Floor Insulation

Jan 29

TEMP: 34° / partly cloudy 

By buying a trailer from Tumbleweed, the bottom of the trailer comes completely sealed with steel so you don't have to deal with covering the bottom and can immediately begin installing the insulation.


  1. Start by measuring the joist cavities of the trailer. You want to subtract roughly 1/2" from all sides because you are going to use foam insulation to seal everything into place.
  2.  Cut the rigid insulation with an Exacto knife. The one end of most of the cavities had a lip that we needed to slid the top insulation layer under. To fit, we cut a 2.5" wide, .25" deep row on that side so that the insulation would slide right under.
  3. Our rigid is 1.5" wide, and the depth of the trailer is 3" so we stacked 2 layers of the insulation. This will give us an R14 rating*, which will be good for the floors in a colder location like Colorado.
  4. Use adhesive glue to secure the rigid insulation in place in the cavities. You'll want to add weight to the insulation then to hold them in place.
  5. Fill the edges of the rigid insulation with the foam insulation. This will expand above the top of the trailer but you will cut the excess off when dried. We learned that it's best to take it slow when moving around the perimeter and fill them entirely as you move along because foam insulation is messy and moving slow makes things cleaner. We weren't sure how long it'd take for the foam to dry in the cold, but it ended up taking roughly 6+ hours. You need this to completely dry in order to make cutting off the excess easy.
  6. Cut the excess with an Exacto knife when dry.
  7. Next, we placed a line of the mounting tape around the black steel frame. The reason for doing this is that the cold air will travel through the steel easily and by adding the tape it will act as a small barrier for the cold before it hits the plywood floor which will sit on top of this.
Securing the rigid to the trailer and then adding a second layer of rigid insulation.

Securing the rigid to the trailer and then adding a second layer of rigid insulation.

Using granite to hold down the rigid insulation.

Using granite to hold down the rigid insulation.

Holding everything in place with weights.

Holding everything in place with weights.

Cutting excess foam when dried.

Cutting excess foam when dried.

*R-Value represent the extent to which insulation resists heat flow; a higher R-value means more insulating value.



Rigid Insulation

Owens Corning - FOAMULAR 150 1-1/2 in. x 4 ft. x 8 ft. R-7.5 Scored Squared Edge Insulation Sheathing

Roughy 10, with excess pieces after cuts


Loctite - PL Premium 28 fl. oz. Polyurethane Construction Adhesive

Roughly 4 

Spray Foam

GREAT STUFF - 16 oz. Gaps and Cracks Insulating Foam Sealant with Quick Stop Straw

roughly 12 cans

Mounting Tape (cold air barrier)

Frost King -E/O 1-1/4 in. x 3/16 in. x 30 ft. Camper Mounting Tape for Trucks

5 rolls

Vapor Barrier

HDX - 10 ft. x 25 ft. Clear 6 mil Plastic Sheeting

1 sheet