Trailer extending / re-enforcing advice and help

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I have purchased a used trailer that was about 12' x 6' with dual 5200# axles.  My plans for it (and what i've already been moving towards) is to make it a 20' x 8' trailer (minus wheel well cut outs) and essentially build a travel trailer on top of it (a tiny home).  I am a bit worried about the trailer rebuilding as this will essentially be the foundation.  I have already got 4' added on to the front and another 4' added on to the rear, as well as re welded on the trailer tongue.  The metal used in the original 12' of the trailer is 2.5" x 2.5" by 3/16" wall square tubing.  It looks like it has been modified one already and I would guess it's possibly 25 years old??? (big guess).  I have purchased an additional 48' of the same size tubing for the extensions.  I will also be putting a 2"x6" pressure treated subfloor with blocking on top of the frame as well as 3/4" TNG plywood.  All wood will be glued and screwed.  You can look at the following pictures for some visual aid and to wrap your head around my problem of do I need more frame re enforcing or will the frame + subfloor be enough to handle a 10,000lb GVW ( or possibly less weight)
Reply:PS That is not me welding.  You can see what I mean by the trailed had been worked on before with those holes above the triangular spring equalizer.  In the sketchup drawings, any grey metal in original, anything light blue is metal that is not drawn in (the angular pieces are were we cut off the trailer tongue from.  and the straight pieces are angle iron braces that have been welded in from original.  Any grey with red marking is everything new that is or will be welded in.  You can also get an idea of the subfloor and how it will fit together,  The outside walls will be essentially taking most of the load.  and the final picture is what a tiny house looks like when completed.
Reply:Looks real good to me. Trailer was in real good shape to start with, looks like you have brake axles and plenty of load capacity. Depending on the finished tongue weight you might want the tongue to go further back. I still expect the anti trailer mod h8ters to try and flame you.Only thing I would recommend for sure is dont waste any trailer square footage on a porch like the one in the pic. I would say make your self a ramp or stairs and hinge them to the side of the house so you can lift it up like a draw bridge for transport.old Miller spectrum 625 Lincoln SP-135 T, CO2+0.025 wireMiller model 250 and WP-18V torchCraftsman 100amp AC/DC and WP-17V torchCentury 115-004 HF arc stabilizerHome made 4 transformer spot welderHome made alternator welder
Reply:That's going to be a slick looking trailer, heavy too I think.Only two  things I can see is I would extend the two 'A' frame braces back to the next set of bunks, there's going to be a lot of twist on the tongue and without it the majority is on the single piece of tubing running from the coupler back to the first bunk.Put a reinforcement couple of feet long (2 x 3 angle maybe) over the holes above the center mount for the spring, taper the ends and don't weld the ends neither. Me, I would have put the reinforcement on first and then welded the oscillating beam to that, it'll keep the water out as well......Mike
Reply:Motel6 is $39 a night. They have an ice machine right down the hall to the left.Bubble gumTooth pixDuct tapeBlack glueGBMF hammerScrew gun --bad battery (see above)
Reply:You started with a nice heavy tongue. Then you cut it apart and replaced those two legs with one square tube.Since you are building a box, your highest bending moment will be at the front of the trailer. You have left very little material to deal with this when you chopped off the "A" frame tongue.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:As I see it you have 2 weak spots, one critical. They are where you spliced the tubes to extend the frame and the tongue in the front. Your house will help with the tube splice, but I still would want more there. And your center tube in the tongue is good, but not enough. The side braces do almost nothing to help carry the weight, they only help with lateral stress. If I was doing it I would cut off all the old A-frame parts on the tongue and extend them back to meet the side rails. That would help carry the weight in front. You upper structure will carry most of the main frame, but make sure you plate the splices. I just like to make sure any frame splices are more than strong enough. If your going to remove the house and use it as a flatbed, then you will need more than that.Last edited by welderj; 06-17-2014 at 12:17 PM.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:Where the extensions are welded on to the trailer, there is a 12" long plate (6" on each side of the weld) over the weld and it is welded all the way around. I hadn't thought about extending the "a frame" parts back but will definitely be looking in to that. I was also thinking maybe a couple braces between the 3rd and 2nd last cross braces. The axles are about in the middle but I will be having the heavier part of the building on the front
Reply:The trailer does have electric brakes on both axles as that is what's required here in BC Canada.  The trailer did have a fairly new coat of black paint as well as new pressure treated 2x6 floor boards (will come in handy for the floor joists).  I will likely be cleaning the trailer the best I can and doing a couple coats of tremclad on it.Yes, I don't plan on wasting sq/ft on an entrance porch.  The only time I would was if I plan to do an over hang on the front or rear to help keep the weight down.  As of yet I don't overly have a floor plan decided out, But I have seen ideas for the fold out / hinged deck which would help the "feel" on the space
Reply:Originally Posted by mrmikeyThat's going to be a slick looking trailer, heavy too I think.Only two  things I can see is I would extend the two 'A' frame braces back to the next set of bunks, there's going to be a lot of twist on the tongue and without it the majority is on the single piece of tubing running from the coupler back to the first bunk.Put a reinforcement couple of feet long (2 x 3 angle maybe) over the holes above the center mount for the spring, taper the ends and don't weld the ends neither. Me, I would have put the reinforcement on first and then welded the oscillating beam to that, it'll keep the water out as well......Mike
Reply:Originally Posted by BurpeeMotel6 is $39 a night. They have an ice machine right down the hall to the left.
Reply:as I've asked someone else with the same comment,  Do you think it would be best to weld something between the front a-frame and where it was cut off from, or off set a straight back brace 4" or so, or continue that from a-frame on the same angle out to the sides?.  What kind of material would be best?also, since I don't fully understand the mechanics of it all. why will the front suffer from more bending?  will the back suffer from some as well since there is not as much bracing?? or is it basically because the front a-frame and middle bar are attached to the front cross brace of the trailer, it will really want to turn it up?
Reply:Originally Posted by welderjAs I see it you have 2 weak spots, one critical. They are where you spliced the tubes to extend the frame and the tongue in the front. Your house will help with the tube splice, but I still would want more there. And your center tube in the tongue is good, but not enough. The side braces do almost nothing to help carry the weight, they only help with lateral stress. If I was doing it I would cut off all the old A-frame parts on the tongue and extend them back to meet the side rails. That would help carry the weight in front. You upper structure will carry most of the main frame, but make sure you plate the splices. I just like to make sure any frame splices are more than strong enough. If your going to remove the house and use it as a flatbed, then you will need more than that.
Reply:Originally Posted by tiny house bradWhere the extensions are welded on to the trailer, there is a 10" - 12" long rectangular plate (5"-6" on each side of the weld. I believe my co-worker was calling it a fish plate) over the weld and it is welded all the way around. I hadn't thought about extending the "a frame" parts back but will definitely be looking in to that,  If you look below as to what i've asked other commenters, what would you suggest the best way to help out the front a-frame part?, . I was also thinking maybe a couple braces between the 3rd and 2nd last cross braces. The axles are about in the middle but I will be having the heavier part of the building on the front
Reply:That pic is a park model cabin/RV.  Very popular with couples and the senior crowd.  Rules state you can build up to 400 sq ft without a permit, it is considered an RV if you leave the axles on. Extended window seats, porches (even covered and enclosed),eves, and lofts are not included in the 400 sq ft. They are meant to be moved like mobile homes and set up long term. I have built about six and bought several for our resort, they are very popular.  Cavco is one of the main MFG's. They take advantage of every sq inch in the design. Too heavy for every day transport. Google park model log cabins for ideas, remembering the 400 sq ft rule. KOA has their own design that Cavco builds that is a very well laid out design. They run between $40,000-$60,000.  The big advantage in California is they can be installed without a permit as long as they go into a permited campground.
Reply:Like said before, extend the a frame back.  Now something not said. Good clear wood is very strong.  So use it to your advantage. Weld vertical straps (2"x1/4") to the frame front, back, and center, maybe 4 sets.  3 or 4 of the house rails run full length of the trailer, not side to side. Side to side does nothing for strength where needed. The steel straps would go up and over the beams (notch the beam a 1/4" where it does so the top edge is still flush) and weld to the side of the frame. Drill a 3/8 hole or two all the way thru and bolt the beam and straps together. Also dispense with the cross framing in the wood joist as well. Use the galvanized roll strapping some at the hardware store. Screw it to the outside edge of a joist about halfway up, run it over the top and down under the next one then over the next one and so on putting a screw where it runs over the top edge or so. Make sure it's terminated on the outside flats just not at the top edge. Go back a dot and do it again but opposite this time.  Called x bracing and it's stronger and lighter than standard bracing especially with the twisting and jarring going down the road. Also remember that nails and drywall screws have no place here!  Use a quality star or Robertson drive deck screws.  Also the outside walls need sheathed in at least a light ply.  When doing so run horizontally and offset the vertical joints from each other so they don't line up. Use polyurethane construction adhesive and screws. Tying things together like mentioned above lets the whole structure wook together and share the load with less weight. For even better weight/strength ratio just sparingly use vertical 2x2s for framing and glue in the Dow blue board with foam adhesive.  Use a batten and router to cut channels for wiring and glue/screw another light ply to the interior. The blue-board will give superior insulation as well.  Use some steel straps to attach these side panels down to the steel farme as well at least in front and back.
Reply:Also notice that the trailer has what appears to be mobile home axle and tires. 14.5"???  I suggest if you really are going to pull it any distance to change them out for standard trailer axles and tires.  The are only meant for a one way trip and tires are difficult to obtain. In several states it illegal as wellFrom Dexter Axles AXLES - Can mobile home axles be reused?The Dexter MH (mobile home) type axle is designed for limited usage in the delivery of manufactured homes and has a one-time limit use. The axle has steel forged spindles that are not precision ground. The brake assembly is welded onto the beam and not intended to be field replaced. Additionally, the bearing package is smaller than the more expensive service type axle. Most MH axles are also equipped with a single leaf spring suspension for very heavy loads. We do not have components that would convert MH axles to servicable assemblies. \
Reply:Originally Posted by firebrick43Also notice that the trailer has what appears to be mobile home axle and tires. 14.5"???  I suggest if you really are going to pull it any distance to change them out for standard trailer axles and tires.  The are only meant for a one way trip and tires are difficult to obtain. In several states it illegal as wellFrom Dexter Axles  AXLES - Can mobile home axles be reused?The Dexter MH (mobile home) type axle is designed for limited usage in the delivery of manufactured homes and has a one-time limit use. The axle has steel forged spindles that are not precision ground. The brake assembly is welded onto the beam and not intended to  be field replaced. Additionally, the bearing package is smaller than the more expensive service type axle. Most MH axles are also equipped with a single leaf spring suspension for very heavy loads. We do not have components that would convert MH axles to servicable assemblies. \
Reply:I've had those special tires pass me at high speed several times when I neglected the sticker that say's "Check lug torque before each trip"   Originally Posted by mad welder 4Wow. I never liked mobile home axles and the stupid little doughnut tire/wheel assembly they have.I see a ton of trailers around here with reused mobile home axles and tires.
Reply:The trailer will be having new brakes, hubs and rims/tires with 8 bolts. We are not allowed to use MH axles here I because of their limited life and you have to have bolt on backing plates (opposed to welded on). Luckily all my backing plates are bolted on so it's all good and possible someone converted it to hm hubs and tires?
Reply:I have 14.5 lowboy tires on my tri-axle. They are not MH brakes either. You can buy LEGAL tires in 14.5". Look at Carnival equipment. Lots of those trailers have the same wheels!
Reply:Nice. I did not know that. I have heard that 14.5 is hard to get around here but I'll be checking out carnival!
Reply:i have been thinking that having the joists run front to back on the front third and rear third of the trailer would be beneficial.  The strapping you are referring to i think is called all-round.  Do you think it would be stronger than actual blocking between the joists?  I was planning on welding on 4" - 5" tabs on the trailer where I could then bolt them through some floor joists to help hold the house on to the trailer.    I think I will be needing 2x4 walls due to the fact that the temperature around here can get as cold as -25c (-13f) but the average might be around -10c (10f).  I was thinking I will use poly isocyanurate foam for the flooring and possibly the same for the walls/ roof or maybe mineral wool (roxul) I want this tiny house to be efficient so any electricity and gas usage is minimal.  I do plan on using a good quality glue as well as screws for attaching everything.  I know I can get torx screws for a flooring screw gun from work so I should have some good solid construction.  A best friend is an electrician, so I'm sure he will help me with wiring  and good deals.  This trailer seems to be taking for ever though.  All the extending, patching, suspension, re-wiring and such... and I will still have to do all the sub-floor framing and sheeting.  Lots of work... but lots of learning as well.  I'm really looking forward to it all coming together, but right now it seems like lots of little work and not seeing major changes
Reply:Running the joist fore and aft on just the front and back third is not going to gain you as much as the center half. The stress riser is the axles and if you look at a loaded trailer you will see it.  I know 20' are probably expensive but 16' 2x6's aren't bad.  The tabs you were going to thru bolt would be fine for the middle of the joist but the front and back ends should be up and over and back down. If not it's will likely crack at the bolt and split horizontally loosing stiffness and strength. Remember that the forces on the joist are OPPOSITE of a standard house joist because of the axles. As for the blocking, in a normal house it's fine(but a pain to install). To racking, vibration, and jolts going down the road is going to cause issues with end screwed blocking splitting.  The cross strapped braces is going to put stress in shear on the fasteners instead of tension like the the blocking. Poly iso cyanate is better than even dow blue board in insulating value. I hate to work with it(gritty) but good stuff. Rock wool is stiff enough but not the values as blue board.  Don't recommend bead board for its low strength and lower insulation value. I would not recommend any loose or roll formed insulation such as cellelous or fiberglass.  Vibration going down the road is going to settle and loose serious value.  I have seen several rvs torn apart and ones using fiberglass had nothing in the top 10" or so. Even if you use 2x4" make sure the cavity is completely filled and there is a thin ply skin glued and screwed on both sides.  That is where your strength is