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woodchip clay with cellulose infill #22196 01/09/10 01:58 AM
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Devin Smith Offline OP
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I'm just beginning to put up light framing and wood sheathing, which I plan to infill from within. I'm using board and batten siding over horizontal 2x4 nailers attached to 3x4 studs 30" o.c. roughly 1' outboard of the frame.

My question is in regards to combining woodchip clay with cellulose to boost insulation values. Has anyone on the forums done this? My thought was to infill the stud cavities (4" stud plus 2" nailer= 6" of woodchip clay) tight against the sheathing. Then I would use very light studs maybe 2x2 12" o.c. and sawn lath w/ cellulose infill. Seems like it would improve the performance of the wall quite a bit. I'm not sure what I would use to separate the two materials-- maybe some type of sheet material like burlap.

Any thoughts on putting the cellulose on the inside versus the outside? Conventional solar design wisdom would place thermal mass ***inside*** the insulation, but in terms of mitigating moisture, outside seems like the way to go. I've considered using straight cellulose-- 1' thick cellulose walls would be pretty awesome insulation. But clay seems like the perfect solution to inevitable moisture infiltration. I've also pondered mixing cellulose or some other relatively high r-value material in with the woodchip clay, though it would likely not perform as well thermally as keeping the two materials as discrete layers.

If I go the woodchip clay route, my current plan is to board and batten directly over the empty wall cavity-- no sheathing or secondary drainage plane. How are others detailing the installation of wood siding over natural enclosure systems?

-Devin Smith
Rockingham, VT

Re: woodchip clay with cellulose infill [Re: Devin Smith] #22199 01/09/10 03:10 AM
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TIMBEAL Offline
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No joke, do each wall differently and get back to us on how it functions, what was easy and what was not, where problems arose in the installation and so on.

I would place the clay mass on the inside. I also would be concerned with moisture migrating into the cellulose and what that would look like. It may not be an issue.

I don't like moisture barriers.

I am watching a bare clay wall exposed to the weather with a minimal roof over hang and am seeing no problems what so ever. With a layer of boards I would say a clay wall would be fine. I would like to see a render applied to the exterior clay wall before the boards go on and after it has cured for some time to seal it up nicely, let it shrink than apply the render and plaster, before applying the boards.

I heard a report of someone who used wood chip and clay and did not like how it functioned during the heating season, they applied a layer of foam over the outside to seal it up.

On a three season home I would not hesitate to build a clay wall, I am waiting for hard input on how such a wall system functions in the cold winter. I just don't know.

Just a few thoughts.

Tim

Re: woodchip clay with cellulose infill [Re: TIMBEAL] #22200 01/09/10 04:35 AM
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bmike Offline
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dry cellulose or wet?
did you say 2x2 of cellulose? that will get you about R6 or 7 in addition to your clay wall?

i think you would want to understand your climate to make the choice. both materials can be hygroscopic. which will take on and give up moisture at a quicker rate? should this go to the oustide or inside based on climate / interior conditions / etc.? my guess would be cellulose inside, clay out.

and - why would 12" think cellulose pose moisture issues? you'd want to use sticky cellulose to keep things from settling and to provide a tight air barrier...

here's a friend who is doing a 12" thick wall with conventional construction - 2 walls framed with a spacer:
blog link



Mike Beganyi Design and Consulting, LLC.
www.mikebeganyi.com
Re: woodchip clay with cellulose infill [Re: Devin Smith] #22213 01/10/10 09:36 PM
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Devin Smith Offline OP
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Tim, I will be applying the exterior boards first, and then infilling from within as I am living in the cellar hole below the frame and want to get things enclosed (tarps for walls currently). So render is not really an option. Having the mass on the inside may be advantageous. However, consider that either way, the dew point could likely occur at the interface between the woodchip clay and the cellulose. I fear moisture buildup in the cellulose directly behind wood siding, while the woodchip clay packed tightly against the siding would seem to mitigate any moisture issues, and eliminate the need for a vapor barrier or drainage plane. By the way, siding is to be vertical kiln dried pine shiplap boards (8") with batten strips over the joints for double coverage.
As to the performance of woodchip clay, I know people in New Hampshire with a straw clay house, and they think it quite efficient. I suppose it depends a lot on the size of the woodchips and a bit on the species of wood. R-values for softwood are ~1.25 per inch for solid wood, so a 12" wall would be ***at least*** r-15. Sawdust probably approaches cellulose in r-value (since it is basically cellulose and lignin) which is in the neighborhood of r-3.

Mike, I have a 1' cavity to fill, and was talking about using 6" of woodchip clay and 6" of cellulose. I mentioned 2x2 studs to hold lath and plaster for the finished interior wall.

Re: woodchip clay with cellulose infill [Re: Devin Smith] #22217 01/10/10 11:37 PM
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TIMBEAL Offline
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Devin, if you don't mind could you explain how the two 6" walls are studded?

I can't quite wrap my mind around where the dew point will fall in the wall system. Can anyone pin point that? Will enough warm air pass through the clay wall to condense in the cellulose, maybe a vapor barrier on the exterior of the boards then the cellulose? I can't see the clay section getting that wet to rot the stud and boards captured in the wall.

I understand warm air meeting cold air and condensing, this could happen at different points within the wall depending on the season and conditions?

You will want to pay attention to window buckets and moisture collecting at these points and where that will go.

Tim

Re: woodchip clay with cellulose infill [Re: TIMBEAL] #22541 02/05/10 03:10 PM
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Jordan Finch Offline
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Devin,
You have come up with responses to all of the important issues in a breathable wall system, but of course, have also introduced a host of secondary questions as well. As an example: 5 1/2 years ago I built a 32' x 34' TF w/ 15' eave walls and a 8/12 pitch w/ Foard's R-30ish panels on the roof. I planned the walls as 12" thick woodchip clay, cypress clapboards on the exterior, a 3 coat clay based plaster on the interior. The frame is wrapped w/ 2x12 top and bottom plates w/ 2x3 studs, 2' o.c. Working with a handful of recommendations from Steve Chappell, we ran 1/2" x 1 1/2" poplar lath, 3" o.c., on the entirety of the inside of the stud work and window openings - jambs splayed 30 deg. or so; a must with thick wall construction, it gives you the most natural light and the opportunity for a deep windowsill/seat, and a chance to use all of those 3 - 4' slab and board cutoffs, thoughtful orientation of live-edge material can be used with great success as well.
Now with the interior totally lathed off, we hung sheets of clear plastic to protect the frame and floor from the inevitable overspray of goop(more poly than I usually care to use, especially in a throw away application, but it did its job perfectly and kept the planed and oiled frame very, very clean.

Next we hung 4-5' of lath on the exterior and, after having built a big culvert type mixer and two 4'x16' bins for media transport, we would drive the 12,000lb/50' tele-handler to the wall with a full load and two men on the platform. The platform was positioned to be level with the top of the last course of lath and the men would shovel/scoop/scrape the woodchip and clay into the cavity. A couple of tamps with a digging bar in the corners and then hang 4-5' more lath, move the machine, refill and repeat as necessary. 5 guys, 10 days, about 2,600 cu. ft or sq. ft - the wall is 12" thick.
Installed in May, blessed with a dry summer, began plastering in Sept. This system requires a good bit of moisture and consequently, adequate time and airflow to dry, hence the the 1 1/2" spacing on the lath - just enough to keep the material from falling out, but as much air as possible. The trick of putting some grass seed or been sprouts in the wall as a moisture meter is pretty cool too. They open after a week or two and die when the wall is dry enough to cover with either plaster or wood. The rain screen debate: I opted to place another piece of lath as furring strip in line w/ all of my studs to create a 1/2" airspace between the woodchip clay and the siding, now a true rainscreen. However, I neglected to plaster the exterior surface, or even wrap it w/ kraft paper - at this point in my life there was no way I was using Tyvek! The rainscreen is designed to draw air from below and ventilate at or near the underside of the roof surface, which is great, but when you don't have an air barrier between it and a porous material, you get air infiltration into the living space. The biggest challenge with woodchip and clay is this: it needs to breathe, but softly. The density of the material will assist in the air barrier function (like dense-pack (dry) cellulose), but can never be "sealed" in the modern sense with tape and glue and film and latex.
Quick Conclusions
-Don't install wet mix woodchip and clay against wood cladding(other than temp. plywood slipforms, ala Robert LaPorte)
-Seal woodchip and clay from exterior; design should reflect this, a tall VA farmhouse on a sloping site was not directly adaptive to this method of construction. The exterior was not plastered because it would've required thousands of dollars in scaffolding rental. When building natural/traditional be smart, think cottage style, stay single story or close to the ground when possible, utilize hip roofs to avoid big gable faces, etc. and always ask yourself if your design is commensurate with your method.
-I say either all cellulose or all woodchip clay, each with thoughtful detailing. I'll say more later as to why, but I've got to run.

Peace,
Jordan

Re: woodchip clay with cellulose infill [Re: Jordan Finch] #22542 02/05/10 05:04 PM
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Gabel Offline
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Now there's some good info. Thanks Jordan.

Re: woodchip clay with cellulose infill [Re: Jordan Finch] #22543 02/05/10 05:05 PM
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bmike Offline
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Jordan -

Thanks for the lengthy hands on response...

-Mike


Mike Beganyi Design and Consulting, LLC.
www.mikebeganyi.com
Re: woodchip clay with cellulose infill [Re: bmike] #22544 02/05/10 05:59 PM
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TIMBEAL Offline
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Yes, very nice, thanks.

I have a question, the render on the exterior, which you skipped?, would you have done it if the building had been lower?

One way around the gable ends is to insulate the ceiling/attic floor and have the roof not heated. The gable ends can be frames with studs and sided, a wall build over the infilled section.

Is the reason for not infilling against a permanent wall surface due to the drying ability?

Tim

Re: woodchip clay with cellulose infill [Re: TIMBEAL] #22546 02/05/10 11:47 PM
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Jordan Finch Offline
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I think the exterior render is key, and yes I would have done it if there had been easier access.

I appreciate the "cold-roof" idea, but in this house, and nearly all of them I design, I was trying to utilize the full vaulted space by including a third story "hay aisle" if you will(there are some pics you can see through my blog link below). But why not a hip roof if you are going with a flat ceiling inside? You know, like a rancher? grin

Honestly, exposed TF roof systems over stone, cob, brick, cordwood, rammed earth, straw clay, woodchip clay or even straw bale walls (think sling braces, and crucks and steep thatch or slate roofs)- that's what I find exciting and rewarding to build.
But in my mind, some portion of the full roof has to be visible with several loft/jetty spaces nooked in, and maybe some eyebrow dormers if time allows.
And if speed or something else dictates that you insulate in a more "conventional" manner, then blow 6 - 12" of dense pack cellulose into a larsen truss wall system of light gauge material and be done with it. Clay plaster skimcoat over blueboard interior, wood siding of your choice and hung in any orientation (shingle, clapboard, board and batten, etc.) on the exterior.
Q:"Is the reason for not infilling against a permanent wall surface due to the drying ability?"
A: Yes.

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