Archive for the ‘Landscape Walls’ Category

Cross Section of a Straw Bale Landscape Wall/Rubble Trench Foundation

Many people have recently asked me about landscape walls. As a result of those inquiries, I’ve drawn up a cross section of a landscape wall and rubble trench foundation for you to check out below. This is a basic design that can be used in most locations. Some building departments allow for rubble trench foundations within the codes while others are less accustomed to them. Be sure to discuss the potential to use this design before you commit to the design. You may need to make changes to the system or simply educate the building officials around the effectiveness of the rubble trench design.

I’m open to feedback on the design. If you think there’s a better system, let me know. I always like to hear how other people do things. As a builder, I always spent time visiting other contractor’s job sites and talking to them about how they did things. I’ve learned a LOT by talking to others and I continue to learn this way today. One detail I often put into landscape walls in wet climates is a metal wall cap. The caps are custom made by the local metal shops (those who fabricate metal roofing are best) to fit over the top of the finished wall. You need to provide some anchoring points for the caps within the wall, but that’s not shown here. Simply let in a 2x at the top of the wall so that the bottom edges of the roof cap can hit it during installation. be sure to install the wood nailers before the mesh so that the mesh can lock them tightly in place. Get the wall cap in a color that matches or compliments your plaster and you’ll barely notice it’s there (or you’ll see it as an asset to the design).

One point around landscape walls and moisture. It’s really not that big of a deal if the bales get wet and ultimately rot out. That matters BIG TIME in a house, but a wall is just that, a landscape wall. The bales are not acting as insulation, they’re basically acting as forms for the plaster. Once the mesh is properly installed and you add 1 1/2″ of plaster to each side of the wall (all the way up and over actually), the bales can rot out without the wall collapsing. Of course, the overall strength of the wall is better with the bales in place, so protect them as best you can. Just don’t loose sleep over water getting in through a failed washer on a screw that attaches your wall cap. The wall will be fine!

Bales As Soundproofing

Many of you have written to me in recent months asking about using straw bale walls for soundproofing against noisy streets and neighborhoods. I have responded to a lot of you individually, but figure it’s better to give everyone this information as well.

I have to start with a funny story. Last night, as I was trying to go to sleep, the outside gate was swinging and banging in the wind. The gate is attached directly to the side of the house we’re currently renting (no, it’s NOT straw bale, and thus the funny story). My wife was still awake and so I asked her if she could go outside and close the gate. She did and when she got there, I could hear she was having trouble getting it to latch. Without leaving my bed I said, “you have to lift the gate up and push it towards the house while you latch it.” She thanked me for the input, latched the gate and came inside. We both laughed when we realized we had just had a clear conversation, with no difficulty hearing each other, right through the wall of our house!

What a sorry state of affairs it is when we can actually talk through our walls. The walls are insulated, by the way, but even still, they are easy to talk through. That would never happen in a straw bale house, I guarantee it! In fact, when my crew would work on straighten walls, after they were all stacked, they would often use walkie talkies to communicate with the person on the other side of the wall. Without those, they would have to walk over to a window opening and reach their heads out to communicate with each other.

So the answer to the question is yes. Yes, straw bale buildings are incredible insulators from sound. If you live on a very loud street or perhaps you back to an interstate, these walls will eliminate almost all of the noise that you currently live with. You can build a straw bale house or consider building a straw bale landscape wall. Although not as good as an entire house of straw, they still work really well to eliminate sound.

The science is in the density. Sound travels as waves. When it moves through hard material, it travels in fast, short waves. When it travels in soft material, the wavelength increases and slows down. Now look at a straw bale wall. The outer plaster skin is hard and dense and so the sound waves move through it at high speeds; however, when they hit the bales, the sound waves slow down. The key here is the interior plaster. In order for the sound waves to escape the soft bales, they would have to accelerate to get into the hard plaster skin. They can’t do that and so end up absorbed in the bales. Voila, sound proofing 101.

Straw Bale Landscape Wall Construction

Do you live in a loud neighborhood? Are you tired of looking at the same style wood fence around every home in your neighborhood? Building a straw bale landscape wall instead of a typical privacy fence around your garden may be a better choice. The straw bales not only provide privacy but also superior sound proofing. If you live on a busy street, near a loud school, or near the highway, you’ll find the sound proofing qualities of a straw bale wall amazing. In addition to the privacy and sound proofing, straw bale landscape walls are beautiful. They are more elegant and original than any conventional landscape wall be it wood, stone or concrete block. The natural undulations and curves make straw bale walls more comfortable for the human experience as well. It may sound strange, but straw bale walls can actually help calm the people in your home. Studies have shown the calming effects of straw bale walls on horses and humans alike. It seems the natural beauty of straw bale walls is more than just pleasing to the eyes.


Landscape Walls and Rubble Trench Foundations

It must be something in the air. I have received a bunch of emails about building landscape walls in the last week. This after a long drought of such questions. So, I guess it is time to talk about them again. The majority of the questions I have been getting are around the foundation system and the restrictions of building a landscape wall with bales.

(Note that in the diagram below, the foundation is not properly insulated. I use this photo solely as an example of a deep rubble trench assembly)

Let’s start with the foundation. I prefer a rubble trench foundation for landscape walls as the need for concrete is low and the need for positive drainage is high. I want water to move away from the wall. I also don’t want the wall to heave and shift with water and freezing cycles. A rubble trench foundation does a great job of protecting the wall from such concerns and also provides a strong foundation for the wall to sit on. Check out the image of a standard rubble trench above. Note that the gravel goes below the frost line and that the drain in the bottom moves any water away from the wall. It is best to slope the bottom of the trench with a 1/8″ per 1′ slope from end to end. On a long wall, this can be a big difference in depth from the start to the end of the wall, so be prepared for that. The drain should be wrapped in soil fabric and then covered with clean 1 1/2″ river rock. The round river rock is best because it does not need to be compacted mechanically. It will compact on its own under the weight of the material above it. Being that you are surrounding a plastic pipe with the rock, this is a good idea as a mechanical compactor that close to the pipe would probably break it. Once you have the river rock in place, you can add recycled rip rap (old concrete scraps) or rock. I prefer to use 3/4″ minus gravel and then compact it in 4″ lifts as I fill the trench. For me, compaction is key and rip rap is hard to compact well. You can use the ri[p rap and then pour a very wet concrete slurry into the trench to bond all the rip rap together. The slurry flows into the voids between the rip rap and makes one big solid unit of the material. Be sure to get the mix ratio right on the slurry or you will end up with a bunch of cracked, flaky junk in the trench.

The question of how to top that trench is the next issue. A standard application, as shown in the above image, is to use a steel rebar reinforced concrete cap. This cap serves a few purposes. First, it ties the whole system together in one solid piece. Second, it provides a base for the structure above it and gets that structure off of the ground. Third, it provides a place to attach hold downs and anchors for the above structure. This is a simple and accepted method in most jurisdictions. The use of concrete is obviously not the most green application, so there are other options. On a house, I would likely stay with the concrete cap or grade beam, because of the uplift resistance it provides. For a landscape wall, I am willing to let that go and move into a more green concept.

Another option is to use earth bags. These are poly bags, like standard sand bags, filled with dirt and a small amount of concrete to help them set. Although not a great picture, you can see above how they are stacked on top of the rubble trench to provide the lift above grade for the structure and how they create a surface for the wall to be built on. The bags in this picture need to be tamped down in place such that they end up level and fulyt compacted. This is a bit harder than leveling a concrete grade beam, but worth the effort to stay “green.” One thing earthbags don’t provide is any resistance to uplift forces so anchor bolts are not an option with this system. That is fine on a small landscape wall, but not something I would recommend on a house as I mentioned above.

The biggest limitation with landscape walls is the out of plane forces. This is the loads, like wind, that are placed on the surface of the wall that may make it fall over. You must be careful to design for this. As the wall gets taller, you will need to add buttress walls to support the out of plane direction. I have another blog post about buttress walls so I won’t go into that again here. Nonetheless, be aware of the need to add them if your wall starts to get tall. You can limit or avoid buttress walls by curving your landscape wall so there are no straight, unsupported runs. The curves will actually create support for themselves along the length of the wall.

Another limitation is the weather resistance of the wall. As you can see on the cob wall at the start of this post, roofs are a good idea to protect the wall from weather. That said, there is nothing wrong with building a wall without a roof as long as you don’t mind the eventual rot of the straw in the wall as long as you plan for it. If you use steel mesh to reinforce the plaster and strong plaster (either lime or cement based) then the eventual rot will not be a concern. The mesh and plaster will ultimately support themselves even after the bales rot out some 40 years from now. Being that the bales are not used for insulation in this application, they can be considered natural plaster forms and their sacrifice is acceptable. If you want to delay that rot, consider using a pond liner over the top of the wall extending down the top course. Place the liner under the plaster mesh so that the plaster is still attached to the steel for the reasons discussed above (strength and longevity).

Have fun with this project. You can do all kinds of things with landscape walls and create really special spaces in your yard or garden.

Basics of a Bale Landscape Wall

I received an email today about a bale landscape wall. The wall will be about 4′ tall and 125′ long. The questions ranged from what type of foundation is best and what kind of waterproofing is needed to where to find bale needles. I have included my response below.

Sounds like a fun project! If you keep the wall at 3 bales high, you will end up with a four and a half foot wall, roughly. You will need to raise the bales off of the ground by at least 6″. The foundation you use depends on the soils you have. In most cases, you should be able to dig a trench deep enough to drop below the frost line and then fill it with compacted gravel. For the top 6″ before the top of the trench, and for 6″ above grade (12″ total) form a concrete bond beam. You will need to hold the bales off of the concrete with pressure treated sills which should be attached to the concrete with anchor bolts about 4′ on center. I suggest using 4×4’s and then nail 20 penny nails into those sills at 6″ on center on both sills (there will be one on each side of the foundation to support the bales as in the house details.) To protect the bales from rain, which is important as you suggest, use either a metal fabricated cap (specially made) over the top of the wall or a pond liner draped over the top and down the sides about one bale course under the plaster. The barley straw will be fine as long as it is dry and the bales are tight. You will want to wrap the wall in mesh so to strengthen it. Finally, we have bale needles for sale and twine can be purchased at your local farming supply store. You will want two needles so that one on each side of the wall can be used to sew the mesh together quickly. Good luck with the project.