing hut....
since this doesn't have dwelling status, we're wondering about the pros and cons of filling our twin plinth wall which will support the bales with bubble wrap/plastic bottles and the like. Can't see why moisture should be any more of a problem than using some sort of polystyrene based material....Of course the ideal would be maxit/leca/hasopor but money is short and unwanted plastics more than plentiful....
Your responses would be most welcome.

Generally the essence of insulation is the prevention of the through flow of air or preventing convection currents, often both. So when insulating your void the plastic will need to prevent both of the above. The bubble wrap would work well providing it is packed tight enough to prevent any through flow and if it is packed that tight then convection would also be stopped. The plastic bottles pose more of a problem as it would be difficult to pack them tight enough to work. If the bubble wrap was used to pack around the bottles then this would help but care in packing would be needed.

Convection currents will set up in a gap larger than about 20mm so in theory there could be a convection current set up in a plastic bottle which would transfer any heat from the bottom of the bottle to the top where it could be transferred on to the next insulating element so if the bottle was vertical you would have heat transfer over say a 30cm distance by convection within the bottle.

I would suggest using plastic bottles laid carefully on their side with a layer of bubble wrap packed on top, and then another layer of bottles so filling the void with alternate layers of bottles and wrap. I would expect this to be vapour open given the air spaces between the bottles.

Better than nothing especially if you are using otherwise waste materials.

Thank you for your thoughts. I found this a few days ago which I found very inspiring. Yes, we used Leca for our house which helps to facilitate downward motion of any moisture. Not sure yet which way to go; it seems alot of unwelcome work to squash everything down. What about jiffy bags? Wonder if the paper on them is a problem?
https://www.scribd.com/document/140771227/Plastic-Waste-Insulation-Re-Use-PET

(I hope it's alright to paste the link....?)

interesting video...

https://www.youtube.com/watch?v=WxyTcFG0YH4

gg

Posted By: owlmanHow about filling the large e.g.(2Ltr) bottles with expanding foam, experiment with the amount, let set then trim excess and replace cap, then use horizontally, slope to the outside.

Err, what's the cost of doing that? And how to achieve a slope?

Hmmm...

But surely " a few cans of foam" would tend to negate the GREEN aspects of using spent plastic, non ?

gg

+1
Good point, DJH - my cans of foam provide 15 litres when expanded.
Cost = 7 Euros per can or say Six Pounds.

For slightly less than this price, I can get a board of 60 mm XPS dimensions 60 cm x 125 cm = 45 liters I think...

or three times as much...

gg

We also have a load of used celotex. Is this not a good idea inbetween two lime/flint/brick walls which will support the bales? What way shoud they be used for max moisture downward moving?