It’s impossible to separate house design from construction method. What can be built with one construction method cannot necessarily be built with every method. Sometimes the plan is driven by the design, and sometimes the design is driven by the plan. In all cases the design should be driven by site and lifestyle. In some cases the plan is driven by ability and resources. In our case, we are trying to consider all aspects; cost, ability, site, lifestyle, method.
In designing a house, I want something I could actually accomplish by myself. By that I mean, I want a house that could be constructed within my limited physical ability. Before I could plan on a design I had to have a do-able construction technique and a plan to pull it off.
I’ve actually been doing research on building methods for about 10 years. There is no method I haven’t researched, right down to stick and mud huts.
While doing research I ran across Thomas J. Elpel‘s low cost slipforming technique. The method he used to construct his house in Pony is really neat (slipforms used in concert inside and outside). The possibilities with this technique are definately intriquing! Uh, a few small problems . . . I’m still at the point where I can’t lift rocks and we have no rocks native to our local. I really like the way it looks. Elpel is definately a guy who can think outside the box.
Then Elpel’s brother said “what if” and Elpel took a short sojourn in another direction. The house Elpel and his brother Nick built using tilt wall construction is absolutely awesome . . . but boy those walls are massive. The Elpels hired a crane to set the walls in place. I love the method and think it is very innovative and full of inspiring possibilities, just not right for me, what I can do and where I live.
Then Dani Gruber from Colorado queried Elpel about his technique and what he thought might be possible (one slipform is replaced by a stay in place SIP)! To the disbelief of many, she, with the help of her 73 year old father, built the stone portions of her house using this untested version of Elpel’s technique. I recommend visiting her and reading up on this. It’s interesting stuff and a very fun read. Then Elpel took his own words to heart, building a two story home using the same technique. Both Dani and Elpel’s houses are wonderful . . . not me, but wonderful. Lots of lovely thermal mass . . . unfortunately it’s on the outside of the building, but lovely regardless.
So, to build a house. Hmmm. My problem is actually twofold. Lack of money and impinged physical ability. I’ve got plenty of brain power and a good array of experience, but brainpower and experience alone isn’t going to get the job done. While I’m healing and my physical ability is improving, it’s time to get busy planning.
I’ve got construction experience, it’s just not in house construction. I have mechanical aptitude, I’m really good at sequencial organization and I’m just a bit better than average in understanding the physics of things. I’ve done plumbing and electrical and have done a few pole buildings. With all that I should be able to figure out how to build a house without spending a fortune and overstressing myself. (One of the benefits of the internet is you can snicker and I won’t hear it. Snicker to your heart’s content.)
I’ve been researching trying to find a home building method that would fit both my current budget and physical limitations. From within this double handicap I have to think and work smarter. I’ve got to pinch my pennies until they whine and use my few physcial resources very wisely.
One of my resources is surplus EPS foam. Terry’s brother is peripherally connected to the industry and has supplied us with surplus in the past, and will hopefully do so again in the future. The foam panels we’ve gotten are in varying sizes and thicknesses, but free, which is the really important part.
In looking at different building techniques I think EPS/ferrocement tiltwall construction will fill the bill. Ferrocement is low tech, flexible in technique, structurally strong and low cost. Ferrocement done horizontally should be within my physical means.
Ferrocement over EPS foam should produce a panel I wouldn’t need a crane to lift and it will cost less than regular cement. It will require a fraction of the cement of either the Elpels’ tiltup construction or either of their slipform methods. I can’t physically ferrocement the vertical walls of an entire building, but I can build individual panels horizontally that can be tilted into place and joined using standard ferrocement techniques. I’m aware before I start I’ll have to pay special attention to cold joints.
Let me stop here for a minute and explain. I am NOT wrapping the EPS foam in ferrocement. To do that would be unwise, producing a thermal bridge which would negate the value of the EPS foam. In simpler terms, ferrocement connecting the inside layer and the outside layer would allow heat and cold to travel fairly unrestricted from the outside to the inside. In cold weather, everywhere the ferrocement connecting layer bridged to the inside of the house, condensation would form. Here in the northwest, where there’s condensation like that, there’s eventually mold. Where there’s mold you can bet the house’s occupants have health issues. I already have health issues, I don’t need any more, and certainly none that I can avoid by applying brainpower.
To use ferrocement tilt wall construction I have some obstacles to navigate. Most of what I need is more information. My knowledge has gaps and my experience has holes. I’m great at research, so these are obstacles I can navigate.
- I need to be able to cut the foam and glue it together to form the thermally complete sheets of foam I need for walls and roof. I’ve got a schematic (thanks Dusty) for a hot wire cutter to build and test. Glueing the pieces together to make a whole I can handle. I can handle cutting the panels to shape (including the beveled edge) once I have finished refining with the cutter technology. I’m thinking I need at least two different configurations for the foam cutters. I need one that will act like a big chop saw or huge paper cutter, with the hot wire on an arm that pivots down to cut foam. I need one that is stationary through which I can push the foam to cut the foam to the correct thickness.
- I need to figure out how to fasten the electrical boxes onto the bottom of the mold in such a way as to keep the concrete out of the box as the concrete is worked over and into the reinforcing, while still ensuring the box will be firmly held in place. I also have to be able to lift the panel off the mold and not leave the boxes behind. Plastic and clay might be the answer. I’ll have to do some testing on this.
- I need to find the perfect fasteners for connecting the inner and outer layers of ferrocement through the foam. I’ve seen a number of different types of connectors, but most of them are designed for regular cement, not ferrocement. I’ll keep researching, test driving any I think might work. Wire is not ideal. Whatever the material is, it should not provide a thermal bridge between inside and outside ferrocement panels. As a last resort I can use wire, but I am going to work hard to find a viable alternative.
- I need to know how much reinforcing I need so I can have a structural layer of ferrocement outside and a plaster (thermal mass) layer inside. I may find I’m doing it backward, that I need the structural layer inside and a plaster layer outside. For now I’m going to assume I need structural inside and out, as if the house will actually be a building inside a building with the roof built ala mxSteve (my hero) in layers (ferrocement, insulation, ferrocement). From a couple different places on the web I found structures in the process of construction that show me how I can do the roof and make the inside thermally separate from the outside. Everywhere I look the reinforcing is three or four layers (more for water tanks) with varying sizes of reinforcing rod. Two layers of welded wire sandwiching a layer of reinforcing rod and a cover layer of plaster mesh. If I actually have to have both inside and outside structural is will increase the cost of the building, but not as much as building with regular cement and reinforcing. If I can increase the reinforcing and have only the outside (or inside) structural, that would be ideal.
- I need to figure out how much reinforcing I have to put over windows, doors and archways as headers.
- I need to figure out how to fasten my lift cables to the panels to lift them without distorting the exposed reinforcing, damaging or warping the panel. I also need to know how long the panel has to cure before I can safely lift it. Too long and I have major cold joints, too soon and the panel disassembles. Dayton’s got cement in place connectors, but they’re meant for regular cement and aren’t designed for the thinness of ferrocement. More research is needed. I may have to cement in bolts that can be removed after the wall is in place. Once the bolts are removed the holes can be foamed closed.
- I need to figure out how to lift and maneuver the walls into place (note to self: research lifting frames). We have a farm tractor and it’s a simple matter of physics, I just need to do the research and testing.
- I need to confirm the connecting method for the electrical conduit where the walls join so I can complete the electrical runs. I need to talk to the local electrical consultant to see if he wants to advise on this project.
- I need to figure out the bond beam that will run around the outside top of the walls. The bond beam will be part of the tie for the wall to roof connection and it will help distribute the roof load. (We have 64 psf snow load here.)
I know how I want to fasten my ferrocement panels together once they’re set in place. The joining technique the Elpels used (which is totally awesome) won’t work for ferrocement unless I want big bulky joints . . . which I don’t. By staggering the layers of reinforcing and leaving the reinforcing around the edges of the panel exposed, I will be able to hogring the layers of reinforcing together after the wall is tilted into place. Then I can ferrocement the exposed reinforcing inside and out. The top I will leave exposed until I am ready to do the bond beam. For the foundation I will set the wall ends on poured pier blocks and pour the foundation under the panel incorporating the rebar extending down from the panel and out from the pier blocks and up from the base foundation. The roof will be done monolithically as well. Once the building is done it will be one monolithic unit, very strong and secure.
As far as actual construction goes, a lot of the time will be spent on preconstruction. We’re using surplus EPS foam in all shapes, sizes and thicknesses. The pieces will first have to be hot wire sliced (thanks, Dusty, for the tips on creating this tool) to thickness, then sized, shaped, glued/joined to make a thermally complete 12’x9′ panel. The sides and top of the panels will have to be angle cut to meet the adjoining walls and roof. Constructing a panel out of scraps may take as long as a day and is very dependent on the size, shape and thickness of the scraps we’re working with. There’s no point in building this house if the foam is not going to completely seal the inside of the house thermally. Looking at steel stud construction drives me nuts because of the thermal breaks and insulating skins. Arg!
Once the EPS panel preconstruction is done the ferrocement layers (inside and out) will have to be preconstructed. I will need a spreader/lifting rig for this once it’s done so it can be moved onto the panel mold intact and unbent. I’ve got this figured out. I have a general idea how the reinforcing will have to be staggered, but I won’t be able to confirm the technique until I get a chance to test it.
For placing connectors from one ferrocement layer to the other I’m sure I’ll need a jig. Lay the jig on the foam and make the holes to accept the connectors. Lay the jig on the newly laid ferrocement to place the connectors. Place the foam over the ferrocement making sure the connectors go through the holes. Fill the holes with foam, lay the final layers of reinforcing and cement in place. I wonder if there’s a way I can use cable ties for this . . . I’ll have to give it more thought. This method sounds cumbersome. I’ll have to play with this some more.
Panel layup will procede as follows.
- The EPS panel will be preconstructed with window, door, connector locations, electrical conduit and box placement locations prepared.
- The interior and exterior reinforcing will be preconstructed with the appropriate window and door openings and header reinforcing in place.
- The electrical boxes will be fastened to the bottom of the mold and sealed against cement incursion.
- Temporary door and window bucks are assembled in place in the mold.
- The preassembled inside layer of reinforcing is placed into the mold.
- Ferrocement layer connectors are applied to the reinforcing.
- Wet sand is packed around the outside edges of the reinforcing to keep it clear of cement.
- Cement is applied to the exposed reinforcing. A hand vibrator judiciously used will help get everything covered and leveled.
- At this point the first layer of ferrocement can be allowed to set up. This will allow the foam layer to be placed over the connectors without displacing them. I’ve seen connectors that get pushed through the foam into the bottom layer of cement, but they are again for rc, not ferrocement. I want to be sure I have a good connection between layers and I want assurance the reinforcing layers have been engaged. If I can’t find what I want I’ll have to step back and punt. I know I won’t use something thermally conductive, so I want to leave wire out as an option.
- The foam layer is laid over the ferrocement layer.
- The connector holes in the foam panel are foamed closed. (If I can come up with effective push through connectors I won’t have to deal with this issue.)
- Ferrocement reinforcing is laid over the foam and connected to the connectors.
- Wet sand is applied to the perimeter.
- Cement is applied to the exposed reinforcing. A hand vibrator judiciously used will help get everything covered and leveled. Texture can be rolled onto this layer of cement.
- Once the concrete has set the panel is lifted into position.
- The foundation under the panel is poured.
- The exposed reinforcing layers are individually hogringed to the matching reinforcing for the adjacent panel and the joint is ferrocemented closed.
- Repeat for the number of walls needed.
I figure I can use two layouts for the 26 walls as every pod wall is identically sized in width though not identical in height. One layout will be for the majority (20-9’x12′) of the walls. Six of the walls will be 12′ wide and 9′ at one end but extra tall at the other. All six of the exception walls will be the same shape.
Ferrocement walls are very strong, but will they support a clearspan roof for a 29′ wide octagon. I’ve been struggling with concepts for load bearing support of the roof beams. I also need to construct the bond beam without producing a thermal break in my walls. This link is for an open topped water tank. It gives me a starting point. I envision something like the image on the right . . . which I got from looking at this link.
It’s time for you to see the steps I went through before selecting a final floor plan.
On to the floor plans overview.
If you comments or questions, you can reach me at mailto:firstname.lastname@example.org?Subject=House Two.