During my initial research on utility trailers for my tiny home I wondered why, if DOT trailer width limitations allows for 8’6″ don’t they make a trailer deck to that width?
When you’re thinking about your tiny home design, you must keep in mind a couple of factors where you do not want the trailer deck to extend to the maximum allowable width.
First, keep in mind that the depth of your walls, if you use 2×4’s (1.5″x3.5″ real measurement) for your wall construction and then there is an additional exterior rated sheet goods, plus a vapor barrier (depending on your climate), and siding or shingles you’ll end up with a wall thickness of somewhere between 5.5″-6.5″. That being said, you’ll have an additional 1″-4″ extending beyond your structural wall components.
Will you have a roof overhang?
You options will vary depending on the slope of your roof. This brings up not only roof overhang factors, but also overhead factors. Some roof coverings require an overhang of at least 2″. Other require more. Check with your manufacturers for these specifications.
My rule for making sure you are within legal size limitations is to check here; http://drivinglaws.aaa.com/laws/trailer-dimensions/
…then subtract 2-3″ from your state’s listed height (trailers fluctuate from tip to tip depending on how level it is in-tow), subtract the installed depth of the chosen roof covering. For the tiny home width calculation, work backward from the needed roof overhang minus maybe 1″-2″ to be safe on your states width limitations, then subtract your chosen wall covering, you’ll have the exterior framing dimension – This will be your actual trailer width dimension.
For you interior dimension you then take the number you’ve arrived at above and subtract the 3.5″ (2×4’s width) from both sides (=7″) and you’ll have the actual tiny home interior dimension.
There are many existing tiny home plans out there. You may want to choose one of these to make things a little easier.
Here’s an example from the tinyhousetalk website;