Doug Piltingsrud, PhD, of Sustainable Housing Resources, LLC presenting information on research into light straw/clay construction at the 22nd Annual Energy Fair in Custer, Wisconsin on June 18, 2011. Taped and edited by Duane Brewer for JATV.
One of my favorites. Relies on large crew of volunteers. In a homestead situation virtually the same product could be made more simply. A large tank could be mixed with an auger, solids could be allowed to settle and slip could be gravity fed to the trommel. The bottom few inches of the tank would contain sediment that could be used for cob or dumped. One tank, one machine, no pumps.
The same tractor that powers the auger could spin the trommel. Or straw could simply be immersed in the tank and fished out with a hay fork . Material would drip out on a sloped tray which returns excess slip to the tank.
Straw should spend as little time as possible in the tank.
The same could work for wood chip clay but a net would retrieve chips from tank. Not a fish net. Probably a scoop shovel with lots of drain holes.
Science and the ability to deliver consistent measurable results are needed to make the technique acceptable to building officials and thus more widely used. I believe the findings of all the science that he reports on are significant. Instead of talking generalities he gets down to the brass tacks of exactly what the results were using a specific set of ingredients. The desired condition was straw and soil with a certain % clay content with an R value of 1.7 per inch. Now it is known how to achieve that…consistently.
I disagree as to it relying on a large crew of volunteers. One person can shred the soil. The same person can mix the slip. That same person can filter the slip. That same person can pump the slip into the tumbler while adding the straw. That same person can haul the light straw/clay mix to the wall and put it in the wall. Everything is slower with one person, of course. Very few systems can get past that limitation
In the 6 minute video I see a system for accomplishing the mixing which accomplishes the goal. None of the items are particularly high tech looking but that, I’m sure, does not give credit to the many iterations which failed to meet expectations which were tried previously. I don’t believe this is a final system. I believe the door is wide open for the next iteration which simplifies the process. In fact, I believe that is precisely the challenge all of us need to be working on; how to use technology and methods to increase efficiency of both output and energy input.
His finding that straw without clay absorbs moisture much more readily than straw with clay is predictable. I did not predict the extent to which clay slip straw sheds water. Quantifiable information that can only be anecdotal on the homestead. I especially found his comments on blue clay to be informative as this is the type of clay I have available.
I believe you are correct; the same thing can be accomplished utilizing other methods. The question is this: Can the alternative provide the same consistent measurable results? If it can then it’s a winner.
The thought of using forms to make preformed and dried bricks of light straw clay intrigues me. I see these as being used in a situation where installing wet light straw clay (or cob) in an existing home is a problem due to the lengthy drying time. Obviously much lighter than cob if you really don’t need cob to accomplish the job. For example if you wanted to create a sculpted room look but have weight limitations. I believe there is a niche these bricks can fill. No pun intended.
The data that I never see presented is some sort of cubic ft. per man hour. Of all the information that might be available for this and other systems, this is the one that trumps all others for me. It's the only way I can calculate the cost honestly.
Traditionally straw from the threshing floor was used for light clay construction. This included a small amount of grain. The grain would sprout, the barley would find it's way to light, and for a few weeks you had green walls. This pumped the water out of the wall. The mat of roots and barley straw on the surface helped provide key for the lime plaster that was applied later.
I can vouch for the longevity of the finished product. In about 1978 I helped my dad insulate an old farmhouse near Kitchener Ontario Canada that had straw clay in the attic. The place was built by German immigrants probably about 1870.
If we have any members in Europe or elsewhere and you have straw clay insulation, please send us a photograph.
Fiberglass generally becomes home to rodents and I doubt that it would last a century in a farm setting.
I felt compelled to chime in on this topic as it has become of great interest to me recently after seeing and being a part of several light clay-straw houses being built where i live.
I wanted to first address the issue of labor and mechanization. While the process shown in the shorter video would produce a great product, especially the clay slip refinement, it is not necesary. Ive seen it done with a pile of dry clay thrown in a mortar mixer, rocks and all. The organics float to the top and the big rocks stay in the mixer, leaving a good slip to pour out after some mixing. its one process where the more the merrier, but it could be done on a rather skeleton crew also.
The second thing is about the sprouts that grow out of the wall. Its pretty cool to see, as i doubt you could get straw that was 100% seed free, even if they claim it, so you always have a few random sprouts, which is actually the beauty of it because they are built in moisture meters. When they die off, no more moisture!
Thirdly i want to relay a story told to me about a light clay-straw house and density. After you form up the walls and pack the cavity of the mix, pull the forms, and then it dries, you end up with a very dense wall, much denser then a straw bale. The story goes, there were several straw bales stacked against an unfinished (unplastered) clay-straw wall under a wood shed roof. After several months during the winter, when the bales were moved again, it was noticed that the bales had several tunnels and burrows that mice were living in. Against the wall, you could see several spots that were like small cone shapes scratched into the wall, where the mice tried to burrow in but the density prevented it. The walls become remarkably dense and provide amazing shear resistance.
If you are at all interested in learning more about this process, I would encourage you to visit The Eco Nest website. They are based out of the SW/west coast and do workshops through out the year all over the country, which is where i learned about this ancient revival.
So when used as insulation in an attic, it is sort of loosely laid down or how? And it resists rats? I've seen firsthand how happily rats like fiberglass in my mother's basement and don't want to repeat that at our house.
In the straw bale list they say that no form of straw is really good for ceiling insulation. If you pack it, it's significant load, and it's not very good insulation. If you don't pack it, it has too many air paths through it. At this point blown in cellulose insulation is the best combination of green and cheap.
As to rats. I don't know if anything deters rats. Rats chew through pipe. Keep the poison bait containers full, and change brands every time you see an increase in rat crap.
Oh, and get a terrier. They hate rats.
That's one problem we don't have. No rats in Alberta. Really. We spend several million a year on the Rat Patrol that responds to any sighting, and monitors the borders, and places like grain terminals. If one comes in, they saturate the area with baits and traps. The idea is that most of the time when there is a stowaway on a truck there is only one, and if you act fast, you can kill it before their friends come. Gotto get them before they write back home and say how tasty Alberta grain is.
I agree with Botsford, straw would not make a good ceiling insulation. I am a fan of blown in cellulose blown in, or wool batts are nice, but expensive. In the house im building now i will most likely blow in cellulose in the rafter cavity, and then put a layer of rigid foam on top, and then a metal roof. Rigid foam is great for roof applications as its a stable dimension, and has a great capacity for insulation.
I'm confused: Blown in goes in the attic space. Rigid foam on top of the rafters, just below the metal roof? Not sure I see the point. Most of the time you want the attic space to be as close to ambient outside as possible.
Note that every foam I'm aware of is awfuly toxic when it burns in a low oxygen environment. And once it gets going, it;s hard to stop. Most building codes require that it not be exposed becuase of the fire risk. So if you used it on a roof, you have to put down some form of OSB or plywood, then your foam, then the metal.
Not a very friendly product to produce -- moderately high embedded energy, high transport costs because of the bulk, hard to recycle because of the bulk.
I think if I were using foam as part of the package, I'd do it on the bottom of the ceiling joists. So it would go
Pressure fit foam between the ceiling joists. Would not be as good for insulation, but you could see the joists for hanging the gyprock.
One of the reasons I like blown insulation generally is that it fills the corners. It's really hard to lay batts in the edges of a 3:12 pitch roof, and have them properly snug to everything. Last year I blew in another foot of insulation on top of 6" batts. Took my stepson and I 2 hours to do the whole thing. Has cut the wood use in half.
I agree that blown in is tough to beat. You are right that foam has a higher embodied energy cost, which is why i dont advocate SIP houses, but in moderation i think its lifespan can make up for its energy costs. I use it on the outside of the envelope, to create a seamless thermal break. So for instance in the roof i will be doing, its a vaulted ceiling, no attic space, so it would look like this:
1x3 or 1x4 fir strapping
3" rigid poly iso foam
5/8 or 3/4 OSB (or cdx in my case)
12" BCI engineered joist rafters
filled with insulation (blown cellulose or batts)
drywall or cdx
Gotcha. Cathedral ceilings look cool, but they are tough to insulate. One warning: You want a foam that has some vapour permiabiliity, otherwise you have, in effect, 2 vapour barriers on your roof sandwiching the insulation. The strawbale people have discovered that want the cold side of an insulated wall to be about 10 times as permiable as the warm side. Otherwise you get some degree of condensation somewhere in the insulation. You need to be paranoid about the detailing of the vapour barrier too, espeially around electrical boxes and any plumbing that penetrates it.
Given the price of foam, would there be merit in just increasing the cord of the roof truss, then venting the space above the insulation?
Secondly. Blown insulation settles. How do you keep continuous coverage over the ceiling as it settles. I've got a cathedral ceiling in part of my house. There is no way I an get into that space to add insulation, or even check the status of what is happening.
I really really like construction that allows maintenance.
E.g. If you have a flashing that works loose or 20 of the metal screws that hold the metal down aren't down quite tight enough, and after 5 years the neoprene washer starts to leak -- now what?
My ideal of house construction is that you can replace any one piece without having to rip out 30 pieces, and have a 9 stage repair job. It never works like that, but I make darn sure with my renos that ALL the plumbing is accessible. Anything that will break or wear out in less than 50 years is designed to be replaced without harming the gyprock. (One trick: Buy a square good quality MDF cabinet door, paint the backside well so it doesn't soak up moisture, and mount the bathroom exhaust fan on the door. The door screws through the gyprock into a rough opening. Now the next time I replace it, I have a larger opening to work with.) If I ever build again, there will be some way other than mounting the breaker panel in an outside wall too. Real tough to add a circuit. I like crawl spaces, and suspended ceilings, as it reduces the hidden runs. I love putting the back of a closet adjaent to the bath/shower wall -- then doing the back of the closet with wood paneling held by screws instead of gyprock.
NO plumbing goes in an outside wall, with the exception of outside taps. And they are all long stem valves to get inside where it is warm.
Put shutoff valves on every branch line. You really don't want to shut off all the hot water for the entire house to replace a washer in the bathroom sink. Especially when you are an hour's drive from town.
Whenever you work on electrical, use a fine point permanent marker, and write down the breaker number on both the electrical box and the cover plate. Saves you grief next time.
Give thought to the height of outlets. Lamps are fine with knee high outlets. But every room should have an outlet that is at light switch height. Makes the vacuuming a lot easier. I used to like computer plugs to be at desktop height, but now I screw a power bar either to the wall or to the desk.
I prefer blown cellulose in attics. Fiberglass has lower R value and it is the perfect home for vermin, it settles far more, catches on obstructions and loses R value at sub-zero temperatures. When installed in wall cavities, fibreglass melts away when exposed to flame thus providing a fire corridor. I've attemted burns on both products. Cellulose impedes fire by smothering it. Not what you would expect from a wood product. They don't write that on the fiberglass bag.
I've installed over 200,000 sq ft of these products. Have recycled probably 20,000. The cellulose is usually good. The fiberglass is usually ruined by vermin.
We should get back to straw clay.
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