Can I use dry leaves or leaf-cob as insulation infill for cob wood home?

Howdy,

I’m currently in the process of building an off grid tiny home. This build has been done with the intention to use as much natural and recycled materials possible for several reasons. Due to this, planning as not been a thing & the house has taken it’s own course of guidance. Unfolding, showing us what it wishes to be with what we have.
We live in southern West Virginia. Slightly concerned about out moderate cold winters. At this moment looks like we will be finishing the walls with cord wood & clay cob because both are abundant on the land. We financially are running into issues with insulation… and even straw is a large amount of money, time, and fuel to get here.
We don’t have a wood chipper & have had very little saw dust collected.
Today, I noticed just how abundant in leaves we are.

So I pondered, can we use leaves as infill insulation?

If so, do we mix with lime for pest control and leave be? Or should we practice a light-straw slay method and make a slip or slit out of it?

Anyone have any feed back or suggestions?
We will definitely be utilizing passive solar as we have a large green house that is south facing on the home. (Earthship style)

No windows except entry door else where on the home for maximum bio mass.

And are build on a peir foundation for moisture control.

I wonder about it’s density/ potential r-value/ rot or complications.

Thanks in advance.

Hi Dani,
I have never heard of using leaves for fill in a permanent house, which doesn't mean it wouldn't work. I would be concerned about the rot issue. I suspect that they would decompose, which would compact what is there, and potentially infiltrate the cobwood with fungus... which I can't imagine is good for a wall :)

If there was a way to put perfectly dry and sterilized leaves into the walls... maybe it could work?

Are the walls being built in such a way that you could get access to them down the road? I know you want to use natural materials as much as possible, but maybe you could do something over the winter while you save up... then take it out and replace it with something more natural. I know up here people are always giving away fiberglass insulation that was removed for various reasons on craigslist. Usually its a little beat up... sometimes its in smaller pieces... but it is usually free. Just a thought.

Thanks for response, Matt. Really Appreciate your feed back.

We too have pondered all those logical options. Logical isn’t always a luxury, at least at this time for us 😆

I’ve found research of the rvalue of leaves & do know that in the days before farmers produced massive crops such as straw leaves were used.

Just can’t find any how to info like the abundance of other eco resources.

Was just looking for anyone who had experience with it. So many different hybrids such as using chip and clay infill etc. when straw isn’t around, manure.

Rot would definitely be of concern. Though straw is biodegradable and doesn’t break down either when used properly.

I’ve link this study on leaves as insulation down below if anyone just wants to take a look. Doesn’t make it truth but found it interesting.

Hi Dani,
The link you posted is not accessible to the permies. It is pointing to your device instead of to a website. Just a heads up.

I don't see that much difference between using straw or using leaves.  Or a combination of leaves and naturally available dry grasses.  I would think if you could process the leaves with the slip and get them installed into your wall cavities BEFORE they have a chance to dry out completely and become brittle, then you stand a better chance of having a mixture that will create lots of air pockets and not become a heavy, dense, compact mass.  Once the clay slip is dry, I don't see why the leaves would decay any more than straw would.  I'd at least put a couple of hours into making a test panel and see what happens.

I think I would be inclined to use  cardboard instead of leaves.

Thomas Tipton wrote:I don't see that much difference between using straw or using leaves.  Or a combination of leaves and naturally available dry grasses.  I would think if you could process the leaves with the slip and get them installed into your wall cavities BEFORE they have a chance to dry out completely and become brittle, then you stand a better chance of having a mixture that will create lots of air pockets and not become a heavy, dense, compact mass.  Once the clay slip is dry, I don't see why the leaves would decay any more than straw would.  I'd at least put a couple of hours into making a test panel and see what happens.

✨Reply: Thanks for your feed back. A test panel will definitely need to be done. I appreciate your perspective on before leaves are completely dry. I’ve pondered this, as I wouldn’t want them to become dust when attempting slip. + they get wet in the slip anyhow. At the same time, some air pockets are what also creates the possibility for insulation. I’ll have to play around and update.

It’s possible we may end up making a mix of things we have on hand. Wood chips, leaves, and paper too.

Any suggestion on how to actually test “test panels” for insulation purposes for nice built? Currently living in a tent, thought about bringing one panel in at a time and placing it near door to see which one made the biggest difference on draft? 🤷‍♀️

William Bronson wrote:I think I would be inclined to use  cardboard instead of leaves.

✨Replay
Appreciate your feed back & link. We’ve looked into cellulose concepts, and it maybe one I experiment with / play with hybrid creations.

We love using cardboard/ junk mail to line the bottom of our raised beds with & before we lived where there was an insane amount of leaves, used it to cover some plants for winter.

The school I've been with for 30 years in the Himalayas has been doing natural building for that whole time. About 8 years ago we started experimenting with various versions of "straw-clay". The problem is that locally, biomass is in such short supply that straw is actually fed to the cows in winter! So we also tried leaves, sawdust, and wood shavings, which are some of the only biomass that becomes waste products here. Unfortunately for us, the clay mixed with leaves was completely soft and would crumble quickly. The wood-shavings were a bit better, would crumble a bit but can be used for insulation where they are not load-bearing or experiencing traffic. Straw mixed with clay has by far better ability to hold together.

I also agree with the comment above where leaves might grow fungus that decays not only themselves but the wood in the structure. Condensation inside wall cavities is complex and hard to predict. Initially maybe you could use the leaves temporarily, externally, in sacks propped up against the external walls, at least the lower parts, as you gradually afford more permanent solutions.

Rebecca Norman wrote:The school I've been with for 30 years in the Himalayas has been doing natural building for that whole time. About 8 years ago we started experimenting with various versions of "straw-clay". The problem is that locally, biomass is in such short supply that straw is actually fed to the cows in winter! So we also tried leaves, sawdust, and wood shavings, which are some of the only biomass that becomes waste products here. Unfortunately for us, the clay mixed with leaves was completely soft and would crumble quickly. The wood-shavings were a bit better, would crumble a bit but can be used for insulation where they are not load-bearing or experiencing traffic. Straw mixed with clay has by far better ability to hold together.

I also agree with the comment above where leaves might grow fungus that decays not only themselves but the wood in the structure. Condensation inside wall cavities is complex and hard to predict. Initially maybe you could use the leaves temporarily, externally, in sacks propped up against the external walls, at least the lower parts, as you gradually afford more permanent solutions.

Reply: Thanks Rebecca, appreciate this so much. I’m truly an experience kind of person and was hoping to here from someone who had experimented with this idea. Straw is fed to live stock here too and is one of the reasons we were having trouble obtaining.

Dani,  One of the things that I don't believe was mentioned in this thread was the use of lime, or portland cement in addition to, or instead of, the clay in your biomass.  I am aware that much work has been done on using a lime cement slurry to wet the biomass before it is packed into a form.  The cement does a better job of retaining the form and extricating the moisture from the biomass as it cures.  It also makes the biomass rot and insect resistant.  Flame retardance is another fortunate by product.  I did not bring it up before as you noted that your remote location made procuring supplies difficult, but I thought I'd bring it up as you should know all your options.  If you are not already familiar with Hempcrete, take a few minutes and look into it.  I think Leafcrete could be a thing if you wanted to try it.