Monday, September 16, 2013
The Start of my First "Micro-Micro" home: Planning Phase 2 - and some eye opening realities.
I will have to build the front door, I just can not find a 6 foot 2 inch tall 24 inch wide door out there except for paying a carpenter to make it for me. I don't want to spend $1500 on a custom door, so I will be building it myself. Windows, I have discovered are available. 17" wide by 24" tall double hung windows are available commercially, they are aluminum frame, but only $50 each. I still may just make my own windows, and I will have to make the ones for the loft as nobody makes a 18"X18" diamond window that opens.
My Construction is going to be simple. 2X2 walls, 2X4 for the loft floor, and 2X4 for the roof (because I am going to bird mouth the ends and do traditional roof construction) 1/4" plywood for all exterior surfaces and interior wall finish. with 1/2 for the loft floor and the main floor. Vynal siding or Cedar siding is possible as they both are close to the same weight. I dont trust either to deliver any structual stability to the microhome, so the 1/4" plywood sheathing will still be installed.
I feel better with 16" spacing on studs for 2X2 studs, I may try 20" on the roof and loft to save a little weight by cutting out 2 2X4's from the construction. The loft will add strength to the whole building. I am still very worried about weight, so I really need to calculate things out exactly, then compare to the real world. Let's start with the weight of a 2X4...
So, let's assume the 2x4 is eight feet long. A 2x4's actual dimensions are 1.5" x 3.5", so its volume is 1.5 x 3.5 x 96 = 504 cubic inches. Divide that by 12 to get 0.2917 cubic feet The nearby link shows the weight densities of common lumber. Let's assume it's made of pine, which is pretty common. If we use the high end of the range, pine has a weight density of 34 pounds per cubic foot, so 0.2917 x 34 = 9.9167 pound = 158.7 ounces, more or less, depending on the type of pine and the corresponding density. So my calculations are a bit more conservative than the estimates I made. 1 Linear foot of 2X4 is 1.25 pounds, so 1 linear foot of 2X2 is .65 pounds. That is a little lighter and makes me feel better. for the framing. It is actually surprising how heavy wood really is and how even a tiny house can weigh a TON in short order even when using smaller lumber for framing. Let's try and get a better calculation for the plywood. This one is easier as the APA has a specification that the manufacturers are supposed to follow.. 3 pounds per square foot per inch of thickness.. So if we calculate that out, .75 pounds per square foot of 1/4 inch and 1.5 pounds per square foot for 1/2 inch This is darn close to my guessimates. I found that 2 inch foam board is about .3 pounds per square foot, and Cedar lap siding is .5 pounds per square foot.
We can now run some real weight calculations, and things get heavy fast. the wall framing will weigh about 40 pounds, the sheathing on the outside and the paneling on the inside of the walls will weigh 330 pounds. The insulation for those walls will weigh 62 pounds. The trailer frame is 350 pounds, and the floor plus insulation is 77 pounds. The Loft being built from 2X4 and covered in 1/2 ply will weigh a whopping 208 pounds. The last bit is the roof, and this will be heavy. 3 feet 4 inches to the peak from the loft floor. with 3" of insulation and 1/4 sheathing on the outside and inside as paneling. PLUS the tar felt and metal roofing. Each rafter will be 4 foot 8 inches to give us the 12/12 pitch that we need for the headroom inside. using 2X4's we have 25 of the boards at 4.67 long and 1.5 pounds per foot. Gives us 370 pounds for the roof. So we are already at over 1400 pounds and we have not added anything inside. like flooring, siding outside, windows, trim, electrical, furniture, etc... I can easily see it hitting 2000 pounds without much effort. and this is going for light weight and nothing inside it. My other concern is that I have the BULK of the weight in the entire trailer above the 6 foot level making the Center of gravity dangerously high for the wheel width, just by guessing I place the CG at the 7 foot mark above the deck on a trailer with a 6 foot wide tire stance.
This means that my PopUp trailer find will NOT be a good candidate for the microhome project. It will make a fantastic Large Teardrop camper though so that will be my project for that frame. I need a trailer that can hold 3000 pounds, preferably 3500 pounds. and I still have no idea how I am going to get the center of gravity to a location that does not make me afraid for my life. A CG that high will mean a trailer tip over If I ever had to swerve. I am starting to wonder if ANY of the microhome designers out there ever put any engineering into CG and towing safety.. I am also starting to wonder about safety of 2X2 construction with well over 700 pounds of just the building on the walls. add another 500 pounds for 2 people and gear in the loft and you now have a 1200 pound LIVE load on the 2X2 walls. I am certian that 2X4 and 2X6 will easily handle it, but that will drastically increase the weight to the world of 4500 pounds finished.
I do know that this will slow down my build process, but having real information instead of trudging ahead on a guess and a golly is a good thing. I still need to get more weight and design information going, but Instead I am changing to building a teardrop camper for the spring to get some construction experience with the trailer I already have. I am not abandoning the microhome project, but I am seeing a feasibility problem creeping in that will exceed my limits. I need to be able to tow it with my Jeep and at what I see is becoming a 4000-4500 pound project is beyond the towing ability of my current vehicle. At that point you might as well build a larger microhome because the needed jump up in tow vehicle and trailer size will allow you to build a much larger microhome that will be far easier to live/camp in. Even just increasing the size to 7.5 feet wide and 16 feet long will give a drastic space increase.