Looking for opinions on my insulation idea

I'm looking into combining various aspects of natural building but have to stick to certain conventions for one reason or the other.

Long story short: I'm curious about the merit of dense packing finely chopped straw mixed with borax or lime in a conventionally framed wall.

I don't see why the material wouldn't insulate decently, and with the right ratio it wouldn't rot.

Concerns that come to mind for me are: 1)if straw won't pack dense enough and I may need to cut it with cellulose. 2)Finish material required on the interior. 3)If the exterior will be fine with conventional house wrap, sheathing, etc...

My thoughts are I can treat it exactly like I would cellulose as long as I can get the right size chop on the straw and right ratio to borax or the like.

Hi Jesse, welcome to Permies.

I think your idea will work. I do want to mention that dense packing of an insulation lessens its ability to insulate. Any material that insulates, be it fiberglass, goose down, straw or cellulose, works by having millions of tiny air gaps. It's these teeny tiny air pockets in a material that make it reduce the transfer of heat, and by packing something dense that reduces the amount of air pockets and lessens its insulative effectiveness. Light and fluffy insulates best. Hope this helps!

I agree with James, the evidence is against your idea.
Do you have an issue with modern insulation products, otherwise try wool it does work.

one inch of straw have an R-Value of 1.5
So to insulate your roof to R-30 you will need about 20inches. With foamboard you would only need 6inches.
Will your walls and roof be 20inches thick aka like a strawbale house?

I think it is a great idea to build a post and beam house with non-structural strawbale in-fill.

Living in a cold climate, I have seen chopped straw used to add insulation to non-human-dwelling buildings that housed livestock or were not permanent in the long term. It was effective in that application.

If the proposal is for a permanent human dwelling, then I strongly suggest that this is a Very Bad Idea.

I lived for two decades in an old farmhouse that had been insulated with wood shavings. Good idea, right? It was packed in tight, stayed dry, and did indeed provide genuine insulation.

Except, there was a significant health cost. Even when kept dry, in a dry climate, it was starting to break down. There was fine dust, but worse, there were molds using the tiny amount of moisture available and creating spores. The dust and spores would work itself out through every nook and cranny, electrical boxes, unpainted joints, you name it. Over time, the constant exposure began to wear on our health. We had to walk away from 20 years of planting and building and start over.

With straw, there is no way you can properly pack it into every tiny nook and cranny. Temperature differentials and cold spots will allow pockets of moisture to form. The straw already contains all the decomposers to make this happen. If it starts to cause problems, how will you remove it? 10-20-30 years down the road? In a finished house, that's a massive undertaking.

Enough rant from me. I will just wrap with: please don't do this in a long-term dwelling.

Straw-clay aka "light clay" or "slipstraw".. is just straw coated lightly in watery clay. Then you pack it to a goldilocks density.

The idea as I understand it is that the straw is thoughly coated in clay to preserve it, and I figure it packs better to boot; did a tiny bit at a workshop once, but didn't compare to dry straw...


But you will definitely need thick walls. Kinda hard to see how you'd come out ahead, between the wasted floorspace and likely lower r-value. I would look elsewhere to save money at the cost of time, personally..

D Nikolls wrote:Straw-clay aka "light clay" or "slipstraw".. is just straw coated lightly in watery clay. Then you pack it to a goldilocks density.

Thanks, that's interesting. I haven't seen that before.

ive seen shredded newspaper used for insulation. it was first soaked in boric acid solution then dried. to make it both fire proofed and bug proof. works great and much cheaper and probably more environmentally friendly than corning products from big box store.
I would assume it would work equally well with dried straw or hay. need lots of space and good dry weather to dry it out after soaking it in boric acid solution.

I too have seen shredded newspapers used, but at the time there was no TV, and since then better products have been developed.
In fact if you think newspaper, loose straw etc works get a laser temperature gun.
I use one with my experiments and I can say that the commercial products work much better than alternatives.

works great and much cheaper and probably more environmentally friendly than corning products from big box store.

- have you evidence
- straw may be a fire hazard
- with the price of newspapers and the lack of readers it may cost more since you might have to buy them.
- do rodents build nests in paper or straw

I cannot comment on fire/rodent hazards for home-made insulation.

I can say from experience that deer mice do not like commercial cellulose insulation. They don't like Rockwool either. They loooove fiberglass batting, and will happily nest and reproduce in it.

Memory is fuzzy, but I recall that I tried a fire test on commercial cellulose insulation and it didn't burn worth a damn. But that was hella long ago, so buyer beware.

If what I saw was a modern processing plant making the newspaper insulation they did fire testing and once treated with boric acid it passed fire tests.
im not talking about houses like mine that are 150 yrs old and have layers of newspaper between the boards on exterior walls

here's one brand, not sure if its the one I saw story about

https://www.nuwool.com

how recycled paper insulation is made

One of the unspoken issues of straw bale homes is the rodent factor...they need such a tiny hole to get in (a mouse can negotiate a hole well below an inch in diameter).  This leads to a wall full of rodent urine, feces, and bugs.  This is all assuming the straw is not damp, or already harboring mold spores, bugs, mice, etc.

As mentioned by others, it is the trapped air within insulation that provides the R-Value, and why we insulate structural concrete, there is not enough trapped air to provide adequate insulation.  It is why bricks commonly have three holes in them, to up the R-Value.

Blown in Cellulose (shredded newspaper), Denim (shredded jeans), or wool are all "Eco-friendly", albeit more costly options.  Fiberglass or foam are less Eco-friendly, perhaps, but likely less costly as they do not require professionals to install.  Spray on foam is likely the most expensive and least Eco-friendly, but generally gives the most insulation per inch, and negates the need for a vapor barrier (assuming this structure is to be airtight).

I get it, no one wants to cut costs on the items that are visible within a new home, such as surface finishes.  Going with second hand appliances, cabinets and furniture; arborite instead of stone for counters, or lino instead of wood for floors are all things relatively easy to upgrade later on - insulation is darn near impossible to "change" down the road.  

In my opinion, insulation the the last thing you want to compromise on.  Failed insulation is the devil to remediate, leads to higher heating/cooling requirements, and can lead to health issues with the actual structure (rot, mold) and humans housed within it.

Might be worth a consult with someone familiar with your type of build, the weather conditions in your area.  I would also consult your insurance agent; in case there are fire or other concerns that would cause them to refuse to insure your building (assuming you intend to insure).

I have to admit I found that video interesting.
I will follow it up.
I wonder if that is the product blown into existing cavity wall spaces on weatherboard houses.