Determining amount of straw for insulation

Hello and good day,

I am making plans to build a home that is extremely low cost and nearly had a stroke calculating the cost for traditional housing insulation. I also would prefer to keep synthetic nonsense out of the place as much as possible so I was drawn to straw like how cob houses use.
I will have approx 500 sqft to insulate, and the stud space are not straw bale width, they will be more like a normal house width.

I have never worked with straw bales before, but am assuming I will be using the normal 2ft by 3ft size small-ish bales.
Can anyone tell me how many I would need so I can calculate the cost?

More detail is required to help.
- you cannot just use strawbales where you had designed a stud wall.
- you may find a product called Earthwool, made from recycled plastic bottles I think very good.
- are you using it for wall or ceiling insulation?

Julian Hearn wrote:I will have approx 500 sqft to insulate, and the stud space are not straw bale width, they will be more like a normal house width.

I would suggest you consult with a strawbale builder (someone like Uncle Mud/Chris McClellan). You will save a LOT of effort and probably more money than any consulting fee.

It takes 5-10 times longer when you have to split the bale's, it is best to engineer the walls properly from the beginning and not follow conventional practices.

Jeff, Are those people on this forum?

John, I am looking up earthwool and like the price but the R value is only like 2 or 5 at highest so Im not sure itd be the best to use. And I would be using it for wall and ceiling.

Thanks for the replies!

Julian Hearn wrote:Jeff, Are those people on this forum?

Uncle Mud

Hi Julian and belated welcome!
It might help the calculations if you give an idea of your climate zone.

If you're looking to use straw bales is there a reason that you're not designing the stud work around them? I suspect that you'll have more problems if you don't follow the normal unconventional building methods (if that makes sense!)
Good luck!

well said NancyI may have used 'more normal unnormal'

Nancy Reading wrote:Hi Julian and belated welcome!
It might help the calculations if you give an idea of your climate zone.

If you're looking to use straw bales is there a reason that you're not designing the stud work around them? I suspect that you'll have more problems if you don't follow the normal unconventional building methods (if that makes sense!)
Good luck!

Its looking like it'll be North Georgia in the US... low elevation, very clay rich soil, humid air most of the time. And as for the stud thing I was planning on building a conventional house (stud space size- wise anyways) and wanted to absolute cheapest insulation option. If the R value will not be high enough with that option, I will reconsider but I dont know how it work hence my being here lol.

I have seen strawbale used on the inside of a stud framed house with tradtional external cvladding and earth plaster on the srawbales.
The room sizes need to be larger to start with though.

I think several people have already pointed out that using straw bales with modern stud building practices may cause more headaches than you want.

If you want cheap, I would normally say that pink fiberglass stuff. You don't want synthetic. I would suggest rockwool (mostly stone and slag, so fairly "natural"), sheep wool insulation, hemp batt insulation, or hempcrete. All of those are natural and would work fine with stud construction... but they are also fairly expensive.

In general, for a house, especially something on the inside of the walls, I would be looking for the best I could afford... not the cheapest, but I get it, especially with prices rising.

Given your restrictions, straw might be the cheapest option, but make sure you include the cost of plaster and maybe compare it to something like rockwool or hemp batt insulation. For a 500sqft house it might not be too bad. You might also be able to build your frame, then just stack the bales of straw around the outside and cover it in plaster. Your roof would have to be a bit wider to cover things, but there is no reason the insulation has to go in between the studs. You might be able to save on the outside cladding of the house if its done right.

Good luck and let us know what you choose and how it goes.

PS this thread talks about some realities of straw bale houses. Some people like them and others have not had very good luck with them.
https://permies.com/t/113626/Straw-Bale-Don