Installing the Trusses

The bottom portion of the tiny house has now been sheathed in 1/2 inch plywood and it is time to install the trusses! The sides of the trusses have not been cut, making the rafters a full 8 feet long. This may seem extreme, but with our limited crew, the long rafters helped get the truss on top of the wall frame.

The truss raised and one edge of the rafter was set on top of the wall frame. I guided the edge of the rafter along the edge of the wall frame as my dad walked the truss towards the structure. This effectively raised the truss onto the wall using its framing as a ramp system. Once the truss was on the wall frame, it was securely screwed into place.

The truss replaces the long board that was originally used to square the wall frames. Now that the plywood sheathing is in place, they are no longer needed. 

The trusses are raised, but we were concerned that they may fall over since they are only screwed on at their base. To fully secure them, we set stays inside the structure, nailed to the vertical sections of the trusses and set against cleats nailed to the subfloor. The stays were then connected via a horizontal member which tied the whole structure together and prevented any motion fore/aft of the walls, frames, or trusses.

Our next step is to raise the main beam of the house, the equivalent of a keel on a boat. It is equally as massive as a boats keel, weighing 130 pounds, spanning 18 feet, and needs to be set in a small channel 13 feet in the air. We have our work cut out for us!

Squaring the Walls

Now that the walls have been erected, it is time to square everything up. The wall frames contain notches at their corners where support boards will be placed to hold the tops of the walls steady as we build. By setting the upper width equal to the lower width, the wall becomes a rhombus, and slight adjustment will convert it into a square.

These support boards can be seen hanging out beyond the wall frame. They are nailed into place but need to be removed as construction progresses. Nailed boards can be reluctant to release, so the ends hang beyond the frames so we can bang them upwards to remove them at the appropriate time.

Now that the frames are all tied together, it is time to square the structure. The lateral slant was addressed first, then the fore/aft slant was taken care of later. To set the lateral slant, my mom stood at the corner of the structure with a square and measured as my dad and I pushed on the wooden stays to align the walls. The principle is simple, the stays inhibit the walls from falling towards them, and since they are all tied together, the structure is stable. If we needed to go in one direction, we would lift the stays out of the grass on the side we needed to come towards and push on the opposite side. This would pull the frame over and straighten the whole assembly. We oriented the short side first, then the taller side.

To set the fore/aft slant, I tied a bowline to the top of the front wall and led the line to a strong attachment point in the bed of the truck. I tied a bight in the line and formed a truckers hitch which gave me a purchase system to pull the assembly forward in a controlled manner. Once it was square, I tied off the truckers hitch and verified that the structure appears straight in respect to the trailer.

Once both axis were rectified and squared, we began sheathing the structure in 1/2 plywood. This locked the structure into place and prevents any wracking of the frames. As the plywood panels were installed, we began taking down the wooden stays.  

Our next step will be to fully secure the plywood sheathing to all the studs.

Tiny House Assembly

All the individual parts have been assembled as best they can before any "true" construction has occurred. Everything had been sitting in wait during our two week long period of rain, waiting for the clouds to part and construction to resume.

The trailer was driven out from the carport and set on the grass near an outlet and all the wall frames were carried out to the trailer. Each wall was set up with the frame tilted outward and supported with long wooden stays to keep them in place.

The walls were coming together nicely and quickly!

In no time flat, we had all four walls up! Then we realized that we had built the house backwards. The pop-up is supposed to face the truck and the low end hangs off the back! This meant that everything came down and had to be reassembled.

We were much faster setting the walls up the second time around! Now that the pop-up is facing the truck, we are able to continue building.

Butt Blocks

The scarf joint for the ridge beam has dried in the clamps for a full week, now it is time to prepare the butt blocks.

The butt blocks flank the sides of the joint and can hold both beams together without the scarf. Having the scarf and butt blocks is overkill and mental insurance for my peace of mind. If I overbuild that important structural member, I won't have to worry about it being strong enough for the task!

The butt blocks extend 2 feet past the scarf on each side of the joint to further support the whole structure. The boards are through bolted to apply pressure and keep everything close and tight.

The problem with the assembly is I am working alone and these boards are very heavy.

I decided to do each board individually and then assemble everything once. I started by measuring and drilling the holes on the scarfed board.

Then I set the first butt block under the scarfed board and drilled again. After each hole, I would put a bolt through it to hold it all in place and avoid the boards from squirming around. The bolts helped keep all the holes aligned for the further steps.

After this, I flipped the boards over onto the other butt block and drilled down through the bolt holes. I would pull the bolt, drill the hole all the way through, and then re-seat the bolt. This was a very slow and tedious process, but it resulted in a perfect fit where all the bolts lined up.

After all the holes were all drilled, I planed and sanded the faying surfaces of the boards and prepared them for the final glue-up.

I took this moment to sand all the other surfaces as well and to radius the corners of the butt blocks.

I then positioned the king beam in a vertical position and set the butt blocks next to it with the faying surfaces properly oriented. This was my last time to check that everything was in order, as the next step involved permanent glue!

I painted Titebond III wood glue onto the faying surfaces of the butt block and king beam with a paint brush. I set the glue-up upside down so that any drips will drip out onto the top of the beam and not be visible from inside the house. 

I positioned the first butt block with the through bolts and mated it closely to the king beam. Then I painted glue on the second butt block and set it onto the bolts. With the bolts going all the way through the joint, I began tightening them down. I decided not to use washers since the bolts were not long enough to run all the way through the joint and fit the washers. Without the washers in place, they had just enough thread exposed to engage the nuts.

Tightening the bolts all the way only sank the heads and nuts into the wood a small amount. The glue and scarf joint will be plenty strong without washered bolts in place. 

On a final note, the grain orientation is important when setting up a joint like this. The grain orientation in the scarf joint should be identical, that way any warping will not stress the joint. 

The ideal grain orientation for any and all of these boards is called "Quarter sawn" where the grain runs diagonally across the end grain. The problem is this kind of wood is exceedingly expensive in these sizes. The next best grain is called flat sawn or rift sawn. These have grain running along the width of the end grain. These boards are easy to spot in a pile because the end grain looks like rainbows. The worst grain to use would be vertical grain because the fasteners would cause the board to split along the grain.

The reason Quarter sawn is ideal is because it will not warp. Vertical grain will warp very minimally, but the tendency to split makes it undesirable for such a beam.

Flat or Rift sawn boards tend to warp in all sorts of directions. They can twist, cup and bow! This may sound like the worst grain pattern to use for such a beam, but understanding what they are going to do helps you eliminate its ability to warp. 

When you look at the end grain, keep in mind that the rings want to lay flat. This means that those rainbows will become flat lines and the board will cup on the side that the rainbow apexes. When you set your butt blocks on the beam, if you set them so that they arc in a ring around the beam, they will end up pulling off the beam and opening up the seams.  

By setting the butt blocks like I have here, the apex of the rainbow faces the beam. As they warp, the edges of the beams will be smashed into the beam which will cause them to further tighten the seam while the middle of the board will pull off of the beam. The through bolts will counteract this action and keep the board smack up against the beam. The warping process will actually make the butt block junction even stronger since both sides are pushing in symmetrically.

As far as twisting goes, care must be taken to keep the beam dry until it can be coated in oil or varnish and be sure to keep it resting on a flat surface at all times. Once in place in the structure, the beam will be fastened to the walls and trusses, unable to twist or cup. 

Understanding how the boards will try to warp can actually help you create the structure that you desire. Working with what the wood wants to do can make the whole building process go so much easier.

Scarfing the Ridge Beam

The ridge beam runs from the front of the house to the back of the house and is one continuous piece of wood that supports the entire roof structure. Naturally, this timber needs to be very strong!

I chose to use a 2x12 of Douglas Fir for this beam as it will be more than strong enough to carry out the task at hand. The problem is our tiny house is 18 feet long and the longest cut I can easily get is only 16 feet long. This is where this beam gets complicated.

In order to reach the full 18 feet, I decided to scarf two pieces of wood together and then reinforce the joint with butt blocks on either side.

The scarf was calculated and drawn out on the timbers. I highlighted cracks and checks in the wood to make sure that these defects were removed in the cut.  The cut was made with a circular saw a bit proud of the line. I then brought the faying surface right down to the line with a jack plane, chisel, and a rasp. All this work payed off because they fit very well on their first test fit!

Dry test fit shows how tight the seam is between the two boards

I made a 4 foot scarf with nibbed ends, creating a very secure and sturdy junction between the two boards. A little bit of fine tuning got the boards very close together, producing a very tight seam that will be very strong once glued.

I separated the boards and set plastic wrap under them to prevent them from gluing themselves to the wood beneath them.

After applying a liberal amount of glue to the faying surfaces, I presented the edges of the scarf to make sure everything is lined up properly.

I then set the five clamps to hold everything together very tightly and squeeze out the excess glue.

For extra insurance I set 4 long screws to into the boards at an angle to help pull them together and offer structural support as well.

The clamps were all tightened down fully with the four 4-3/4" long screws holding the scarf nice and tight for the next few days while the glue sets. After the glue fully cures, the excess will be removed with a block plane as I prepare the sides of the boards for the butt blocks which will really tie it together!