Mobile Foundations – Solid Beginings


Wow, are we behind. The walls and roof are now framed and I’ve begun the process of sheathing. We have a storm moving through (former tropical storm Simon) and I have a day away from building to give some updates.

We initially planned to place our floor joists at the same level as the trailer frame allowing for ample loft space (while keeping under the 13’6” road limit). That plan quickly dissolved as we saw the complexities involved in that plan and we began laying our boards over the frame.

We employed a simple framing plan with the boards laying on their sides extending out over the metal trailer frame. The main trailer i-beams are spaced at 6′ and we want a full 8′, so we’ll have a bit of a cantilever. To support the cantilever and allow for additional space for insulation as well as sewer plumbing we used 2x6s for the joists. At the wheel wells, rather than having a step, we elected to lay the OSB directly over the gap in framing. We will add additional support in the walls to accommodate this weak point.


We rented a pneumatic stapler and air compressor to apply flashing to the underside of the sub-floor. The thick aluminum will provide a weather, pest and radiant barrier. The flashing is sold in 75′ rolls at widths of 10 or 14 inches and is easy to work with. This is a worthwhile step and we used it as our sole underlayment for the sub-floor. Make sure to buy plenty of foil tape for all of your seams.

A mentioned, we decided to place our sewer plumbing in the sub-floor. This will be very convenient later when we work on the walk-in shower and the kitchen sink, which sits on a peninsula. Using PVC primer and glue, we shouldn’t have to worry about leakage any time soon.

As for insulation, we went with cellulose. Both of the big box stores supply this recycled newspaper as a blown-in insulation option. We placed it by hand since we didn’t have a very large area. This is a very inexpensive (roughly $100 for a 170 sq. ft. floor, 5.5 inches deep), green (85% recycled content), and effective (R-3.7/inch) insulation. It turned out to be alot of work breaking this stuff up and placing by hand, not to mention the sun reflecting off the aluminum flashing.


To finish up the sub-floor, we placed 5/8” OSB. Our 24” spacing proved true and the placement went without issue. The floor feels very solid and I can’t tell where the studs/cavities are while walking.


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