Monday, November 26th, 2007 | Popularity: 69%
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.
Photo Credit: Sierra Log Homes
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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.
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.
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. Check out the photo below from log homes-thefuntimesguide.com.
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.
Popularity: 69%
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Andrew Morison is a licensed contractor specializing in straw bale and green construction. He has shown thousands of people how to build their own straw bale projects through his comprehensive series of instructional straw bale, concrete foundation, and plastering DVDs. You can check these out at http://www.LearnStrawBale.com.
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November 27th, 2007 at 10:21 am
I too own property with a steep slope and have been wondering if I can still build a bale building on it. It seems like using the pole foundation like you describe would not really support the weight of a heavy straw bale structure above it. How can I be sure that it will be safe in an earthquake prone area? Thanks.
November 27th, 2007 at 10:53 am
The key is to make sure the posts, beams, and bracing are engineered by a professional. These structures can be very strong if properly designed and implemented.
November 29th, 2007 at 9:27 am
You say “There is simply no way around foundation engineering when working on slopes.” But in the load-bearing video, don’t you build on piers because the ground slopes? Does that mean engineering may not be necessary if you build really small, or if the slope isn’t too severe?
November 29th, 2007 at 11:35 am
TC,
That is correct. If the building is small and/or the slope is not steep, you can usually build a foundation to code with no engineering. When you get into two stories and larger structures, the loads are much bigger and so the foundation must be capable of handling the weight and the pressures of the slope.
March 9th, 2008 at 5:37 pm
Andrew, I want to build a very small studio (224sq ft, one story@12″ high) on a slight grade. I wanted to do this on a pole-built system, using four uprights connected by a crossbeam “platform” floor with a daylight basement. I was told placing straw baless on this platform would cause the dew point to rise into the bales and make them rot- is this true?
And as a second question, do you think this project is doable for $3500?
March 10th, 2008 at 12:03 pm
Shan,
I do not see there being any problem whatsoever with the raised floor system. You can add some cheap insurance by using the roofing felt and gravel or insulation underneath the toe ups to keep any migrating moisture away from the bales. If, however, you are creating a conditioned space in the daylight basement, then there should be no additional moisture to worry about. If the basement will be unfinished and unconditioned, you will need to provide adequate ventilation to keep air movement high and thus moisture build up low. The price seems reasonable, but will depend on material costs in your area and the labor costs you deal with. If you plan to do the work yourself, then you should be fine; however I doubt you will be able to complete the structure with paid labor for the price you name.
April 20th, 2008 at 3:49 pm
Can bales be used below ground?
April 22nd, 2008 at 8:42 am
I do not recommend that bales be used below grade. I believe the risk of decomposition is far too high.
April 22nd, 2008 at 10:14 pm
When you build a wood basement, you can spray a water/insect coating over the wood. I hoped a similar method could be used. When using bails below grade/ground level.