Building the post and beam framing

Putting up the walls on a round building borders on being fun, especially with insulated concrete forms like Perform Wall. It’s an easy exercise that brings a fairly fast reward. As long as you’ve planned ahead a bit and have installed the proper rebar, j-bolts, window and door framing and such. Once that is done the real work begins though.

The first thing that must be done is to figure out how to put some sort of sill on the top of the wall. This will be secured to the wall with the J-bolts that were previously placed into the concrete channels of the ICFs. Usually this would be a dimensioned piece of lumber. Due to the shape of the walls however, this is not a particularly good option. The curve of the outer wall requires either multiple straight pieces that need to be securely joined, or some sheet material (Plywood) that is cut to a curve. I opted to make the sills of two pieces of 3/4” plywood cut in the shape of the wall’s curve. The photo below shows the curve being applied to a sheet of plywood. As each curved piece is 12 inches deep, there are several pieces available in each 4 foot by 8 foot piece of plywood. Given the proximity of the plywood to concrete, the bottom piece is cut from pressure treated plywood.

Sill Template

The template, above, is shown with a freshly cut sill piece. The template is clamped to the sheet of plywood and a circular saw run along it’s edges.

Cutting the sills

This photo shows the sill being cut with the template clamped to the sheet of pressure treated plywood. I don’t have a photo of installing these pieces, but it’s pretty straight forward. The pieces are installed as overlapping sills over a foam plastic sill cover. Holes are drilled for the J-bolts and they are glued together to make a single circular sill.

The next piece of the puzzle is the framing of the first floor ceiling. I decided that I didn’t want to do a normal spider web style ceiling, given the waste inherent in it’s coverging rafters. The resulting design is a post and beam style ceiling with exposed beams and 6 support posts surrounding a center room roughly 10 foot in diameter. I was able to get beetle killed timber cut to 6×12 inch beams 16 feet long, which just barely fit the design.I used local beetle killed joist boards as well, although it was more expensive than normal dimensional lumber.

The Tower lift

Building this part of the house took the longest and was the most involved from an engineering standpoint. Since I was working alone and didn’t have access to expensive (to rent or buy) lift equipment, I had to improvise. I used some previously used bracing material to build a central tower which became the center pivot for a lift arch. For lifting I used come-alongs and a block and tackle. Using this I was able to lift the large timbers used in the ceiling. As there were at most two people involved in building this house, the importance of this device can not be emphasized enough.

Building the lift tower

The photo above shows me building the central tower used in the lift. I’m kneeling on the center concrete pad that the posts will be achored to. A ball bearing from a swivel castor is mounted to the top of the tower. This is bolted to the beam (made of more scrap boards) which extends from the tower top to the outside wall, where a rider is assembled which rides on the sill plates. It’s at this point that the roundness of the walls becomes very important, as well as the placement of the tower in the exact center of the circle. The rider must stay on the sill plate at all times. The beam must be strong enough to hold the heavy beams that will be lifted. Once the tower was placed, every other piece of the device was built in place. The come-alongs and block and tackle were placed over the beam at various places to facilitate lifting. The base of the tower was attached to the post hold down plates to keep it from tipping. A plumb-bob was used to place the center of the tower over the center point of the house.

Bringing in the timbers

Shown above is the lift in place and being used to pull beams into the house from a trailer parked outside the doorway. A roller stand and saw horses are used to facilitate the move. The beams are not completely dry having been sawn from the tree the week before, thus they are very heavy. The supports for the tower are visible and are important in keeping the tower from being pulled towards the beams. Note the drain pipe already placed in the floor.

Moving timbers

Here the lift is being used as it was designed, to move large timbers around the building site. This timber was previously pulled in onto the saw horses from a trailer. Now it is being moved into it’s position within the house so it can be prepared for assembly. A block and tackle is used on the right hand side to hold the timber end up while a come-along is used on the left while the lift rolls around the circle atop the wall. Later the lift will be used to position the timbers on top of the wall and interior posts.

Around the outside of the wall and on top of the sills, I place 4×12 inch timbers on edge. The ceiling support timbers will attach to these on the outside wall to spread their weight over a larger area of the wall top. Otherwise all the weight of the timber and the ceiling members it supports would be on a 6” section of wall. This is a potential problem, especially where a timber ends up over a door or window opening. The following photo shows me attaching these 4×12s to the sill plates. I used galvanized angle iron brackets to connect these pieces, and where ever possible used the J-bolts holding the sill plates to also hold the brackets. As the 4×12 timbers were not curved, this created an 18 sided polygon on top of the round wall, 4 inches wide. The ends of the 4×12s were angled and lag bolted together. Later nail plates were added to these joints.

After the 4×12s were installed securely, it was time to start the frame. In the photo above you can see a post (6in x 6in x 10ft) laying on another beam. This post and it’s 5 mates are bolted to brackets on the center foundation pad with the smaller “pin” facing up. Two large (6 in x 12in x 16 ft) beams set on each post at right angles to each other creating bays for the ceiling joists to be placed.

Blind dovetail joints are used to connect adjoining support timbers. This is where I get to use some skills acquired by my days as a guitar maker. I used similar, but much smaller, joints to afix guitar necks to guitar bodies. Here I scale the design up to securely join large timbers. In the finished structure, these joints face down. The one I show here (“A”) is visible directly over my head as I sit in the breakfast nook and write this.

This work was all done with hand tools: Hand saws, Framing chisels and Hand planes were the only cutting tools used. Great care had to be taken that each joint matched surfaces interally. As a precaution I used steel brackets to re-enforce each joint. These brackets are hidden by the ceiling materials and not visible in the finished structure.

In the above photo it’s possible to see the small square hole at the end of the timber. That hole lines up with an extended “pin” on the post upon which it will sit. It positions the beam firmly on the post. The next beam is placed over this beam with an angled lap joint. The angle of the lap joint forces the upper beam to slide into the lower beam. Both beams are held in place by angle iron brackets and lag bolts, which, as before, will be hidden in the ceiling. As a younger man I would probably have not used the brackets, but being older and wiser now I over build where ever I can.

Above is the basic frame structure in place. All six posts are up and all but one has it’s attending beams in place. That last one shows the angled lap joint awaiting it’s mate. The center tower lift is still in place as it’s needed to finish lifting the remaining timbers.

From above, the structure of the frame is more visible. On the left, the first ceiling joists can be seen. Towards the back it’s possible to see two 4in x 12in x 16ft timbers that are joined into the main beams. This allows for 5 parallel bays for joists on each side of the house. Each bay is 8 feet wide. The beams make up the longer distances so the joists can be relatively short and not as deep. Using 2in x 8in joists allows 4 inches of the beams to be exposed.

And finally the joists are installed. I left the tower lift in place although I didn’t use it much for raising rafters. It was faster to just lift the smaller joists up by hand and cut the in place. As I used rough cut beetle killed lumber for the ceiling joists, I had to cut each board down to use the metal joist hangers.

Initially, I had planned on building a central spiral staircase to access a finished upstairs area. In the end we decided not to finish the upstairs and installed a pull down attic ladder instead. The center area was blocked in with joists matching the rest of the ceiling.

The next step was to install the attic floor. This was a fairly simple proceedure somewhat complicated by the need to cut the outside off as a circle. It would have been simple enough to draw a circle with a nail and string, cutting the circle with a saw, but I seem to never like doing things simple. After taking down the tower lift, I used the swivel castor again as part of a large jig to trim the outside of the floor.

The circular saw was bolted to this contraption and I walked it around the circle. Some times it takes a lot of work to be lazy.