Cob vs hay bale vs aircrete

I kind of happened upon natural building recently. Why? I’ve built houses for a good period of my life and so I’ve always known I would eventually build my own house. I liked the free sculpting ability of cob and its thermal mass and I knew I wouldn’t want to build a “traditional” home. Or wood frame insulated home. Now I do live in a cold humid and very rainy area in which contraction and freezing might cause some issues with cob.

What I’ve been envisioning is a somewhat Dutch style white stucco 6x6 beam supported structure single level most of the time maybe double level. This of course would take some time with cob for sure and I wonder about the resale ability of cob homes.

I checked into the thermal mass of cob vs the r value of traditional.

Now hay bale wasn’t very interesting to be but in NS I saw that paper about building hay bale homes and it roused some novel interest.

Today I happened upon aircrete and it does seem to be the fastest to build a home with easiest least labour intense method and if mixed myself quite cheap.

However the point of this post is me trying to find and studies on the efficiency of the 3 materials compared to eachother. Aircrete is water permiable so naturally I wonder about what materials I’d need to keep moisture out of my house. Anyone have insight on which of the 3 is the MOST energy efficient

Welcome to the forum!

Maybe this will help:

https://www.buildwithrise.com/stories/aircrete-everything-you-need-to-know

Mark ruhl wrote:I kind of happened upon natural building recently. Why? I’ve built houses for a good period of my life and so I’ve always known I would eventually build my own house. I liked the free sculpting ability of cob and its thermal mass and I knew I wouldn’t want to build a “traditional” home. Or wood frame insulated home. Now I do live in a cold humid and very rainy area in which contraction and freezing might cause some issues with cob.

What I’ve been envisioning is a somewhat Dutch style white stucco 6x6 beam supported structure single level most of the time maybe double level. This of course would take some time with cob for sure and I wonder about the resale ability of cob homes.

I checked into the thermal mass of cob vs the r value of traditional.

Now hay bale wasn’t very interesting to be but in NS I saw that paper about building hay bale homes and it roused some novel interest.

Today I happened upon aircrete and it does seem to be the fastest to build a home with easiest least labour intense method and if mixed myself quite cheap.

However the point of this post is me trying to find and studies on the efficiency of the 3 materials compared to eachother. Aircrete is water permiable so naturally I wonder about what materials I’d need to keep moisture out of my house. Anyone have insight on which of the 3 is the MOST energy efficient

I moved to Florida and I had a dream of buying a shipping container then insulating it with straw bales on the outside....        After looking at it closer I decided that it would be the perfect haven for mold and mice ( the straw )   so I moved away from this idea because of the high humidity.

I looked at cob and I found like you that rain and cob do not mix, that one needs to protect the cob from rain thus people build roofs over cob.

An Idea I had recently was to build in cob or aircrete then cover the structure with a billboard tarp....    The downsides to that would be perhaps building a mold haven, but  perhaps if one ran a dehumidifier in the structure one could mitigate that problem.

I have built a rocket stove out of aircrete,  and I want to experiment with foam crete, and dust crete.

I recommend "aircrete harry's "  channel on youtube as he has excellent videos showing the process.

Mark ruhl wrote:
However the point of this post is me trying to find and studies on the efficiency of the 3 materials compared to eachother. Aircrete is water permiable so naturally I wonder about what materials I’d need to keep moisture out of my house. Anyone have insight on which of the 3 is the MOST energy efficient

Hey Mark,

Welcome to Permies!

I don't have any experience with aircrete but straw bale, light clay straw and cob with earthen/lime finishes are all very vapor permeable so any moisture that ends up in the wall can escape. To keep moisture out of the house I think large roof overhangs are more important than wall systems, especially overhangs over windows and doors.

Regarding thermal properties straw bale and light clay straw have an R-value 1.5-2 per inch. Cob has a very low R-value (~.5 per inch). We live in a warm humid climate where we use mechanical cooling for about half the year so I like to use light clay straw or straw bale on the exterior walls and cob in the interior (e.g. earthen floor, trombe walls).  The cob is in perpetual shade and in the case of the earthen floor absorbs heat/cool from the ground keeping it cooler inside. In a colder climate you can orientate your house so the majority of your windows face sunward so the low winter sun can shine through and heat up your interior cob elements.

Hello Mark!


If your "Aircrete" is made with concrete, then there is toxic stuff involved.

Your natural building options are far superior.


Straw bale will give you a higher R value.  

Cob will give you more thermal mass.

If you are concerned about moisture I would look at mycoinsulation.

Here is Beau explaining the process:



Here is another video where we are installing the mycelium in a roof:

Mart Hale wrote:

Mark ruhl wrote:I kind of happened upon natural building recently. Why? I’ve built houses for a good period of my life and so I’ve always known I would eventually build my own house. I liked the free sculpting ability of cob and its thermal mass and I knew I wouldn’t want to build a “traditional” home. Or wood frame insulated home. Now I do live in a cold humid and very rainy area in which contraction and freezing might cause some issues with cob.

What I’ve been envisioning is a somewhat Dutch style white stucco 6x6 beam supported structure single level most of the time maybe double level. This of course would take some time with cob for sure and I wonder about the resale ability of cob homes.

I checked into the thermal mass of cob vs the r value of traditional.

Now hay bale wasn’t very interesting to be but in NS I saw that paper about building hay bale homes and it roused some novel interest.

Today I happened upon aircrete and it does seem to be the fastest to build a home with easiest least labour intense method and if mixed myself quite cheap.

However the point of this post is me trying to find and studies on the efficiency of the 3 materials compared to eachother. Aircrete is water permiable so naturally I wonder about what materials I’d need to keep moisture out of my house. Anyone have insight on which of the 3 is the MOST energy efficient

I moved to Florida and I had a dream of buying a shipping container then insulating it with straw bales on the outside....        After looking at it closer I decided that it would be the perfect haven for mold and mice ( the straw )   so I moved away from this idea because of the high humidity.

I looked at cob and I found like you that rain and cob do not mix, that one needs to protect the cob from rain thus people build roofs over cob.

An Idea I had recently was to build in cob or aircrete then cover the structure with a billboard tarp....    The downsides to that would be perhaps building a mold haven, but  perhaps if one ran a dehumidifier in the structure one could mitigate that problem.

I have built a rocket stove out of aircrete,  and I want to experiment with foam crete, and dust crete.

I recommend "aircrete harry's "  channel on youtube as he has excellent videos showing the process.

Why a tarp though why not construct a more formal roof tarps are like you said mold havens and it will ruin your structure along with causing a health issue

Samantha Lewis wrote:Hello Mark!


If your "Aircrete" is made with concrete, then there is toxic stuff involved.

Your natural building options are far superior.


Straw bale will give you a higher R value.  

Cob will give you more thermal mass.

If you are concerned about moisture I would look at mycoinsulation.

Here is Beau explaining the process:

Here is another video where we are installing the mycelium in a roof:

My only problem with straw is the walls are going to be hit with rain and a steady freeze that for about 6-8 months out of the year and temps can reach -30 so mycelium so I feel like it’s gonna die as when I grew mushrooms they don’t tend to love low temps

>Why a tarp though why not construct a more formal roof tarps are like you said mold havens and it will ruin your structure along with causing a >
>health issue

I have other uses that I have been thinking about other than living in.       One is a sand battery to store heat, another is a sand / cob oven.      I do not know if mold would be an issue,  I was just working out the design and considering options, this is all new to me, and I often brain storm.

Mark ruhl wrote:
My only problem with straw is the walls are going to be hit with rain and a steady freeze that for about 6-8 months out of the year and temps can reach -30 so mycelium so I feel like it’s gonna die as when I grew mushrooms they don’t tend to love low temps

Hello Mark!


The mycelium grows to fill the space in the wall cavity and then it dies.   It is dead when it is insulating your house, so it is totally ok for it to freeze.


If you are using straw bales you will need to cover them with adobe or cob to protect them from the weather.   Use a cob mix heavy in manure to give water resistance.