On Saturday 7/2/16, Mikey finished cutting the last remaining piece of 5/8” plywood subfloor and fastening it in place.   There was a fairly quiet but enjoyable celebration of the accomplishment (probably some iced tea - no cake).

The plywood is arranged in six large and six smaller pieces, covering the six major rectangular spaces formed by the framing beneath.  Because a single piece of 8’ ply would not span the 99” floor completely (and 10’ long plywood does not seem to be readily available in our area), we decided to cut and stagger the pieces so that the larger pieces spanned across all but one of the joist cavities, with the last piece filling the remaining void. All joints between pieces are centered on 2x4 joists or blocking pieces, with an allowance of about 1/16” between adjacent pieces (lengthwise only) to allow for expansion. Unfortunately the fir plywood we ordered did not come “sized for spacing”, so we weren’t able to add spacing in both directions (I don’t believe this is as much of a concern with subflooring as it is with sheathing).

After each piece was cut and before it was installed, holes had to be bored in numerous locations wherever the threaded anchoring rods welded to the steel perimeter framing of the trailer protruded up through the subfloor framing.  The rods are 5/8” diameter, and after some initial experimentation with fitting the pieces (and a couple mishaps), Mikey settled on 7/8” diameter for these holes. 

Placing the cut pieces over the rods involved both of us, and some warping of the plywood made the placement a little challenging; but once the plywood was fitted over the rods, each piece dropped into place and only a very little trimming of the outside edges was needed on a few pieces to make them flush with the edges of the perimeter wood framing beneath.  After the pieces were in place and before they were glued and screwed down, we used some concrete patio blocks to flatten out the sheets. After about 24 hours the warping was completely resolved.

The plywood is fastened with #9 2 1/2” R4 GRK screws 6” apart on edges and 12” in the field. Before fastening down, we laid a bead of PL Premium adhesive to the top of all the joists, as is typically recommended for flooring.

A single thin coat of Thompson’s Water Seal was applied to the completed subfloor to keep it from absorbing any water while exposed to the elements (though we are doing our best to keep everything under tarps anyway).

Any concerns about plywood not lying flat on the subfloor framing because of rigid foam insulation being too tall turned out to be unfounded - with all screws holding the plywood in place, the resulting subfloor surface was completely flat, and - inexplicably - perfectly level in all directions! Note that if you are filling your floor cavities with rigid foam, anything thicker than 5/8” plywood is really overkill for the subfloor (even at 19 3/16” spacing), as the foam adds an immense amount of rigidity to the floor.

Next up (pun intended): Wall framing!

The completed 2x4 framing for the Tiny House floor was divided effectively into 30 rectangular spaces by joists and blocking pieces installed to stabilize them. These rectangles were of roughly similar lengths and widths, and all were 3.5” deep - the width of a 2x4.  Mikey’s plan called for each space to be filled with rigid foam insulation, to be provided in three layers of 2”, 1” and 1/2” thicknesses respectively.   A grand total of 90 rectangles of rigid foam had to be cut from available 4x8 sheets of the three thicknesses.

The bottom layer in each space, 2” thick, was cut allowing for a 1/4” gap on all sides between the rigid foam and the surrounding 2x4 framing.  The 1/4” gap was filled with Great Stuff Pro, dispensed with a handy foam gun attachment from several 20-oz. aerosol cans. A nice foam gun can be had for ~$30-$50 and is highly recommended if you’re going to be doing a significant amount of foaming. It will allow you to reuse the same container of Great Stuff until it’s fully used up. We used the “Doors & Windows” variety of Great Stuff, since it doesn’t expand as much and cures with a bit of flexibility, to hopefully allow for some shrinking/expanding of the framing.

Before installing 2” foam in all spaces, a trial application of the next layer - 1” thick - was made in 3 spaces to validate the technique and check if there would be enough room left above each 1” piece to allow a 1/2” piece to fit flush with the top surfaces of surrounding wood framing.  Two of the first spaces we had done to be re-done entirely (not easy) because the bottom piece of foam was slightly bowed and the top 1/2” piece would consequently protrude above the framing. This was before we developed a good system for installing the 2” pieces, using clamps at each end of the piece to hold it down while the Great Stuff cured.

After the trial, the thirty 2” pieces were installed -foamed in place - throughout.  Next, excess foam had to be cut away so that the next, 1” layer would lie flat on the first layer.  Once the 1” layer was complete, Michael considered a key decision: whether to go ahead with the 1/2” layer as initially planned or leave it out to ensure that the plywood subfloor would lie completely flat on the 2x4 framing.  If the 1/2” layer did not fit perfectly, some of the subfloor weight (and weight of structure above) would be supported by rigid foam rather than the framing itself!  (The rigid foam was effectively incompressible).

Michael decided to proceed with the planned 1/2” layer, and there was an immediate need for me (Jon) -who had been cutting almost all the foam rectangles to that point - to get busy and cut thirty more pieces, this time 1/2” thick.  A race was on, with Michael trimming excess foam, vacuuming up trimmings, and placing 1/2” pieces about as rapidly as Jon could cut them.   The 1/2” pieces were not foamed in place; they were cut to the full dimensions of the cavities and simply pressed into place after trimming excess foam above the 1” layer.

The cutting process itself merits some attention.  Among all the spaces to be filled, there were two different widths (wide and narrow) and two different lengths (long and short).  For each rigid foam layer, there were 16 long & wide pieces, 8 short & wide pieces, 4 long & narrow pieces, and 2 short & narrow pieces.  Width markings for cutting the 4x8 sheets were simplified and expedited somewhat by use a of a homemade marking gauge of length 17 3/16” (for wide dimension) and another gauge a half-inch longer for marking out of full-dimensional 1/2” layer pieces.  Michael’s excellent cordless Ryobi jig saw (fairly light) was used for all cuts.

When the final 1/2” piece was put in place near nightfall on 6/19/16, there was nothing but satisfaction with the decision to install all three layers. With only a few tiny exceptions, the entire expanse to be covered by plywood subfloor was so totally flush that it looked like the cavities were filled with something like reflective liquid mercury (foil backing on rigid foam was shiny).

On to the plywood!

Every house - tiny or huge - needs some kind of a yard, and Michael’s Process Tiny House is no exception.  Long before any pieces of steel were welded to start building the custom trailer, Michael had already designed and created a marvelous little idyll to serve both as a pleasing view from his future residence and as a restful place of respite.

Fondly known to him and his family as “The Grove,” this special place was carved out of a wooded area that was a small meadow just thirty years ago.  Now surrounded by tall young oaks and maples and birches, The Grove is graced by a network of apparently meandering but artfully placed stone pathways, branching out from a peaceful seating area with cedar single and double adirondack chairs.  A small fountain and a wind chime make their soft sounds; and ferns, hastas, small evergreens, and other plantings are neatly situated among the paths.  After dark, a set of six solar-powered luminaries scattered throughout the area come on automatically and can be seen from many yards away in all directions.  There is also a place for a possible future fire pit for small evening or late-night gatherings.

The Grove is an ideal spot to sit and read or just enjoy the outdoors with a glass of iced tea in shaded relief on a hot day.  Every member of Michael’s family enjoys spending at least a few moments daily or weekly in this natural retreat where their worn nerves can be rejuvenated.

On Monday 6/6/16 Mikey decided to take the day off from work because the weather was great and he wanted to work on Tiny House. 

We started on cutting 2” rigid foam insulation pieces to fit into joist cavity spaces. We worked on saw horses set up out by the willow tree (to keep toxic dust away from places where Holly, our Sheltie, hangs out).  He tried using the new Ryobi cordless jig saw; it worked great but the blade was not quite long enough to cut completely through 2” foam.  The cut pieces were left hanging by the foil backing, so he cut through that with a small utility knife from underneath, like using a letter opener, and it made a clean cut.  

Each piece is separated from surrounding wood framing by 1/4” on all sides which he fills with Great Stuff Pro foam, squirted into the crack with a special nozzle from a tall, 20-oz, aerosol can. Each space is 3.5” deep, and the plan is to fill the depth of each with 3 rectangles of rigid foam, one above the other: a 2” layer on the bottom, then a 1” layer, and on the top, a 1/2” piece.  Not much room for error - the bottom piece needs to be perfectly flat against the sheet metal under it so that when the next two pieces above are added, the plywood flooring will not have to compress the (incompressible) rigid foam under it.

The first couple of 2” pieces were bowed slightly downward in the center, and once the surrounding foam was in place and solidified, it was hard to force the 2” piece to lie completely flat.  Solution: when first placing the rigid foam block in the space, hold the ends downward against the sheet metal with a small wood scrap held by a clamp to the adjacent framing wood, and leave the clamped scraps in place until Great Stuff foam has solidified (perhaps 20 minutes). 

About 10:15, Mikey had to leave for a doctor appointment.  When he returned, we had to pump water off the trailer tarp before we could start putting cut foam rectangles in place - lots of water from 2” rain Sunday.  At 1:40, with 3 pieces in place, I had to leave for a dental appointment, after which I went to England Hardware for some items and looked for more Great Stuff Pro, which they didn’t have.  When I got back from England’s, Mikey had completed 1/6 of the whole trailer with 2” rigid foam - a total of 5 cavities, but he was running out of Great Stuff Pro.  So then he took off for Home Depot to get more; after returning he completed 5 more spaces with rigid foam for a day’s total of 10.   

We didn’t get as far as we had hoped - a long way to go with insulation before we can start the plywood subfloor.

Yesterday and Saturday together, we must have gotten at least 2” of rain - real downpours at times. Whenever that much water collects, whichever one of us is available goes out to the trailer and pumps out all the pools formed on top of the big tarp, within the joist cavities.  The pump works great until its small inlet on the bottom gets clogged with debris (continually dropped by trees above), so I wrapped it in some fabric screening held by a rubber band, and it clogs less frequently.

We are finally done with all the details of floor framing.  Monday 6/6 is supposed to be clear, and we plan to start cutting pieces of rigid foam insulation and installing them in the joist cavities.