Guest post from Bob Cromer, one of our readers.
“Here is my idea on low cost insulation.
1) Take a 55 Gallon 6 mil garbage bag.
2) Fill the bag with sawdust, so that it is ~6″ thick when laying flat.
3) Use a thermal PVC welder and close the bag off, leaving roughly 3″ not sealed.
4) Make up a plastic pipe “T” that will accept a shop vac hose with a valve to stop the flow, a 6″-12″ straight piece of plastic pipe with a ladies stocking piece over the end, and a small diameter threaded hose running to a welding Argon tank.
5) Insert the stocking end into the almost sealed bag and evacuate the air from the bag, similar to a vacuum storage bag.
6) Re-populate the Argon back into the bag.
7) Remove the “T” and finish sealing the bag.
My estimate is that bag will have R40 across its thickness. The argon basically increases standard sawdust from R2.5 per inch to over R6 per inch. The cost for this bag will be less than $0.50 each, closer to a quarter.
There will be a lot of uses for this insulation. Sawdust is inexpensive but somewhat heavy.”
Bob Cromer
Could this method be used with perlite with less weight (but more expense, obviously)?
Yes, search our blog for a long list of potential bag fill materials. Just be aware that you’ll need to stabilize the walls with loose fill materials like perlite, scoria, etc. or the bags will shift and fall over. Use the search engine on the right side of the page and look for the article Scoria Casita. He explains exactly how to stabilize walls like this.