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Strawbale Questions & Answers
by Stephen Morris
We are privileged to have several excellent straw bale contractors as supporters of this publication. Your local straw bale builders will likely be your best source of information, but this piece answers some interesting questions regardless of location. I know this is the first time I've heard of a straw bale dog house
In a Post and beam construct, can the bales be stacked on the narrow part rather than wide? I understand the R-Value would be less, but to add to an already existing (West facing) wall -this might do what I need it to do. (Shield the afternoon sun from heating the house)
In terms of stacking on edge, it is possible, but it is difficult with post and beam because the strings interfere with notching the bales. To remedy this, you have to stack in front of the post and beam so that it remains exposed, or create a loose clay slip infill around the posts. This is messy and not easy to accomplish. I personally think stacking on the flat is MUCH better. If you have an existing wall you wish the wrap with bales, on edge or on the flat will both work. I hope this helps.
I am building a straw bale dog house with 2 rooms and an entrance chamber type thing. It is one I can walk in without having to go on all 4's. [It is practice for a house, can you tell?] My question is also about paint.
First, is there a good scrubbable paint I can use inside? I would like to be able to keep a little clean in there.
Second, I plan to paint potted plants along the walls outside instead of trying to landscape it since one of the dogs "landscapes" already. Is it OK to use just any old paint for that? I won't be covering anywhere near the entire wall. How much of a wall can I cover with any old paint before I start getting into trouble?
The key with paint is to use the right kind and the right quality. You could try and find a threshold of when you cause problems to the house, but I don't think that is a good idea. I would recommend using quality paint with a high vapor transfer rate. Radiant heat is fantastic and a great compliment to SB homes; however, it may be a bit much for the dog house!
The roof comes down to loads and design. You could do a shed roof (one sloped direction only) and use framing lumber large enough to handle the extra load of sunbathers. For example, if 2x8s 2 feet on center are required, you could use 2x10s instead. The idea is to strengthen the roof assembly so you don't fall through or bow the roof into a sag. Good Luck and have fun.
I need the name and locations for a two string bale supplier that might provide rice straw bales to my property. Can you recommend a contact or two?
Try one of the following links and see if anything is listed there: www.strawlocator.com, www.hayexchange.com and www.agriseek.com/sale/e/Ag-Products/Plant/Cereal/Straw-Bale
Hello, My name is Frank and I recently purchased your DVD series. We are about to put a bale addition onto our 1790 farm house. I have been watching the DVD over and over and have a question about the construction technique. What joins the bales together? In other projects I see, the bales are pinned together using bamboo or re-bar. Does the wire take the place of the stakes? I saw in part of the video when a twine was passed through the wall and tied to a piece of bamboo, however, I thought that was for earthquake zones. Can you clarify? The county we live in here in Maryland does not have any bale houses and I want my project to sail through the inspectors.
Frank, You are right on the money when you ask if the welded wire mesh replaces the pinning. The fact is that the mesh does a much better job of attaching the bales to the frame and to each other than the pins did. Consider that the mesh is heavily stapled off to the framing and then is tied to the mesh on the other side of the wall (this is the section with the small pieces of bamboo. You could use twine stretched over several inches without bamboo). The mesh completely encapsulates the bales and attaches them to the frame. Good luck.
I feel that meshing up the walls with metal-mesh is like sitting in a metal box, especially if there is a thunderstorm approaching. What can I use instead?
Unfortunately most building codes that apply to straw bale construction require you to use the 14 gauge 2"x2" welded wire mesh because it provides protection from shear forces. This is the preferred system of most straw bale builders.
There is research using a plastic mesh in place of the wire, but it is not even close in strength. If you really want to avoid using the mesh, you could use a 16 gauge metal strapping from Simpson Strongtie and place it at 45 degrees throughout the building. You need to wrap the strapping around the two toe ups before you frame and keep the strap coiled up at the exterior toe up. This provides the required nailing surface for the strap. After your walls are up, bend the strap so that it runs at a 45 degree angle and nail it to the top beam. This takes some pre planning so you avoid windows and doors and get a good angle on the strap. You may need to run a wood block at the wall half height and run two straps in narrow areas. The straps need to run in both directions so there is always a strap in tension as they do not function in compression. Then you can use the plastic mesh (orange contractor fencing with a tight diamond grid is best) to shape the walls.
Does thickness of plaster help moisture problems?
Sort of. If the plaster is at least 1 ¼" thick, it will help keep direct moisture off the bales. Be sure to use a plaster that breathes or the problem will be made worse. I like the Natural Hydraulic Lime (NHL). It does a great job as a breathable material and reduces most if not all moisture problems.
I have heard that metal in bales can cause dampness due to condensation does this not apply to the two inch welded grid (welded wire mesh)?
The grid is considered thin enough to not introduce a lot of condensation. The idea is that the condensation forms where there is a drastic temperature difference. The grid does not fit that concept as it is so small it does not contain a temperature gradient large enough to introduce condensation.
I am researching steel frame construction for possible hurricane/tornado resistant type home, can I utilize Straw as the insulating medium for the outside walls, sandwiching the straw between an outer and inner steel wall?
Straw can be used with steel framing although you need to isolate the steel from the straw with roofing felt so condensation does not enter the bales.
Since I live in sunny England there is of course an issue with rainfall and splash back onto the plaster wall. Do you have any suggestions that can help me with this problem?
There are two main ways to protect against rain splash. The first is to use a house wrap or building paper around the bottom three courses of bales. Simply staple the wrap to the bottom toe up under the bales and then use landscape pins to hold the wrap in place along the top edge. This works fairly well. The other option is to build pony walls that actually raise the bales away from the floor by about two feet or so. Two feet is a good number because you can use one piece of either drywall on the interior or plywood on the exterior ripped in half to cover twice the distance in sheathing. This also provides a chase for all the wiring and plumbing in the walls. You can use the space below the pony walls (short framed walls) to run all of that stuff while avoiding the bales entirely.
Can straw be used in states where the humidity is high in summer months?
In terms of humid states, it depends on how humid and if the area gets a chance to dry out. If the relative humidity is so high that the bales would reach and sustain moisture contents of 20% or higher, then you cannot build with bales. I do not know the comparison of bales with foam. Bales are generally rated as R-40. Perhaps that will help.
How do I go about plastering the ceiling?
Plastering the ceiling is very much the same as plastering the walls. You will likely drop a lot of plaster in the process, so glasses and a hat are a good idea. The ceiling will only be a finish coat of plaster as it will be drywalled, not baled. If you use the Natural Hydraulic Lime (NHL) for the finish coat, increase the amount of lime in the mix to make it a bit stickier. You don"t have to do a lot. If you removed two shovels full of sand per bag of NHL, that would do it. If you are using the premixed finish NHL, you may want to run a bit more water in it to make it more workable. In other words make spread further. If you are using a different plaster, like earth or gypsum, the key is experimentation. You want the mix to be sticky, that is for sure. Be sure to use some type of joint reinforcement at the ceiling edges. This could be paper or fiber drywall tape embedded in the wall plaster and mudded to the ceiling. I would suggest you do the ceiling before the final coat on the walls but after the scratch and brown on the walls.
ABOUT THE AUTHOR
Andrew Morrison is the founder and owner of A. C. Morrison Construction, LLC, a company specializing in straw bale construction. Andrew has a passion for straw bale construction that is matched only by his desire to teach his knowledge to others. Andrew is the creator and builder of the Straw Bale Village, a community of 15 straw bale homes in the National Historic Landmark City of Jacksonville, Oregon. He is a skilled, licensed General Contractor (CCB License #161204) with experience in designing and building both conventional and straw bale homes. Andrew has owned A. C. Morrison Construction, LLC, since 1996. Andrew received a BA degree from Hampshire College in 1995 for Glacial Geology. He also has a degree in construction technology. Please visit his professional web site.
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