Archive for the ‘Foundations’ 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!

Anchor Bolts for Toe Ups

There are so many options for anchor bolts these days that it is hard to know what to use. I believe I have found the best option for most straw bale projects. Keep in mind that with both interior and exterior toe ups, there are a LOT of anchor bolts in a bale house. Because of this, expense has to be considered; however, it should not be the main factor.


The standard J-Bolt, shown above, is used in most sill/toe up to concrete foundation application. The problem with the j bolt is that it has to be set in place before the concrete is poured. This means that the finishing of the concrete is harder to accomplish in a flat, even surface. Having to trowel around each of the many bolts is a pain, especially those located for the interior toe ups. Secondly, the interior toe ups are not usually installed until later in the building process and so the anchor bolts, sticking out of the foundation, become a major tripping hazard.

I have moved toward using the above pin style anchors by Simpson Strong Ties® instead of the J-Bolts where permitted by code and or design (be sure to check with your engineer or code official). These bolts are easy to install after the concrete has set up and right before you actually need them. Much safer all the way around in terms of tripping, ect.. Be sure you don’t have any radiant floor heating tubes in the area as hitting one of those when installing a bolt will ruin your day.

Saving Concrete Stakes From Your Foundation Pour

Concrete stakes are essential to just about any foundation project. In fact, they are used on almost all concrete projects that a home owner is likely to encounter. If you recognize the stakes in the image above, then you must have used them before. If you don’t know what they are, allow me to explain. Concrete stakes are used to hold the concrete form boards in place prior to and during a concrete pour. They stay in place until the concrete has hardened enough to remove the forms. At about $5 each, they are not cheap, and an average home foundation can easily use 200 or more of them. Making sure that you are able to get each one out after the pour is well worth the effort, but does not always happen.

If you wonder why the stakes would get left behind, check out the photo below. The way the stakes are installed, they will end up exposed to the concrete when it is poured even though they are placed on the outside of the form. The concrete will flow out from under the form boards and around the stakes and if they are not removed before the concrete hardens, they will become a permanent member of the foundation. The picture below is a bit of an extreme situation as the forms are usually cut more tightly to the ground; however, even a little space for the concrete to flow around the stakes can cause them to stick, forever.

So how do you stop concrete from flowing out from even the smallest holes in the forms? You can waste your time trying to stop it at every little opening as you pour, but you will likely end up losing the battle and also missing the finishing time window for your pour. I have a better way: foam pipe insulation.

This material is designed to go around plumbing lines and it works just as well around concrete stakes. It can be cut with a razor knife and placed in seconds. I cut it tight to the bottom of the form and to the ground. It does not matter how much concrete spills around it as the foam can stay in place (on the outside of the form boards), and I can still pull my stakes out from inside the foam. The image below shows an example of where I needed to support a form board that would float over a widened footing. I had to stake the form board in place, but that meant having a stake right in the middle of the footing. With the scrap foam, I isolated the stake from the footing and still supported the form board. When the pour was complete, I allowed the concrete to harden and then pulled the stake, leaving a small piece of foam in the footer. This foam was tiny compared to the oversize footer and so the strength of that footer was not compromised. Without the $0.99 worth of foam, I would have sacrificed a $6 stake.

No matter what the job, from a small pad to a sidewalk or a house foundation, there is no reason not to take the extra time to protect your stakes from over poured concrete. The tip above is quick, easy, and inexpensive. In all, it is well worth the effort.

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.

Elephant Poop

elephant-poops.JPGOkay so it’s not poop, but it could be from a distance! These are piles of extra concrete. It is so important to calculate materials well and it could be the straw that breaks your back. (I meant that pun by the way.) In this case, the truck load was too short for what the concrete guys had planned so they had to thin the slab thickness which ultimately left a lot of excess concrete. To be sure, I mentioned it to the concrete company owner. It was a mistake, and not a huge deal because the slab in this case was so small; however, on a big job, the little extras can run wild quickly.

Estimating is very difficult to do well, especially if you are new to construction. Even well seasoned professionals make mistakes, so a little extra money in the construction budget for mistakes is a great idea. That said, the better you can get at estimating the more economical your house will be. Take some time to learn the basics of estimating. Get a book or two on industry standards. I suggest you add at least 10% to the industry standard as that standard takes into account professional builders working at a rate common to the industry: something you will likely not be doing.

On most materials like framing lumber and roofing, you can underestimate and the impact will be small on the building. For items like concrete which have to be poured all at once, you don’t have that luxury. In cases like that, I recommend you split your pour into several smaller pours. That way, you can get the basic idea on the first two sections. If you have extra mud, you can place in the next section and spread it out. It will simply reduce the amount of mud you need in the next pour via displacement. By the time you get to the final pour, you should have a good idea of exactly how much mud to order. This also makes finishing the slabs easier on your back and knees!

Building with Straw Bales on a Steep Slope

Today I received the following question and I thought it was worth sharing my response with you all. Here’s the question, my response follows:
“Well the time for using all this information is almost upon us. We are looking at a property at the moment to build on; however, it is quite a steep property. Do you have any ideas or photos of straw bale houses built on steep sites with out doing major earth work? Thanks in advance.
Regards Chris and Jenny”

Keep in mind that straw bale houses do not have to be built on slab foundations. In fact, straw bale walls work very well on top of framed floor systems, but be sure to include their weight in any engineering of the floor system. There are a number of ways to work on steep slope sites. Perhaps the best use of space is to incorporate a daylight basement into the design. This allows the owner to utilize the space under the house that would otherwise be wasted. The construction of the foundation to support three stories as opposed to two in a slope situation does not add that much cost and, again, you get the finished space out of it. In fact, it could be used as the first story and then only one story could be added above it so the foundation would not have to support three floors. You can see in the photo below that some additional foundation work is required to hold back the earth on the uphill slope; however, if the slope is very steep, the depth of the retaining wall will be limited.
daylight-basement.jpg
Photo Credit: Sierra Log Homes

Another option for a steep slope building site is to utilize a pole structure concept. In other words, if you do not want to enclose the space below the house as a daylight basement and want to avoid as much additional foundation work as possible, you can build the house on a stilt like structure. This foundation limits the amount of necessary concrete and can support a home of adequate size above it. The size of the home will dictate the size of the concrete footers and poles as well as the bracing in between them. This style of construction is often used in flood prone areas along the coasts and, of course, in steep terrain. The sketch below will give you an idea of how these foundations work. The sketch is courtesy of the Food and Agriculture Organization of the United States. The height of the poles will also have an impact on how much cross bracing is required. This type of foundation will have to be engineered professionally as will the daylight basement. There is simply no way around foundation engineering when working on slopes.
pole-foundation-detail.jpg

Another option is to create a hybrid system that uses both the pole foundation and daylight basement technology. Portions of the home can be enclosed with the daylight foundation concept, while the remainder of the home is supported by poles. This is a good idea when you want to use some of the space beneath the house, but not all of it. By employing both options, you can get the space you want while saving money on the foundation by using the poles.

No matter how many stories you choose to build or what system you choose to employ, building on a slope is more expensive than building on a flat lot. You will have to get some good numbers from a local concrete contractor for the cost of any foundation in this situation before you purchase the land or design the house. It is crucial that you know what costs you will encounter before you commit to the lot. As mentioned above, you will also need to hire an engineer for the structure. Happy Baling.

Evaluating the Building Site

I often tell people the first step in building a straw bale house, or any house for that matter, does not actually take place during construction but rather in the design room. In truth, this is not quite accurate. For a really good design, the first steps must take place in the field during site evaluation.

Every site is different and therefore requires attention to different details. For example, does your building site have drainage concerns? Where does the sun travel during the day? How much organic material and fill will need to be removed from the site prior to construction? These and other questions like these need to be addressed early on in the design process in order to yield a home design that truly incorporates the house into the site. In the following video, I walk you through a sample site evaluation. This evaluation is obviously truncated for time, but gives you an idea of what is involved in performing a site evaluation. Take as much time as you can spare for the evaluation. You will be happy you did in the end.

People often contact me asking for stock straw bale house plans. I tell them that I can offer them several options; however, the best option is a custom design for their specific site. Although it is possible to use plans from a different site on your property, it is not ideal. Consider that the subtle differences in topography, wind, solar access, drainage, and more can have a huge impact on the efficiency of any home, even a super efficient straw bale home. If the original design depends heavily on prevailing winds for cooling and solar gain for heating and both of those aspects are missing or limited on your building site, the home will not perform the way it was designed. For that reason, it is always best to design the home for the site you are working with. In order to best design that home, a site evaluation must be performed so that all of the assets and short comings of the site are known from the beginning.

How much time is needed for a site evaluation depends on the site itself and the amount of detail you want to collect. Some of my clients have spent a year or more living on their land in a yurt, tent, or mobile home so that they can get to know the ins and outs of the property. In the end, the site that one of my clients had originally chosen for their home was abandoned and a second site was used. Had they not spent the time they did on the property prior to building, they would have made a fairly significant mistake in the placement of the home. Although not always as drastic as this first case, all of my clients who spend time on their land before they build have reported gratitude for doing so. Of course, spending a year or more on a piece of land before starting design and construction is very often not possible. Just keep in mind that the more detail you can gather about the land before you break ground or even start designing, the better.

Here’s a cool tip I learned several years ago.
The full moon follows the same path as the sun will 6 months and 12 hours later. In other words, if you want to see how the winter sun will enter your home, watch the full moon in a summer month. If you want to know how to keep the sun out of a building during the summer, watch a full moon in the winter and see how it travels across your land. This simple tip can save you thousands on your heating and cooling bills.

Another tip along the same lines is this: contact you local power company. Boring you may say, but it is actually very powerful. Some companies will provide a free service and give you a disposable heliodon. This device is used to simulate the path of the sun across the sky on a model of your home. The value of this is that you can place a scale model of your home on the site or even on a desk with a small, stationary spotlight and investigate how the sun will play into the house at different times of the day, month and year. This simple tool can help you make adjustments to your design before you break ground…very cool!

Be sure to perform your site evaluation early and gather as much detail as you can. The more you learn about your land before you start designing the better. You may even discover new things about your property you had not previously noticed. One thing is for sure, you will know in the end that the site you chose is the best one available and you will know how best to take advantage of all the assets your land has to offer. When all is said and done, you will have a house that becomes part of the site, rather than a house that simply sits on top of the site. There is a very big difference between the two!

For more information on this topic please click this link to enjoy the article on Site Evaluation written by my design colleague Chris Keefe.

As always please feel free to comment on this post. Scroll down to leave your feedback or comments.

Happy Baling
Andrew

Know Your Ground

I just went through a humbling process on a new home construction project. I used a soils report prepared by a geotechnical engineer and provided by the land owner for a home site I was to build a custom home on. The soils report showed that there was fill from ground level to 3 feet down and that below that (from 3′ to 7′, the depth of the test pit) was “medium stiff, red-brown clayey SILT; moist.” That spelled out native soil to me and the report further stated that the foundation requirements for such soils were standard spread footers over a compacted rock base of roughly 4″ thickness.

Here’s where the humility comes in: I actually proceeded as if this engineered report was accurate. That seems like a fair assumption, but proved very expensive. The report was a couple years old, and when I compacted my gravel base on the site, the City wanted a new geotechnical report report they would approve the compacted fill and allow me to form my footers. I called my own geotech and asked him to come out for a site visit. he had us dig a test pit and when we did so, he was not convinced the soils that were quoted at 3′-7′ were in fact native. He asked my backhoe driver to keep digging. It was not until 13′ down that we knew he was right. We starting bringing up 40 year old garbage! The “soil” the previous geotech had identified was in fact 40 year old fill over an old personal garbage pit in the old property owner’s back yard.

A simple foundation changed to something very elaborate. We had to follow the native soils below the fill line all the way around the house and pour a sand/cement slurry to fill the now very deep, three feet wide holes. All of the rock had to be removed from the site so it would not end up contaminated and then replaced on the finished grade after the slurry was poured. The ultimate cost of this work was over $7000 and a time delay of one month ensued from the date of the geotech report request to that of completion of the new requirements. Yikes! So, know your ground. Know what is under your ground. Be certain that what you are building on is solid and can hold your structure. Although this was a slow pain in the rear end to deal with, I always prefer to deal with potential problems up front rather than having to fix them after the fact. The time and money spent on this project far outweighs the potential disaster that could have occurred had we not been required to get a new report. Of course, the fact that I relied on a previous geotech report is something of a frustration. The report, although 2 years old, should have been accurate and it was not. You can be sure I will write a letter to the company owner of the old geotechnical engineers on that one!

Securing Straw Bales to the Foundation

Here is a response to a student doing a case study of straw bale homes in North Carolina. He had a good question about how the bales of an existing structure in Alabama might be connected to the foundation. I think the details of the connection are worth mentioning here as well.

I am glad to see that you have chosen such a cool topic for your case study! Perhaps the most important distinction to make is that the homes are made with straw bales, not hay bales. Hay would be a food source for many critters and would also run the risk of fire because of the higher moisture contents within hay bales. Straw on the other hand has no food value and is extremely dry, typically around 8% moisture content during installation.

The old style of construction has changed significantly in recent years so how the bales were attached to the foundation in the building you are studying is hard to say. In today’s homes, we use a system that bolts 4×4 sills to the foundation. Those sills are place on the interior and exterior faces of the bales so each bale is held up n both sides at the bearing points. The space between the 4x4s is filled with gravel and/or rigid insulation. 20 penny nails are then driven into the sills at 4″ on center staggered from one side of the sill to the other (both sills are nailed and treated as separate entities when measuring the layout of the nails). The nails are only driven in until firmly secured in the sills and about 2″- 3″ of nail is still exposed above the sills. The bales are then placed on the nails and held tightly in place by the “grab” of the nails. That is the easiest and most effective way of connecting to the foundation.

Natural Slab Floor Over a Concrete Slab

I was recently asked if it is possible to do an earthen or cement skim coat over a slab foundation. The answer is yes, you can do a skim coat of either clay/straw (earthen floor) or cement over the top of a concrete slab; however, there are minimum thicknesses that need to be maintained. At least 3″ of concrete are required unless a specialty skim coat is used (this takes extra skill).

There are specialty coating systems available that can be used if you have the skills, but in general, they are much more difficult to finish well. In fact, it may be easier to simply finish the concrete in such a way that the foundation slab can be used as the finish floor of the home. Be sure to protect the floors during construction. If you plan to acid stain the floor, make it a point to know the details of that art. For example, you would want to know that a stack of lumber left on the concrete during construction will cause the stain to fail in that area leaving a blank or discolored straight line that will not look very good at all in the finished floor. You will also have to be very clear with any subs that the slab is the finished floor and inform them that they cannot write notes on the floor with a construction crayon or snap lines with red chalk. There are many things to keep in mind here and some basic knowledge is a must. Knowing what to watch out for ahead of time will be a life saver in the end!

When applying a skim coat of stray and clay, it is a good idea to use about 2″ of material to get proper adhesion and compaction. Be sure to apply the earthen floor in lifts. In other words, apply one inch of material and then let it cure. Moisten the surface of the cured floor and apply another 1/2″ for proper adhesion to the base coat and then apply the final 1/2″ while the previous 1/2″ is still moist. This will ensure a tight bond between all the coats. Compact and finish the floor as you would any earthen floor. In most cases if an earthen floor is used, you can eliminate the concrete slab altogether and build the earthen floor over compacted gravel lifts. A foundation can be poured to carry the loads of the home and then the gravel and earthen floor can be built up inside the foundation.

If an existing concrete slab is to be covered, many options are available and the ones listed above are just two of many.

Straw Bale Homes & Basements

This video is from my online video newsletter called “The Straw Bale Minute”. It focuses on straw bale homes and basements.

All of my short videos can be found on YouTube at http://www.strawbale.com/videos.

Please check them out, rate them, and post comments. Your help efforts will actually help move the videos up the line and thus get them in front of more people who find them interesting. Thanks for your help!

Bale Walls Over a Basement

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 I am often asked if a straw bale house can be built over a basement. The answer is always yes. A raised floor system, either over a basement or crawlspace, is no different than building a second floor on a bale home. Interior footings will likely be necessary to carry the load of the floor system. In some cases, you may need to step these down into a lower sectional basement for continued support. Once they are poured and in place, you can build your stem walls. You can use poured concrete or block, depending on your desired finish result.

With your stem walls in place, simply add your floor system to the top of the wall. Be sure to account for the dead weight of the bale walls when calculating your floor joist size and spacing and when considering how many interior beams or girders will be required to split the load across the span of the house. In some cases, you may need to build a secondary bearing wall directly below the interior face of the bale walls to transfer that load off of the joists. When necessary, this actually creates a great place for running plumbing and electrical in a finished basement.

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