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Does a straw/clay wall need to be open on both sides to dry?  RSS feed

 
Joseph Davenport
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My friend has a shed on his property built in the sixties. It is in fantastic shape with the inside a standard stick-frame design. it has no insulation but has plywood siding on the outside covered with cedar plank siding. I am wondering, if I infill with straw/clay for insulation will I need to take off the siding and plywood for the straw/clay to dry properly, or if I could just infill and (temp/airflow/humidity levels permitting) it would dry fine on its own? I would like to turn this into a small house for my family, and am wondering what the labor/costs would be involved.
 
Jami McBride
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Both sides open to the air is highly recommended, some have tried open on the outside in dry hot climates.

You could use wool or straw and apply natural plaster over it on the inside....
 
Kate Nudd
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Joseph,Hello
What a great project to do for your home.
I have read of numerous people doing this.
Also,people have used it for roof/ceiling insulation.
A couple of links below.
All the best.

http://digginginthedriftless.com/2010/06/01/get-your-hands-into-strawclay/
http://danatdr.blogspot.ca/2007/10/insulating-my-new-house.html
 
Joseph Davenport
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Kate, thanks for the links. It would appear that the guys at Dancing Rabbit went ahead and put insulation in without removing the siding. I wonder if running a fan and a dehumidifier inside during drying would help not having both sides open?

Jami, I thought about straw with plaster over top, but from what I understand this would lower the insulation value and there is the issue of fire. I may be wrong but I believe the clay mixed with the straw keeps it from being combustible. I'm also afraid that wool would be rather expensive, and both wool and straw would invite rodents.

Also, what is the detriment in not having both sides open? It is an issue of mold in the plywood if it doesn't dry fast enough, or does having a permanent siding impede moisture passage through once dry and risk structural failure?

Just trying to understand options and repercussions. Thanks for the input guys!
 
R Scott
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Location: Kansas Zone 6a
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You will definitely get mold issues unless you are in the desert. You may also get permanent water damage to the plywood or siding. Look into additives like borax or lime for mold deterents.

Everything on clayslip straw I have seen says to get as much time as possible to let it dry--open both sides and done as soon as possible to have most of the dry season to let it cure, and some ran their woodstoves in the summer to bake the house dry.

 
Jami McBride
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Location: PNW Oregon
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I have had similar experiences as R Scott, and I would add that there will always be people who push the envelope and just try it. It may or may not work out, but it definitely is a combination of factors. What is your climate and are you thinking about starting this now (fall)?

Fans help, but the air won't reach to the back wall section.

Joseph Davenport wrote:Jami, I thought about straw with plaster over top, but from what I understand this would lower the insulation value and there is the issue of fire. I may be wrong but I believe the clay mixed with the straw keeps it from being combustible. I'm also afraid that wool would be rather expensive, and both wool and straw would invite rodents.
Also, what is the detriment in not having both sides open? It is an issue of mold in the plywood if it doesn't dry fast enough, or does having a permanent siding impede moisture passage through once dry and risk structural failure?


It's an issue of mold, yes, on the plywood and decomposing of your straw in the wall. If you do not use such things as a house wrap material or other moisture sealant and you don't live in a very humid climate any mild moisture will move out of your walls the same as it moves in. But there are situations such as bathrooms where you'll want to block the room moisture from entering your walls altogether.

 
Joseph Davenport
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I wasn't planning on starting this fall. Next spring would be the earliest I would attempt anything. Living in the Willamette Valley it sounds like my chances of getting away without both sides open is nil. I suppose I will have to see if the siding is, hopefully, NOT part of the structural support and remove it for the straw/clay or find an alternative insulation I think will work well. Thanks for all the replies!
 
Peter DeJay
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Location: Southern Oregon
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Considering that it is probably only a 2x4 wall, drying of a 3 1/2 inch light straw-clay (LSC) wall from one side wouldn't be a problem at all, since most LSC walls are 12 inches. The problem lies in that by having the siding and sub-siding you lose out one one of the major benefits of a LSC wall, that of its vapor permeability. There would be no way to mitigate the mold that would form on the inside of the sub-siding. Eventually it would dry but it would be a surface that would be prone to moisture, and since its not vented it would tend to stay there longer. As much as I love LSC, I would advise an alternate in this application. You could try just stuffing plain straw in the bays if you can't afford wool batts or blown in.
 
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