Installing the subfloor on the bus was the very first non-demolition work that we got to do during this bus conversion and we were SO excited about it. We got our first few plywood panels down and then spent about half an hour just sitting on them and reveling in it like “Here we go!!! We’re finally actually doing it!!!” Here’s a short summary of how we installed the subfloor on our bus conversion and what tools we used during that process.

Disclaimer (as always): We are not professionals. We are learning this as we go and I created these posts merely to offer guidance to other bus conversion novices like ourselves.

How We Installed a Subfloor on Our Bus

1. Rust-proofing and sealing the metal chassis

Rust can be a huge problem during school bus conversions, but we were fortunate enough not to have any rust on our floors at all. There was a lot of old reddish-brown adhesive from the original rubber flooring that scared us at first but we scraped most of that off of the floor. After scraping away some of the chunkiest bits of adhesive, we went around and sealed all of the holes in the floor with Flextape. There was quite a lot to seal, all of the holes were leftover from when the previous owner had removed all of the seats.

After all the small holes were sealed, we painted the entire floor with a gallon of Flat Black Rust-Oleum Oil-Based Enamel Paint. We chose Rust-Oleum after some research because it is a paint that prevents rust and corrosion from occurring on metal surfaces.

After the paint had dried, we were left with just two more holes to seal next to the side exit door. These had been put in by the previous owner for their future plumbing system. After careful consideration, Emmett and I decided that we did not want to have two big holes in that location. We then sealed them by gluing thin sheet metal down over/around them with Liquid Nails. You can just barely see Emmett working on that project in the “after” picture below.

2. Framing out the floor sections with furring strips

This step of the process was relatively straightforward. Emmett and I measured out each section to determine how many furring strips we would need to lay down for the subfloor framing. To avoid any more holes in the floor, we decided that the framing would be glued down. So, we put each strip into place using Loctite Multipurpose Construction Adhesive and weighed it with cinderblocks that we’d found in a rubbish pile near our worksite. We ended up having to place the framing down in three stages; we did not have enough cinderblocks to do it all at once.

3. Placing foamboard insulation within the framing

Our station wagon was not big enough for the 8 foot long foam-board insulation and plywood that we needed for our next two phases of this project. Thus, we rented a U-Haul van for one day. Once all the supplies were at our worksite, we measured all of the foam-board out and cut it to size for each section. After placing the newly cut sections, we sealed the seams between foam-board and furring strips with HVAC tape for added insulation. We were pretty pleased with the results - even when some of our foam-board cuts were less than perfect.

4. Installing plywood panels over the insulation

This process was quite time consuming - mostly because we had a few tricky areas to work with as we progressed. The board above the gas tank floor hatch in the front of the bus proved to be the trickiest of all. Anyway, over the course of three visits, we got all 7 and a quarter pieces of plywood cut to size and placed on the furring strips. We glued the plywood (using Multipurpose Loctite again) along the furring strips to reduce squeaking when walking. (This was something we learned from a YouTube video done by professional subfloor installers). After all the boards were in place, we drilled them onto the furring strips using interior wood screws. And voila, the subfloor was complete!

Tools & Materials Used for Subfloor Installation

1. Prepping/Rust Proofing

Paint Scraper

1 Roll of FlexTape

6-Piece Paint Set (2 Brushes + Pan + Liner + 2 Foam Rollers)

Paint Pole

1 Gallon Flat Black Rustoleum Paint

2. Furring Strip Placement

RYOBI 18-Volt ONE+ Cordless 6-1/2 inch. Circular Saw

Measuring Tape

Contractor’s Pencil

(22 Count) 1"x3"x8" Furring Strips

(3 Count) Premium Multipurpose Loctite Construction Adhesive

3. Foamboard Placement

Utility Knife

(8 Count) 0.75 inch 4x8 R-4 Unfaced Polystyrene Foamboard Insulation

(2 Count) 3M 2.5" HVAC Tape

(2 Count) Dow Restartable Straw Gaps and Cracks 12-oz Spray Foam Insulation

4. Plywood Panel Install

RYOBI 18-Volt ONE+ Cordless 6-1/2 inch. Circular Saw

Measuring Tape

Contractor’s Pencil

RYOBI 18-Volt ONE+ Cordless Drill

(3 Count) 3/4" Yellow Zinc Flat Interior Wood Screws

(8 Count) 11/32 4x8 Pine Plywood Panels

Premium Multipurpose Loctite Construction Adhesive