So the year is over. It didn’t exactly go as I had hoped, but we are definitely in a better position to build next year than we were a year ago, more on that in my January kick off post. It is a bit frustrating as I put off doing other things because we expected to build, but such is life. This past month, I took things pretty easy. I only called one person for a quote (a very reasonable sounding plumber that I will bug again in January), and I put some time into building the home virtually.
Virtual construction is a way to run thru the process of building without the huge expense. I individually model each stud, track, buck and ICF piece and then assemble them as I would in the actual construction. Along the way, I am thinking about sequencing and other assembly problems. I try to build to the plan, but make notes when I need to make changes so things will fit. Of course, the computer could make things a bit too easy, for instance, I could just array my studs along and have perfect spacing. Instead, I tried to build things more manually by inserting and positioning each piece.
The below image shows the first steps of my basic construction plan.
I would start by pouring the footing, which includes a lot of precise layout, rebar, form work, etc. Actually, once that footing is done, I will be much more relaxed for the rest of it. I would then set the track (curved or straight) for my steel studs into the top of the footing with Tapcon screws. Then I would place wooden window and door bucks to guide the spacing of the studs. The Marinoware steel studs and steel frame jambs would be set (plumb) and screwed into the tracks. Flat straps are screwed to the outside of the studs to increase the rigidity of the assembly. Metal lath is screwed to the inside of the studs and track, partially to add rigidity, but mostly as a curved backing to catch and form the shotcrete.
Along the way, I spent a lot of time figuring out steel stud placement. I am planning to use “balloon framing” so that load bearing walls will line up and I won’t need to spend as much time or money on laying the curved track. Since the steel studs will just be fancy integral formwork, I don’t need to follow strict structural guidelines. Instead of 2ft or less spacing, I can go a bit wider and not need to cut as many studs for windows, etc. I can vary the placement of the studs to line up with windows and doors across the various levels. For instance, there is an opening directly above the basement opening (shown above). If I shifted the main floor opening by a few inches, I could use one long steel frame jamb instead of needing to place two. I could also align the guest bathroom door with a mezzanine window buck and simplify the framework there also.
After all the steel studs, rebar and conduit are in place, with metal lath to keep things stiff and catch the shotcrete, we would shoot the basement walls 8 inches thick. Since the steel studs are 4 inches deep, this would leave 4 inches beyond the studs. The rebar, just outside of the steel studs, would be nearly in the middle of the wall.
Even though many of the steel studs go thru 3 floors (balloon framing), only the basement shotcrete would be applied in this phase. The top of this shotcrete wall would be cut/troweled roughly level six inches below the floor level. We may even be able to set the column base plates in before the shotcrete sets completely. We would then setup the steel columns and ring beam (I will need a crane of some sort) that will later support my concrete arches. I may do a little MiG welding to tack things in place at this stage.
This assembly looked fine at first, but I later discovered that the ring beam intersected the door buck by several inches. This was a mistake I had not caught earlier. I decided the best fix would be to notch the ribs… These thumbnails illustrate.
The floor system I have chosen uses ICFs (Insulated Concrete Forms) to support the concrete (instead of the wooden subfloor the architect/engineer specified, so yes, I will need to get this stamped by an engineer at some point, I was quoted $800 for that). These QuadDeck ICFs have light steel joists built-in to reduce the number of temporary supports needed. The ends will rest on the shotcrete walls with an inch or two of polystyrene overlap (roughly cut with a hotwire) and be tied in with bent rebar pieces.
This next image is a detail of the rebar (shotcrete and other details are not shown for clarity). Horizontal rebar is wire tied to the outside of the steel studs and should increase the stiffness of the formwork. I considered threading it thru the holes, but that would probably be quite a hassle. The vertical rebar is wired to the inside of the horizontal rebar, but with 8 inches of thickness, there is some flexibility here if needed. Rebar is placed before the shotcrete, and then some pieces are bent down into the ICF channels as needed. More can be added later and bent upward if necessary. I anticipate some issues in certain locations where the QuadDeck spacing clashes with the steel stud spacing, but it should be manageable. I also considered/modeled rebar placement between other ICF sections.
After the ICF forms are placed, they can be walked on. The electrician and plumber should appreciate how easy it is to set conduit and piping into the ICF decking. The ICFs are about 7 inches deep and we will be adding 5 inches of concrete on top of that, so there is plenty of room to work. We also plan to lay radiant flooring across the top of the ICFs. There are little plastic clips that screw into the polystyrene easily to support the radiant tubing. We will screw a form to side of the wall to contain the poor. It will only need to support 12 inches of concrete, so it shouldn’t be a problem.
Some of you may need a cross section vertical to understand the quad deck floor properly… Here it is. Basically, the ICFs form the “negative space” so that the concrete forms a nT (like a single or double-T, but continuous) beam across the spans. Where we meet a wall, the ICF is cut away so the concrete rests on the wall (tied in with rebar not shown here). On the left side of this example, I have cut away some of the ICF in order to create a concrete cross beam above the stairs to the basement. After the concrete is poured, the ICFs remain to provide insulation against heat and noise. They will ensure that my radiant heat goes up.
Now that there is a floor to walk on, additional studs, conduit, bucks, etc. are added in preparation for the main floor shotcrete. Since many studs penetrated from the floor below, this additional work is just incremental. I have not modeled it all yet, but it will include the fill walls under the ribs, the walls around the spiral stairs, etc. Once these walls are up, I will want to model the arches across the donut vault, the hop across the basement stairs, etc.
Here is a final look at how far I got during my Christmas break…
This process has been interesting so far and has resulted in a number of small changes. For instance, I noticed that the original plans placed the mezzanine windows such that the east one was right up against the east wall. When I built the 3D model, I placed the stud so that it would be at the surface of the 8 inch thick wall, but realized that one of the 12 inch thick ribs actually intersected the studs supporting the window. If I wanted to build the balloon wall before placing the ribs, I would need to move the stud by at least 4 inches to clear the rib. I also planned to put in a 14″ sun tunnel thru that corner to bring daylight to the guest bathroom, and that would also have passed in front of the window… So I decided to move all the mezz windows over by 16 inches. Since the steel studs were also framing main floor and basement doors, those would also need to move (to keep the steel stud layout simple). In the computer, this was much much easier to fix than it would have been if I had discovered the issue during the actual construction.
Similarly, I decided to lower the basement egress windows by 6 inches, I added a door way in the basement, etc.