Straw insulation

[MomOf4]

I asked recently if anyone had been watching Invention Nation on the Science channel...

On the most recent show I watched, they used a mixture of clay, water and straw to insulate a house built of what looked like normal stick built construction. The inside of the house was OSB instead of drywall.

They built forms with OSB and 2x4's, attached those to the outside of the wall (where siding would be attached), packed in the straw and clay mixture, and moved up the wall with the forms. When they were done, they removed the forms and it was a thick, packed mixture with very high insulating value. They evidently continued with normal construction and added siding.

They said this house would not need any source of AC due to the high insulating value of the straw. Knowing what little I know about straw bale construction, it seems very realistic. The benefit would be that this could be used on existing construction, downside is the amount of labor involved.

My question is, does anyone have experience with this mixture - if so, could you please share any tips (ie, ratios, etc)?

We are turning the chicken coop, turned storage, back into a chicken coop this winter, and I would like to try this as an experiment in the chicken coop. If it works well, we may just try this on our house since it has little to no insulation (just siding on outside, plaster and lathe inside, and remnants of blown insulation that has shrunk and fallen down). We would have to remove siding, and do one wall at a time, but I think in the long run, it may be worth all the labor.

Any advice?

[Smallhold]

Medieval houses and even older style farms are built here for open air museums. They mostly have cob walls and insulate perfectly. Cool in summer, wam in winter.
Isn't there such a museum in the USA where they give a course on how to build? If you Google Foteviken you can see a lovely set of small farms I've seen built a couple of years ago.

http://www.foteviken.se/engelsk/index_e.htm

[MariaAZ]

Sounds like good ol' adobe to me, the native Americans have been using it for ages to build with. There are plenty of old houses made of the stuff in the desert Southwest. My brother rented a room in an adobe house when he went to college in Tucson, he said the utility bills were real low and the temperature stayed pretty consistent throughout the year.

Here's a link to an article on adobe in Wikipedia

[susieM]

over here, it was cowpoop, straw, and mud.

[SolarGary]

Hi,
I saw the same program -- thought it was pretty interesting.

I believe that it is different than adobe and different than cob -- it appears to me that the clay/mud content is much less than for these.

Found a couple links that appear to be the same construction:
http://livingindryden.org/2004/07/gr..._bethel_g.html


http://www.designcoalition.org/featu...ode/NMcode.htm

http://www.econest.com/nm_guidelines.htm

I have not seen any reported R values for these walls. It would seem to me that the clay content would reduce the R per inch from that of a straight strawbale wall?
I guess I'm a bit doubtful about what the advantages are over regular strawbale construction, which seems like less work?

Gary

[Shinsan]

From what you've described, it sounds like a rammed earth system, but using adobe instead of a soil/sand/cement mixture. (The recipes for these mixtures appears to be endless, I might add.)

SolarGary, that livingdryden site is interesting. The construction method shown there was not uncommon in Britain and Aust, as it appears to be a post and beam framework with an infill. In its simplest form, that type of infill here is known as 'wattle and daub'. The lathes, or 'wattles', were usually made from thin branches of acacia trees, (which to this day are known as 'wattle trees' in Aust), and clay/mud was 'daubed' onto the structure to form a reasonably solid wall. (Panels, made by weaving thin saplings around thicker uprights, were known as wattles, and were used as portable fencing to make small sheep or pig pens, and the term carried over into the building game.)

I'm rather sceptical of the R values given in Aust for mud-brick/adobe: The low values often quoted don't seem to match the practical experience of people who live in such houses as are built with those materials. There is a feeling amongst owner-builders that, in these cases, the ratings are being used as a way for many councils to make obtaining building permission as dificult as possible. R values also don't take into account the manner in which people actually live in a house. ie; Do the occupants enjoy open windows with fresh air blowing through the house? Does their use of doors, used as their lifestyle dictates, allow for circulation of temperatures? All variables that can make R values a nonsense at times.

[YuccaFlatsRanch]

My house is strawbale. 20 inch thick straw walls. R-value comes a lot from the ability of the insulation to trap air pockets. Remove these trapped air pockets and you have the insulation ability of MUD. I would assume that mud insulates about as well as ROCK and castles were COLD.

BTW with R-50 walls parts of my house today are cold-er. We have about a 30 mph wind out of the north and the wind tries and does get through every little nook and cranny.

[Wolf mom]

Builders in Az are now making double walled adobe. Wall, space, adobe. Much better insullating factor with all wires, plumbing etc. run between the walls.

[Shinsan]

Similar story here, Wolf mom, though some are built with insulated cavity walls: mud brick - insulation (usually polystyrene) - mud brick, and then there are some that have been built with the mud brick inside, insulation, then weatherboard outside. (I think that's 'clapboard' in the US.) Most of these have been built with the intention of satisfying R rating requirements, and are to a large extent somewhat experimental.

YFR. The coldness of stone castles may have been due more to their geographic location and the large open spaces that would have been difficult to heat adequately. Castles in Spain and places like Morroco were generally not cold, due to their thermal mass absorbing heat throughout the day, and retaining it for much of the night.
Mud brick houses also rely on thermal mass to regulate the heat within, and while it may take some time to absorb a lot of heat in colder weather, it also retains that heat for quite some time.

[MomOf4]

Originally Posted by SolarGary

I guess I'm a bit doubtful about what the advantages are over regular strawbale construction, which seems like less work? Gary

The advantage I see is we could use the existing cavity within our walls and fill with the mixture, and re-cover with the clapboard siding - if we were to attempt strawbale, we would have to build a whole new framework around the house, re-do the windows, and a whole new roof to accommodate the thickness of the walls. Not to mention, answer to the tax assessor and local building inspectors - with the mixture packed in the cavities, our house itself would not change.

Once concern I do have is fire resistance though. I think this method would be more apt to fire because there is no adobe or concrete covering it...

I agree it seems like less work to do straight strawbale construction, but we have to work with what we have existing, which is a house built in 1888 with true 2x4 oak studs. New construction is a different story.

I think I may try to experiment in the chicken coop, and let you all know how that works.

Thanks for all the feedback!

[SolarGary]

Originally Posted by MomOf4

The advantage I see is we could use the existing cavity within our walls and fill with the mixture, and re-cover with the clapboard siding - if we were to attempt strawbale, we would have to build a whole new framework around the house, re-do the windows, and a whole new roof to accommodate the thickness of the walls. Not to mention, answer to the tax assessor and local building inspectors - with the mixture packed in the cavities, our house itself would not change.

Once concern I do have is fire resistance though. I think this method would be more apt to fire because there is no adobe or concrete covering it...

I agree it seems like less work to do straight strawbale construction, but we have to work with what we have existing, which is a house built in 1888 with true 2x4 oak studs. New construction is a different story.

I think I may try to experiment in the chicken coop, and let you all know how that works.

Thanks for all the feedback!

I see what you mean.

But, I think that you would be better off insulating the wall cavities with cellulose. Its treated for fire and bugs. It has a very good R value -- around 3.7 per inch, and if installed properly, it will never settle.

Strawbales work very well even though they don't have a very high R value per inch because they are thick (lots of inches). I think that for your wall situation, you won't have the thickness you need to get a good total R value with straw, and adding the clay will (I think) only lower the R value.

If you are residing anyway, I'd also think about putting a layer of rigid foam insulation under the new siding. The good thing about this is that it is continuous over the studs, so that the studs don't act as thermal bridges between to let heat get through the insulation.

If you use this whole wall R-value calculator:
http://www.ornl.gov/sci/roofs+walls/...NS/SimCalc.htm

For a 2X4 stud wall with cellulose insulation, it gives R10.02

For a 2X4 stud wall with cellulose + 1 inch rigid foam it gives R14.18

Both are a lot better than what you have, but the rigid foam does add quite a bit.

Gary

[tiogacounty]

Originally Posted by SolarGary

If you are residing anyway, I'd also think about putting a layer of rigid foam insulation under the new siding. The good thing about this is that it is continuous over the studs, so that the studs don't act as thermal bridges between to let heat get through the insulation.


Gary

Gary, I built a home in 1990 with a layer of plywood sheathing topped by a layer of Dow Blueboard. The windows were defective and the sills allowed water to penetrate the wall cavity. Within seven years the north wall of the home was in a state of structural collapse. The foam had trapped water in the wall and everything, studs, plates, headers, and plywood was rotted. The garage wall was built with the same windows and felt paper over plywood as a water barrier. This wall showed evidence of water discoloration on the sill and plywood, but ZERO rot. the reason is that the wall was able to dry out effectively between rain events. These results have been effectively duplicated over the last decade with spectacular failures of "dryvit" style foam and synthetic stucco siding systems. The Bottom line, IMH experience is that foam can be a great product, but installing it as exterior sheathing is a foolish thing to do, and can lead to a disaster. Simply put, it is a highly effective vapor barrier in the case of extruded polystyrene.(blueboard, Foamular etc....) Or a horribly effective sponge in the case of expanded polystyrene.(white beadboard)

[fishhead]

I second the blown-in cellulose insulation. I researched it for my house but hit a snag in the owner built construction. My 30'x30' house would have cost under $250 to insulate 2 walls (60').

[Traci Ann]

We have researched and are building walls inside our farm house and insulating with the bluejean insulation. There was an article in, I think, backwoods home sometime in the last year (again I think...). These walls will only be on the outer walls of the house, will also stucco outside when done.

[WisJim]

"Blueboard" and similar foam products are good vapor barriers, and as such should be used on the warm side of the wall unless you already have a good vapor barrier on the heated side of the walls. The problem with using it in older homes, under the siding, is that the older homes don't have a good, tight, well sealed vapour barrier on the inside of the walls, so the moisture in the walls is trapped under the foam-board insulation on the outside of the walls, causing problems like Tioga mentioned.