Tiny House Weight Debate

How do you calculate the weight of your tiny house? How do you know if your trailer can handle it?  There are several ways these things can be determined, it all depends on your situation, as does everything… Here is my logic and some of the tools I used to get there.

First step

The first thing to decide would be if you already have a trailer you’re going to build on? If so then you have to decide how much it can carry and design within this.  I am not going to go through the details of how to find out how much your trailer can already carry. Andrew already did a stellar job of demystifying that over at Tiny r(E)volutions HERE.   Once you know the max weight design your house using the basic principles below.  

Note:  If you buy plans they generally come with a gross build-out weight to them. That is handy to use so long as you know you’re going to use those plans with no/minor modifications. If however you are going to change some materials around (say you want granite counters instead of plastic laminate counters) you can use some basic calculations with the tools below. Add that to their weight to verify that you’re in the right range still.  

Guesstimate

What if you design your own tiny house? How can you guesstimate your weight so you know how much your trailer will have to hold? So you can buy the correct trailer?  Rough estimates say your house will be approximately 500# per foot of length. There is a lot of variation with that though.

My case

For those of you who have followed my project, you know that I pretty much had the house designed before I got the trailer. The trailer I found needed to be modified to hold the weight I needed it to. Because I had these known modifications, I was able to more accurately plan my axles. Both the location and the maximum weight.  I purchased a duel 7000 pound (each) capacity axle, flat-bed, goose-neck trailer. Initially I was planning on a concrete floor (6000 # in itself). I ended up installing a third axle just to be safe.

If you are going to go this way and customize your trailer be sure to calculate in the weight of your trailer. Mine is just shy of 3000 pounds for all the steel. If you add 6000 for the floor it brings it to 9000 pounds. Before you even add the house!  So two 7000# axles would only leave me 5000 pounds for the rest of the house in that example. I was boarder line if I could make that work so I welded on a third axle. This allowed me to go up to 21,000# total. Allowing me 12,000 for the rest of the building materials.  Through the design process I have since nixed the concrete in favor of much lighter weight tiles so my trailer is overkill.

Material Counts

Tiny houses are small enough that you can pretty easily take a volume or square foot count fairly painlessly. You have to do this to buy your materials anyway.  Once you have those calculations you can apply weights to materials and get a pretty decent idea of where you’ll stand.

I have collected a list of common building materials that you can use.  I add a contingency onto the end weight to account for things that are harder to pin down. Things like the  faucets, hardware, furniture etc. I suggest about a 20% contingency. That may seem high but it’s better to be over than under!   Make a material list and add things up. If it’s too heavy you can start to massage your finishes to make things work out better. This is a pretty important part of the process so spend some time on it.  

Common Material Weights:

Wood Stud, 2×4 (pine):      1.31#/linear foot

Wood Stud 2×6:    2.05#/linear foot

Metal Studs:  1#/linear foot

SIPs Panels, 6″:   3.47#/square foot

Insulation, rigid – 1″:  1.5#/square foot

Insulation, batt 1″: .04#/square foot

Insulation, spray-in 1″:  .5#/square foot

OSB Sheathing, 3/8″:  1.22#/square foot

OSB Sheathing, 1/2″:  1.63#/square foot

OSB Sheathing, 5/8″:  2.03#/square foot

Plywood, 3/8″:  1.08#/square foot

Plywood, 1/2″:  1.44#/square foot

Plywood, 5/8″:  1.8#/square foot

Gypsum (drywall), 1/4″: 1.1#/square foot

Gypsum (drywall), 3/8″:  1.65#/square foot

Gypsum (drywall), 1/2″:  2.2#/square foot

Gypsum (drywall), 5/8″:  2.75#/square foot

Metal Roofing: 2.5#/square foot

Asphalt Roofing: 2#/square foot

TPO Roofing:  .7#/square foot

Carpet: .3-.7#/square foot

Porcelain tile: 4.5#/square foot

Hardwood Floor (birch), 1/2″: 2.4#/square foot

Hardwood Floor (oak), 1/2″: 2.05#/square foot

Hardwood Floor (poplar), 1/2″: 1.45#/square foot

Wood Planks (pine), 1/2″: 1.46#/square foot

Cement, 1″: 12#/square foot

Granite, 1/4″: 3.6#/square foot

Hardie Board Siding, 1/2″: 3#/square foot

Linoleum: .75#/square foot

For a more comprehensive list click HERE.

Notes

For a more comprehensive list of various woods click HERE. A board foot is equal to a 1’x1’x1″ section of wood. You can do simple math from there to get to your thickness/width.

You’ll notice some of these are assembly weights. If that is the make-up of your wall skip adding up the individual materials. Just use that weight per /square foot of wall.

Other Components

In addition to your building material weights you will need to account for your appliances. The best way to do that is, if you order them on amazon there is an exact weight.  If not you can get an idea on how much a stove similar to the one you’re getting will weigh. Again, lean to the cautious side and round up. If you are going to have a water tank on board – or a water heater – use it’s ‘when full’ weight. (water weighs 8.34# per gallon).

Once you have all of that added up figure out your contingency. I use 20% to account for all those little pieces that it wouldn’t be efficient to add up.  Then you have your weight or at least a healthy stab at it to get you started!

Hopefully that is a semi helpful bit of info!  Anyone else?  How did you determine this?  Did you figure it out beforehand or just build?