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What is Wood duff - a silly question

 
Nancy Reading
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I've been browsing around and looking at the wofati threads and I'm not familiar with the term "wood duff".
I thought at first it might be sawdust, but then some threads mentioned it in connection with kindling.  Is it the small bits and pieces of wood that are too small to be useful?  The sort of bark and twiglets I am collecting off my kitchen floor after bringing the wood in that I am thinking of making biochar from?
I think it is maybe an American term and as a Brit. it is unknown to me.

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Robert Ray
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It could be a regional definition as well. To me in the PNW wood duff is the pine needle, bark, twig accumulation on top of the soil. It can get quite thick depending on what type of trees are about.

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Nancy Reading
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Thanks Robert, That's pretty much what I guessed.  I don't think we have an equivalent term.  Maybe "leaf litter" would be closest.  I'll go back to considering wofati.....

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Dan Boone
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I would define it as the woody debris on the floor of coniferous forests, composed mostly of needles and especially cone fragments.  Analogous to "leaf litter" in a deciduous forest.  In the boreal forests of my youth, it was frequently a foot or two thick under large stands of big black or white spruces, and the bulk of it was the shredded cones fragments left behind by hungry squirrels after they tore cones apart for the seeds.

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Coydon Wallham
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Looking at the use of "wood duff" as a layer in wofatis WRT Passive Annual Heat Storage- is there a source that explores the details further? Paul's main wofati article just brushes on it and I'm wondering if it is covered in John Hait's book or somewhere else.

Paul shows the duff as a layer on top of dry dirt, between the layers of plastic that make the building's "umbrella".
Anyone care to weigh in on any of these topics?:
1) Why both dirt and duff?
2) Why duff on top of dirt?
3) Does it make a difference if they are mixed?
4) How do (dry) dirt/sand/duff/logs each compare in R value used as building insulation?

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Glenn Herbert
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If the dirt/duff layer is on top of a membrane, I would guess that the dirt is expected to be non-pokey, while the duff may contain twigs or other material that could puncture a membrane. Of course, that presumes the "dirt" in the location does not have sharp stones or gravel in it.

If driving equipment over the structure to place material, duff would easily shift and possibly tear up whatever is beneath it, while dirt would stay in place unless bulldozed.
 
Coydon Wallham
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Here's the image from richsoil.com:

Although the duff is under the plastic layer, I think weight pushing the plastic membrane 'into' the duff would have the same effect as vice-versa.

Has anyone made a layer like this for a PAHS oriented building?

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Anne Miller
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Well, I have been an American my whole life an never really heard of wood duff so I asked Mr. Google and I am not sure he has heard of it either ...

Maybe this is a Wheaton Labs term?

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Coydon Wallham
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Living in the Midwest all of my life, I've heard the term used occasionally but not in a precise context.

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Christopher Weeks
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Also mostly a Midwesterner (USA) here. I've heard the term enough that I don't question it, but I'm not sure I've heard/read it defined. I would have said it's another term for leaf-litter. But I guess it's more specific than that like some of the folks up-thread have said.

https://www.sciencedaily.com/releases/2020/02/200224165303.htm wrote:a deep, dense layer of partially decomposed pine needles

 
Glenn Herbert
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I have never heard the term defined, but seen it used in context where decomposing pine needles makes the most sense. I would just be concerned that when gathered in quantities needed for a wofati roof, it would be hard to avoid the occasional fallen branch piece which could puncture membranes.
 
Ben Zumeta
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It seems to be used most commonly in conifer country of the Pacific coast of North America in reference to woody debris accumulated on the forest floor, or on the shoulders of large tree limbs. On old growth tree limbs that function as Galapagos Islands of evolution unto themselves, this duff decomposes to soil that hosts one of the most densely biodiverse ecosystems on Earth. A cubic meter can have 1500 invertebrate animals and 100,000 fungal species (Noss 1998). Duff is good stuff.

This is all just my opinion based on a flawed memory

 
Coydon Wallham
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Ben Zumeta wrote:Duff is good stuff.


Now I remember where I've heard of it...
Duffbeer.jpg
[Thumbnail for Duffbeer.jpg]

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Nancy Reading
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I'm starting to get duff under my spruce trees now - lovely mycelium in it too!

I think that if the membranes weren't protected (sheep fleeces?) then you might want to sieve the duff for spiky bits.
sprueduff.JPG
forest floor litter
forest floor litter

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Nancy Reading
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Nancy Reading wrote:- lovely mycelium in it too!



This sparks off a thought - I wonder if the roof duff could be a candidate for mycelium insulation? Would there be advantages over the straight duff? Or more difficult to make?

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Randy Butler
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Here in Maine duff is commonly used as a term for the soft layer of nearly black decomposing evergreen needles.
It's underneath the sticks and cones that rake up easily, and above the layer where gravel starts.
Occasionally, between the duff and the gravel, there is what most folks would consider dirt - something in which you can plant stuff.
Most of my spot is missing the dirt - unless I truck it in, or mix my compost with the gravel.
Of course a good deal of my patch goes from tree debris to duff to granite ledge.  I reserve those areas for growing rocks.
 
paul wheaton
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Wood duff is defined mostly by:  what do you have?

It could be:

   - sawdust
   - wood chips
   - pine straw
   - bark
   - twigs
   - branches
   - pine cones
   - leaves

I suspect that this list could be tripled.

Hell, it could be straw.  Including moldy, gross straw.  

Basically, a high carbon plant material that has little to no value, but that you have lots of.


 
Coydon Wallham
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Pine straw. Awesome. Just learned I'm a permaculture millionaire!

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