DIY Shredder Creates Insulation

Plenty of us have experience with paper shredders, but there are all kinds of machines designed to completely destroy other materials as well, from metal and plastic, to entire cars. [Action BOX] built their own heavy-duty shredder capable of dismantling things like cell phones and other robust handheld objects, but after seeing what it would physically shred they decided to give it an actual job creating insulation for the attic space in their garage.

The shredder itself uses opposing metal plates arranged on sets of two cylinders, with each cylinder powered by it’s own large motor. In total, the entire system uses around 1.5 kW, so to make their green insulation project as green as possible they decided to power it with an equivalent amount of solar panels. For the insulation they’re using a year’s worth of boxes from various deliveries, and after a time-consuming process preparing the boxes for the shredder, shredding the strips of cardboard, and packaging it in garbage bags their efforts netted them enough to partially fill the space between four ceiling joists.

Despite not having nearly enough to insulate a garage after all of that work, they still went through the effort to test their insulation against similarly sized fiberglass batts. Despite a brief hiccup where their test equipment caught on fire, they found the cardboard shreds were only slightly less efficient than the fiberglass. They even went as far as to address any concerns with flammability by treating some of the cardboard with a boron solution to add a measure of fire resistance. While this didn’t turn out to be the cost-effective solution they had hoped, as a proof-of-concept it’s certainly feasible especially for those who can’t head to a big box store to buy insulation directly. If you can buy your insulation at the store, though, there are a lot crazier things to do with it.

Thanks to [Jordan] for the tip!

28 thoughts on “DIY Shredder Creates Insulation

  1. This is a terrible idea as implemented. Proper cellulose insulation is treated with boric acid to reduce flammability and it’s attractiveness to critters. Those trash bags certainly won’t help mitigate the chances/spread of fire either.

    1. Hmm, I see boron is in the write-up, doh! I missed that part of the video. Nevertheless, I think the trash bags are a bad idea.

      I did not perform as well as the fiberglass because it was a coarse shred. Normal cellulose insulation performs better than fiberglass, but it’ more lite confetti than strips, which traps more air.

      1. Yes, cellulose insulation performs great, and is much more eco-friendly than fiberglass. This is why I choose it 12 y ago and my heath bill is still very low (heath pump + wood burner), even during cold winter. I used a thickness of 20 cm ( 2/3′) for the wall (with 2 air gaps and a layer of wood wool on the exterior side) and 30 to 40 cm (1′ to 1’1/3) for the roof. The only drawback is that some mice find a way to use it too :-( But hey, if you are living in the country…

  2. Shredders are hard. I worked on a project where we designed our own. As you can tell from this video, they take a LOT of motor. And stall detection/reverse/forward is mandatory if you’re shredding things that might jam. We were just barely able to get ours to work on a 20A 120V outlet.

  3. Knowing the R value of trapped air I’ve often wondered how effective bags of air blown to fill the spaces would do over having the space filled with stuff that traps air but lets it slowly pass through? Perhaps Mylar or some long lasting plastic, aluminized.

    1. Heat moves in three ways: conduction, convection, and radiation. Air stops conduction, but it convects: it moves around the cavity and circulates between the hot and cold side. The insulation needs to fill up the space to stop this bulk air movement, so it’s a balancing act between greater conduction through the insulation medium itself, and filling up enough of the space so the air doesn’t just breeze through.

    2. The effective version of the low-materiality approach you’ve suggested are vacuum panels. They are an engineering challenge and relatively expensive, but some inroads have been made on creating vacuum panel siding.

      Alternatively, you can use a high molecular weight gas, preferably one with zero ozone depletion or global warming potential.This is why better double and triple-pane windows are argon filled.

      1. That’s also why windows aren’t filled with carbon dioxide. Poke around the web and you should be able to find the results of an experiment with multipane CO2 filled windows. Turned out they let through more infrared than when filled with plain air, and were much worse when positioned vertically VS horizontal.

      2. Vacuum panels have the same problem as the 70’s invention of just wrapping everything in plastic and closed cell foam to stop air leaks – it doesn’t pass moisture, so it’s like living inside a bottle. Soon enough you get condensation and moisture traps along the insulation and the house turns moldy underneath the interior paneling.

        1. That’s what an HRV/ERV is for: provide a controlled volume of fresh air with minimal loss of energy. However, condensation in the walls as you’ve described is not merely a function of humidity/air flow, it happens if the ratio of continuous insulation versus cavity insulation is incorrect, allowing for moisture that passes through the cavity to condense between the two because the inside of the exterior insulation is too cool.

          1. The theory is fine, but the way houses are built in practice results in places where the ventilation doesn’t “reach” and some corner of your bottle house will develop mold problems. It’s almost impossible or at least impractical to design it so the whole house gets even ventilation throughout. Then there’s the problem that the contractors and the builders almost never do it properly anyways. That’s why plastic films and foams for insulation turn out bad.

          2. I’m reminded of a house where they stapled the plastic barriers in using regular iron staples because they were cheaper than stainless, which of course meant that they would rust off and leave holes in the tarp.

            But you only notice that 20-30 years later when the house is ruined.

        2. Open cell foam is the worse foam for moisture; since air can get in the foam itself and condense water. If you bond closed cell foam directly to the outer wall and don’t put a separate kind of insulation or vapor barrier after it, you don’t form any cavities for moisture to get trapped, and of course no condensation can occur inside the foam.

          But like Bob said, that’s what ventilation is for. The ones who come up with ideas and standards for better insulating houses have shown that it takes less power to run a vent with a heat exchanger than you waste on heating/cooling air leaks / drafts. Plus, normally houses have exhausts in the kitchen, bathroom, and/or the room containing the clothes dryer, but their intake air is purely what leaks in, unless it’s a nice day and there’s an open window. The hrv and erv’s deliberately filter the air with whatever level of filtration you pick.

          1. The problem of air-blocking insulation is that it’s like trying to dry your clothes flat on your kitchen table. It takes considerably longer because the water can only come out through one side, so the back of the shirt remains wet even as the front looks dry.

            In the case of the house, it’s dependent on ventilation and air flow inside the rooms, which is uneven and unpredictable in the end. It almost never works as planned.

          2. There’s no problem when you keep the “towel” from getting soaked in the first place by not letting water soak thru the walls or condense inside the insulation. Elsewhere the popular “let’s screw a bunch of sheets of plywood/osb/etc onto a stick frame and staple plastic to it” approach was mentioned, so if that’s the kind of wall you mean, then we might partly agree. If you sandwich some absorbing material (eg plywood) between two things that don’t pass vapor well or at all, then it’s going to be hard to deal with the water that gets in e.g. by soaking thru holes in the plastic. If you’re stuck with that kind of thing, then it may be easier to use porous insulation than to seal your walls properly. I think I mentioned bricks elsewhere as something else that doesn’t do well with no way to dry out.

            What I was suggesting somewhere is to not do that kind of stuff, and instead use e.g. metal with foam sprayed directly onto it. Then there’s no middle layer. The ventilation doesn’t need to dry a soaking object, what it needs to do is help handle humidity. If it’s swampy outside you still need an air conditioner, but otherwise by circulating and exchanging air with the outside you prevent normal activities like breathing, cooking, washing, etc from raising the humidity uncontrolled to levels that cause condensation to begin in various areas. That said, I would take advantage of the lack of need to fill the entire stud cavity with spray foam, and instead let the area be vented in the crawlspace or such, so that air exchange can still happen albeit at a reduced rate vs the rooms themselves.

    3. Buy a bunch of small carboard boxes, say 8in cube. Assemble them, empty; and stack them in the space you wish to insulate.

      If you fill them with perlite or other light batting they’re even better.

      problem is any space that can become critter homes will.

  4. Re: insulation, cellulose is a green way to dump a bunch of it in the attic of a leaky house. Even if this isn’t the best example, it still seems useful. Mineral wool is a nice alternative to fiberglass, but for a modern building you really want to think about the flow of air and humidity, which makes your theoretical r-value misleading.
    The way I like the idea of the most is to use closed cell spray foam directly on the inside of the outer walls. It has disadvantages but an advantage is excellent insulation and vapor impermeability. You don’t need thick walls and you neatly partition the inside and outside in a long-lasting way.

      1. I believe mineral wool also tends to pull ahead in durability and longevity, but yeah even the first one is nice.
        The foam seems great for a new building but you’re right that it can be a non-option sometimes, either due to access or a need for something permeable to let water escape. If you can’t exclude moisture completely between the insulation and the outer wall, it might be better to stick with other kinds of insulation and just plan on keeping your walls well ventilated and dry. Metal can work, bricks won’t like it, as an example.

  5. What about using a hole saw to access the stud spaces from the outside, the spray foam insulation into each cavity? We have a local insulation company selling this service. Seems like good option for an older house, especially if one is getting ready to replace the siding.

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