Our subfloor sandwich is quite the cornucopia of materials and we were eager to install it right after reinstalling the metal wall panels. Once it was complete we could consider the bus’s interior shell complete.
First … Draw on the walls
That’s right … we grabbed a permanent marker and doodled on the walls before we laid down any material. We wanted the edges of neighboring plywood boards to meet halfway on the metal beams, but our first layer, a vapor barrier of felt paper, would shroud the frame entirely. We needed an alternate way to locate the beams.
By drawing 3″ lines on the walls to indicate the beam locations, we could still discern where to place our plywood’s edges. These locations also informed us where we could tie in interstitial fasteners to the frame.
Here is our subfloor sandwhich starting from the bottom (right above the bus frame) to the top which is visible inside the bus. It’s total depth is 1.625″ :
- Bottom layer = 30# felt roofing paper
- 2nd layer = 1/4″ plywood
- 3rd layer = 1×4 lumber framing with ¾” rigid foam insulation boards sandwiched inbetween
- Top layer = 5/8” plywood
We considered not putting insulation because we imagined that we would never be in a terribly cold climate. I’m glad we did because that’s exactly where we ended up spending our winters – in snow. Fellow converters complained on Bus Conversion forums that the rigid foam squeaked while the bus was moving. We solved this by leaving about a 1/2″ gap between the insulation boards and the lumber.
Application of the First 2 Layers
As I mentioned above, we layed the roofing paper across the open bus frame. With our beam locations indicated we were able have the edges meet equally on the frame. Unfortunately, we sometimes we had to cut off as little as 1/2″ from 4′ x 8′ board of plywood so that the edges would end up in the middle. We thought it was a worthwhile extra step so that the floor would be structurally sound.
Starting at the front of the bus, we tackled the most intricate part first. In addition to cutting around the wheel wells, we had little notches for frame pieces to consider. We actually had to redo this first piece because it just wasn’t fitting well. We hated to waste material, but we were getting frustrated jiggling and wiggling the thing in. I’m glad we saved our sanity at the cost of another sheet of ply.
As soon as the 1/4″ plywood was installed, we drew more lines to indicate the beam locations. This time we drew right on the board using the lines marked on the wall.
Application of the Last Layers
The 3rd layer required a lot of measuring and cutting because we were trying to match our lumber to the frame below. More measurements and cutting were needed for all the insulation boards that fit in between the 1x4s. After a dry fit test, we glued each board and lumber piece onto the 1/4″ ply with construction adhesive. Immediately after the 3rd layer was glued down, we put more glue on top of those pieces and laid a (precut and pre-tested) layer of 5/8″ ply on top.
The rain barrels (recycled 5 gallon buckets) Uncle Frankie had left out for the chickens came in handy as they were placed on top of the entire sandwich of wood and insulation so that the adhesive would dry with the pieces in the correct place. Don’t worry PETA, we left some barrels of water out for the chickens to stay hydrated.
Right after we put all the buckets down, Michael continued to really fasten the floor to the bus’s frame. He used 2″ and 2 1/2″ Tek Screws that self-tapped.
All in all the subfloor took about 2-1/2 days to complete.